tag:theconversation.com,2011:/us/topics/egg-47678/articlesEgg – The Conversation2023-09-21T02:29:20Ztag:theconversation.com,2011:article/2119172023-09-21T02:29:20Z2023-09-21T02:29:20ZCurious Kids: what came first, the chicken or the egg?<figure><img src="https://images.theconversation.com/files/549468/original/file-20230921-15-j14ijn.png?ixlib=rb-1.1.0&rect=92%2C16%2C5497%2C4232&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock/Edited by The Conversation</span></span></figcaption></figure><blockquote>
<p><strong>What came first, the chicken or the egg? — Grace, age 12, Melbourne</strong></p>
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<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>Hi Grace!</p>
<p>Thanks for this great question. It’s an age-old dilemma that has left many people scratching their heads. </p>
<p>From an evolutionary perspective, both answers could be considered true! It all depends on how you interpret the question.</p>
<h2>The case for the egg</h2>
<p>When the first vertebrates – that is, the first animals with backbones – came out of the sea to live on land, they faced a challenge. </p>
<p>Their eggs, similar to those of modern fish, were covered only in a thin layer called a membrane. The eggs would quickly dry up and die when exposed to air. Some animals such as amphibians (the group that includes frogs and axolotls) solved this problem by simply laying their eggs in water – but this limited how far inland they could travel. </p>
<p>It was the early reptiles that evolved a key solution to this problem: an egg with a protective outer shell. The first egg shells would have <a href="https://phys.org/news/2020-06-hard-eggshells-evolved-dinosaur-family.html">been soft and leathery</a> like the eggs of a snake or a sea turtle. Hard-shelled eggs, such as those of birds, likely appeared much later. </p>
<p>Some of the <a href="https://www.nature.com/articles/s41598-019-40604-8">oldest known hard-shelled eggs</a> appear in the fossil record during the Early Jurassic period, roughly 195 million years ago. Dinosaurs laid these eggs, although reptiles such as crocodiles were also <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0171919">producing hard-shelled eggs</a> during the Jurassic.</p>
<p>As we know now, it was a line of dinosaurs that eventually gave rise to the many species of birds we see today, including the chicken. </p>
<p>Chickens belong to an order of birds known as the Galliformes, which includes other ground-dwelling birds such as turkeys, pheasants, peafowl and quails. </p>
<p>Specifically, chickens are part of a galliform genus called <em>Gallus</em>, which is thought to have started changing into its modern species between 6 million and 4 million <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7014787/">years ago in South-East Asia</a>. Domestic chickens only began appearing some time within the <a href="https://www.smithsonianmag.com/smart-news/researchers-pinpoint-date-when-chickens-were-first-domesticated-180980212">past 10,000 years</a>.</p>
<p>This means hard-shelled eggs like the ones chickens lay are older than chickens themselves by almost 200 million years. So problem solved, right? </p>
<p>Well, it’s a matter of perspective.</p>
<h2>The case for the chicken</h2>
<p>If we interpret the question as referring specifically to chicken eggs – and not all eggs – the answer is very different.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/549469/original/file-20230921-24-bdrveo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&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">No fowl play here.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>Unlike most species of animals, the modern chicken didn’t evolve naturally through evolution. Rather, it’s the result of domestication: a process where humans selectively breed animals to create individuals that are more tame and have more desirable traits.</p>
<p>The most famous example is the domestication of wolves into dogs by humans. Wolves and dogs have <a href="https://www.scientificamerican.com/article/how-wolf-became-dog/">almost entirely the same DNA</a>, but are very different in how they look and behave. Dogs came from wolves, and so scientists consider dogs to be a subspecies of wolf.</p>
<p>Similarly, chickens came from a species called the red junglefowl, which is found across Southern and South-East Asia. Researchers think red junglefowl were first drawn to humans thousands of years ago, when <a href="https://www.arch.ox.ac.uk/article/major-new-international-research-reveals-new-evidence-about-when-where-and-how-chickens-were">people started farming</a> rice and other cereal grains. </p>
<p>This closeness then allowed domestication to take place. Over many generations the descendants of these tamed birds became their own subspecies. </p>
<p>Technically, the first chicken would have hatched from the egg of a selectively bred junglefowl. It was only when this chicken matured and started reproducing that the first true chicken eggs were laid.</p>
<h2>So which answer is the better one?</h2>
<p>That’s completely up to you to decide. As is the case with many dilemmas, the whole point of the question is to make you think – not necessarily to come up with the perfect answer. </p>
<p>In this case, evolutionary biology allows us to make an argument for both sides – and that is one of the wonderful things about science.</p><img src="https://counter.theconversation.com/content/211917/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ellen K. Mather 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>Evolutionary biology and the fossil record reveal a great deal about the origins of chickens and eggs.Ellen K. Mather, Adjunct Associate Lecturer in Palaeontology, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2078372023-07-06T20:21:44Z2023-07-06T20:21:44ZEggs are so expensive right now. What else can I use?<figure><img src="https://images.theconversation.com/files/534516/original/file-20230628-21-na5m3.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1279%2C852&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.pexels.com/photo/a-man-in-a-black-shirt-cracking-an-egg-6944027/">Vlada Karpovich/Pexels</a></span></figcaption></figure><p>The price of eggs <a href="https://www.abc.net.au/news/2023-06-14/egg-shortage-high-prices-blamed-on-shift-from-cage-to-free-range/102474282">is rising</a>. So many of us may be looking for cheaper alternatives. </p>
<p>First, the bad news. Nothing can replace a boiled, poached or fried egg. </p>
<p>Now, the good news. Lots of other ingredients can make foods puff and rise, give your meal a rich taste, or hold together ingredients.</p>
<p>So try using some of these egg substitutes and save the real eggs for your breakfast.</p>
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<strong>
Read more:
<a href="https://theconversation.com/how-to-save-50-off-your-food-bill-and-still-eat-tasty-nutritious-meals-184152">How to save $50 off your food bill and still eat tasty, nutritious meals</a>
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<h2>Why are eggs so popular?</h2>
<p>Eggs are incredibly <a href="https://www.foodstandards.gov.au/science/monitoringnutrients/afcd/pages/default.aspx">nutritious</a>. They’re a <a href="https://www.mdpi.com/2072-6643/11/3/684">rich source</a> of protein, vitamins A and D, pigments called carotenoids, and minerals.</p>
<p>Eggs are also versatile. We use them to make a range of savoury and sweet foods, sauces and drinks, not to mention breakfast.</p>
<p>Their popularity and versatility lies in the unique characteristics of the two main parts of the egg – the white and yolk. Each contribute <a href="https://www.amazon.com.au/Food-Cooking-Harold-McGee/dp/0684800012">different properties</a> in cooking.</p>
<p><a href="https://www.mdpi.com/2072-6643/11/3/684">Egg yolk</a> is about 55% water, 27% fats, 16% protein (with small amounts of carbohydrate). <a href="https://www.mdpi.com/2072-6643/11/3/684">Egg white</a> is about 10% protein and 90% water, with only traces of fat and carbohydrates. Different types of protein in egg white contribute to them foaming when whisked.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/five-foods-that-used-to-be-bad-for-you-but-now-arent-50333">Five foods that used to be bad for you ... but now aren't</a>
</strong>
</em>
</p>
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<h2>Eggs are versatile</h2>
<p>Eggs have a <a href="https://www.sciencedirect.com/science/article/pii/S0268005X2200131X?casa_token=1yXlEb1uvwQAAAAA:s3h5KCozwn-hjIn6kLOEoW45An255V6Z0G8TcJAQgTejfLEwV7nKqkS6VPWXiNkNxR4m5Mr2lHc">different role</a> in different types of cooking.</p>
<p><strong>1. Eggs are a raising agent</strong></p>
<p>Beaten or whisked eggs act as a raising agent by creating pockets of air in foods, which expand with cooking, making the foods puff and rise. This gives baked products like cakes, biscuits and muffins volume and an airy feel. </p>
<p>Using just the egg white leads to a remarkably light and delicate foam, as we see in meringues. In mousse and souffles the whites and the yolk are beaten separately, then mixed together. This leads to a light, airy and smooth texture. </p>
<p><strong>2. Eggs hold together other ingredients</strong></p>
<p>Eggs combine ingredients and hold them together during cooking. This gives foods – such as vegetable or meat patties – their structure.</p>
<p><strong>3. Eggs bind other liquids</strong></p>
<p>The liquid from eggs binds other liquids from other ingredients in the recipe into a soft, moist and tender mass. We see this in scrambled eggs, omelettes and egg custard.</p>
<p><strong>4. Eggs act as emulsifiers</strong></p>
<p>The egg yolk contains different proteins (livetin, phosvitin) and lipoproteins (lecithin). These act as emulsifiers, allowing fat and water to mix together in foods such as mayonnaise and hollandaise sauce.</p>
<p><strong>5. Eggs boost flavour</strong></p>
<p>The fat in egg yolks helps carry and release the flavour of some fat-soluble components of food. These foods <a href="https://www.sciencedirect.com/science/article/pii/S0924224401000796">may taste differently</a> without the eggs. Eggs also contribute to foods feeling soft in the mouth.</p>
<p>As eggs have different roles in cooking, you may need different egg substitutes depending on the outcome you want. Here are some cheaper (and vegan) options.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/eight-cracking-facts-about-eggs-150797">Eight cracking facts about eggs</a>
</strong>
</em>
</p>
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<h2>Aquafaba</h2>
<p>Aquafaba is the liquid drained from cans of bean – typically from chickpeas as it has the most neutral flavour. This is the all-round winner, especially as most of us probably throw it away without realising what a gem it is. </p>
<p>Aquafaba is <a href="https://www.sciencedirect.com/science/article/pii/S0924224421001424?casa_token=P45Z4G2SFdsAAAAA:DRy8adcAU_QHl96LONyWOEhUXvrExVZsJ18xKvc8OiPYeVKHSOkGOKefiixXFPY9UhdscEaHF70">versatile</a>. You can whip it up like egg whites to form a foam that can be used to make meringue (even pavlova), gelato, in baked goods, and for binding ingredients in patties. It also contains emulsifiers and can be used to make mayonnaise.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Chickpeas in strainer sitting over glass of aquafaba" src="https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534518/original/file-20230628-15-2hvg8r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=490&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Aquafaba is the liquid drained from cans of beans, usually chickpeas.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/close-aquafaba-filtered-chickpea-broth-used-1907028793">Shutterstock</a></span>
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<p>You’ll need different quantities of aquafaba depending on the recipe. Generally, though, you use about two to three tablespoons of aquafaba to replace the volume of fluid from an egg.</p>
<p>On the downside, aquafaba can taste a bit beany. So it is best to use it with stronger flavours to overcome this.</p>
<p>Nutritionally, <a href="https://www.sciencedirect.com/science/article/abs/pii/S0924224421001424?via%3Dihub">aquafaba</a> has small amounts of carbohydrate (about 2.6g/100 millilitre), and negligible levels of protein (about 1.3g/100 millilitre). </p>
<p>You can also freeze aquafaba.</p>
<h2>Vinegar and baking soda</h2>
<p>Mixing a teaspoon of baking soda with a tablespoon of vinegar can replace an egg in most baked goods. This produces carbon dioxide, which is trapped into air pockets, and makes foods rise.</p>
<p>This is a very cheap option, however its success may be limited by how heavy the rest of the ingredients are. This combination also has very little nutritional value.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-apple-cider-vinegar-really-a-wonder-food-86551">Is apple cider vinegar really a wonder food?</a>
</strong>
</em>
</p>
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<h2>Commercial egg replacements</h2>
<p>These are available at most supermarkets, are very cheap compared with eggs, have a long shelf life, and are easy to use, with instructions on the packaging.</p>
<p>Typically, they contain different starches from potato, tapioca and pea protein (which act as leavening agents and form foams), along with raising agents. They are recommended for use in baked goods. However they have very little nutritional value compared to an egg.</p>
<h2>Flaxseed meal and chia seeds</h2>
<p>Use either a tablespoon of flaxseed meal, or chia seeds, added to about three tablespoons of water. Allow the mixture to sit for a few minutes to form a gel. </p>
<p>The gels can be used in baked goods, however this option isn’t as cheap as the others, and has a slight nutty taste. </p>
<p>Both these seeds provide nutritional value. They are both rich in the plant-based omega-3 fatty acid called alpha-linolenic acid. We <a href="https://academic.oup.com/ajcn/article/59/6/1304/4715808">can convert</a> this fatty acid into healthy omega-3 fatty acids, but at a slow rate. These seeds also provide fibre, polyphenols and antioxidants.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Chia seeds in a bowl, in a spoon, spilling onto surface" src="https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534946/original/file-20230630-27-kgb8rn.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">You can add chia seeds to water to form a gel.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/healthy-chia-seeds-wooden-spoon-on-331447064">Shutterstock</a></span>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/does-tiktoks-chia-lemon-internal-shower-really-beat-constipation-heres-what-science-says-188744">Does TikTok's chia-lemon 'internal shower' really beat constipation? Here's what science says</a>
</strong>
</em>
</p>
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<h2>Tofu</h2>
<p>Tofu, which is made from soybeans, is widely available and fairly cheap. It has the most “eggy” appearance and so makes it ideal as a substitute for scrambled eggs and in quiche. However, you will need to use silken tofu and puree it. </p>
<p>Tofu is highly nutritious and provides protein, fat, calcium, polyphenols and anti-oxidants. </p>
<p>You could also use soy flour. Add one tablespoon to three tablespoons of water, then use immediately in baking and for binding ingredients together. However, soy flour does not contain calcium, which tofu does.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/is-fake-meat-healthy-and-whats-actually-in-it-187532">Is fake meat healthy? And what's actually in it?</a>
</strong>
</em>
</p>
<hr>
<h2>Mashed fruit</h2>
<p>Mashed bananas or applesauce are also used as egg substitutes. These mainly act to bind and hold moisture in the food and help carry the flavours. </p>
<p>You also get the nutritional value of the fruit. Due to the natural sugar that in fruit, this will sweeten your baked goods so you will need to drop the sugar by about a tablespoon (or more) for each piece of fruit you add.</p><img src="https://counter.theconversation.com/content/207837/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Evangeline Mantzioris is affiliated with Alliance for Research in Nutrition, Exercise and Activity (ARENA) at the University of South Australia. Evangeline Mantzioris has received funding from the National Health and Medical Research Council, and has been appointed to the National Health and Medical Research Council Dietary Guideline Expert Committee.</span></em></p>There are lots of other ingredients you can use to make foods puff and rise, give your meal a rich taste, or to hold together ingredients.Evangeline Mantzioris, Program Director of Nutrition and Food Sciences, Accredited Practising Dietitian, University of South AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1504962020-12-15T13:20:28Z2020-12-15T13:20:28ZVirgin births from parthenogenesis: How females from some species can reproduce without males<figure><img src="https://images.theconversation.com/files/374837/original/file-20201214-17-2nde3j.png?ixlib=rb-1.1.0&rect=0%2C0%2C5463%2C3006&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Getting the job done. A female Asian water dragon (Physignathus cocincinus) produced a daughter (left) without the assistance of a male. </span> <span class="attribution"><a class="source" href="https://nationalzoo.si.edu/news/scientists-confirm-facultative-parthenogenesis-smithsonians-national-zoos-asian-water-dragon">Skip Brown/Smithsonian’s National Zoo</a></span></figcaption></figure><p>An Asian water dragon hatched from an egg at the Smithsonian National Zoo, and her keepers were shocked. Why? Her mother had never been with a male water dragon. Through genetic testing, zoo scientists discovered the newly hatched female, born on Aug. 24, 2016, had been produced through a <a href="https://doi.org/10.1371/journal.pone.0217489">reproductive mode called parthenogenesis</a>.</p>
<p>Parthenogenesis is a Greek word meaning “virgin creation,” but specifically refers to female asexual reproduction. While many people may assume this behavior is the domain of science fiction or religious texts, parthenogenesis is <a href="https://doi.org/10.1038/sdata.2014.15">surprisingly common throughout the tree of life</a> and is found in a variety of organisms, including plants, insects, fish, reptiles and even birds. Because mammals, including human beings, require certain genes to come from sperm, <a href="https://doi.org/10.1159/000090812">mammals are incapable of parthenogenesis</a>.</p>
<h2>Creating offspring without sperm</h2>
<p>Sexual reproduction involves a female and a male, each contributing genetic material in the form of eggs or sperm, to create a unique offspring. The vast majority of animal species reproduce sexually, but females of some species are able to produce eggs <a href="https://www.britannica.com/science/parthenogenesis">containing all the genetic material required for reproduction</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A microscopic view of a translucent water flea show four round eggs inside." src="https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=418&fit=crop&dpr=1 600w, https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=418&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=418&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=526&fit=crop&dpr=1 754w, https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=526&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/373966/original/file-20201209-19-1x4523.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=526&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 female freshwater water flea (<em>Daphnia magna</em>) carrying parthenogenetic eggs.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/microscopic-view-of-freshwater-water-flea-royalty-free-image/841300586">buccaneership/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>Females of these species, which include <a href="https://doi.org/10.1002/evl3.30">some wasps</a>, <a href="https://doi.org/10.1086/283761">crustaceans</a> and <a href="https://www.scientificamerican.com/article/asexual-lizards/">lizards</a>, reproduce only through parthenogenesis and are called obligate parthenogens.</p>
<p>A larger number of species experience spontaneous parthenogenesis, best documented in animals kept in zoo settings, like the Asian water dragon at the National Zoo or a <a href="https://doi.org/10.1111/j.1095-8649.2008.02018.x">blacktip shark at the Virginia Aquarium</a>. Spontaneous parthenogens typically reproduce sexually, but may have occasional cycles that produce developmentally ready eggs.</p>
<p>Scientists have learned <a href="https://doi.org/10.1098/rspb.2009.2113">spontaneous parthenogenesis may be a heritable trait</a>, meaning females that suddenly experience parthenogenesis might be more likely to have daughters that can do the same.</p>
<h2>How can females fertilize their own eggs?</h2>
<p>For parthenogenesis to happen, <a href="https://doi.org/10.1534/g3.112.005421">a chain of cellular events must successfully unfold</a>. First, females must be able to create egg cells (oogenesis) without stimulation from sperm or mating. Second, the eggs produced by females need to begin to develop on their own, forming an early stage embryo. Finally, the eggs must successfully hatch. </p>
<p>Each step of this process can easily fail, particularly step two, which requires the chromosomes of DNA inside the egg to double, ensuring a full complement of genes for the developing offspring. Alternatively, the egg can be “faux fertilized” by leftover cells from the egg production process known as <a href="https://doi.org/10.1002/mrd.21266">polar bodies</a>. Whichever method kicks off the development of the embryo <a href="https://doi.org/10.1525/bio.2009.59.7.3">will ultimately determine the level of genetic similarity</a> between the mother and her offspring.</p>
<p>The events that trigger parthenogenesis are not fully understood, but appear to include environmental change. In species that are capable of both sexual reproduction and parthenogenesis, such as <a href="https://doi.org/10.1371/journal.pone.0115099">aphids</a>, stressors like <a href="https://doi.org/10.1111/een.12080">crowding and predation</a> may cause females to switch from parthenogenesis to sexual reproduction, but not the other way around. In at least one <a href="https://doi.org/10.1007/978-90-481-2770-2_15">type of freshwater plankton</a>, <a href="https://doi.org/10.5762/KAIS.2016.17.4.692">high salinity</a> appears to cause the switch.</p>
<h2>Advantages of self-reproduction</h2>
<p>Though spontaneous parthenogenesis appears to be rare, it does provide some benefits to the female who can achieve it. In some cases, it can allow females to generate their own mating partners. </p>
<p>The sex of parthenogenetic offspring is determined by the same method sex is determined in the species itself. For organisms where sex is determined by chromosomes, like the XX female and XY male chromosomes in some insects, fish and reptiles, a parthenogenetic female can produce offspring only with the sex chromosomes she has at hand – which means she will always produce XX female offspring. But for organisms where females have ZW sex chromosomes (such as in snakes and birds), all living offspring produced will either be ZZ, and therefore male, or <a href="https://doi.org/10.1098/rsbl.2010.0793">much more rarely, WW, and female</a>.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"976632933531316224"}"></div></p>
<p>Between 1997 and 1999, <a href="https://doi.org/10.1111/j.1095-8312.2012.01954.x">a checkered gartersnake kept at the Phoenix Zoo</a> gave birth to two male offspring that ultimately survived to adulthood. If a female mated with her parthenogenetically produced son, it would constitute inbreeding. While inbreeding can result in a host of genetic problems, from an evolutionary perspective it’s better than having no offspring at all. The ability of females to produce male offspring through parthenogenesis also suggests that asexual reproduction in nature may be more common than scientists ever realized before. </p>
<p>Biologists have observed, over long periods of time, that <a href="https://doi.org/10.1016/0022-5193(71)90058-0">species that are obligate parthenogens frequently die out</a> from <a href="https://doi.org/10.1038/s41514-018-0025-3">disease</a>, <a href="https://doi.org/10.1073/pnas.87.9.3566">parasitism</a> or <a href="https://doi.org/10.1002/evl3.30">changes in habitat</a>. The inbreeding inherent in parthenogenetic species appears to contribute to their short evolutionary timelines. </p>
<p>Current research on parthenogenesis seeks to understand why some species are capable of both sex and parthenogenesis, and whether occasional sexual reproduction might be enough for a species to survive.</p><img src="https://counter.theconversation.com/content/150496/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mercedes Burns has previously received funding from the National Science Foundation. </span></em></p>Parthenogenesis, a form of reproduction in which an egg develops into an embryo without being fertilized by sperm, might be more common than you realized.Mercedes Burns, Assistant Professor of Biological Sciences, University of Maryland, Baltimore CountyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1507972020-12-01T16:44:03Z2020-12-01T16:44:03ZEight cracking facts about eggs<figure><img src="https://images.theconversation.com/files/372017/original/file-20201130-21-zuzh18.jpg?ixlib=rb-1.1.0&rect=44%2C8%2C5852%2C3925&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/top-view-brown-eggs-carton-box-796082269">Krasula/Shutterstock</a></span></figcaption></figure><p>One of life’s true miracles, the humble egg is maybe one of the most versatile foodstuffs on the planet. It’s formed in 24 to 26 hours and hens can lay up to <a href="https://www.fresheggsdaily.blog/2017/05/how-long-does-it-take-chicken-to-lay-egg.html">250 eggs a year</a>. The incredible egg is pure protein and there are numerous (both sweet and savoury) methods to prepare this natural <a href="https://countryroadsmagazine.com/cuisine/recipes/100-ways-to-fix-an-egg/">nutritional powerhouse</a>. </p>
<p>Eggs can be added raw to smoothies, they can be fried, boiled, scrambled or poached and can be eaten for breakfast, lunch, tea and dinner. </p>
<p>They can be bought nearly anywhere, they last for a number of weeks, they are relatively inexpensive and they can do magical things to <a href="https://www.thekitchn.com/how-to-cook-an-egg-in-many-many-ways-cooking-guides-from-the-kitchn-211289">baked goods</a>. </p>
<p>We all know how easily they can be knocked up into a meal, but there’s also a lot more to the egg than meets the eye. Here’s all the things you need to know about the mighty egg.</p>
<h2>1. Eggs are ancient history</h2>
<p>Humans have been <a href="https://food.ndtv.com/food-drinks/10-different-types-of-edible-eggs-1784859">eating eggs</a> since the dawn of human time. <a href="http://www.foodtimeline.org/foodeggs.html">The Ancient Romans</a> ate peafowl eggs and the Chinese were said to be fond of pigeon eggs. When most of us think of an egg it’s usually the kind laid by a hen, however quail, duck, goose and turkey eggs are also among those consumed. Ostrich and Emu eggs are possibly the largest edible eggs weighing in at 1-2kg. Then there’s also fish eggs such as Caviar and Hilsa – a delicacy packed with essential nutrients. </p>
<figure class="align-center ">
<img alt="Toast with avocado, spinach and fried egg, top view." src="https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372021/original/file-20201130-15-1r6rzbj.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">Eggs make a meal out of it.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/toast-avocado-spinach-fried-egg-top-753380983">Anna Shepulova/Shutterstock</a></span>
</figcaption>
</figure>
<h2>2. Eggs = a nutritional powerhouse</h2>
<p>Eggs are considered one of the most <a href="https://www.healthline.com/nutrition/why-are-eggs-good-for-you">nutritious foods on the planet</a>. They are a natural source of inexpensive, high quality protein – more than half the protein being found in the white, which also includes vitamin B2 and lower amounts of fat than the yolk. The protein in eggs helps to lower blood pressure, optimise bone health and increases muscle mass. </p>
<p><a href="https://www.healthline.com/nutrition/selenium-benefits">Eggs</a> are also rich sources of selenium – an antioxidant that is important for thyroid function and our immune system and mental health – along with <a href="https://theconversation.com/why-covid-makes-it-more-important-than-ever-that-pregnant-and-breastfeeding-women-take-vitamin-d-148863">vitamin D</a>, <a href="https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/%20%20and%20various%20minerals%20including%20calcium">B6, B12</a>, <a href="https://www.healthline.com/nutrition/best-foods-high-in-zinc">zinc</a> , and <a href="https://www.nhs.uk/conditions/vitamins-and-minerals/iron/">iron</a>. They are good sources of <a href="https://pubmed.ncbi.nlm.nih.gov/26404361/#:%7E:text=Although%20eggs%20are%20known%20for,generally%20considered%20as%20antioxidant%20foods.&text=Some%20lipophilic%20antioxidants%20such%20as,to%20produce%20antioxidant%2Denriched%20eggs.">antioxidants</a> and can also help to reduce the likelihood of <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5611842/">macular degeneration and eye cataracts</a>.</p>
<h2>3. They used to have a bad rep</h2>
<p>For many years eggs were <a href="https://theconversation.com/five-foods-that-used-to-be-bad-for-you-but-now-arent-50333">considered to be unhealthy</a> due to the high levels of cholesterol found within them. In fact it was recommended to limit the amount eggs eaten. But this fact originated from what are now considered incorrect conclusions drawn from early research stating that dietary cholesterol contributed to <a href="https://www.nhs.uk/news/food-and-diet/eating-egg-day-does-not-raise-risk-heart-attack-or-stroke/#:%7E:text=%22Eggs%20are%20NOT%20bad%20for,also%20quite%20high%20in%20cholesterol">raised blood cholesterol</a>. Many people believe cholesterol to be harmful, but the truth is that it’s essential for our <a href="https://www.ncbi.nlm.nih.gov/books/NBK9898/">bodies to function</a>. So despite what you might have heard, there’s no recommended limit on how many <a href="https://pubmed.ncbi.nlm.nih.gov/16340654/">eggs you can eat</a>.</p>
<h2>4. But they’ve always been symbolic</h2>
<p>In many cultures worldwide, the egg is <a href="https://www.huffpost.com/entry/easter-eggs-history-origin-symbolism-tradition_n_1392054">a symbol</a> of <a href="https://www.dailynews.com/2010/04/02/easter-eggs-are-symbols-of-new-life/#:%7E:text=Eggs%20have%20signified%20new%20life,that%20they%20embody%20Christian%20teaching%20or%20https://www.alimentarium.org/en/knowledge/eggs-symbol-life">new life</a> , fertility and rebirth. They have signified new life far back into the mists of human origin, long before <a href="https://blogs.loc.gov/folklife/category/material-culture/eggs/#:%7E:text=Whether%20this%20is%20true%20or,celebrated%20at%20the%20vernal%20equinox.&text=Orthodox%20Christians%20in%20Mesopotamia%20took,a%20symbol%20of%20Christ's%20blood.">Christianity</a>. Indeed, an ancient Roman proverb said that all life comes from an egg.</p>
<figure class="align-center ">
<img alt="Artists display painted multicolored Easter eggs against the background of a historic building" src="https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372019/original/file-20201130-19-1tbwq29.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">The Easter Festival in Kyiv, Ukraine.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/kyiv-ukraine-april-07-2018-easter-1312183439">S.Borisovich/Shutterstock</a></span>
</figcaption>
</figure>
<h2>5. No, eggs are not chicken periods</h2>
<p>You may have heard <a href="https://www.peta.org/features/eat-chickens-period/">the rumour</a> that eating an egg is eating a chicken’s period. But as chickens are not mammals they do not have wombs and so the egg is actually classed as both the egg and the womb. So it’s not the same as the <a href="https://www.selvabeat.com/home/bad-egg">human reproductive system</a>. Eggs laid on a daily basis by chickens and sold commercially have <a href="https://www.canr.msu.edu/news/can_you_hatch_an_egg_bought_from_the_store#:%7E:text=Most%20eggs%20sold%20commercially%20in,and%20have%20not%20been%20fertilized.&text=Given%20the%20right%20nutrients%2C%20hens,and%20laying%20of%20the%20egg">not been fertilised</a>. If they are provided with the correct nutrients hens will lay eggs with or without having been in the presence of a rooster. In fact the only thing chickens need to lay eggs <a href="https://cutt.ly/khlZiaQ">is light</a>. </p>
<h2>6. COVID has increased demand</h2>
<p>Egg sales have skyrocketed during the pandemic, surpassing 13 billion for the first time <a href="https://www.independent.co.uk/life-style/egg-sales-uk-flexitarian-diet-meat-free-vegetarian-plant-a8800901.html">since the 1980s</a>, which in turn has led to a significant rise in the <a href="https://econlife.com/2020/04/coronavirus-egg-demand/">cost of eggs</a>. </p>
<p>The demand for eggs has historically been strong during tougher <a href="https://www.latimes.com/business/story/2020-04-08/egg-prices-rising-coronavirus">economic stretches</a>, possibly due to the fact that they are a relatively cheap source of protein and other nutrients and are also an extremely versatile ingredient. And with more time spent at home, the current pandemic has led to more families cooking from scratch, <a href="https://www.washingtonpost.com/business/2020/03/26/shortages-eggs-stress-baking/">baking and eating at home</a> – so more egg use. </p>
<figure class="align-center ">
<img alt="Hens in the garden." src="https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/372020/original/file-20201130-15-1byxne3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">More people are choosing to keep hens in their gardens.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/happy-free-chicken-garden-122971255">Imcsike/Shutterstock</a></span>
</figcaption>
</figure>
<h2>7. Battery cages are banned in the EU</h2>
<p>Over 90% of eggs produced in the UK have the <a href="https://www.egginfo.co.uk/egg-facts-and-figures/production">Lion trademark</a>. This means the hens and eggs are guaranteed to be British, with all hens vaccinated against salmonella and kept to higher welfare standards than the law demands. Across the EU, conventional “battery cages” have been banned. And in the UK, they have been replaced by larger, “enriched” <a href="https://www.nfuonline.com/sectors/poultry/poultry-news/enriched-colony-cages-the-facts/">cages</a> which can allow hens to express more of their natural behaviours, such as perching, dustbathing, and nesting.</p>
<h2>8. So many uses</h2>
<p>Eggs are not just for eating. They have many more uses both in and <a href="https://goodyfeed.com/8-uses-eggs-besides-cooking-eating/">around the home</a> and garden – alongside being great in <a href="https://www.medicalnewstoday.com/articles/323602">homemade beauty products</a>. Eggs can make a great homemade glue, leather cleaner and can even work as plant food. The shell is also a surprisingly <a href="https://morningchores.com/egg-shell-uses/">useful resource</a> and a vital and <a href="http://www.meandmybody.com/news_article.php?newsArticleId=9">important part</a> of this nutrient packed wonder food. Just some of the many uses for eggshells include feeding your compost pile, using as an abrasive drain cleaner or as pest control in the garden. And the eggshell membrane can even be used as a makeshift plaster for any cuts or grazes – just make sure you clean it thoroughly first.</p><img src="https://counter.theconversation.com/content/150797/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hazel Flight 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>Here’s all the things you need to know about the mighty egg.Hazel Flight, Programme Lead Nutrition and Health, Edge Hill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1116052019-04-16T00:56:00Z2019-04-16T00:56:00ZCurious Kids: why do eggs have a yolk?<figure><img src="https://images.theconversation.com/files/263073/original/file-20190311-86713-1w9k5xk.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4000%2C2000&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Yolks are a great source of vitamins, minerals, fats and proteins packaged up by the female animal for an embryo.</span> <span class="attribution"><span class="source">Emily Nunell/The Conversation CC-NY-BD</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>Why do eggs have orange stuff inside? – Rafael, age 7.</strong></p>
</blockquote>
<hr>
<p>This is a very interesting question. That orange stuff is called a yolk. It’s a great source of vitamins, minerals, fats and proteins packaged up by the female animal for an embryo (the developing cells that turn into a baby).</p>
<p>You probably know that the yellow bit inside a <a href="https://www.exploratorium.edu/cooking/eggs/eggcomposition.html">chicken’s egg</a> is the yolk, but in fact a lot of animals lay eggs that have yolks in them. However, not all animal eggs have a yolk!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269230/original/file-20190415-147483-i0tsqt.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">Having a yolk in the egg allows the developing animal to stay inside the egg a bit longer, which may boost its chances of survival. The downside is the mother will need to work harder to find food to get the nutrients needed to create a nutritious, fatty yolk.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/postsumptio/4020034256/in/photolist-78eJ8s-qnw67A-m1NhhS-bjoyLr-4pP5mR-m1NfUG-4z9TrA-m1NdXW-m1MooF-m1Mp9D-m1LPTc-m1Nfr7-m1Mn2x-m1Nhnw-m1Mna8-5UYBZ4-m1LQtv-m1LQEx-m1Mp1x-8dnZjx-4z5vot-m1Mp4t-m1NdDu-m1MoFz-m1Mk6Z-m1Movp-ndugz5-dMPRSj-6giHHB-sMDV7-924KmZ-4z5ymX-m1NeDq-m1LPhT-4z9P3Y-4z9KYm-m1MmGe-5UYHZp-7E2iPM-m1LNTr-6giEXF-4z5CcB-chZF9y-6cqrJD-5T4fW9-4z5zKV-m1MpVi-iqJGMU-4z9Kw7-m1NfqW">Flickr/Kai C. Schwarzer</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-is-it-true-that-male-seahorses-give-birth-92843">Curious Kids: Is it true that male seahorses give birth?</a>
</strong>
</em>
</p>
<hr>
<h2>A contest called evolution</h2>
<p>To understand why different animal species have different types of eggs, you need to know that all living things change slowly over time, through a process called evolution. </p>
<p>When a living thing is born with a special difference – what we would call a “trait” – sometimes this trait helps them live and survive better than someone who doesn’t have that trait. This trait may help them live longer and have more babies. </p>
<p>Because of these differences in survival, eventually, the trait that lets one individual living thing live and prosper will become quite common and be found all throughout a species. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269229/original/file-20190415-76831-1kp8lah.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">Lots of animals lay eggs.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/renemensen/13999038614/in/photolist-nk3JsJ-UcJpWd-bnUYXz-6XRxuK-oVZybS-sRLfv-goidJK-pmoXAi-2a4H7DA-e1HoA-QNr5t2-g5pkb-5kGcQB-XyYh6d-2fgZrjP-29t5Muj-hTU13S-TZxNQN-cX98L1-9smmCj-j1N1eN-67uVh1-dnzQ6y-56pKff-Jme988-QdHmX1-e4iMc-4x5dCp-phKL6Q-6y7k78-7VDKdV-9smqk7-UfcgQX-czgWzL-f9gpuV-8bfuEk-gcFzyx-4NxF6R-8knipd-a5GjCW-6w1vJN-q897zF-WwhsPZ-oLAoJC-67V8vC-aesrXh-e9Wayf-phN8LG-95hEdg-28gZtMU">Flickr/Alias 0591</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Back to eggs</h2>
<p>Imagine you are a worm living millions of years ago. You produce heaps and heaps of eggs that develop quickly into little worms. But most of the babies die because they are small and have to find food straight after hatching. They can’t go far because they are very little and so most starve to death (or are eaten by bigger creatures). </p>
<p>But what if <em>some</em> of those eggs happened to contain a little bit of fat from the mother? Compared to its brothers and sisters, the fat will allow the worm to spend just a little bit more time growing inside the egg and less time looking for food after hatching.</p>
<p>The worms that were lucky enough to have that fat inside the egg are more likely to survive long enough to have their own babies. And they pass on the fatty-egg trait to their own worm kids. Soon this fatty-egg trait becomes quite common.</p>
<p>So the worm who was able to feed its babies when they’re still inside the egg had more babies survive, and a yolk evolved.</p>
<h2>Which eggs have a yolk and why?</h2>
<p>Eggs with tiny bits of yolk are found in animals such as earthworms, leeches, clams, mussels, starfish, sea urchins, and marine arthropods (shrimp, lobsters, crabs) and some insects. These animals produce huge numbers of eggs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269234/original/file-20190415-147480-qwqj3v.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"></a>
<figcaption>
<span class="caption">Shrimps/prawns lay a large number of eggs. if you look closely, you can see a lot of small, light pink eggs inside this prawn’s body.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/pacificklaus/6238206580/in/photolist-avfrtS-9gXfqS-9jUzwk-cJKRMy-3EStPp-es6PC5-pStD3S-a21u7k-dGX1VV-27AicgD-DvVkvy-vJn61Y-7jkae5-7BcZxY-orbpeb-6piTvi-8Jcyr6-SNMUSo-L74heh-rB1kRD-nWFuHh-7Ena12-efNtE2-RARHQj-7WD6BG-okBqcH-2dBS1qF-6hpNfB-r1ngDq-ZLVXX6-efUeyU-9RFUsZ-vrWRfK-b1ovpx-5rwSWC-bhsARX-c6aHH7-6cVyYr-qSaoiy-5a5jR7-azXRn5-KhGmvC-CM6sVf-Ru2Bhu-7Bv9Sg-hrz4L-7b9d2J-9ftT55-RjF8r2-9DHYor">Flickr/Klaus Stiefel</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Most of the babies that grow in these sorts of eggs have to go through a lot of steps before they reach the adult stage. First they have to grow into a larvae (which is what we call a junior body, and often looks a bit like worm). </p>
<p>The babies have to change into a larvae so they can eat, and after having eaten a bit they develop into an adult (think of caterpillars that eventually turn into butterflies). </p>
<p>Animals that produce eggs with a bit more yolk have babies that can fully develop and skip the larvae step, such as in hagfish and snails. </p>
<h2>Big yolks for big babies</h2>
<p>Eggs with really large yolks are found in animals that produce very few eggs, and the offspring can use the yolk to develop completely. These sorts of eggs are found only in cephalopods (squid, octopus and nautilus) and some vertebrates (animals with backbones). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269235/original/file-20190415-147505-k155et.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">Here are some squid eggs.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/elevy/6997601241/in/photolist-bEmx4g-7cp3XJ-54Kcg7-oGTCfa-aVdxsx-Td7PU3-SNMUSo-7TB6qh-Eowd4-HASXW-264RqVJ-UwY3ew-USEwFj-fucnDE-cqAAEu-qVA694-55Hsc2-edbXFT-aVdwGZ-78aQpw-fYuHkA-7JFe3e-edbWsa-48ABw1-GNprt-r415Sp-2eymSWb-dqjDWz-5Kxnfh-9ENYfi-ooDKoi-8fURLU-b7Q2Q2-95uD9Q-bZnrbm-b7MZQF-5EdFaf-75fkpB-b7NGNi-3HcrC-6ywmip-7BvaEM-9n44pZ-oRjAEj-7Bvazx-6jUK4a-7ByZmq-6jUJmn-edbWGR-RUrfeH">Flickr/Elias Levy</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Vertebrates that produce eggs with large yolks include bony fish, cartilaginous fish (<a href="https://www.australiangeographic.com.au/topics/science-environment/2018/08/the-weird-world-of-shark-eggs/">sharks</a> and rays), reptiles, birds and egg-laying mammals (platypus and echidnas). </p>
<p>The rest of the mammals (animals that don’t lay eggs) have found a different system. They have a placenta, which is a kind of a feeding sack linking mother to embryo inside the mother’s body. This system allows the developing embryo or fetus to get nutrients straight from the mother. That’s how you were grown!</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-does-glow-in-the-dark-paint-work-92438">Curious Kids: How does glow in the dark paint work?</a>
</strong>
</em>
</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/111605/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>A yolk allows a developing animal to stay in an egg longer, boosting its chance of survival. The downside is the mother has to work hard finding extra food so her body can create a nutritious yolk.Maggie J. Watson, Lecturer in Ornithology, Ecology, Conservation and Parasitology, Charles Sturt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/888732018-01-09T19:36:04Z2018-01-09T19:36:04ZCan I prevent food allergies in my kids?<figure><img src="https://images.theconversation.com/files/199171/original/file-20171214-27555-jq68k5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There's still a lot we don't know about why more children have food allergies today. </span> <span class="attribution"><span class="source">from www.shutterstock.com</span></span></figcaption></figure><p>With the rise in food allergies over the last ten to 20 years, parents are understandably concerned about what – if anything – can be done to reduce the chances of their child developing a food allergy. Expectant mums often ask whether there’s anything they should eat, or avoid eating, to reduce the risk of food allergy in their child. </p>
<p>In the past, some guidelines recommended mums avoid eating “allergenic” foods (foods that commonly cause reactions in individuals with food allergy) during pregnancy and breastfeeding. This advice has now been removed because it hasn’t prevented food allergies in the child. So what do we know (and not know) about the link between foods eaten during pregnancy and food allergies in children?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-we-get-allergic-to-food-82503">Curious Kids: How do we get allergic to food?</a>
</strong>
</em>
</p>
<hr>
<h2>What is a food allergy?</h2>
<p>There are many different types of reactions to foods. Those involving the immune system are classified as allergies. </p>
<p>The type of allergy most studied is called “IgE-mediated” food allergy (IgE refers to immunoglobulin - the antibodies produced by our immune system). In IgE-mediated food allergy, the immune system responds to a particular food or foods in the same way it would respond to something dangerous. It causes symptoms that we call an allergic reaction. Food allergy can occur to a wide range of foods, but common culprits are peanut, tree nuts, egg, milk, soy, wheat, fish and shellfish. </p>
<p>For people with this type of food allergy, reactions generally occur rapidly, sometimes within minutes of ingesting the food. Common symptoms include hives (raised wheals that resemble mosquito bites), vomiting, and swelling of the lips, eyes, or face. Less commonly, reactions can involve the airways or circulation, resulting in potentially life-threatening symptoms like difficulty breathing, wheezing or collapse.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/199173/original/file-20171214-27597-1qua1fh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Peanuts should be introduced before one year of age.</span>
<span class="attribution"><span class="source">from www.shutterstock.com</span></span>
</figcaption>
</figure>
<p>In Australia, IgE-mediated food allergy now affects around <a href="http://www.jacionline.org/article/S0091-6749(11)00135-7/abstract">one in every ten babies</a>, and around <a href="http://www.jacionline.org/article/S0091-6749(17)31017-5/abstract">one in 20 older children</a>. It usually develops in infancy or early childhood, and can be lifelong. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/food-allergies-linked-to-overactive-immune-system-at-birth-53100">Food allergies linked to overactive immune system at birth</a>
</strong>
</em>
</p>
<hr>
<h2>Can we prevent children from developing food allergy?</h2>
<p>The normal response to eating a food is “tolerance”. In other words, the immune system sees the food as harmless and does not mount a response. Interventions to prevent food allergy aim to promote the development of tolerance.</p>
<p>Ten years ago, no one knew how this could be achieved. Since then, there have been major advances. Perhaps the most important is the recent discovery by researchers in the UK that peanut allergy can be prevented in some children who are at high risk of developing it. </p>
<p>In a <a href="http://www.nejm.org/doi/full/10.1056/NEJMoa1414850#t=article">study</a> in which 600 children with eczema or egg allergy were randomly assigned to either eat or avoid peanut, those who started eating peanut earlier (before they were one year old) were less likely to have peanut allergy at age five than those who avoided peanut. Studies have also shown eating egg earlier may protect against egg allergy, although this protective effect does not appear to be as strong as for peanuts. </p>
<p>As a result of this study, <a href="https://theconversation.com/introduce-eggs-and-peanuts-early-in-infants-diets-to-reduce-the-risk-of-allergies-65564">parents are now advised</a> to introduce foods like peanut and egg to infants before one year of age.</p>
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Read more:
<a href="https://theconversation.com/introduce-eggs-and-peanuts-early-in-infants-diets-to-reduce-the-risk-of-allergies-65564">Introduce eggs and peanuts early in infants' diets to reduce the risk of allergies</a>
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<p>Although this is an important advance in knowledge, the research also showed this isn’t effective for everyone. Some children develop food allergy very early in life, too early to benefit from being given foods like peanut before one year. </p>
<p>It’s also clear infant diet isn’t the only factor that determines whether a child develops a food allergy, since most children do not develop food allergy regardless of the age when foods like peanut and egg are first given. And some children develop food allergy even with an optimal diet. </p>
<h2>Maternal diet and food allergy</h2>
<p>Immune responses to foods like egg and peanut can be detected in some infants in the first few months of life, before these foods are introduced into the infant diet. This means food allergy prevention might need to start earlier than previously thought. </p>
<p>A <a href="https://cosmosmagazine.com/biology/peanut-antigens-in-breast-milk-may-protect-kids-from-allergy">recent study in mice</a> reported that milk from mothers exposed to egg protein protected offspring from developing allergic reactions to egg. This protection was strongest when the mothers were exposed to egg proteins during both pregnancy and breastfeeding. At the moment it’s not known whether this is also the case in people.</p>
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Read more:
<a href="https://theconversation.com/what-are-allergies-and-why-are-we-getting-more-of-them-40318">What are allergies and why are we getting more of them?</a>
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<p>The Australasian Society of Clinical Immunology and Allergy <a href="https://www.allergy.org.au/patients/allergy-prevention/ascia-guidelines-for-infant-feeding-and-allergy-prevention">does not recommend excluding</a> allergenic foods during pregnancy or breastfeeding.</p>
<p>We don’t know yet whether eating more of foods like peanuts or eggs in pregnancy can reduce the risk of the child developing a food allergy. But answers should be available soon. A <a href="https://www.nhmrc.gov.au/media/releases/2017/33-million-wa-researchers-promises-healthier-future">study led by researchers</a> at the University of Western Australia is about to look in detail at how the amount of egg and peanut eaten by mums relates to their child’s risk of having an egg or peanut allergy.</p>
<p>This is a large study which will take several years to complete, but hopefully we will be able to provide evidence-based advice for maternal diet, the same way we can for infant diet, very soon.</p><img src="https://counter.theconversation.com/content/88873/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jennifer Koplin receives funding from the National Health and Medical Research Council of Australia. </span></em></p>Parents are now advised to introduce foods like peanut and egg to infants before one year of age.Jennifer Koplin, Research Fellow, Population Health, Murdoch Children's Research InstituteLicensed as Creative Commons – attribution, no derivatives.