Tag Archives: Evolution

The Evolution of Good Taste (Biology)

Does evolution explain why we can’t resist a salty chip? Researchers at NC State University found that differences between the elemental composition of foods and the elemental needs of animals can explain the development of pleasing tastes like salty, umami and sweet.

Taste tells us a lot about foods before they are swallowed and digested, and some tastes correspond with the elemental composition of foods. For example, an aged steak lights up the umami taste receptors, because it has a high concentration of the element nitrogen, which occurs in amino acid molecules. Nitrogen is essential for survival, but often occurs in low concentrations relative to the demand by animals. Likewise, sodium is limited in many foods in nature – think of life before supermarkets. So if you need sodium to survive – and all animals do – you are more likely to have adapted a taste for, and seek out, salty foods.

“Nutritional imbalances, even at the elemental level, can limit the growth and metabolism of animals,” says Lee Demi, a co-author of the study and postdoctoral researcher in NC State’s Department of Applied Ecology. “We posited that animals should have evolved the ability to taste, and enjoy, certain elements and nutrients that are most likely to be limiting for growth, due to their low concentrations in typical foods.” 

To investigate this hypothesis, Demi and colleagues compared the body elemental composition of three animal groups (mammals, fish, and insects) to the elemental composition of plants, the base of most food webs. They predicted that animals who eat foods composed of particular elements that are rare or unpredictable are more likely to have taste receptors that reward them for finding those same elements.

“Because animals have very limited ability to change their elemental composition, the old adage that ‘You are what you eat’ doesn’t really apply,” says Demi. “Rather, animals are rewarded with pleasing tastes for ‘eating what they are’, at least from an elemental composition perspective, which helps reduce the prospect of dietary nutrient limitation.”

This is particularly important for omnivorous and herbivorous animals that eat a variety of different foods which vary in nutritional quality. Within this framework, taste becomes a tool that helps consumers prioritize which foods they should search for and consume, so they don’t waste time on foods that have less of these necessary elements. Equally, taste can also inform consumers to avoid foods that contain too much of an element they need. This is why eating a handful of chips is more attractive than eating a handful of table salt. 

Where you are on the food chain can predict the complexity of your taste systems. Some top predators, like orcas, have lost many taste receptors over evolutionary time. This study suggests that predators are less likely to experience strong elemental imbalances in their diet than herbivores or omnivores. Because their prey already match their elemental needs, predators experience less selective pressure to maintain elaborate taste systems. However, these top predators have kept their taste for salt, which can be harmful if overconsumed.   

“Affinity for certain foods must have strong evolutionary drivers, because without taste, animals would be forced to overconsume everything in the hopes of hitting the magic ratio of elements needed for growth and development,” says Benjamin Reading, co-author of the study and a professor in NC State’s Department of Applied Ecology. “They would need to eat way too much and end up excreting huge quantities of those things they need less of, which is not efficient.”

The research team also found strong evidence of convergent taste evolution in mammals, fish, and insects. Each group, although far apart on the phylogenetic tree, all have adapted tastes that prioritize the same infrequent elements, including sodium, nitrogen and phosphorus.

“Phosphorus is particularly intriguing because this recently discovered taste is most strongly linked to phosphate, which is also the primary form of phosphorus in many nucleic acids, ATP, phospholipids, etc.,” says Brad Taylor, a co-author of the study and professor in NC State’s Department of Applied Ecology. “Phosphate is the most readily available form of phosphorus for uptake by plants, and often the primary growth limiting element in organisms and ecosystems. So, links between the elemental form, taste receptors, organismal needs, and ecosystem are really direct.”

While the neurobiological process of taste has been extensively researched, this study is the first to explore taste as an evolutionary tool for optimal foraging. The researchers suggest that this may open a new area of thought on how taste can indicate how animals impact their environments through foraging, nutrient-cycling, and other core principles of ecology.

The paper, “Understanding the evolution of nutritive taste in animals: Insights from biological stoichiometry and nutritional geometry,” is published in the journal Ecology and Evolution. The paper was co-authored by Michael Tordoff of the Monell Chemical Senses Center; and Rob Dunn from NC State’s Department of Applied Ecology and the Natural History Museum of Denmark.

The work was supported by the U.S. National Science Foundation [grant number 1556914] as well as the Department of Applied Ecology and Dr. Jules Silverman at North Carolina State University. 

Provided by NC State University

How Butterflies Make Transparent Wings: MBL Scientists See The Invisible (Biology)

Many animals have evolved camouflage tactics for self-defense, but some butterflies and moths have taken it even further: They’ve developed transparent wings, making them almost invisible to predators.

A team led by Marine Biological Laboratory (MBL) scientists studied the development of one such species, the glasswing butterfly, Greta oto, to see through the secrets of this natural stealth technology. Their work was published in the Journal of Experimental Biology.

Although transparent structures in animals are well established, they appear far more often in aquatic organisms. “It’s an interesting biological question because there just aren’t that many transparent organisms on land,” notes lead author Aaron Pomerantz, a PhD candidate in Integrative Biology at the University of California, Berkeley. “So we asked the question, what is the actual developmental basis of how they create their transparent wings?”

Butterfly wings are known for their colorful patterns, created by tiny, overlapping, chitinous scales that reflect or absorb various wavelengths of light to produce colors. Pomerantz says that although scale coloration has been intensively studied, investigating the developmental origins of transparency in land-based butterflies hadn’t been done before. “Transparency is sort of the opposite of color,” he says.

Haetera species of clearwing butterfly. © Aaron Pomerantz

Pomerantz and his co-authors, including his PhD advisor and MBL Director Nipam Patel, were inspired by the work of students in MBL’s Embryology course, in which Patel teaches. “I decided to bring some of the transparent butterfly and moth species I had in my collection, which I never really looked at in detail, to the course and present it as a challenge for the students to look at how these wings were transparent,” Patel says. “A group of students took that on by imaging the wings with various microscopes. And they realized that pretty much any way you could think to make the wing transparent, some butterfly or moth had figured out how to do it. That’s what got us looking in more detail at the development of transparency.”

Building on that work, the researchers used confocal and scanning electron microscopy to construct a developmental time scale of how transparency emerges in Greta oto, from the pupal stage to adulthood. They found that the glasswing butterfly’s wings develop differently than opaque species, with a lower density of precursor scale cells in the areas that will later develop as transparent. At a very early stage, scale growth and morphologies differed, with thin, bristle-like scales developing in transparent regions and flat, round scale morphologies within opaque regions.

“What Greta oto does is to make fewer scales and to make them in these very different, bristle-like shapes,” Patel explains. “But getting the scales out of the way is only part of the problem of creating transparency. Aaron also made a series of observations about nanostructures on the wing that prevent glare in bright sunlight. When light hits these little arrays of nanostructures, it doesn’t reflect off — it goes straight through. So that gives much better transparency,” he says.

“As humans, we think we’re so brilliant because we figured out how to put anti-glare coating on glass, but butterflies basically figured that out tens of millions of years ago,” Patel says.

Unusual wing scales and nanostructures are only part of the story. A second layer of waxy hydrocarbon nanopillars lies atop the wing surface, providing further anti-reflective properties. The researchers examined the reflectivity of the wings before and after removing the waxy layer with hexane.

“We measured the amount of light that reflected off the wing,” says Pomerantz. “Those experiments demonstrated that that upper layer was very important for helping to reduce that glare.” Biochemical analysis showed that the waxy layer is mostly composed of long chain n-alkanes, similar to those found in other insect species. “They’re primarily thought of as something that helps prevent an insect from drying out or desiccating. But in this case, it seems like they’re used for these anti-glare properties as well.”

Future research directions may include delving more deeply into the how these transparent structures evolved. Pomerantz points out that “if we can learn more about how nature creates new types of nanostructures, that can be very informative for human applications.” The work is making the secrets of natural transparency considerably less opaque.

Featured image: A glasswing butterfly feeding at flowers in Costa Rica. The remarkable transparency of these butterflies allows them to be “invisible”, and the antiglare coating of their wings helps to prevent them from being given away by any glare of sunlight off their wings. © Nipam Patel

Reference: Aaron F. Pomerantz, Radwanul H. Siddique, Elizabeth I. Cash, Yuriko Kishi, Charline Pinna, Kasia Hammar, Doris Gomez, Marianne Elias, Nipam H. Patel; Developmental, cellular and biochemical basis of transparency in clearwing butterflies. J Exp Biol 15 May 2021; 224 (10): jeb237917. doi: https://doi.org/10.1242/jeb.237917

Provided by Marine Biological Laboratory

Scientists Uncover the Mysteries of How Viruses Evolve (Biology)

An international team of researchers have shed new light on the early stages of viral evolution.

The team say their findings have implications for the treatment of viruses in future.

Researchers from the Universities of York and Leeds, collaborating with the Hilvert Laboratory at the ETH Zurich, studied the structure, assembly and evolution of a ‘container’ composed of a bacterial enzyme.

The study  – published in the journal Science – details the structural transformation of these virus-like particles into larger protein ‘containers’.

It also reveals that packaging of the genetic cargo in these containers becomes more efficient during the later stages of evolution. They show that this is because the genome inside evolves hallmarks of a mechanism widely used by natural viruses, including Covid-19, to regulate their assembly.

That mechanism was a joint discovery of the York and Leeds team. Professor Reidun Twarock, from the University of York’s Departments of Mathematics and Biology, and the York Cross-disciplinary Centre for Systems Analysis, said: “Using a novel interdisciplinary technique developed in our Wellcome Trust-funded team in Leeds and York, we were able to demonstrate that this artificial system evolved the molecular hallmarks of a ‘virus assembly mechanism’, enabling efficient packaging of its genetic cargo.”

In its evolution, the artificial virus-like particle efficiently packages and protects multiple copies of its own encoding messenger RNA.

Professor Peter Stockley from the University of Leeds’ Astbury Centre for Structural Molecular Biology, said “What’s remarkable is this artificial virus-like particle evolves to be more efficient in packaging RNA. Our collaboration shows that following the evolutionary steps the encapsidated messenger RNAs incorporate more Packaging Signals than the starting RNAs. In other words, the phenomenon we have been working on in natural viruses “evolves” in an artificial particle, and the results in this paper therefore describe a process that may have occurred in the early evolution of viruses. This understanding enables us to exploit these containers as delivery vehicles for gene therapeutic purposes.”

About this research

Researchers from the Universities of York and Leeds collaborated with the Hilvert Laboratory at the ETH Zurich to study the virus-like particles.

Featured image credit: ETH Zürich / Stephan Tetter

Reference: Rebecca Chandler-Bostock, Carlos P. Mata, Richard J. Bingham, Eric C. Dykeman, Bo Meng, Tobias J. Tuthill, David J. Rowlands, Neil A. Ranson, Reidun Twarock, Peter G. Stockley. Assembly of infectious enteroviruses depends on multiple, conserved genomic RNA-coat protein contacts. PLOS Pathogens, 2020; 16 (12): e1009146 DOI: 10.1371/journal.ppat.1009146

Provided by University of York

Review: Most Human Origins Stories Are Not Compatible With Known Fossils (Paleontology)

Fossil apes can inform us about essential aspects of ape and human evolution, including the nature of our last common ancestor

In the 150 years since Charles Darwin speculated that humans originated in Africa, the number of species in the human family tree has exploded, but so has the level of dispute concerning early human evolution. Fossil apes are often at the center of the debate, with some scientists dismissing their importance to the origins of the human lineage (the “hominins”), and others conferring them starring evolutionary roles. A new review out on May 7 in the journal Science looks at the major discoveries in hominin origins since Darwin’s works and argues that fossil apes can inform us about essential aspects of ape and human evolution, including the nature of our last common ancestor.

Humans diverged from apes–specifically, the chimpanzee lineage–at some point between about 9.3 million and 6.5 million years ago, towards the end of the Miocene epoch. To understand hominin origins, paleoanthropologists aim to reconstruct the physical characteristics, behavior, and environment of the last common ancestor of humans and chimps.

“When you look at the narrative for hominin origins, it’s just a big mess–there’s no consensus whatsoever,” said Sergio Almécija, a senior research scientist in the American Museum of Natural History’s Division of Anthropology and the lead author of the review. “People are working under completely different paradigms, and that’s something that I don’t see happening in other fields of science.”

There are two major approaches to resolving the human origins problem: “Top-down,” which relies on analysis of living apes, especially chimpanzees; and “bottom-up,” which puts importance on the larger tree of mostly extinct apes. For example, some scientists assume that hominins originated from a chimp-like knuckle-walking ancestor. Others argue that the human lineage originated from an ancestor more closely resembling, in some features, some of the strange Miocene apes.

In reviewing the studies surrounding these diverging approaches, Almécija and colleagues with expertise ranging from paleontology to functional morphology and phylogenetics discuss the limitations of relying exclusively on one of these opposing approaches to the hominin origins problem. “Top-down” studies sometimes ignore the reality that living apes (humans, chimpanzees, gorillas, orangutans, and hylobatids) are just the survivors of a much larger, and now mostly extinct, group. On the other hand, studies based on the “bottom-up”approach are prone to giving individual fossil apes an important evolutionary role that fits a preexisting narrative.

“In The Descent of Man in 1871, Darwin speculated that humans originated in Africa from an ancestor different from any living species. However, he remained cautious given the scarcity of fossils at the time,” Almécija said. “One hundred fifty years later, possible hominins–approaching the time of the human-chimpanzee divergence–have been found in eastern and central Africa, and some claim even in Europe. In addition, more than 50 fossil ape genera are now documented across Africa and Eurasia. However, many of these fossils show mosaic combinations of features that do not match expectations for ancient representatives of the modern ape and human lineages. As a consequence, there is no scientific consensus on the evolutionary role played by these fossil apes.”

Overall, the researchers found that most stories of human origins are not compatible with the fossils that we have today.

“Living ape species are specialized species, relicts of a much larger group of now extinct apes. When we consider all evidence–that is, both living and fossil apes and hominins–it is clear that a human evolutionary story based on the few ape species currently alive is missing much of the bigger picture,” said study co-author Ashley Hammond, an assistant curator in the Museum’s Division of Anthropology.

Kelsey Pugh, a Museum postdoctoral fellow and study co-author adds, “The unique and sometimes unexpected features and combinations of features observed among fossil apes, which often differ from those of living apes, are necessary to untangle which features hominins inherited from our ape ancestors and which are unique to our lineage.”

Living apes alone, the authors conclude, offer insufficient evidence. “Current disparate theories regarding ape and human evolution would be much more informed if, together with early hominins and living apes, Miocene apes were also included in the equation,” says Almécija. “In other words, fossil apes are essential to reconstruct the ‘starting point’ from which humans and chimpanzees evolved.”

This study was part of a collaborative effort with colleagues from the New York Institute of Technology (Nathan Thompson) and the Catalan Institute of Paleontology Miquel Crusafont (David Alba and Salvador Moyà-Solà).

Featured image: The last common ancestor of chimpanzees and humans represents the starting point of human and chimpanzee evolution. Fossil apes play an essential role when it comes to reconstructing the nature of our ape ancestry. Printed with permission from © Christopher M. Smith

Reference: Sergio Almécija, Ashley S. Hammond, Nathan E. Thompson, Kelsey D. Pugh, Salvador Moyà-Solà, David M. Alba, “Fossil apes and human evolution”, Science  07 May 2021: Vol. 372, Issue 6542, eabb4363 DOI: https://doi.org/10.1126/science.abb4363

Provided by American Museum of Natural History

Microfossil Found in Scottish Highlands Could Be ‘Missing Link’ in Early Animal Evolution (Paleontology)

Freshwater fossil displays multicellularity 400 million years earlier than previously established

The billion-year-old fossil of an organism, exquisitely preserved in the Scottish Highlands, reveals features of multicellularity nearly 400 million years before the biological trait emerged in the first animals, according to a new report in the journal Current Biology by an international team of researchers, including Boston College paleobotanist Paul K. Strother.

The discovery could be the “missing link” in the evolution of animals, according to the team, which included scientists from the U.S., United Kingdom, and Australia. The microfossil, discovered at Loch Torridon, contains two distinct cell types and could be the earliest example of complex multicellularity ever recorded, according to the researchers.

The fossil offers new insight into the transition of single celled organisms to complex, multicellular animals. Modern single-celled holozoa include the most basal living animals and the fossil discovered shows an organism which lies somewhere between single cell and multicellular animals, or metazoa.

“Our findings show that the genetic underpinnings of cell-to-cell cohesion and segregation — the ability for different cells to sort themselves into separate regions within a multicellular mass — existed in unicellular organisms a billion years ago, some 400 million years before such capabilities were incorporated into the first animals,” said Strother, a research professor in the Department of Earth and Environmental Sciences at Boston College.

The fossil’s discovery in an inland lake shifts the focus on the first forms of early life from the ocean to freshwater.

Animals, or etazoa, are one of only five groups of organisms that have evolved complex multicellularity – organisms that grow from a single cell that develops into a myriad of different cells and tissues. Animals probably evolved from unicellular ancestors that went through multicellular stages during their life cycles, said Strother, an expert in paleobotany and palynology, the study of fossil spores and pollen. Land plants, too, achieved complex multicellularity when they evolved from simpler algal ancestors some time during the early Paleozoic from about 500 to 400 million years ago..

“We describe here a new fossil that is similar to living unicellular relatives of animals, belonging to the group Ichthyosporea,” said Strother. “Our fossil shows life-cycle stages with two different kinds of cells, which could be the first step toward the evolution of complex multicellularity in the evolutionary lineage leading to the Metazoa.”

The study was based on populations of cells preserved in the mineral phosphate that were collected from billion-year-old lake deposits found in the northwest Scottish Highlands, Strother said. Samples are prepared in rock thin sections which allow microfossils to be seen under the light microscope or with a focused ion beam microscope.

The microfossils were discovered as part of an ongoing project to describe life living in freshwater lakes one billion years ago, using samples collected in Scotland and Michigan by Strother beginning in 2008, with support from NASA and the National Geographic Society, and now the Natural Environment Research Council in the UK.

The new fossil has been described and formally named Bicellum brasieri in the new report.

Strother said the discovery has the potential to change the way scientists look at the earliest forms of life on Earth.

“Our study of life in billion-year-old lakes is challenged by our ability to determine which kinds of organisms are represented in these deposits,” he said. “Previously we have assumed that most of what we see in these deposits are various kinds of extinct algae, but the morphological features of Bicellum really are more like those of modern-day unicellular relatives of animals. This is causing us to broaden our approach to reconstructing the diversity and ecology of life on Earth one billion years ago.”

The discovery will allow researchers to expand upon a more thorough reconstruction of the life-cycle of Bicellum, Strother said.

“Armed with comparative morphology with modern day Ichthyosporeans, we may be able to recognize additional morphogenic stages and determine how a single generative cell divides to become a multicellular cell mass,” he said.

Featured image: This enhanced image of Bicellum brasieri shows an outer wall of sausage-shaped cells enclosing an inner cell mass. The fossil reveals multicellular structure in an early animal form 400 million years earlier than previously established. © P.K. Strother

Reference: Paul K. Strother, Martin D. Brasier et al., “A possible billion-year-old holozoan with differentiated multicellularity”, Current Biology, 2021. DOI: https://doi.org/10.1016/j.cub.2021.03.051

Provided by Boston College

Small Galaxies Likely Played Important Role in Evolution of the Universe (Cosmology / Astronomy)

A new study led by University of Minnesota astrophysicists shows that high-energy light from small galaxies may have played a key role in the early evolution of the Universe. The research gives insight into how the Universe became reionized, a problem that astronomers have been trying to solve for years. 

The research is published in The Astrophysical Journal, a peer-reviewed scientific journal of astrophysics and astronomy.

After the Big Bang, when the Universe was formed billions of years ago, it was in an ionized state. This means that the electrons and protons floated freely throughout space. As the Universe expanded and started cooling down, it changed to a neutral state when the protons and electrons combined into atoms, akin to water vapor condensing into a cloud. 

Now however, scientists have observed that the Universe is back in an ionized state. A major endeavor in astronomy is figuring out how this happened. Astronomers have theorized that the energy for reionization must have come from galaxies themselves. But, it’s incredibly hard for enough high energy light to escape a galaxy due to hydrogen clouds within it that absorb the light, much like clouds in the Earth’s atmosphere absorb sunlight on an overcast day. 

Astrophysicists from the Minnesota Institute for Astrophysics in the University of Minnesota’s College of Science and Engineering may have found the answer to that problem. Using data from the Gemini telescope, the researchers have observed the first ever galaxy in a “blow-away” state, meaning that the hydrogen clouds have been removed, allowing the high energy light to escape. The scientists suspect that the blow-away was caused by many supernovas, or dying stars, exploding in a short period of time. 

“The star-formation can be thought of as blowing up the balloon,” explained Nathan Eggen, the paper’s lead author who recently received his master’s degree in astrophysics from the University of Minnesota. “If, however, the star-formation was more intense, then there would be a rupture or hole made in the surface of the balloon to let out some of that energy. In the case of this galaxy, the star-formation was so powerful that the balloon was torn to pieces, completely blown-away.”

The galaxy, named Pox 186, is so small that it could fit inside the Milky Way. The researchers suspect that its compact size, coupled with its large population of stars—which amount to a hundred thousand times the mass of the sun—made the blow-away possible.

The findings confirm that a blow-away is possible, furthering the idea that small galaxies were primarily responsible for the reionization of the Universe and giving more insight into how the Universe became what it is today.

“There are a lot of scenarios in science where you theorize that something should be the case, and you don’t actually find it,” Eggen said. “So, getting the observational confirmation that this sort of thing can happen is really important. If this one scenario is possible, then that means that there are other galaxies that also existed in blow-away states in the past. Understanding the consequences of this blow-away gives direct insight into the impacts similar blow-aways would have had during the process of reionization.”

In addition to Eggen, the research team included Claudia Scarlata and Evan Skillman, both professors in the School of Physics and Astronomy at the University of Minnesota, and Anne Jaskot, an assistant professor of astronomy at Williams College. 

The research was funded by grants from the University of Minnesota and NASA. Researchers made use of the NASA/IPAC Extragalactic Database (NED) and NASA’s Astrophysical Data System.

Read the full paper entitled, “Blow-Away in the Extreme Low-Mass Starburst Galaxy Pox 186” on The Astrophysical Journal website.

Featured image: The University of Minnesota study shows that high-energy light from small galaxies, like the Pox 186 galaxy depicted above, may have played a key role in the reionization and evolution of the Universe. Credit: Podevin, J.f., 2006

Provided by University of Minnesota

Insect Evolution Was More Complex Than Previously Assumed (Biology)

Certain signalling proteins, which are responsible for the development of innate immune function in almost all animals are also required for the formation of the dorsal-ventral (back-belly) axis in insect embryos. A new study by researchers from the University of Cologne’s Institute of Zoology suggests that the relevance of these signalling proteins for insect axis formation has increased independently several times during evolution. For example, the research team found similar evolutionary patterns in the Mediterranean field cricket as in the fruit fly Drosophila, although the two insects are only very distantly related and previous observations suggested different evolutionary patterns. The new findings show that the evolution of axis formation in insects was actually much more complex than previously thought. The study has been published in eLife.

Signalling proteins play an important role in the early development of embryos. They are secreted by animal cells to influence the formation of other cells. The primary function of the so-called Toll signalling pathway is in the defence against pathogens (innate immune response). In insects, it is also involved in the division of the insect body along the dorsal-ventral body axis. Since the immune function has been found in almost all animals, but the axis formation function has only been found in insects, scientists wondered about the evolutionary history of this new role. Moreover, depending on the insect species, the significance of Toll for developmental processes differs. While axis formation in the fruit fly and flour beetle depend substantially on Toll, representatives of distantly related species, such as the wasp Nasonia and the milkweed bug Oncopeltus, rely more heavily on other signalling pathways. ‘Surprisingly, we found that the Toll signalling pathway plays a significant role in an insect that is separated by almost 400 million years from the species we studied so far,’ said Professor Dr Siegfried Roth from the Institute of Zoology. ‘The new study suggests that there might be several instances in which Toll independently acquired important functions in insect axis formation. For future studies, this means that our system allows us to explore mechanisms of parallel evolution.’

Featured image: University of Cologne scientists found out that the Toll signalling pathway is important not only for innate immune response, but also for axis formation in various insects. © Roth/Pechmann

Reference: Matthias Pechmann et al., “Striking parallels between dorsoventral patterning in Drosophila and Gryllus reveal a complex evolutionary history behind a model gene regulatory network”, Evolutionary Biology, 2021. DOI: 10.7554/eLife.68287

Provided by University of Cologne

What Does the Study of Domesticated Birds Tell us About the Evolution of Human Language? (Biology)

Looking for keys of the human language evolution in bird singing

Language is one of the most notable abilities humans have. It allows us to express complex meanings and transmit knowledge from generation to generation. An important question in human biology is how this ability ended up being developed, and researchers from the universities of Barcelona, Cologne and Tokyo have treated this issue in a recent article.

Published in the journal Trends in Cognitive Sciences, the article counts on the participation of the experts from the Institute of Complex Systems of the UB (UBICS) Thomas O’Rourke and Pedro Tiago Martins, led by Cedric Boeckx, ICREA research professor at the Faculty of Philology and Communication. According to the new study, the evolution of the language would be related to another notable feature of the Homo Sapiens: tolerance and human cooperation.

The study is based on evidence from diverse fields such as archaeology, evolutionary genomics, neurobiology, animal behaviour and clinical researcher on neuropsychiatric disorders. With these, it shows that the reduction of reactive aggressiveness, resulting from the evolution and process of self-domestication of our species, could have led to an increase in the complexity of speech. According to the authors, this development would be caused by the lowest impact on brain networks of stress hormones, neurotransmitters that activate in aggressive situations, and which would be crucial when learning to speak. To show this interaction, researchers analysed the genomic, neurobiological and singing-type differences between the domesticated Bengalese finch and its closest wild relative.

Looking for keys of the human language evolution in bird singing

A central aspect of the approach of the authors regarding the evolution of the language is that the aspects that make it special can be elucidated by comparing them to other animals’ communication systems. “For instance, see how kids learn to talk and how birds learn to sing: unlike most animal communication systems, young birds’ singing and the language of kids are only properly developed in presence of adult tutors. Without the vocal support from adults, the great range of sounds available for humans and singing birds does not develop properly”, note researchers.

Moreover, although speaking and bird singing evolved independently, authors suggest both communication systems are associated with similar patterns in the brain connectivity and are negatively affected by stress: “Birds that are regularly under stress during their development sing a more stereotypical song as adults, while children with chronic stress problems are more susceptible to developing repetitive tics, including vocalizations in the case of Tourette syndrome”.

In this context, Kazuo Okanoya, one of the authors of the article, has been studying the Bengalese finch (Lonchura striata domestica) for years. This domesticated singing bird sings a more varied and complex song than its wild ancestor. The study shows that the same happens with other domesticated species: the Bengalese finch has a weakened response to stress and is less aggressive than its wild relative. In fact, according to the authors, there is more and more “evidence of multiple domesticated species to have altered vocal repertoires compared to their wild counterparts”.

The impact of domestication in stress and aggressiveness

For the researchers, these differences between domestic and wild animals are “the central pieces in the puzzle of the evolution of human language”, since our species shares with other domestic animals particular physical changes related to their closest wild species. Modern humans have a plain face, a round skull and a reduced size of teeth compared to our extinct archaic relatives, Neanderthals. Domestic animals have comparable changes in facial and cranial bone structures, often accompanied by the development of other traits such as skin depigmentation, floppy ears and curly tails. Last, modern humans have marked reductions in the response measures to stress and reactive aggression compared to other living apes. These similarities do not stop with physical since, according to researchers, the genomes of modern humans and multiple domesticated species show changes focused on the same genes.

In particular, a disproportionate number of these genes would negatively regulate the activity of the glutamate neurotransmitter system, which drives the brain’s response to stressful experiences. Authors note that “glutamate, the brain’s main excitatory neurotransmitter, dopamine, in learning birdsong, aggressive behaviour, and the repetitive vocal tics of Tourette syndrome”.

Alterations in stress hormone balance in the striated body

In the study, authors show how the activity of glutamate tends to promote the release of dopamine in the striated body, an evolutionary old brain structure important for learning which is based on rewards and motor activities. “In adult songbirds, the increase in dopamine release in this striatal area is correlated to the learning of a more restricted song, which replaces experimental vocalizations typical of young birds”. “Regarding human beings and other mammals -authors add-, dopamine release in the dorsal striatum promotes restrictive and repetitive motor activities, such as vocalizations, while other more experimental and exploratory behaviours are supported by the dopaminergic activity of the ventral striatum”. According to the study, many of the involved genes in the glutamatergic activation that changed in the recent human evolution, codify the signalling of receptors that reduce the excitation of the dorsal striatum. That is, these reduce the dopamine release in this area. Meanwhile, these receptors tend not to reduce, and even promote, the dopamine release in ventral striatal regions.

The authors say these alterations in the balance of stress hormones in the striated body were an important advance in the evolution of vocal speech in the lineage of modern humans. “These results suggest the glutamate system and its interactions with dopamine are involved in the process in which humans acquired their varied and flexible ability to speak. Therefore, the natural selection against reactive aggressiveness that took place in our species would have altered the interaction of these neurotransmitters promoting the communicative skills of our species. These findings shed light on new ways for comparative biological research on the human ability of speech” conclude researchers.

Featured image: Researchers analysed the genomic, neurobiological and singing-type differences between the domesticated Bengalese finch (see image above) and its closest wild relative. © University of Barcelona

Reference: Thomas O’Rourke et al., “Capturing the Effects of Domestication on Vocal Learning Complexity”, Trends in Cognitive Sciences, 2021. DOI: https://doi.org/10.1016/j.tics.2021.03.007

Provided by University of Barcelona

The Chillest Ape: How Humans Evolved A Super-High Cooling Capacity (Biology)

Penn Medicine discovery illuminates human sweat gland evolution

Humans have a uniquely high density of sweat glands embedded in their skin—10 times the density of chimpanzees and macaques. Now, researchers at Penn Medicine have discovered how this distinctive, hyper-cooling trait evolved in the human genome. In a study published today in The Proceedings of the National Academy of Sciences of the USA, researchers showed that the higher density of sweat glands in humans is due, to a great extent, to accumulated changes in a regulatory region of DNA—called an enhancer region—that drives the expression of a sweat gland-building gene, explaining why humans are the sweatiest of the Great Apes.

“This is one of the clearest examples I’ve ever seen of pinpointing the genetic basis for one of the most extreme and distinctively human evolutionary traits as a whole,” said the study’s senior author, Yana Kamberov, PhD, an assistant professor of genetics at Penn Medicine. “This kind of research is important not only because it shows how evolution actually works to produce species diversity but also because it gives us access into human biology that is often not possible to gain in other ways, essentially by learning from tweaking the biological system in a way that is actually beneficial, without breaking it.”

Scientists broadly assume that humans’ high density of sweat glands, also called eccrine glands, reflects an ancient evolutionary adaptation. This adaptation, coupled with the loss of fur in early hominins, which promoted cooling through sweat evaporation, is thought to have made it easier for them to run, hunt, and otherwise survive on the hot and relatively treeless African savannah, a markedly different habitat than the jungles occupied by other ape species.

Kamberov found in a 2015 study that the expression level of a gene called Engrailed 1—EN1 in humans—helps determine the density of eccrine glands in mice. EN1 encodes a transcription factor protein that, among many other functions, works during development to induce immature skin cells to form eccrine glands. Because of this property, Kamberov and colleagues hypothesized that perhaps one way in which humans could have built more sweat glands in their skin is to evolve genetic changes that increased the production of EN1 in the skin.

The activity of a gene is often affected by nearby regions of DNA called enhancer regions, where factors that activate the gene can bind and help drive the gene’s expression. In the study, Kamberov and her team identified an enhancer region called hECE18 that boosts the production of EN1 in skin, to induce the formation of more eccrine glands. The researchers showed that the human version of hECE18 is more active than that of ape or macaque versions, which would in turn drive higher levels of EN1 production.

Kamberov and her colleagues also teased apart the individual mutations that distinguish human hECE18, showing why some of them boost EN1 expression—and showing that rolling back those mutations to the chimp version of hECE18 brings the enhancer activity down to chimp levels.

Prior studies of evolved human-specific traits, such as language, generally have tied such traits to complex genetic changes involving multiple genes and regulatory regions. In contrast, the work from Kamberov and her team suggest that the human “high-sweat” trait evolved at least in part through repeated mutations to just one regulatory region, hECE18. This means that this single regulatory element could have repeatedly contributed to a gradual evolution of higher eccrine gland density during human evolution.

While the study is mainly a feat of basic biology that shines a light on human evolution, it also should have some long-term medical relevance, Kamberov said.

“Severe wounds or burns often destroy sweat glands in skin, and so far we don’t know how to regenerate them—but this study brings us closer to discovering how to do that,” she said. “The next step in this research would be to uncover how the multiple activity enhancing mutations in hECE18 interact with each other to increase EN1 expression and to use these biologically key mutations as starting points to figure out what DNA-binding factors actually bind at these sites. Basically, this provides us with a direct molecular inroad to discover the upstream factors that by activating EN1 expression get skin cells to start making sweat glands.”

Support for the research was provided by the National Science Foundation (BCS-1847598) the National Institute of Arthritis and Musculoskeletal and Skin Diseases (R01AR077690), the McCabe Fund, the Penn Skin Biology and Disease Resource-based Center (P30AR069589), and the National Institute of Child Health and Human Development (F32HD101230).

Featured image: Over time, humans gradually evolved a stronger enhancer for activating Engrailed 1 gene expression, resulting in more sweat glands and making them the sweatiest of the Great Apes. © Penn Medicine

Reference: Daniel Aldea, Yuji Atsuta, Blerina Kokalari, Stephen F. Schaffner, Rexxi D. Prasasya, Adam Aharoni, Heather L. Dingwall, Bailey Warder, Yana G. Kamberov, “Repeated mutation of a developmental enhancer contributed to human thermoregulatory evolution”, Proceedings of the National Academy of Sciences Apr 2021, 118 (16) e2021722118; DOI: 10.1073/pnas.2021722118

Provided by Penn Medicine