tag:theconversation.com,2011:/id/topics/pheromones-4868/articlesPheromones – The Conversation2023-06-20T17:37:31Ztag:theconversation.com,2011:article/2066602023-06-20T17:37:31Z2023-06-20T17:37:31ZInternet of microbiota: could synthetic probiotics help prevent our natural bacteria from going astray?<figure><img src="https://images.theconversation.com/files/532974/original/file-20230620-19-6ltoty.jpg?ixlib=rb-1.1.0&rect=0%2C59%2C1997%2C1353&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Having a healthy _E coli_ community in our intestinal system is essential to good human health.</span> <span class="attribution"><a class="source" href="https://pixabay.com/fr/photos/koli-bact%C3%A9ries-escherichia-coli-123081/">Geralt/Pixabay</a></span></figcaption></figure><p>Animals use chemical substances called <a href="https://www.americanscientist.org/article/how-animals-communicate-via-pheromones">pheromones</a> to communicate with each other and attract mates, mark territory, and signal danger. Plants release volatile organic compounds to attract pollinators and repel predators. Communication using molecules, known as “molecular communication”, is also useful to humans, albeit in a way that goes unnoticed by us – it plays a critical role in the interactions between the trillions of natural bacteria that live in and on our bodies.</p>
<p>Indeed, the <a href="https://www.theguardian.com/news/2018/mar/26/the-human-microbiome-why-our-microbes-could-be-key-to-our-health">human microbiota</a> – the natural bacteria inside the human body – use <a href="https://asm.org/Articles/2020/June/How-Quorum-Sensing-Works">“quorum sensing”</a> molecules to organise themselves and communicate with their human host. The microbiota is crucial for our health since it involves a wide range of physiological processes, including digestion and immune system regulation, besides producing certain hormones and other essential molecules.</p>
<p>Specifically, the gut microbiota directly affects the central nervous system and influences the host’s moods, behaviour, and cognition via the <a href="https://www.healthline.com/nutrition/gut-brain-connection">“gut-brain axis”</a>, a complex network that connects the two through signalling pathways involving molecules. This communication based on exchanges of molecules within the body is essential for maintaining <a href="https://www.livescience.com/65938-homeostasis.html">homeostasis</a> (that is, cell stability), and has been linked to many physiological processes such as neural development and dopamine metabolism. Conversely, when any failure in these communication networks occurs or when the microbiota population is not optimal, it can result in serious conditions, including <a href="https://www.mdpi.com/1422-0067/20/9/2115">autism spectrum disorder</a> and <a href="https://www.nature.com/articles/s41582-022-00681-2">Parkinson’s disease</a>.</p>
<p>Despite the multiplexed benefits of gut microbiota, its population and how well they operate in the body cannot be controlled by humans since they are independent organisms that live within us. To alleviate these issues, a field of research explores human-made alternatives that could substitute for these organisms, making things more controllable and predictable. Recent research has shown that <a href="https://www.bdebate.org/en/news/artificial-bacteria-will-live-our-bodies-treat-certain-diseases-0">artificial bacteria</a>, also called “synthetic probiotics”, could offer a promising new approach to treating gut-brain axis disorders. These artificial bacteria would use molecular communication, as it occurs naturally in living organisms, but here as a bio-inspired communication paradigm that uses molecules to transfer information.</p>
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<figcaption><span class="caption">Molecular communication in a nutshell (Biophysical Communication Engineering Lab).</span></figcaption>
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<h2>What are artificial bacteria?</h2>
<p>Artificial bacteria <a href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.826479/full">can be designed</a> to interact with the gut microbiome and the central nervous system to modulate and interfere with communication networks within these systems. For instance, they can be programmed to produce specific molecules that <a href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.826479/full">modulate the growth and activity of specific bacteria in the gut microbiome</a>, or to produce neurotransmitter-like neuronal signalling molecules that can <a href="https://pubs.acs.org/doi/10.1021/sb5002505">modulate the nervous system’s activity</a>.</p>
<p>Artificial bacteria can also be designed to mimic the function of a type of natural bacteria, who are called <a href="https://www.bbcgoodfood.com/howto/guide/what-are-probiotics-and-what-do-they-do">probiotics</a> and who have beneficial effects on the gut-brain axis: they can restore or maintain the balance of the gut microbiota, which may help to ameliorate the symptoms of gut-related disorders, such as <a href="https://www.nature.com/articles/s41467-022-31171-0">inflammatory bowel disease</a>, <a href="https://www.nature.com/articles/s41467-022-31171-0">infectious diarrhoea</a>, and <a href="https://www.mdpi.com/2072-6643/12/7/1973">irritable bowel syndrome</a>.</p>
<p>The active use of artificial bacteria in the treatment of gut-brain axis-related disorders is projected to make significant breakthroughs. The ability to engineer microorganisms to perform specific functions or behaviours will be a key enabler for <a href="https://pubmed.ncbi.nlm.nih.gov/28976641/">preventing the proliferation of pathogens and achieving homeostasis in the body</a>. For example, by developing artificial bacteria to produce antimicrobial peptides, we can target and kill harmful bacteria with greater precision, avoiding the development of antibiotic resistance. Similarly, by programming artificial bacteria to promote the growth of beneficial microorganisms in the gut, more effective communication between microorganisms can be established, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7137092/">promoting the restoration of homeostasis</a>.</p>
<p>The development of intestinal biosensors and artificial bacteria to detect disease-related biomarkers enables using them as diagnostic tools. However, the first step in developing diagnostic tools is understanding the communication between natural bacteria and the brain. Accordingly, mimicking it via artificial counterparts might eventually help us tackle many conditions, such as mood disorders and autism, in the foreseeable future.</p>
<h2>How to develop artificial bacteria?</h2>
<p>Molecular communication is a bio-inspired communication paradigm that uses molecules to transfer information as it occurs naturally in living organisms, with several analogous examples in nature as exemplified throughout the article. This communication paradigm paves the way for the realisation of various foreseen applications.</p>
<p>In the context of molecular communication, artificial bacteria refers to the development of engineered bacteria that can communicate with each other and human cells at the molecular level. This envisioned organism is nothing but a <a href="https://www.frontiersin.org/articles/10.3389/frcmn.2021.733664/full">network of systems transmitting and receiving, or, in engineering speak, “transceiving” molecules at the microscale or the nanoscale</a>.</p>
<p>This bacteria-based transceiver can send and receive molecular signals inside the human body to further sense and control biological processes in real time. As stated before, envisioned artificial bacteria is a perfect candidate for biomedical applications of nano-communication networks such as diagnosis and treatment of diseases, health monitoring, drug delivery, and bio-hybrid implants. Yet, the design and fabrication of these bio-compatible devices necessitate cross-disciplinary efforts that benefit from the accumulated knowledge in the fields of information and communication theory, nanotechnology, molecular science, and many others. These involve developing energy and molecule-efficient, low-complexity, and reliable communication techniques, as well as realistic molecular communication channel models validated through experiments.</p>
<p>These transceivers can also be designed for developing “lab-on-chip” technologies, which are miniaturised laboratory systems that can be used to perform various diagnostic and analytical tests for the gut-brain axis. Although there is a vast number of ongoing research projects and developed testbeds on this topic, no experiments in living systems have been done. Many ongoing <a href="https://nwcl.ku.edu.tr/axa.html">research projects</a> are actively working toward bringing this paradigm into reality. A notable example is the development of <a href="https://www.nature.com/articles/s41598-021-98609-1">a prototype molecular communication receiver using graphene</a>, a nanomaterial with outstanding biochemical properties, along with the <a href="https://arxiv.org/abs/2304.03824">utilisation of biosensor technology</a>.</p>
<p>These works indicate that practical devices are not too far off on the horizon, and given the pace of technological advances, we are in a good position to envision the production of these devices within a few decades. However, the main hurdle that researchers still face is conducting successful testing within living organisms such as mice, rats or any model organisms. Advancements in molecular communication and synthetic biology will pave the way for the next significant milestone for in vivo experiments that might enable diagnosis tools for many diseases, especially gut-related disorders.</p>
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<p><em>Created in 2007 to help accelerate and share scientific knowledge on key societal issues, the AXA Research Fund has supported nearly 700 projects around the world conducted by researchers in 38 countries. To learn more, visit the site of the AXA Research Fund or follow on Twitter @AXAResearchFund.</em></p><img src="https://counter.theconversation.com/content/206660/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Özgür Barış Akan ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Our microbiota is linked to essential physiological processes, but when its communication falters, our health can suffer. Synthetic probiotics offer a promising approach to treating gut-brain axis disorders.Özgür Barış Akan, Professor in electrical and electronics engineering, University of Cambridge, Koç UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1889392022-11-15T13:22:40Z2022-11-15T13:22:40ZAnts – with their wise farming practices and efficient navigation techniques – could inspire solutions for some human problems<figure><img src="https://images.theconversation.com/files/494699/original/file-20221110-21-p2hi2g.jpg?ixlib=rb-1.1.0&rect=10%2C0%2C2235%2C1329&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Leafcutter ants cultivate fungus gardens that feed sprawling colonies.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/three-leafcutter-ants-carrying-leaves-close-up-royalty-free-image/200187319-004">Tim Flach/Stone via Getty Images</a></span></figcaption></figure><p>King Solomon may have gained some of his famed wisdom from an unlikely source – ants.</p>
<p>According to a <a href="https://www.jewishencyclopedia.com/articles/13842-solomon#anchor14">Jewish legend</a>, Solomon conversed with a clever ant queen that confronted his pride, making quite an impression on the Israelite king. In the biblical book of <a href="https://www.biblegateway.com/passage/?search=Proverbs%206%3A6-8&version=KJV">Proverbs (6:6-8)</a>, Solomon shares this advice with his son: “Look to the ant, thou sluggard, consider her ways and be wise. Which having no guide, overseer, or ruler, provideth her meat in the summer, and gathereth her food in the harvest.”</p>
<p>While I can’t claim any familial connection to King Solomon, despite sharing his name, I’ve long admired the wisdom of ants and have spent over 20 years <a href="https://scholar.google.com/citations?user=bnXkcNUAAAAJ&hl=en&oi=sra">studying their ecology, evolution and behaviors</a>. While the notion that ants may offer lessons for humans has certainly been around for a while, there may be new wisdom to gain from what scientists have learned about their biology.</p>
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<figcaption><span class="caption">Ants have evolved highly complex social organizations.</span></figcaption>
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<h2>Lessons from ant agriculture</h2>
<p>As a researcher, I’m especially intrigued by <a href="https://doi.org/10.1093/isd/ixab029">fungus-growing ants</a>, a group of 248 species that cultivate fungi as their main source of food. They include 79 species of <a href="https://wwnorton.com/books/9780393338683">leafcutter ants</a>, which grow their fungal gardens with freshly cut leaves they carry into their enormous underground nests. I’ve excavated hundreds of leafcutter ant nests from Texas to Argentina as part of the scientific effort to understand how these ants coevolved with their fungal crops.</p>
<p>Much like human farmers, each species of fungus-growing ant is very particular about the type of crops they cultivate. Most varieties descend from a type of fungus that the ancestors of fungus-growing ants began growing <a href="https://doi.org/10.1093/isd/ixab029">some 55 million to 65 million years ago</a>. Some of these fungi became domesticated and are now unable to survive on their own without their insect farmers, much like some human crops such as maize.</p>
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<figcaption><span class="caption">Ants started farming tens of millions of years before humans.</span></figcaption>
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<p>Ant farmers face many of the same challenges human farmers do, including the threat of pests. A parasite called <a href="https://doi.org/10.1186/s43008-021-00078-8"><em>Escovopsis</em></a> can devastate ant gardens, causing the ants to starve. Likewise in human agriculture, pest outbreaks have contributed to disasters like the <a href="https://evolution.berkeley.edu/the-relevance-of-evolution/agriculture/monoculture-and-the-irish-potato-famine-cases-of-missing-genetic-variation/">Irish Potato Famine</a>, the 1970 <a href="https://doi.org/10.1126/science.171.3976.1113">corn blight</a> and the <a href="https://theconversation.com/with-the-familiar-cavendish-banana-in-danger-can-science-help-it-survive-64206">current threat to bananas</a>.</p>
<p>Since the 1950s, human agriculture has become industrialized and relies on <a href="https://www.birmingham.ac.uk/research/quest/preserving-and-creating-culture/a-global-history-of-monoculture.aspx">monoculture</a>, or growing large amounts of the same variety of crop in a single place. Yet monoculture makes crops more vulnerable to pests because it is easier to destroy an entire field of genetically identical plants than a more diverse one.</p>
<p>Industrial agriculture has looked to chemical pesticides as a partial solution, turning agricultural pest management into a <a href="https://www.alliedmarketresearch.com/pest-control-market">billion-dollar industry</a>. The trouble with this approach is that pests can <a href="https://islandpress.org/books/chasing-red-queen">evolve new ways to get around pesticides</a> faster than researchers can develop more effective chemicals. It’s an arms race – and the pests have the upper hand.</p>
<p>Ants also <a href="https://mitpress.mit.edu/9780262543200/the-convergent-evolution-of-agriculture-in-humans-and-insects/">grow their crops in monoculture</a> and at a similar scale – after all, a leafcutter ant nest can be home to <a href="https://wwnorton.com/books/9780393338683">5 million ants</a>, all of which feed on the fungi in their underground gardens. They, too, use a pesticide to control <em>Escovopsis</em> and other pests. </p>
<p>Yet, their approach to pesticide use differs from humans’ in one important way. Ant pesticides are <a href="https://doi.org/10.1021/acscentsci.0c00978">produced by bacteria</a> they allow to grow in their nests, and in some cases even on their bodies. Keeping bacteria as a living culture allows the microbes to <a href="https://doi.org/10.1128/AEM.00178-21">adapt in real time</a> to evolutionary changes in the pests. In the arms race between pests and farmers, farming ants have discovered that live bacteria can serve as pharmaceutical factories that can keep up with ever-changing pests.</p>
<p>Whereas recent developments in agricultural pest management have focused on <a href="https://entomology.ca.uky.edu/ef130">genetically engineering</a> <a href="https://www.nature.com/scitable/knowledge/library/use-and-impact-of-bt-maize-46975413/">crop plants</a> to produce their own pesticides, the lesson from 55 million years of ant agriculture is to <a href="https://doi.org/10.3389/fsoil.2022.833181">leverage living microorganisms</a> to make <a href="https://doi.org/10.1007/978-981-16-4843-4_13">useful products</a>. Researchers are currently experimenting with <a href="https://link.springer.com/book/10.1007/978-981-10-0707-1">applying live bacteria to crop plants</a> to determine if they are effective at producing pesticides that can evolve in real time along with pests.</p>
<h2>Improving transportation</h2>
<p>Ants can also offer practical lessons in the realm of transportation.</p>
<p>Ants are notoriously good at quickly locating food, whether it’s a dead insect on a forest floor or some crumbs in your kitchen. They do this by leaving a <a href="https://doi.org/10.1111/j.1365-3032.2008.00658.x">trail of pheromones</a> – chemicals with a distinctive smell ants use to guide their nest mates to food. The shortest route to a destination will accumulate the most pheromone because more ants will have traveled back and forth along it in a given amount of time.</p>
<p>In the 1990s, computer scientists developed a <a href="https://www.sciencedirect.com/topics/engineering/ant-colony-optimization">class of algorithms</a> modeled after ant behavior that are very effective at finding the shortest path between two or more locations. Like with real ants, the shortest route to a destination will accumulate the most virtual pheromone because more virtual ants will have traveled along it in a given amount of time. Engineers have used this simple but effective approach to <a href="https://doi.org/10.1016/j.mcm.2010.04.021">design telecommunication networks</a> and <a href="https://doi.org/10.1007%2F978-3-030-50146-4_25">map delivery routes</a>.</p>
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<span class="caption">Thousands of ants can travel along the same path without causing traffic jams.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/close-up-of-plant-growing-on-field-royalty-free-image/764924521">Esteban Castao Solano/EyeEm via Getty Images</a></span>
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<p>Not only are ants good at finding the shortest route from their nests to a source of food, thousands of ants are capable of traveling along these routes without causing traffic jams. I recently began collaborating with physicist <a href="https://scholar.google.com/citations?user=reX35vUAAAAJ&hl=es">Oscar Andrey Herrera-Sancho</a> to study how leafcutter ants maintain such a steady flow along their foraging paths without the slowdowns typical of crowded human sidewalks and highways.</p>
<p>We are <a href="http://solomon.rice.edu/2019/01/11/field-research-in-costa-rica/">using cameras to track</a> how each individual ant responds to artificial obstacles placed on their <a href="https://www.alexanderwild.com/Ants/Making-a-Living/The-Farming-Ants-Leafcutters/i-rWjNDhM/A">foraging trails</a>. Our hope is that by getting a better understanding of the rules ants use to respond to both obstacles and the movement of other ants, we can develop algorithms that can eventually help program self-driving cars that never get stuck in traffic.</p>
<h2>Look to the ant</h2>
<p>To be fair, there are plenty of ways ants are far from perfect role models. After all, some ant species are known for <a href="https://www.hup.harvard.edu/catalog.php?isbn=9780674241558">indiscriminate killing</a>, and others for <a href="https://theconversation.com/slave-ants-and-their-masters-are-locked-in-a-deadly-relationship-36737">enslaving babies</a>. </p>
<p>But the fact is that ants <a href="https://www.basicbooks.com/titles/mark-w-moffett/the-human-swarm/9781541617292/">remind us of ourselves</a> – or the way we might like to imagine ourselves – in many ways. They live in complex societies with <a href="https://doi.org/10.1007/s00265-015-2045-3">division of labor</a>. They <a href="https://www.simonandschuster.com/books/Ants-At-Work/Deborah-Gordon/9781451665703">cooperate to raise their young</a>. And they accomplish <a href="https://press.princeton.edu/books/hardcover/9780691179315/ant-architecture">remarkable engineering feats</a> – like building structures with air funnels that can house millions – all without blueprints or a leader. Did I mention their societies are <a href="https://www.press.jhu.edu/books/title/10551/secret-lives-ants">run entirely by females</a>?</p>
<p>There is still a lot to learn about ants. For example, researchers still don’t fully understand <a href="https://doi.org/10.1016/j.tree.2020.11.010">how an ant larva develops</a> into either a queen – a female with wings that can live for 20 years and lay millions of eggs – or a worker – a wingless, often sterile female that lives for less than a year and performs all the other jobs in the colony. What’s more, scientists are constantly discovering new species – <a href="https://www.antwiki.org/wiki/Taxa_Described_in_2021">167 new ant species</a> were described in 2021 alone, bringing the total to more than 15,980. </p>
<p>By considering ants and their many fascinating ways, there’s plenty of wisdom to be gained.</p><img src="https://counter.theconversation.com/content/188939/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Scott Solomon receives funding from the National Science Foundation and the Big Thicket Association. </span></em></p>Over hundreds of million years of evolution, ants have come up with some pretty smart solutions to problems of agriculture, navigation and architecture. People could learn a thing or two.Scott Solomon, Associate Teaching Professor of Ecology and Evolutionary Biology, Rice UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1227642019-09-03T13:40:36Z2019-09-03T13:40:36ZStop calling it a choice: Biological factors drive homosexuality<figure><img src="https://images.theconversation.com/files/290563/original/file-20190902-175705-15kuqu2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Biological factors shape sexual preference.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/lgbt-lesbian-couple-moments-happiness-concept-575079754?src=-1-53">Rawpixel.com/SHutterstock.com</a></span></figcaption></figure><p><a href="https://doi.org/10.1126/science.aat7693">Across cultures, 2% to 10% of people report having same-sex relations</a>. In the U.S., <a href="https://www.statista.com/topics/1249/homosexuality/">1% to 2.2% of women and men</a>, respectively, identify as gay. Despite these numbers, <a href="https://www.pewresearch.org/global/2013/06/04/the-global-divide-on-homosexuality/">many people still consider homosexual behavior to be an anomalous choice</a>. However, biologists have <a href="https://us.macmillan.com/books/9780312253776">documented homosexual behavior in more than 450 species</a>, arguing that same-sex behavior is not an unnatural choice, and may in fact play a vital role within populations.</p>
<p>In <a href="https://doi.org/10.1126/science.aat7693">a 2019 issue of Science magazine</a>, geneticist Andrea Ganna at the Broad Institute of MIT and Harvard, and colleagues, described the largest survey to date for genes associated with same-sex behavior. By analyzing the DNA of nearly half a million people from the U.S. and the U.K., they concluded that genes account for between 8% and 25% of same-sex behavior. </p>
<p><a href="https://www.nature.com/news/sex-redefined-1.16943">Numerous studies have established that sex is not just male or female</a>. Rather, it is a continuum that emerges from a person’s genetic makeup. Nonetheless, misconceptions persist that same-sex attraction is a choice that warrants condemnation or <a href="https://www.apa.org/pi/lgbt/resources/just-the-facts">conversion</a>, and leads to discrimination and persecution.</p>
<p><a href="https://wjsulliv.wixsite.com/sullivanlab">I am a molecular biologist</a> and am interested in this new study as it further illuminates the genetic contribution to human behavior. As the author of the book, <a href="https://www.penguinrandomhouse.com/books/608709/pleased-to-meet-me-by-bill-sullivan/9781426220555/">“Pleased to Meet Me: Genes, Germs, and the Curious Forces That Make Us Who We Are,”</a> I have done extensive research into the biological forces that conspire to shape human personality and behavior, including the factors influencing sexual attraction.</p>
<h2>The hunt for ‘gay genes’</h2>
<p>The new finding is consistent with multiple earlier studies of twins that indicated same-sex attraction is a heritable trait.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1508&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1508&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290580/original/file-20190902-175663-baya3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1508&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A new study suggests that genes are responsible for between 8% and 25% of same-sex preference.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/dna-multi-color-isolated-on-white-717211195?src=-1-47">Guru 3D</a></span>
</figcaption>
</figure>
<p>The 2019 study is the latest in a hunt for “gay genes” that began in 1993, when Dean Hamer <a href="https://doi.org/10.1126/science.8332896">linked male homosexuality to a section of the X chromosome</a>. As the ease and affordability of genome sequencing increased, additional gene candidates have emerged with potential links to homosexual behavior. So-called <a href="https://doi.org/10.1038/s41598-017-15736-4">genome-wide association studies identified a gene called <em>SLITRK6</em></a>, which is active in a brain region called the diencephalon that differs in size between people who are homosexual or heterosexual.</p>
<p>Genetic studies in mice have uncovered additional gene candidates that could influence sexual preference. A 2010 study <a href="https://doi.org/10.1186/1471-2156-11-62">linked sexual preference to a gene called fucose mutarotase</a>. When the gene was deleted in female mice, they were attracted to female odors and preferred to mount females rather than males. </p>
<p>Other studies have shown that <a href="https://doi.org/10.1038/nature06089">disruption of a gene called <em>TRPC2</em></a> can cause female mice to act like males. <a href="https://doi.org/10.1126/science.1069259">Male mice lacking <em>TRPC2</em></a> no longer display male-male aggression, and they initiate sexual behaviors toward both males and females. Expressed in the brain, <em>TRPC2</em> functions in the recognition of pheromones, chemicals that are released by one member of a species to elicit a response in another.</p>
<p>With multiple gene candidates being linked to homosexuality, it seemed highly unlikely that a single “gay” gene exists. This idea is further supported by <a href="https://doi.org/10.1126/science.aat7693">the new study</a>, which identified five new genetic loci (fixed positions on chromosomes) correlating with same-sex activity: two that appeared in men and women, two only in men, and one only in women.</p>
<h2>How might these genes influence same-sex behavior?</h2>
<p>I find it intriguing that some of the genes from men identified in Ganna’s study are associated with olfactory systems, a finding that has parallels to the work in mice. Ganna’s group found other gene variants that may be linked with sex hormone regulation, which other scientists have previously suggested plays a large role in shaping the brain in ways that influence sexual behavior. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=846&fit=crop&dpr=1 600w, https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=846&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=846&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1063&fit=crop&dpr=1 754w, https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1063&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/290575/original/file-20190902-175691-1l5i9pk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1063&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Conditions in the uterus during pregnancy are thought to influence the sexual preferences of the child.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/beautiful-pregnant-woman-shopping-bags-outdoors-503149633?src=-1-18">Anna Om/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Males with a genetic condition called <a href="https://ghr.nlm.nih.gov/condition/androgen-insensitivity-syndrome">androgen insensitivity syndrome</a> can develop female genitalia and are usually brought up as girls, despite being genetically male – with an X and Y chromosome – and they are attracted to men. This suggests that testosterone is needed to “masculinize” a prenatal brain; if that doesn’t happen, the child will grow up to desire men. </p>
<p>Similarly, girls who have a genetic condition called <a href="https://www.nichd.nih.gov/health/topics/cah">congenital adrenal hyperplasia</a> are exposed to unusually high levels of male hormones like testosterone while in the womb, which may masculinize their brain and increase the odds of lesbianism. </p>
<p>It’s also possible that hormonal shifts during pregnancy could affect how a fetus’ brain is configured. In rats, <a href="https://doi.org/10.1210/en.2011-0277">manipulation of hormones during pregnancy</a> produces offspring that exhibit homosexual behavior.</p>
<h2>Why does homosexual behavior exist?</h2>
<p>Several hypotheses have been advanced to explain how homosexuality can be beneficial in perpetuating familial genes. One idea involves the concept of kin selection, whereby people work to ensure the passage of their family’s genes into subsequent generations. Gay uncles and aunts, for example, are “<a href="https://doi.org/10.1177/0956797609359623">helpers in the nest</a>” that help raise other family members’ children to nurture the family tree.</p>
<p>Another idea suggests that homosexuality is a “trade-off trait.” For example, certain genes in women help increase their fertility, but <a href="https://doi.org/10.1111/j.1743-6109.2008.00944.x">if these genes are expressed in a male</a>, they predispose him toward homosexuality.</p>
<p>Sexual behavior is widely diverse and governed by sophisticated mechanisms throughout the animal kingdom. As with other complex behaviors, it is not possible to predict sexuality by gazing into a DNA sequence as if it were a crystal ball. Such behaviors emerge from constellations of hundreds, perhaps thousands, of genes, and how they are regulated by the environment.</p>
<p>While there is no single “gay gene,” there is overwhelming evidence of a biological basis for sexual orientation that is programmed into the brain before birth based on a mix of genetics and prenatal conditions, none of which the fetus chooses.</p>
<p>[ <em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=youresmart">You can read us daily by subscribing to our newsletter</a>. ]</p><img src="https://counter.theconversation.com/content/122764/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bill Sullivan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A new study of nearly 500,000 individuals finds that many genes affect same-sex behavior, including newly identified candidates that may regulate smell and sex hormones.Bill Sullivan, Professor of Pharmacology & Toxicology, Indiana University School of MedicineLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/383182015-03-04T06:27:05Z2015-03-04T06:27:05ZThere’s no evidence human pheromones exist – no matter what you find for sale online<figure><img src="https://images.theconversation.com/files/73684/original/image-20150303-31825-z6wbf6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Whatever the adverts suggest, this isn't going to increase your animal magnetism.</span> <span class="attribution"><span class="source">Thinglass/Shutterstock</span></span></figcaption></figure><p>The idea of human pheromones is intuitively appealing, conjuring up the idea of secret signals that make us irresistible to potential partners. But this connection of pheromones with sex may be the wrong way to look at the issue – because despite 45 years of study and various claims over the years there’s still not a lot of evidence that human pheromones exist at all.</p>
<p>The study of pheromones of all kinds is problematic – even the definition is controversial. The word comes from the Greek <em>pherein</em> (to transfer), and <em>hormōn</em> (to excite) and was defined by <a href="http://www.nature.com/nature/journal/v183/n4653/abs/183055a0.html">Karlson and Luscher</a> in 1959 as: </p>
<blockquote>
<p>Substances which are secreted by an individual and received by a second individual of the same species, in which they release a specific reaction, for instance a definite behaviour or developmental process.</p>
</blockquote>
<p>The snag is that that while many researchers agree on the basic properties of pheromones, there is considerable debate over which olfactory (sense of smell) cues represent pheromones. For example, <a href="https://books.google.co.uk/books?hl=en&lr=&id=toDBAgAAQBAJ&oi=fnd&pg=PR11&dq=wyatt+pheromones&ots=C9SwEpRe0-&sig=BUI_usD9Vy3QdPBKg_s7RyeymK4#v=onepage&q=wyatt%20pheromones&f=false">many species use odours</a> to identify characteristics such as species, sex, relatedness and social status. Many researchers label these odours as pheromones; others feel that by the above definition they’re really just smells. </p>
<p>Similarly not all potential pheromones are secreted externally – some species of salamanders transfer chemical signals to another salamander by directly <a href="http://www.sciencedirect.com/science/article/pii/S0003347205803847">injecting them into the bloodstream</a>. Some scientists believe that the response to a pheromone should provide an evolutionary advantage to both the sender and the receiver of the signal, <a href="http://www.jstor.org/discover/10.2307/1313311?sid=21106009567403&uid=4&uid=2&uid=3738032">and do so unconsciously</a>. </p>
<p>So a lack of consensus on pheromones’ definition has led to the over-use of this term. Instead many scientists use the term <a href="http://ipmworld.umn.edu/chapters/flint.htm">semiochemicals</a> to refer to chemicals that transmit some form of specific message that can influence a recipient’s physiology and behaviour.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=483&fit=crop&dpr=1 754w, https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=483&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/73686/original/image-20150303-31833-pamzsm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=483&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">That’s right - just two dabs behind the antennae and they’re all over me.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Bug_aggregation.jpg">L. Shyamal</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Studying smells is hard</h2>
<p>Given these problems why are researchers so interested in pheromones at all? Generally olfaction is one of the most crucial forms of communication in the animal world. Odours have the greatest potential range of any method of animal communication, can be transmitted in total darkness and around obstacles. Unlike signals to be seen or heard, odours also remain in the environment for extended periods, providing the opportunity to lay signals – such as when marking territory. </p>
<p>But studying human pheromones is problematic for a number of reasons beyond definition. Olfactory research can be extremely tricky to conduct: smells are invisible and hard to control, there is no real standardised system for labelling and evaluating odours, and a wealth of potentially confounding variables need to be controlled for. Also the problem is that humans can evaluate signals in a variety of quite divergent ways – it’s rare that we show simplistic stimulus–response reaction. </p>
<h2>Four pheromone candidates</h2>
<p>Four specific substances have been identified as possible human pheromones. </p>
<p>In the 1970s and 1980s, there was a strong focus on testosterone-derived <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1664751/">androstenone</a> and <a href="http://www.ncbi.nlm.nih.gov/pubmed/3608426">androstenol</a>, possible pheromones in pigs also found in human armpits. A number of studies have investigated the effect of these substances on human behaviour, focusing on social interactions and the evaluation of sexual partners. Despite a general pattern for these substances to increase social contact between males and females, findings are <a href="http://onlinelibrary.wiley.com/doi/10.1002/ar.a.20125/full">extremely inconsistent</a>.</p>
<p>In the 1990s the focus shifted to the similar <a href="http://www.scientificamerican.com/article/human-sexual-responses-boosted-by-bodily-scents/">androstadienone</a> and oestratraenol, an oestrogen-derived substance produced in pregnant women. These were the compounds studied in several experiments that examined the <a href="http://chemse.oxfordjournals.org/content/26/4/433.full">vomeronasal organ</a> (VNO) – a tubular structure located in the nasal cavity which, in some species, is involved in processing pheromones.</p>
<p>Several studies <a href="http://www.sciencedirect.com/science/article/pii/0960076091902532">documented</a> finding a VNO in more than 90% of human participants, and reported that stimulating the VNO with artificially-created “putative human pheromones” seemed to stimulate the recipients. This suggested the existence of human pheromones, as a functioning VNO would provide humans the ability to process pheromones.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=550&fit=crop&dpr=1 600w, https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=550&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=550&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=691&fit=crop&dpr=1 754w, https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=691&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/73687/original/image-20150303-31852-3npnfz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=691&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">‘Your powers of magnetic attraction be damned, I’m not kissing a man with nicer braids than mine.’</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Fr%C3%A9d%C3%A9ric_Soulacroix_-_Flirtation_2.jpg">Frédéric Soulacroix</a></span>
</figcaption>
</figure>
<p>However, more recent studies cast doubt on this idea, with <a href="http://chemse.oxfordjournals.org/content/25/4/369.short">no evidence</a> that the few VNOs identified in humans have any functional receptor cells to detect anything – the VNO isn’t actually connected to the brain. And those putative “synthetic human pheromones” provided to the studies that claimed to show evidence of their effect on the VNO? It’s been pointed out that they had been provided by <a href="http://www.erox.com/">EROX</a> – a firm with a commercial interest in patenting and selling them. You’ll find EROX and scores of other firms selling similar products on the internet today.</p>
<p>Research into these four pheromone candidates suffers from all sorts of problems. The substances are used in concentrations between several and millions of times higher than they occur naturally in humans. Experiments tend to be beset with methodological and statistical issues, leading to a contradictory or inconclusive findings. Publication bias leaves it likely that only positive results are published, artificially increasing the amount of supposedly supportive evidence, and findings have often not been independently replicable. </p>
<p>In any case, even if these substances do effect human physiology and behaviour it doesn’t necessarily mean they’re pheromones – there are numerous odours from plants or from industrial chemicals that can produce a behavioural reaction in humans. </p>
<h2>The way forward</h2>
<p>Tristram Wyatt, in his <a href="http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2014.2994">recent paper</a> for the Royal Society, suggests that we move away from the sexual focus on pheromones. Instead we should focus not just on the substance present but on the range of odours that humans are capable of producing from a variety of sites on the body. </p>
<p>Wyatt’s suggestion is the secretions from the areola of mothers’ lactating breasts is a good place to start looking, as smell is very important to suckling behaviour in animals. Any baby, presented with the secretions of any mother, will respond with nipple-searching behaviour, even while asleep.</p>
<p>The search for human pheromones taps into our mysterious sense of smell and appeals to us on an emotional level. Of course, there are also strong commercial motivations to demonstrating their existence and the products that might follow. There is already a well-documented history of this occurring in the field of olfaction research – and these motivations inevitably muddy the water. We need to address these issues with a much more rigorous approach if the science is to progress.</p><img src="https://counter.theconversation.com/content/38318/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark JT Sergeant 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>Do human pheromones exist? Despite the products some would sell you, there’s no hard evidence yet.Mark JT Sergeant, Senior Lecturer in Psychology, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/219712014-01-16T19:31:26Z2014-01-16T19:31:26ZSmells like queen spirit: royal pheromones in insect colonies<figure><img src="https://images.theconversation.com/files/38931/original/xt9s79m5-1389587264.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A queen bee tended by her workers ... but take away her pheromones and they start to act strangely.</span> <span class="attribution"><span class="source">Flickr/KrisFricke</span></span></figcaption></figure><p>Much like people, insect colonies like to know if her majesty is at home. In the ants, bees, wasps and termites (the “big four” of the social insect world), the queen has long been suspected of using special “queen <a href="http://www.smithsonianmag.com/science-nature/the-truth-about-pheromones-100363955/">pheromones</a>” – emitted chemicals which let the workers know where she is. </p>
<p>Despite lots of circumstantial evidence that all social insects have queen pheromones, we mostly had no idea what those pheromones are – but a new paper <a href="http://www.sciencemag.org/content/343/6168/1244899">published today</a> in the journal Science changes that. </p>
<p>Queen pheromones are a very important part of the chemical language of the colony, and workers adjust not only their behaviour but their complete physiology when they smell their queen. </p>
<p>Workers deprived of queen pheromone assume that their mother is long gone and have a go at laying eggs themselves: queens usually handle almost all of the egg-laying in the colony.</p>
<p>Today’s paper, the result of collaboration between biologists and chemists working in Australia (<a href="https://sites.google.com/site/lukeholman/home">me</a>), <a href="http://bio.kuleuven.be/ento/wenseleers/twenseleers.htm">Belgium</a> and the <a href="http://www.facultydirectory.ucr.edu/cgi-bin/pub/public_individual.pl?faculty=68">US</a> showed that by synthesising a copy of some possible queen pheromones, we could “trick” the workers into thinking their queen was still there. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=354&fit=crop&dpr=1 600w, https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=354&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=354&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=445&fit=crop&dpr=1 754w, https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=445&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/38927/original/c6ybj2cx-1389586301.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=445&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Queen termite, tended by workers.</span>
<span class="attribution"><span class="source">Flickr/eyeweed</span></span>
</figcaption>
</figure>
<h2>A royal – yet common – perfume</h2>
<p>We found the first queen pheromones from a wasp and a bumblebee, as well as a previously unstudied type of ant. Adding previous work, we’ve now found the queen pheromone of honeybees, termites and a few more ants. </p>
<p>This allowed us to ask a new question: do all social insects use the same queen pheromone, or does each have a unique version? Surprisingly, the answer is that queen pheromones are similar or even identical across species, even in distantly-related types of social insects. </p>
<p>Bees, ants and wasps all evolved colonial life (and the queen-worker dichotomy) independently, so many researchers expected them to have unique queen pheromones.</p>
<p>The fact that most bees, ants and wasps all have the same “chemical word” meaning “I’m the queen! I’m over here!” suggests that the pheromone existed in the most recent common ancestor of these species, which was a solitary insect that lived about 150 million years ago. </p>
<p>Maybe the pheromone was something used by female insects to signal that they were full of eggs (perhaps to attract the boys), and it was co-opted by primitive queens (who are also chock-full of eggs) to signal to their prototypical workers. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/qnPGDWD_oLE?wmode=transparent&start=54" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">‘Which one’s the queen?’</span></figcaption>
</figure>
<h2>It all makes evolutionary scents</h2>
<p>But why did all the social insects keep the same queen pheromone, instead of drifting apart and evolving very different ones over evolutionary time? </p>
<p>One possibility is that the latter actually did happen: the honey bee is an outlier, since it uses a very distinct, complicated queen pheromone all of its own. </p>
<p>Maybe once more queen pheromones are known, we will find other weird species that have switched to a new chemical language – but the current evidence suggests that most of the bees, ants and wasps stuck to the original queen pheromone, for reasons unknown. </p>
<p>The science drones are working on it: stay tuned!</p><img src="https://counter.theconversation.com/content/21971/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luke Holman receives funding from the Australian Research Council.</span></em></p>Much like people, insect colonies like to know if her majesty is at home. In the ants, bees, wasps and termites (the “big four” of the social insect world), the queen has long been suspected of using special…Luke Holman, Evolutionary Biologist, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.