tag:theconversation.com,2011:/us/topics/i-have-always-wondered-42316/articlesI have always wondered – The Conversation2019-07-05T01:43:07Ztag:theconversation.com,2011:article/1168852019-07-05T01:43:07Z2019-07-05T01:43:07ZI’ve always wondered: how do cyclones get their names?<p><em>This is an article from <a href="https://theconversation.com/au/topics/ive-always-wondered-43449">I’ve Always Wondered</a>, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
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<blockquote>
<p><strong>Who calls cyclones their names? – Guy Mullin, Mozambique.</strong></p>
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<p>In the Australian region, the <a href="http://www.bom.gov.au/">Bureau of Meteorology</a> gives tropical cyclones their name. You can write to the Bureau of Meteorology to suggest a cyclone name, but it is likely to be more than a 50-year wait. </p>
<p>Tropical cyclones are named so we can easily highlight them to the community, and to reduce confusion if more than one cyclone happens at the same time. The practice of naming tropical cyclones (or storms) began years ago to help in the quick identification of storms in warning messages. Humans find names far easier to remember than numbers and technical terms.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279482/original/file-20190614-158917-wao08h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aerial views of flooded areas following Cyclone Idai in March 2019.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/eu_echo/46697536025/in/photolist-2e9v5xt-7jNsbG-2fxpPm6-YqwbUf-2fxpPbB-2fxpPoF-289W2bH-o1qQC-hQngMr-bpuYLm-7jNu7L-47W54r-dTkScR-cdkGF-ePcsUA-47W54t-dTkRXX-Yqw8Tq-dTrwfy-XrMbqc-Yqw9oU-dTrvXG-dTkSti-2dtaLyF-Yqwc5q-Yqw7wY-MMSgzZ-23fuLnn-EXzwTa-Y5zo6q-24xNjNC-Yqw8Wm-YtabVR-YqwbEs-YtaaWX-YqwbZ5-Ytab3P-23wUQjL-s1gp9u-dTrw9s-7FpNyY-YtacfZ-cde82-YtacAP-Yqw7Yu-YqwbLQ-Yqw9zW-XpLBpL-MTmnfM-J9pvfZ">EU Civil Protection and Humanitarian Aid Operations/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
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<strong>
Read more:
<a href="https://theconversation.com/what-are-bomb-cyclones-an-expert-explains-whats-behind-these-intense-winter-storms-89924">What are ‘bomb cyclones’? An expert explains what's behind these intense winter storms</a>
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</em>
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<h2>Clement Wragge began naming cyclones in 1887</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279480/original/file-20190614-158953-16hmv6f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tropical Cyclone Oma captured by NASA international space station.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasa2explore/46316787445/in/photolist-2dyRDfM-2eHh3LC-2dT6aEE-4AzQvA-4E5VHN-2dAdRDg">NASA Johnson/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
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<p>Now, people ask us all the time how we come up with the names for tropical cyclones. It started in 1887 when Queensland’s chief weather man <a href="http://adb.anu.edu.au/biography/wragge-clement-lindley-9193">Clement Wragge</a> began naming tropical cyclones after the Greek alphabet, fabulous beasts, and politicians who annoyed him.</p>
<p>After Wragge retired in 1908, the naming of cyclones and storms occurred much less frequently, with only a handful of countries informally naming cyclones. It was almost 60 years later that the Bureau formalised the practice, with Western Australia’s Tropical Cyclone Bessie being the first Australian cyclone to be officially named on January 6, 1964. </p>
<p>Other countries quickly began using female names to identify the storms and cyclones that affected them.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&rect=33%2C0%2C5509%2C3700&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/278778/original/file-20190611-52748-1sfcuob.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Naming cyclones helps people quickly identify storms in warning messages. Cameras outside the NASAA international space station capture Hurricane Florence in 2018.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/42828606570/in/album-72157697980438442/">NASA Goddard Space Flight Center/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ive-always-wondered-how-do-we-know-what-lies-at-the-heart-of-pluto-101327">I've Always Wondered: How do we know what lies at the heart of Pluto?</a>
</strong>
</em>
</p>
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<h2>How cyclone names are chosen</h2>
<p>While the world was giving female names to cyclones and storms, International Women’s Year in 1975 saw Bill Morrison, the then Australian science minister, recognise that both sexes should bear the shame of the devastation caused by cyclones. He ordered cyclones to carry both male and female names, a world first. </p>
<p>These days the Bureau is responsible for naming tropical cyclones in the Australian region, with the names coming from an <a href="https://public.wmo.int/en/About-us/FAQs/faqs-tropical-cyclones/tropical-cyclone-naming">alphabetical list</a> suggested by the Australian public. These names alternate between male and female. The Bureau of Meteorology receives many requests from the public to name tropical cyclones after themselves, friends, and even pets. </p>
<p>The Bureau cannot grant all these requests, as they far outnumber the tropical cyclones that occur in the Australian region.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/278790/original/file-20190611-52762-c9py2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Trees on the side of the road at Mission Beach, North Queensland, in the aftermath of Cyclone Yasi, 2011. Cyclone Yasi formed in Fiji and maintained the name from that region’s weather agency.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/tk_five_0/5492860149/">Michael Dawes/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-causes-windy-weather-92821">Curious Kids: What causes windy weather?</a>
</strong>
</em>
</p>
<hr>
<h2>Cyclone Oma was named in Fiji</h2>
<p>Cyclone names are reused, but when a tropical cyclone severely impacts the coast, or is deadly, like <a href="http://www.bom.gov.au/cyclone/history/debbie.shtml">Debbie</a> in 2017 and <a href="http://www.bom.gov.au/cyclone/history/tracy.shtml">Tracy</a> in 1974, the name is permanently retired for reasons of sensitivity.</p>
<p>If a listed name comes up that matches the name of a well-known person, or someone in the news for a sensitive or controversial reason, the name is skipped to avoid any offence or confusion. </p>
<p>When a cyclone forms in another region, say near Fiji or in the Indian Ocean, and then travels into the Australian region, the original name given by that region’s weather agency is kept, such as 2019’s Cyclone Oma, which came from Fiji.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/WAbUM0fUbmA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Tropical cyclone Bessie was the first Australian cyclone to be officially named by the Bureau of Meteorology.</span></figcaption>
</figure>
<p>A list of cyclone names around the world can be found <a href="https://public.wmo.int/en/About-us/FAQs/faqs-tropical-cyclones/tropical-cyclone-naming">here</a>.</p><img src="https://counter.theconversation.com/content/116885/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Wardle does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>In 1887 Queensland’s chief weatherman Clement Wragge began naming tropical cyclones, using names from the Greek alphabet, fabulous beasts and politicians who annoyed him.Richard Wardle, Weather Services Manager, Queensland, Australian Bureau of MeteorologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/941652018-03-29T20:56:04Z2018-03-29T20:56:04ZI’ve always wondered: can two chickens hatch out of a double-yolk egg?<figure><img src="https://images.theconversation.com/files/212606/original/file-20180329-189795-18jm4d1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Like two peas in a pod, if the pod was an egg and the peas were chickens.</span> <span class="attribution"><span class="source">Gina Pina/Flickr.com</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au.</em></p>
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<p><strong>Can two chicks be born from a double-yolk egg? - Megan, Berry, NSW</strong></p>
<p>Have you ever wondered how an egg gets to be that layered marvel of yolk inside a membrane, inside albumen inside more membranes and all topped off with a shell? </p>
<p>As wonderful (and complicated) as eggs are, it’s no surprise that they can come out a little odd from time to time. One of the most striking variations is the rare fertilised double-yolk – and yes, this can result in two chicks being born from the same egg.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/B5uDKfQ5vGc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Two yolks become two chicks.</span></figcaption>
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<p>Oddities like double-yolkers, as well as eggs with no shells, no yolk or even double shells, occur when something disrupts the usual egg-making process. </p>
<h2>How eggs are made</h2>
<p>Eggs depend on a really interesting organ called an oviduct.</p>
<p>First of all, a hen’s ovary produces an ovum. (That’s ovary as in singular – except in some raptors, the kiwi and a few other birds here and there, most birds have a single ovary.) The ovary looks like a cluster of tiny grapes, and if you care to dissect a bird, it’s located near the backbone, usually between or on top of the kidneys.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=551&fit=crop&dpr=1 754w, https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=551&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/212602/original/file-20180329-189798-vyttjo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=551&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Left ovary and oviduct.</span>
<span class="attribution"><span class="source">The Poultry Club of Great Britain.</span></span>
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<p>That ovum travels into the oviduct, which is a long and elastic tube that travels in a convoluted way from the ovary to the cloaca (the hole that birds defecate from). Muscle contractions move the ovum through the oviduct and first it enters a section where glandular secretions lay down the albumen (the white of the egg) in four layers. </p>
<p>Next, the egg enters the isthmus (a long narrow tube) of the oviduct, where two membranes are laid down: one to enclose the albumin and one to attach directly to the shell. </p>
<p>Then pigments are laid down. All the egg colours you might see, from random spots and speckles to uniform blue or brown, are actually the product of two colours. There’s buliverdin, which is responsible for blue-green hues, and protoporphyrin, which accounts for brownish reds, all mixed together to make the stunning array of bird’s eggs out there.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=796&fit=crop&dpr=1 600w, https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=796&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=796&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1001&fit=crop&dpr=1 754w, https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1001&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/212594/original/file-20180329-189804-e1eifv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1001&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">ŒUFS.</span>
<span class="attribution"><span class="source">via Wikimedia</span></span>
</figcaption>
</figure>
<p>Finally the hard shell is laid down in the uterus, or shell gland, and consists of calcium carbonate in the form of crystals. Magnesium and phosphate are also included, but in small quantities. This whole process can take between 24 hours and a week depending on the species.</p>
<h2>A delicate balance</h2>
<p>Even the smallest differences in chemical composition of the shell can change the appearance and strength of the shell. If something goes wrong here, then you get abnormal eggs. There are lots of abnormalities possible in eggs such as:</p>
<ul>
<li><p><strong>Extra calcified shells:</strong> Variously termed dusted, white banded, chalky or pink, these seem to happen when an egg gets a little stuck in the oviduct during the time it rotates in the vagina, and gets an extra helping of calcium. Often makes the shell lumpy and bumpy.</p></li>
<li><p><strong>Double shells:</strong> These are very rare and poorly understood. My best guess, based on my research and observation, is that the egg goes through the uterus as normal, then instead of being laid, is sucked back up into the uterus to go through the whole process again. </p></li>
<li><p><strong>No shells:</strong> Eggs with no shells – only the membrane – are also very unusual. They’re thought to occur when the muscle contractions in the oviduct are too fast and the egg literally flies through without a stop at the shell gland for some shell. I’ve seen this in the wild in seabird colonies, once or twice, like someone cracked an egg and just left with the shell.</p></li>
</ul>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/YoBNl4bXt9w?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<ul>
<li><p><strong>Insufficient shells:</strong> Eggs with really soft shells are due to a lack of calcium in the diet. It’s not only chickens that are desperate for calcium. There have been many instances of wild birds seen eating seashells, presumably in an effort to make egg shells without stripping the calcium from their own bones.</p></li>
<li><p><strong>No-yolk eggs:</strong> Also called dwarf or runt eggs, they are usually less than half the size of normal eggs. They are the result of stimulation of the oviduct by a foreign object, like a blood clot. Just like a pearl is made by an oyster wrapping a bit of sand in layers and layers of calcium carbonate, the same can happen in an oviduct.</p></li>
<li><p><strong>Double yolk eggs:</strong> These extra large eggs are very impressive, and some producers have even <a href="http://www.telegraph.co.uk/foodanddrink/foodanddrinknews/11400652/Double-yolk-egg-boxes-launched-by-MandS.html">selectively bred</a> for double-yolkers. They are created when two yolks are ovulated within a couple of hours of each other, like twins, so they end up travelling through the oviduct together. They’re most common when chickens start laying, before their system settles into a steady groove, but as the double yolk chicken breed shows, can be bred for. If both the ovum in the yolk are fertilised, they can both become viable (if a bit squashy) chicks.</p></li>
</ul>
<p>Pretty cool, eh?</p><img src="https://counter.theconversation.com/content/94165/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maggie J. Watson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Eggs are tiny wonders, but even wonders can go wonky sometimes. We look at everything from double-yolkers to eggs with no shell at all.Maggie J. Watson, Lecturer in Ornithology, Ecology, Conservation and Parasitology, Charles Sturt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834972017-10-01T18:40:33Z2017-10-01T18:40:33ZI’ve always wondered: Why don’t hippos get cholera?<p><em>This is an article from I Have Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
<hr>
<blockquote>
<p><strong>Why don’t hippopotamuses get cholera? Why are some animals resistant to waterborne disease? – Phil Morey</strong></p>
</blockquote>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"904481645901656064"}"></div></p>
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<p>The short answer is that cholera has evolved to infect humans, not hippos. Cholera is a disease caused by a curved rod-shaped bacterium called <em>Vibrio cholerae</em>. The disease is characterised by a profuse diarrhoea that resembles “rice water”, and can lead to death within hours.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=489&fit=crop&dpr=1 600w, https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=489&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=489&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=615&fit=crop&dpr=1 754w, https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=615&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/187503/original/file-20170926-12134-1k2k9y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=615&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Transmission electron microsope image of Vibrio cholerae that has been negatively stained.</span>
<span class="attribution"><span class="source">Dartmouth Electron Microscope Facility via Wikipedia</span></span>
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</figure>
<p>Humans contract the disease from water contaminated with human sewage containing the bacteria. As cholera is a waterborne disease, it is prevalent in areas where human sanitation is lacking or less than ideal. Unlike many other diseases, it can’t be passed to us from animals, as malaria is from mosquitoes. </p>
<p>Once ingested by humans, the bacteria attach to the small intestine wall. There they reproduce, and prodcue a toxin called choleragen. The choleragen toxin is made up of two parts, called A and B. The B portion attaches the toxin to the cells in the intestine and the A portion chemically forces electrolytes and water from the intestinal cells themselves, thus leading to massive dehydration, diminished blood loss and ultimately death.</p>
<p><em>Vibrio cholerae</em>, the bacteria that causes cholera, only impacts humans, and can only be transmitted to new human hosts via contaminated water. It’s likely that the disease mechanism is precisely adapted to human-specific molecules in the cell walls of our small intestine, and the molecular structure of the bacteria’s toxins.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=567&fit=crop&dpr=1 754w, https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=567&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/187500/original/file-20170926-12134-6fldo5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=567&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The annotation on this 19th century medical illustration reads. ‘A young woman of Vienna, 23. The same woman one hour after the onset of cholera, and four hours before death.’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/thelostgallery/34934154305/in/photolist-Ve1EZg-7gAbC-mSrZf4-8NZiJR-8NYx98-b3WMo-dYQxNE-ndUgdf-8BeDrA-dYJFxp-dYJKf4-dYJEFn-qxtsfd-dYJRtk-dYJQ3r-dYQmww-dYQn83-dtgVyL-dYQnsU-dYJFhi-dYJFov-dYQo3w-dYJE3M-dYJRj8-7ZFsXd-dYQodf-4rBBBW-dYJR16-dYJJZz-dYQnxN-dYQrsN-dYQwCs-dYQnpS-pTfE1p-dYQo1d-dYQndw-7F6mwh-dYJyeP-dYQp4G-5CLarm-dYJK4i-dYJBFB-dYQyjW-dYJDFx-dthdmj-dYQido-dYJRS4-7iindD-dYJRAn-dYJBk6">Wellcome Library, London, via Flickr/the lost gallery</a></span>
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<p>Over millennia, both the disease-causing organism (pathogen) and host have been evolving counter-strategies against each other: the host to evade the pathogen, and pathogen to invade the host. These battles have led to the bacteria becoming host-specific, and now only able to infect humans.</p>
<p>The cholera vaccine works by taking advantage of this close host/pathogen relationship. It inhibits the action of the B portion of the cholera toxin, hence it prevents the bacteria from attaching to the intestinal wall. </p>
<p>Other waterborne diseases are caused by other pathogens (although the specific mechanisms or molecules involved differ). In some cases, as in cholera, the molecules required for infection are host-specific. Whilst other pathogens are not species specific, they are often associated with more closely-related species than less closely-related species. For example, foot and mouth disease affects cattle, sheep, deer and pigs, because they are all cloven-hoofed animals (<em>Artiodatyla</em>) and thus closely-related species. </p>
<p>Hippopotamuses (<em>Hippopotamus amphibious</em> and <em>Choeropsis liberiensis</em>) are more closely related to cetaceans (whales and dolphins), than humans, and therefore it is not surprising that they have different pathogens. That being said, hippopotamuses, like other animals, are likely to suffer from loose stools (dung) from time to time, whether due to other pathogens, or the quality of the huge amounts of plant material they ingest on a daily basis.</p>
<p>Dung is super important in hippopotamus society. Hippopotamus defecation or “dung showering” involves flicking their tail at the same time as defecating to distribute their dung far and wide, hence dung is used to mark their territory and assert dominance.</p>
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<p>If hippopotamus dung spread a disease like cholera, it could be rapidly fatal for large populations. It is likely that the individuals affected would be removed by natural selection. Those that were resistant, or only mildly affected, would overcome the disease and live on to produce disease-resistant offspring. Over time, it is therefore likely hippopotamuses have adapted to their aquatic environments and thus rarely, if ever, become infected with waterborne diseases.</p>
<p><br></p>
<p><em>* Email your question to alwayswondered@theconversation.edu.au
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* Tell us on <a href="https://twitter.com/ConversationEDU">Twitter</a> by tagging <a href="https://twitter.com/ConversationEDU">@ConversationEDU</a> with the hashtag #alwayswondered, or
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<p class="fine-print"><em><span>Julie Old does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Why are some animals resistant to waterborne disease? A reader wants to know.Julie Old, Associate Professor, Biology, Zoology, Animal Science, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/837162017-09-24T20:03:21Z2017-09-24T20:03:21ZI’ve always wondered: can animals be left- and right-pawed?<figure><img src="https://images.theconversation.com/files/186153/original/file-20170915-16298-1p6agw1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Southpaws seem to be more common among cats and dogs than humans.</span> <span class="attribution"><span class="source">Eric Isselee/Shutterstock.com</span></span></figcaption></figure><p><em>This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
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<blockquote>
<p><strong>While watching my cat engaging in yet another battle with my shoelace, I noticed that he seemed mainly to use his left front paw. Do animals have a more dextrous side that they favour for particular tasks, just like humans? – Mike, Perth.</strong></p>
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<hr>
<p>The short answer is: yes they do! Like humans, many animals tend to use one side of the body more than the other. This innate handedness (or footedness) is called behavioural or motor laterality. </p>
<p>The term laterality also refers to the primary use of the left or right hemispheres of the brain. The two halves of the animal brain are <a href="http://www.rightleftrightwrong.com/brain.html">not exactly alike</a>, and each hemisphere differs in function and anatomy. In general terms, the left hemisphere controls the right side of the body and the right hemisphere controls the left side. </p>
<p>Laterality is an ancient inherited characteristic and is widespread in the animal kingdom, in both vertebrates and invertebrates. Many <a href="http://www.rightleftrightwrong.com/theories.html">competing theories</a> (neurological, biological, genetic, ecological, social and environmental) have been proposed to explain how the phenomenon developed, but it remains largely a mystery. </p>
<h2>Animal ‘handedness’</h2>
<p>Humans tend to be right-handed. Lefties or “southpaws” make up <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3927078/">only about 10% of the human population</a>, and <a href="http://psycnet.apa.org/doiLanding?doi=10.1037/a0012814">more males than females are left-handed</a>.</p>
<p>Great apes show <a href="http://www.sciencedirect.com/science/article/pii/S0166432812006237?via%3Dihub">similar handedness patterns</a> to humans. Most chimps, for instance, <a href="http://video.nationalgeographic.com/video/news/chimps-right-hand-vin?source=relatedvideo">seem to be right-handed</a>. But not many studies have looked at laterality in non-primate animals. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-are-most-people-right-handed-the-answer-may-be-in-the-mouths-of-our-ancestors-69712">Why are most people right handed? The answer may be in the mouths of our ancestors</a>
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</em>
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<p>There is some evidence to suggest that <a href="http://www.sciencedirect.com/science/article/pii/S0376635702001614?via%3Dihub">dogs</a> and <a href="https://www.ncbi.nlm.nih.gov/pubmed/2265897">cats</a> can be right- or left-pawed, although the ratio seems to be more evenly split than in humans, and it is unclear whether there are sex differences. </p>
<p>If you’re a pet owner you can <a href="http://www.dailymail.co.uk/news/article-2195039/Is-pet-right-left-handed-The-test-uses-cheese-sofas-backdoor-out.html">do an experiment for yourself</a>. Which paw does your cat or dog lead with when reaching out for something, or to tap open a pet door?</p>
<p>To test your pet dog, you can place a treat-filled <a href="https://www.kongcompany.com/en-au/kong-101/kong-101/">Kong toy</a> directly in front of your dog and see which paw he or she uses to hold it to get the food out. A dog may use either paw or both paws.</p>
<p>To test your pet cat, you can set a “food puzzle” by putting a treat inside a glass jar and watching to see which paw your cat uses. Don’t forget to repeat it lots of times and take notes to see whether the effect is real or just random chance!</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/ykb46flx47c?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Don’t forget to repeat the experiment lots of times.</span></figcaption>
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<p>Horses also seem to <a href="http://www.equinescienceupdate.co.uk/mslat.htm">prefer to circle in one direction rather than the other</a>. Meanwhile, one study suggests that <a href="http://news.nationalgeographic.com/2015/06/150618-kangaroos-evolution-animals-science/">kangaroos are almost exclusively lefties</a>, although the neural basis for this is unknown. </p>
<h2>Lateralisation and brain function</h2>
<p>In humans, the left hemisphere is mainly associated with <a href="https://www.sciencedaily.com/releases/2014/07/140704134633.htm">analytical processes and language</a> and the right hemisphere with orientation, awareness and musical abilities, although this dichotomy is simplistic at best.</p>
<p>Is there evidence of lateralised brain function in non-human animals too? A team of Italian researchers think so. They found that dogs <a href="http://www.cell.com/current-biology/pdf/S0960-9822%2807%2900949-9.pdf">wag their tails to the right</a> when they see something they want to approach, and to the left when confronted with something they would rather avoid. This suggests that, just as for people, the right and left halves of the brain do different jobs in controlling emotions.</p>
<p>Laterality is also connected to the direction in which hair grows (so-called stuctural laterality), or even to the senses (sensory laterality). Many animals use they left eye and left ear (indicating right brain activation) more often than the right ones when <a href="http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0184933&type=printable">investigating objects that are potentially frightening</a>. However, asymmetries in olfactory processing (nostril use) are less well understood. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186158/original/file-20170915-16320-1o2xq1r.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Research suggests most kangaroos are southpaws.</span>
<span class="attribution"><span class="source">Ester Inbar/Wikimedia Commons</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The left or right bias in sensory laterality is separate from that of motor laterality (or handedness). However, some researchers think that side preference is linked to the direction of hair whorls (“cow licks”), which can grow in a clockwise or anticlockwise direction. More right-handed people have a <a href="https://www.ncbi.nlm.nih.gov/pubmed/14504234">clockwise hair pattern</a>, although it is <a href="http://doctorbarkman.blogspot.com.au/2013/10/can-canine-hair-whorls-predict.html">unclear if this is true of other animals</a>. </p>
<p>The direction of hair growth and handedness are also related to temperament. Left-handed people might be <a href="http://onlinelibrary.wiley.com/doi/10.1002/jts.20222/pdf">more vulnerable to stress</a>, as are <a href="https://www.ncbi.nlm.nih.gov/pubmed/16893254">left-pawed dogs</a> and many other animals. In general, many animals, including humans, that have a clockwise hair whorl are less stress-prone than those with anticlockwise hair growth. The position of the hair whorl also matters; cattle and horses with hair whorls directly above the eyes are <a href="http://www.j-evs.com/article/S0737-0806%2815%2930055-1/pdf">more typically difficult to handle than those with whorls lower down on the face</a>. </p>
<p>Elsewhere in the animal kingdom, snails also have a form of laterality, despite having a very different nervous system to vertebrates like us. Their shells spiral in either a “right-handed” or “left-handed” direction – a form of physical asymmetry called “chirality”. This chirality is <a href="https://phys.org/news/2009-11-rightleft-handedness-snails-lab.html">inherited</a> – snails <a href="http://jeb.biologists.org/content/213/5/v.2">can only mate with matching snails</a>.</p>
<p>Chirality is <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692985/">even seen in plants</a>, depending on the asymmetry of their leaves, and the direction in which they grow.</p>
<p>As an aside, left-handedness has been discriminated against in many cultures for centuries. The Latin word <em>sinistra</em> originally meant “left” but its English descendant “sinister” has taken on meanings of evil or malevolence. The word “right”, meanwhile, connotes correctness, suitability and propriety. Many everyday objects, from scissors to notebooks to <a href="https://plus.google.com/+Vi0letAshes/posts/88cRFZbqZX4">can-openers</a>, are designed for right-handed people, and the Latin word for right, <em>dexter</em>, has given us the modern word “dextrous”.</p>
<h2>Why is the brain lateralised?</h2>
<p>One adaptive advantage of lateralisation is that individuals can perform two tasks at the same time if those tasks are governed by opposite brain hemispheres. Another advantage might be resistance to disease – hand preference in animals is associated with differences in immune function, with <a href="https://www.ncbi.nlm.nih.gov/pubmed/15265650">right-handed animals mounting a better immune response</a>.</p>
<p>Does it matter if your cat, dog, horse or cow favours one paw (or hoof) over another? Determining laterality – or which side of the brain dominates the other – could change the way domestic animals are bred, raised, <a href="http://www.abc.net.au/catalyst/stories/3465535.htm">trained and used</a>, including predicting which puppies will make the best <a href="http://www.sciencedirect.com/science/article/pii/S1090023311003649?via%3Dihub">service dogs</a>, and which racehorses will <a href="http://www.equinescienceupdate.co.uk/mslat.htm">race better on left- or right-curving tracks</a>. </p>
<p>And even if your dog or cat never clutches a pen, or uses one limb more than the other, just be grateful that they haven’t yet developed opposable thumbs!</p>
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<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186157/original/file-20170915-16324-19041s6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em>This article is dedicated to the memory of Bollo the cat, who inspired this question but has since passed away.</em></p><img src="https://counter.theconversation.com/content/83716/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The animal kingdom is full of lefties and righties, although rarely is the ratio skewed as much as it is in humans. If you’re wondering about your own pet, you can find out with a simple experiment.Janice Lloyd, Senior Lecturer in Veterinary Behaviour, Welfare & Ethics, James Cook UniversityRichard Squires, Associate Professor of Companion Animal Medicine, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834952017-09-21T01:05:00Z2017-09-21T01:05:00ZI’ve always wondered: why is the flu virus so much worse than the common cold virus?<figure><img src="https://images.theconversation.com/files/186538/original/file-20170919-32051-1a0x544.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Flu seems to be more deadly than colds, here's why. </span> <span class="attribution"><span class="source">from www.shutterstock.com.au</span></span></figcaption></figure><p><em>This is an article from I’ve Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
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<p><strong>I’ve always wondered why the influenza virus is more potent and dangerous than the common cold virus. They’re both viruses, but what makes the influenza worse that it causes more deaths? - Junting Yeung</strong></p>
<p>Thanks for the question Junting, and we have certainly <a href="https://theconversation.com/this-may-not-be-the-biggest-flu-season-on-record-but-it-is-a-big-one-here-are-some-possible-reasons-82642">seen a pretty bad year for flu in Australia</a>. More than <a href="http://data.gov.au/dataset/national-notifiable-diseases-surveillance-system/resource/1e0cfec8-2db3-445a-b6a6-050ddea5938d">160,000 people</a> have been confirmed to have the flu this year, ranging from mild to severe, and some even <a href="http://www.theage.com.au/victoria/loving-little-angel-father-describes-loss-of-rosie-to-the-flu-20170918-gyk0pp.html">causing death</a>. So why is it the flu can cause death but we don’t generally hear of colds doing the same?</p>
<h2>What is the cold virus?</h2>
<p>In contrast to flu, which is caused by variants of a <a href="https://en.wikipedia.org/wiki/Influenza#Virology">family of genetically related influenza viruses</a>, the “common cold” is caused by <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/colds">more than 200 different viruses</a>, many of which are unrelated. </p>
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Read more:
<a href="https://theconversation.com/h1n1-h5n1-h7n9-what-on-earth-does-it-all-mean-14815">H1N1, H5N1, H7N9? What on earth does it all mean</a>
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<p>Not all common cold viruses are created equally, and the course of a “cold” depends to a degree on which cold virus a person is afflicted by. These viruses share a tendency to infect and replicate most effectively in the cooler environment of the <a href="https://en.wikipedia.org/wiki/Respiratory_tract#Upper_respiratory_tract">upper airway</a>, including the <a href="http://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(03)12162-9.pdf">ears, nose, throat and sinuses</a>. </p>
<p>Rhinovirus is the most common virus responsible, and tends to cause an infection of the upper airway, lasting a few days and improves on its own. Typically, rhinovirus binds to a receptor on the surface of cells in the nose and sinuses. This allows the virus to enter cells, start to replicate, and causes infected cells to produce molecules that lead to inflammation. These inflammatory molecules are <a href="https://www.commoncold.org/understand.htm">thought to be responsible</a> for the symptoms associated with the common cold; runny or blocked nose, sore throat and cough. </p>
<p>Infection is sometimes further complicated by <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/sinusitis">inflammation in the sinuses</a> and <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/ear-infections">middle ear infection</a>. Sometimes, infection can have no symptoms at all. </p>
<p>But infection can be more severe in patients with an <a href="http://www.ijidonline.com/article/S1201-9712(17)30190-X/fulltext#sec0010">impaired immune system</a>, including those with cancer, on medications to suppress the immune response, or those undergoing a bone marrow transplant. Plus, the common cold <a href="http://journal.chestnet.org/article/S0012-3692(15)50116-5/fulltext">may exacerbate or contribute to</a> the development of chronic airway diseases, like asthma.</p>
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<a href="https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186539/original/file-20170919-32019-dwvuq9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Cold viruses tend to be self-limiting, meaning they go away by themselves.</span>
<span class="attribution"><span class="source">from www.shutterstock.com</span></span>
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<h2>What is the flu?</h2>
<p>The <a href="https://www.khanacademy.org/partner-content/stanford-medicine/stanford-influenza/v/flu-pathophysiology">illness you get when you catch influenza (the flu)</a> varies widely, and depends on the person infected (the host), the virus, and secondary bacterial infections that may follow infection with the virus. The flu virus can infect both the <a href="https://www.youtube.com/watch?v=O3f9Fh48EHg">upper and lower respiratory tract</a>, which in part explains its ability to cause severe disease. </p>
<p>Other medical conditions, age and a weakened immune system also play a big part in how much the flu virus will affect the host. Plus, a person’s genetic makeup may predispose them to a more severe <a href="https://www.sciencedaily.com/releases/2014/02/140227142250.htm">inflammatory response</a>, known as a “cytokine storm”. Inflammation is a <a href="https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072482/">normal response</a> that allows our body to fight infection and heal damaged tissue. Paradoxically, too much inflammation <a href="https://www.washingtonpost.com/national/health-science/flus-lethality-is-attributed-to-imzcccmune-systems-overreacting-to-the-virus/2011/11/21/gIQA76GpWP_story.html?utm_term=.5030d977285f">makes the illness from flu worse</a> by causing more swelling and tissue destruction.</p>
<p>For the flu virus to bind to and infect cells in our respiratory tract it uses a molecule called “<a href="https://www.ebi.ac.uk/interpro/potm/2006_4/Page3.htm">hemagglutinin</a>”. <a href="http://www.who.int/mediacentre/factsheets/avian_influenza/en/">Bird and swine flu strains</a>, which cause <a href="https://en.wikipedia.org/wiki/Pandemic">pandemics</a> in <a href="http://www.abc.net.au/news/rural/2017-03-10/avian-influenza-global-spread-concern-for-next-human-pandemic/8342922">humans</a> may have a haemagglutinin molecule on their surface that preferentially binds to receptors in the lower respiratory tract, including the tiny air sacs (alveoli). These alveoli are responsible for <a href="https://www.youtube.com/watch?v=AJpur6XUiq4">transferring oxygen into</a> and taking carbon dioxide out of the blood stream. </p>
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Read more:
<a href="https://theconversation.com/have-you-noticed-australias-flu-seasons-seem-to-be-getting-worse-heres-why-43837">Have you noticed Australia's flu seasons seem to be getting worse? Here's why</a>
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<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=362&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=362&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=362&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=455&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=455&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186541/original/file-20170919-32071-mtlgdw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=455&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The flu affects your upper and lower respiratory tract, and can cause subsequent bacterial infections, making it potentially dangerous.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/hesenrre/3479956205/">Demet/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>Infection and inflammation in the <a href="https://en.wikipedia.org/wiki/Pulmonary_alveolus">alveoli</a>, can significantly impact the ability of the lungs to give the body enough oxygen.
Also, the haemagglutinin molecule rapidly changes <a href="https://www.cdc.gov/flu/about/viruses/change.htm">during and between flu seasons</a>. Since haemagglutinin is an important target our immune system uses to protect against flu, this change means that infection or immunisation in one flu season doesn’t usually prevent future infection. Our immune system only learns to fight off that specific strain, and not the one with the new mutations. This is why it’s <a href="http://www.abc.net.au/news/2017-04-12/flu-vaccine-wont-make-you-immune-but-its-still-important/8436684">important to get immunised for flu every year</a>.</p>
<p>The final aspect making flu so severe is that it makes you more likely to get bacterial infections, by weakening some of the natural defences of the respiratory tract. This includes damage to the surface of the airway, exposing molecules that bacteria can adhere to, and damaging the “<a href="http://www.colorado.edu/Outreach/BSI/k12activities/interactive/actidhpamucociliary.html">mucociliary elevator</a>”- tiny hair-like sturctures in the airway that catch and expel bacteria and mucus from the respiratory tract. These bacterial infections lead to further damage to lung tissue, more inflammatory cells, and can cause severe problems in your respiratory system. It is thought that most of the 100 million deaths that occurred during the <a href="https://en.wikipedia.org/wiki/1918_flu_pandemic">Spanish flu pandemic of 1918</a> were due, at least in part, to <a href="https://www.nih.gov/news-events/news-releases/bacterial-pneumonia-caused-most-deaths-1918-influenza-pandemic">secondary bacterial infection</a>. </p>
<h2>So why are there more flu deaths?</h2>
<p>Both the common cold and flu can cause similar respiratory illnesses, and exacerbate underlying medical conditions. Important in both cold and flu is how the person’s immune system is functioning, and the part of the airway infected.</p>
<p>In patients with flu, infection of both the upper and lower respiratory tract, the resulting local and systemic inflammatory response evoked by the virus, and the secondary consequences of infection are important determinants of how sick we get.</p>
<p>And these are in turn dependent on a combination of viral, bacterial and patient factors, including how effectively the virus infects, replicates and triggers the immune response, and the ensuing tissue inflammation and damage. Together, these can mean a person with the flu can have a spectrum of illness, from no symptoms at all to being potentially fatal.</p>
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<p class="fine-print"><em><span>David Griffin does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Why is it the flu virus is so deadly compared to the common cold virus?David Griffin, Advanced Trainee, Infectious Diseases and General Medicine, The Peter Doherty Institute for Infection and ImmunityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834852017-09-18T02:28:18Z2017-09-18T02:28:18ZI’ve always wondered: does anyone my age have any chance of living for centuries?<figure><img src="https://images.theconversation.com/files/184593/original/file-20170905-9762-kpxfwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">How likely is it that someone alive today may live for centuries?</span> <span class="attribution"><span class="source">Flickr/Santiago Sito</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p><em>This is an article from I’ve Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
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<p><strong>Does anyone my age have any chance of living for centuries? Will younger generations have a chance? - Adam Barclay, 44, Newcastle.</strong></p>
<p>One century? Yes, a decent chance. We might in theory be able to live for centuries. This is a dream that many are working towards - but we aren’t there yet.</p>
<p>The subject of living longer, and more importantly, healthier lives is now a <a href="https://theconversation.com/the-search-to-extend-lifespan-is-gaining-ground-but-can-we-truly-reverse-the-biology-of-ageing-75127">serious, mainstream endeavour in biology and medical science</a>. </p>
<p>Molecular biologists, geneticists, and nutritional scientists are reaching for the ultimate goal of delaying onset of age-related conditions, which would reduce the incidence of nearly every non-communicable disease ageing brings. </p>
<p>Although reduced disease burden is the public health goal that motivates governments and the medical science community to pursue ageing research, it is living longer - finding the elixir of youth, seeking immortality - that captures the public imagination.</p>
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Read more:
<a href="https://theconversation.com/the-search-to-extend-lifespan-is-gaining-ground-but-can-we-truly-reverse-the-biology-of-ageing-75127">The search to extend lifespan is gaining ground, but can we truly reverse the biology of ageing?</a>
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<p>With the exception of wars, famine, or <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4679063/">major economic dislocation</a>, human lifespan has been steadily increasing around the world for the past century. Life expectancy in Australia is around 83 years, the <a href="http://www.who.int/gho/publications/world_health_statistics/2016/Annex_B/en/">fourth greatest in the world</a>. These gains are largely due to improved access to and quality of health care. We are yet to see the impact of therapies specifically targeted to treat ageing, which could turbo-charge this increase in life expectancy.</p>
<h2>What researchers are working on</h2>
<p>Most of the anti-ageing or “geroprotective” compounds under development work by mimicking the effects of calorie restriction or physical exercise. Lifelong calorie restriction, reducing calorie intakes by around 30%, is one of the <a href="https://www.ncbi.nlm.nih.gov/pubmed/12936916">strongest interventions known for extending lifespan</a>. </p>
<p>For the past two decades, research into ageing has sought to determine which genes and molecular pathways are turned on and off by eating less and exercising more. This has resulted in the discovery of a number of pathways (called the <a href="https://www.ncbi.nlm.nih.gov/pubmed/27552971">sirtuins</a>, <a href="https://www.nature.com/nature/journal/v424/n6946/full/nature01789.html">insulin/IGF-I signalling</a>, <a href="https://www.ncbi.nlm.nih.gov/pubmed/23325216">mTOR</a>, and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4287273/">AMPK</a>) that can be manipulated in animals to extend lifespan. An anti-diabetic drug called metformin activates one of these, and is <a href="https://www.ncbi.nlm.nih.gov/pubmed/27304507">being trialled to improve health in old age</a>.</p>
<p>Another way to extend lifespan might be to remove so-called “<a href="http://www.nature.com/nrm/journal/v15/n7/abs/nrm3823.html">senescent</a>”, or old and damaged cells, which <a href="https://www.ncbi.nlm.nih.gov/pubmed/26840489">cause disease</a>. But here’s the thing - those pathways extend lifespan by only up to 30%, which on a “normal” human lifespan of 83 years, takes us to merely one century. </p>
<p>While increasing life expectancy to over a century would be an <em>astounding</em> achievement, this is nowhere near the centuries that many people dream of. To achieve that, the biology of ageing will have to move beyond mimicking calorie restriction, tinkering with metabolism, and trimming away old cells. </p>
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<a href="https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185624/original/file-20170912-11499-p60yex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Calorie restriction is one of the most reliable ways to extend lifespan.</span>
<span class="attribution"><span class="source">from www.shutterstock.com</span></span>
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<h2>Possible future directions</h2>
<p>Instead, we might look to nature for inspiration. The jellyfish <a href="https://www.ncbi.nlm.nih.gov/pubmed/9615920?dopt=Abstract"><em>Hydra</em> has no discernable biological ageing</a>, and is functionally immortal, most likely due to a <a href="https://www.ncbi.nlm.nih.gov/pubmed/19891641">high content of stem cells</a> that can replenish the adult body. Another species, <em>Turritopsis dohrnii</em>, the “immortal jellyfish”, can <a href="http://www.journals.uchicago.edu/doi/abs/10.2307/1543022">reverse back from its adult body into its juvenile state</a>, as a polyp growing on a rock, and then grow back into an adult, and repeat that cycle to achieve near immortality. </p>
<p>So how could we imitate the immortal jellyfish? Well, we could reprogram our “epigenomes” - which is the arrangement that keeps different parts of our DNA code turned on and off. Excitingly, we already know how to do this. There are just four genes, called “Yamanaka factors”, which <a href="https://www.ncbi.nlm.nih.gov/pubmed/18035408">rejuvenate adult cells back into embryonic stem cells</a> - like Benjamin Button, this would mean turning our cells from aged adults back to those of a developing baby.</p>
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Read more:
<a href="https://theconversation.com/why-we-cant-live-forever-understanding-the-mechanisms-of-ageing-7353">Why we can't live forever: understanding the mechanisms of ageing </a>
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<p>In theory, turning these factors on for the right amount of time in the right places could rejuvenate our bodies back into those of young people - at which point, in theory, we <em>might</em> be able to live for centuries. </p>
<p>The trick will be figuring out when, where, how much and for how long to turn these Yamanaka factors on. <a href="https://www.nature.com/nature/journal/v502/n7471/full/nature12586.html">Too much</a>, and our organs could turn into a mass of undifferentiated embryonic stem cells, which could grow back into the wrong tissue type. Too little, and there would be no effect. Getting the <a href="https://www.ncbi.nlm.nih.gov/pubmed/27984723">dosage <em>just right</em></a> could be very powerful. Testing for the first time in humans would be risky. </p>
<p>It’s worth remembering that extending lifespan alone is not the same as extending quality of life or healthy years. Advancement of lifespan should not occur by delaying death following long periods of sickness. Instead, <a href="https://www.ncbi.nlm.nih.gov/pubmed/7383070">shortening the amount of time people are unwell</a> should be the ultimate goal. </p>
<p>At some point prior to death, everyone crosses the threshold of being independent, healthy and active, to becoming dependent, sick and immobile. The duration spent below this threshold is unique to the individual, but everyone agrees this time should be minimal in comparison to the person’s healthy years. </p>
<p>Lifestyle changes, and advances in technology and medicine, aim to maximise the proportion of time spent living life to the fullest and delaying the (unavoidable) onset of age-related conditions. But living for centuries remains a dream – for now.</p>
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<p><em>* Email your question to alwayswondered@theconversation.edu.au
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<p class="fine-print"><em><span>Lindsay Wu is a founder, director and shareholder in Jumpstart Fertility and Life Biosciences. He is also a shareholder in Continuum Biosciences, Senolytic Therapeutics, EdenRoc Sciences, and Intravital. His lab at UNSW Sydney receive funding from the National Health and Medical Research Council (NHMRC) of Australia and Jumpstart Fertility, and has in the past received funding from Cancer Institute NSW and MetroBiotech NSW. His salary at UNSW Sydney is supported by an RD Wright Biomedical Fellowship from the NHMRC. </span></em></p><p class="fine-print"><em><span>Stefanie Mikolaizak works at Robert Bosch Krankenhaus (Hospital) in Germany. RBMF is the medical research department associated with the hospital of the German charity foundation “Robert Bosch Stiftung”. She is currently coordinating the German clinical site of a large multi-centre intervention trial (PreventIT). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 689238.</span></em></p>Reader Adam Barclay, 44, wants to know if someone his age has any chance of living forever.Lindsay Wu, NHMRC Senior Lecturer, School of Medical Sciences, UNSW SydneyStefanie Mikolaizak, Postdoc Fellow, Robert Bosch KrankenhausLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/834892017-09-10T19:40:48Z2017-09-10T19:40:48ZI have always wondered: why is the sea salty?<figure><img src="https://images.theconversation.com/files/184597/original/file-20170905-9729-1xhzlu5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Salt flows down rivers to the ocean.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/river-flowing-into-sea-54528130?src=aiDkohzhFfI4iIemllff3g-1-4">Shutterstock/Masonjar</a></span></figcaption></figure><p><em>This is an article from I Have Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
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<p><strong><em>Why is the sea salty? - Robert Moran, Middlecove</em></strong></p>
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<p>The short answer is that water dissolves the salts contained in rocks, and these salts are carried in the water to the sea.</p>
<p>As raindrops form, they absorb carbon dioxide from the air. The water (H₂O) and carbon dioxide (CO₂) react to form carbonic acid (H₂CO₃). The carbonic acid makes rainwater slightly acidic, with a pH of <a href="https://www3.epa.gov/acidrain/education/site_students/phscale.html">around 5.6</a>. Pure water <a href="http://www.chemicalformula.org/acid-rain">has a</a> pH of 7, which is neutral. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/i-have-always-wondered-why-are-some-fruits-poisonous-83210">I have always wondered: why are some fruits poisonous?</a>
</strong>
</em>
</p>
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<p>So, rain dissolves salts out of the rocks and these salts are carried via runoff to streams and rivers and finally to the sea. <a href="https://oceanservice.noaa.gov/facts/riversnotsalty.html">Rivers carry</a> almost 4 billion tonnes of salt to the sea each year.</p>
<p>But rivers aren’t salty, right? Rivers are definitely not as salty as the sea, but they constantly carry their small salt content into the sea, and as a result the concentration of salt in the sea (which oceanographers call salinity) has built up over millions of years. </p>
<p>In fact, rivers <a href="https://water.usgs.gov/edu/whyoceansalty.html">aren’t the only source</a> of sea salt. Rocks in the sea also play a role, and hydrothermal vents in the ocean floor and subsea volcanoes also supply dissolved salts to the sea.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185014/original/file-20170907-8393-1rxfprq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Super-heated molten lava about to explode into the water.</span>
<span class="attribution"><a class="source" href="https://www.pmel.noaa.gov/eoi/laubasin/laubasin-multimedia.html">NSF and NOAA</a></span>
</figcaption>
</figure>
<p>Over millions of years, the concentration of salts has increased from possibly almost fresh in the primeval sea to where it is now – <a href="http://omp.gso.uri.edu/ompweb/doee/science/physical/chsal1.htm">an average</a> of 35 grams of salt in every kilogram of seawater.</p>
<p>If all this salt could be taken out of the ocean and spread over Earth’s land surface, <a href="https://oceanservice.noaa.gov/facts/whysalty.html">according to</a> the US National Oceanic and Atmospheric Administration, it would form a layer more than 150 metres thick.</p>
<h2>Why are some places saltier than others?</h2>
<p>Salinity varies from place to place in the sea, depending on how close you are to rivers, how much rain falls, how much evaporation occurs, and whether ocean currents are bringing in saltier or fresher water. </p>
<p>In general, the sea is saltier in the subtropics, where evaporation is high due to warm air temperatures, steady trade winds, and very low humidity related to atmospheric circulation patterns called <a href="https://www.seas.harvard.edu/climate/eli/research/equable/hadley.html">Hadley Cells</a>.</p>
<p>The sea is fresher close to the Equator where rainfall is high, and in the Southern Ocean and Arctic Ocean, where sea ice melt in the summer adds fresh water.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185201/original/file-20170908-9603-pqf6ll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">NASA’s ‘Salt of the Earth’ Aquarius map.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/mission_pages/aquarius/multimedia/gallery/pia14786.html">NASA</a></span>
</figcaption>
</figure>
<p>Enclosed seas, such as the Mediterranean and Red Seas, can be very salty indeed. This is because the removal of fresh water by evaporation is much larger than the addition by rainfall, and lower-salinity waters from the deep sea can’t flow in as easily. </p>
<h2>Ocean salinity as a rain gauge</h2>
<p>While the total amount of salt in the sea is pretty constant, the distribution of the salt is changing. Broadly speaking, the salty parts of the ocean <a href="http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3377.1">are becoming</a> saltier, and the fresh parts fresher. </p>
<p>These salinity changes are <a href="http://www.abc.net.au/science/articles/2012/04/27/3488816.htm">caused by changing</a> rainfall and evaporation patterns globally, where wet places are generally becoming wetter and dry places are getting drier.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/i-have-always-wondered-when-do-baby-birds-begin-to-breathe-81754">I have always wondered: when do baby birds begin to breathe?</a>
</strong>
</em>
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<p>This amplification of the <a href="https://oceantoday.noaa.gov/watercycle/">water cycle</a> is a consequence of rising air temperatures due to climate change. Warm air can hold more moisture, so it can receive more evaporated water from the sea or land surface, and then release more when it rains. </p>
<p>Just how fast the water cycle is amplifying is a topic of <a href="https://www.nature.com/articles/srep38752">current research</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/oaDkph9yQBs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Earth’s water cycle.</span></figcaption>
</figure>
<p>Rainfall and evaporation are difficult to measure accurately, particularly over the ocean where <a href="https://science.nasa.gov/earth-science/oceanography/ocean-earth-system/ocean-water-cycle">78% of rain</a> falls. </p>
<p>Ocean salinity, on the other hand, is easier to measure now that we have the global <a href="http://www.argo.ucsd.edu/">Argo program</a>: an armada of profiling floats that measure salinity and temperature from the surface to a depth of 2,000m, and surface salinity measurements <a href="https://www.livescience.com/31527-ocean-salt-measured.html">via satellite</a>. </p>
<p>Ocean salinity measurements are not only being used to understand past changes in the water cycle and reduce uncertainty in climate models, they are helping to improve <a href="http://www.whoi.edu/news-release/salty-oceans-rainfall">seasonal rain forecasts</a> around the world.</p>
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<p class="fine-print"><em><span>Helen Phillips does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A special combination of rain, rocks and subsea volcanoes makes the sea salty.Helen Phillips, Senior Research Fellow, Institute for Marine and Antarctic Studies, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/832102017-09-03T20:05:36Z2017-09-03T20:05:36ZI have always wondered: why are some fruits poisonous?<figure><img src="https://images.theconversation.com/files/184296/original/file-20170901-23986-17y6u4s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It was all the apple's fault: we've been fascinated by poisoned fruit for a long time. </span> <span class="attribution"><span class="source">Jacob Jordaens (1593–1678), The Fall of Man, via Wikimedia Commons</span></span></figcaption></figure><p><em>This is an article from I Have Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
<hr>
<blockquote>
<p><strong>Why are some fruits poisonous when the objective of fruit is, presumably, to be eaten so that the seeds can be widely distributed with nutritive manure? – Sev Clarke, Mt Macedon</strong></p>
</blockquote>
<p>Poison fruit has captured our imaginations for centuries. Snow White’s death sleep was induced by the evil queen’s gift of a poison-laced apple. It is <a href="https://en.wikipedia.org/wiki/Atropa_belladonna">rumoured that deadly nightshade</a>, a plant with naturally occurring fruit toxins, was used to kill a Roman emperor and halt an invasion of Scotland. A deadly dose of ricin from castor beans was administered to a Bulgarian dissident via the <a href="https://en.wikipedia.org/wiki/Georgi_Markov">tip of an umbrella</a>.</p>
<p>More recently, scientists have been trying to understand why some fruits are naturally poisonous. From the vain queen’s point of view it makes sense to poison an apple and feed it to the fairest in the land. But why do some plants offer poison fruit that has the potential to harm – or at least deter – fruit-eating animals? </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/little-shop-of-horrors-the-australian-plants-that-can-kill-you-50842">Little shop of horrors: the Australian plants that can kill you</a>
</strong>
</em>
</p>
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<p>Fruiting plants and fruit-eating animals have “mutualistic relationships”, where each benefits from the other. Plants need to spread their seeds to colonise new territory, recolonise after disturbance, or avoid the dangers of staying at home (for example, if the parent plant harbours pests). </p>
<p>One way of doing this is to encase seeds in nutritious fruit pulp so that animals eat the fruit, digest the pulp, and later excrete the seeds with a helpful fertilising deposit of manure. </p>
<p>Animal-mediated (as opposed to wind- or water-mediated) seed dispersal can be particularly useful for getting seeds to specific locations. If you’ve ever wondered how parasitic mistletoe plants or strangler figs find their way onto branches high up in trees, fruit-eating birds are the answer. But why poison the pulp? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/184298/original/file-20170901-21670-11fijf3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Birds spreading seeds are vital for many plants, so there has to be a very good reason to risk deterring them with toxic fruit.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/qmnonic/8381684421/">Matt MacGillivray/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Don’t you know that you’re toxic?</h2>
<p>First, how do plants poison the pulp? Plants produce a range of chemical compounds, some of which have no apparent function in primary life-maintaining processes and so are called secondary compounds. </p>
<p>Potentially poisonous secondary compounds are produced either in the course of development from seed to adult plant, or in direct response to attacks from plant-eaters. </p>
<p><a href="http://www.journals.uchicago.edu/doi/abs/10.1086/286069">Poisons in fruit pulp</a> are typically produced during development. Unripe fruit is often toxic to protect immature seeds from attack or premature dispersal, but ripe fruit with mature seeds can also be poisonous. </p>
<p>So how do we explain fruit that remains poisonous even when it’s ripe and ready for dispersal? One theory is that a low level of poison in fruit encourages fruit-eating animals to move away from the parent plant (avoiding additional poison), therefore carrying seeds further away.</p>
<p>In some cases toxins cause constipation, ensuring that seeds stay longer in the gut and so increasing the distance they are carried. In other cases – think of prunes – they act as laxatives to ensure the quick passage of seeds with minimal time for seed damage during digestion. </p>
<p>There is <a href="http://www.journals.uchicago.edu/doi/abs/10.1086/286069">some evidence</a> for these hypotheses, but they’re not the full story. </p>
<h2>There’s good fruit-eating and bad fruit-eating</h2>
<p>Not everything that eats fruit is good for the plant. Toxins in fruit might specifically target animals, microbes and fungi that damage its seeds, while being non-toxic to species that are good seed dispersers. The fruit of deadly nightshade is lethal to many mammals <a href="http://www.journals.uchicago.edu/doi/abs/10.1086/286069">but apparently harmless to some birds</a>, and Mediterranean buckthorn fruits are toxic to some insect pests but not <a href="http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0706.2002.990209.x/full">seed-dispersing birds</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/184295/original/file-20170901-22435-19jow2w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The fruit of deadly nightshade is poisonous to many mammals, but not the birds that carry its seeds.</span>
<span class="attribution"><span class="source">Andreas Rockstein/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But poisons often discourage seed destroyers and dispersers alike, so plants face a <a href="http://www.journals.uchicago.edu/doi/abs/10.1086/286069">trade-off</a> between deterring assailants and attracting the animals that safely disperse their seeds. Research so far suggests that how plants balance this trade-off depends on how long they hold onto fruit.</p>
<p>Highly nutritious and attractive fruit is quickly found and eaten as soon as it’s ripe: think of a plum tree stripped by fruit bats in a night or two. These fruits face less risk of damage before they’re safely eaten by the right animals, so protective toxins are less important and are therefore produced in <a href="http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0706.2003.11796.x/full">lower quantities</a>.</p>
<p>On the other hand, plants with less nutritious fruit, rarer or unreliable seed-dispersers, or more predators need to protect their <a href="https://link.springer.com/article/10.1007/s00442-007-0917-6">vulnerable seeds</a> with toxic fruit. </p>
<p>Finally, fruit might be poisonous simply because the rest of the plant is toxic. This is another trade-off some plants make: toxins that protect leaves from herbivores can also end up in the fruit. </p>
<p><a href="http://www.journals.uchicago.edu/doi/abs/10.1086/673258">Recent research</a> suggests that poison fruit may ultimately result from adaptation to a range of animals consuming different plant parts, so we need to consider the whole plant and its interactions with various organisms to understand the origin and function of poison fruit. </p>
<p>Understanding how and why plants produce poison, in their fruit or elsewhere, has led to discoveries that are valuable for reasons other than murder and mayhem. Naturally occurring plant poisons <a href="https://www.amnh.org/explore/news-blogs/on-exhibit-posts/the-power-of-poison-poison-as-medicine/">have been used for a range of medical purposes</a> from painkillers to antimalarial and anti-cancer agents, and there are potentially many more useful plant poisons yet to be discovered in the wild. </p>
<p><br></p>
<p><em>* Email your question to alwayswondered@theconversation.edu.au
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* Tell us on <a href="https://twitter.com/ConversationEDU">Twitter</a> by tagging <a href="https://twitter.com/ConversationEDU">@ConversationEDU</a> with the hashtag #alwayswondered, or
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<p class="fine-print"><em><span>Julian MacPherson Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Plants produce toxic fruit for everything from deterring fungi to causing constipation.Julian MacPherson Brown, Postdoctoral research fellow, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/817542017-08-27T20:08:33Z2017-08-27T20:08:33ZI have always wondered: when do baby birds begin to breathe?<figure><img src="https://images.theconversation.com/files/183257/original/file-20170824-25658-1ottw81.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A quail chick hatching. </span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><em>This is an article from I Have Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au</em></p>
<hr>
<blockquote>
<p><strong>This question dates back to when I was a kid and no one has ever been able to answer it in a convincing way. I have always wondered: when do birds (and other egg-born creatures) take their first breath? And how do they take in oxygen before their lungs are working? Obviously since eggs squeak before they hatch, lungs are functional prior to the hatching… but when is that magical inflation-of-the-lungs moment? And how does it happen? – Gabrielle Deakin, Barcelona.</strong></p>
</blockquote>
<hr>
<p>As <a href="http://www.ucmp.berkeley.edu/mammal/eutheria/placental.html">placental mammals</a>, our first breath of air comes after birth. But egg-born creatures like birds and reptiles don’t have an umbilical cord to feed them oxygen, so how do they breathe? And how can a chick inflate its lungs inside the egg?</p>
<p>First, let’s talk about the eggs themselves.</p>
<p>Eggs laid by birds have shells that are bumpy (at least under the microscope), made almost entirely of calcium carbonate, and have as many as <a href="https://www.exploratorium.edu/cooking/eggs/eggcomposition.html">17,000 tiny pores</a>. Because of these pores, oxygen can travel from the outside world to the embryo inside and carbon dioxide and water move out of the egg in the same way. </p>
<p>Lying between the eggshell and the albumen, or egg white, are two transparent membranes that prevent bacterial invasion, and also develop into a network of blood vessels. These membranes are the <em>chorion</em> and the <em>allantois</em>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183401/original/file-20170825-27655-13ctaau.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Membranes inside the egg move oxygen inside for the embryo, and pass carbon dioxide out.</span>
<span class="attribution"><span class="source">Pixabay</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Reptile eggs can either be hard and almost identical to bird’s eggs, as thin shelled as parchment, or soft and leathery. Most reptile eggs are porous to air and water, and tend to absorb more water from the outside world than bird eggs. Finally, the membranes of reptiles’ eggs are very similar to birds’, but don’t always entirely surround the embryo.</p>
<p>Regardless of these differences, the chorion and allantois have a network of blood vessels which act as a respiratory organ and is the first stage of “breathing” for bird or reptile embryos. </p>
<p>Birds actually go through three stages of breathing in the egg. Reptiles have a similar path, but they skip straight from step one to three. </p>
<h2>Stage 1: embryonic</h2>
<p>Before chicks or reptiles develop lungs, they still need to get oxygen and get rid of carbon dioxide. In placental mammals like humans (and some marsupials), all of this is accomplished by the mother through the umbilical cord and the placenta. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=835&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=835&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=835&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1049&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1049&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183405/original/file-20170825-28045-uaqof1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1049&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some reptiles have leathery shells.</span>
<span class="attribution"><span class="source">Brad Chambers</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In birds, this gas exchange is done by <a href="http://education.seattlepi.com/diffusion-experiments-eggs-4759.html">diffusion</a> (the movement of air from the outside to the inside of the egg) through the eggshell and a complex fusion of the chorion and the allantois called the <em>chorioallantoic membrane</em>. Reptiles also have a chorioallantoic area which functions as a respiratory organ. </p>
<p>In birds, the chorioallantoic membrane develops about three days after incubation begins and takes about two weeks to develop fully. It is highly vascularised (has lots of blood vessels), which allows for the free exchange of oxygen and carbon dioxide. </p>
<p>This membrane also plays a central role in the development of the embryo’s bones, because it transports calcium from the eggshell to the developing chick or embryonic reptile (excluding some reptiles which get some of their <a href="http://www.herpconbio.org/Volume_5/Issue_2/Stewart_Ecay_2010.pdf">calcium from the egg yolk</a>).</p>
<h2>Stage 2: pre-hatching</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183419/original/file-20170825-18691-d11lpz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A bird hatching from the egg.</span>
<span class="attribution"><span class="source">Maggie J Watson</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The <a href="http://chickscope.beckman.uiuc.edu/resources/egg_to_chick/development.html">embryo</a> doesn’t actually breathe via lungs for almost all of its time in the egg. When the embryo is getting close to hatching, a few differences between reptiles and birds emerge. In birds, a few days before hatching, the chick, which is now curled up tightly with its head stuck under one wing and its beak pointed towards the top of the egg, penetrates an air pocket or air cell at the top of the egg. </p>
<p>This air pocket began to form when the egg was laid. A freshly laid egg is the temperature of its mother’s body, but it soon begins to cool. As it cools, the inner shell membranes begin to shrink and separate from the outer shell membrane to form a pocket, which slowly fills with air and gets larger as the egg is incubated. </p>
<p>As soon as the chick breaks into this air pocket, it takes its first breath and the lungs begin to function. The air cell continues to be refilled with air through diffusion. Diffusion through the chorio-allantoic membrane is also still used, but is slowly replaced by lung activity as hatching nears. At the very end of this period, if you put your ear to the egg, you might hear some peeping sounds. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/oQddkMuXi3w?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A chick peeps in the egg. Also visible is a distinctive ‘pipping’ pattern, as the chick hammers the inside of the egg.</span></figcaption>
</figure>
<p>In birds, this sound is made through a structure called a syrinx as birds don’t have vocal chords. But most reptile species don’t have an egg air pocket, so they go straight to stage three.</p>
<h2>Stage 3: post-hatching</h2>
<p>Many egg-born creatures develop a small, sharp protuberance called an “egg tooth” (technically called a caruncle) on their beak or snout. It can be made of hard skin (like in crocodiles and birds) or be an actual extra tooth (like in some lizards and snakes), but regardless, it’s used to break through the egg and falls off or is reabsorbed soon after hatching.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=855&fit=crop&dpr=1 600w, https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=855&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=855&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1075&fit=crop&dpr=1 754w, https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1075&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/183403/original/file-20170825-18691-1xjz2g9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1075&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A baby turtle cracks through its egg.</span>
<span class="attribution"><span class="source">Brad Chambers</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The chick, guided by its wing placement, uses its egg tooth to hammer the inside of the egg. First the egg “stars” (when the beak begins to crack the shell), and then it “pips” (when the beak breaks through the shell). The chick uses its feet to move around in a circle and pierce the egg. The chorioallantoic membrane begins to lose function as it dries out, and the chick then relies solely on its lungs. The chick continues to peep, which tells the parent that hatching is imminent and ensures its clutch mates hatch synchronously. </p>
<p>Reptiles slice through their weakened eggshells (weak now because they’ve extracted most of the calcium) with an egg-tooth on their snouts and start to breathe. Some reptiles (crocodiles) also produce sounds, but unlike birds they use a larynx and vocal cords, very similar to humans.</p>
<p>When you get right down to it, birds and reptiles do pretty much the same thing in the egg. It’s not that surprising, as <a href="http://evolution.berkeley.edu/evolibrary/article/evograms_06">birds and some reptiles are quite closely related</a>. They’ve all evolved specific eggs to both protect growing embryos and provide them with what they need – including air.</p>
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<p class="fine-print"><em><span>James Van Dyke has received funding from the National Science Foundation. </span></em></p><p class="fine-print"><em><span>Maggie J. Watson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Have you ever heard chicks peeping in the egg? Have you ever wondered how they manage to take their first breath in the shell?Maggie J. Watson, Postdoctoral Researcher in Ecology, Conservation and Parasitology, Charles Sturt UniversityJames Van Dyke, Lecturer in Ecology, Charles Sturt UniversityLicensed as Creative Commons – attribution, no derivatives.