Chimpanzees gesture back and forth quickly like in human conversations

When people are having a conversation, they rapidly take turns speaking and sometimes even interrupt. Now, researchers who have collected the largest ever dataset of chimpanzee "conversations" have found that they communicate back and forth using gestures following the same rapid-fire pattern. The findings are reported on July 22 in the journal Current Biology.

"While human languages are incredibly diverse, a hallmark we all share is that our conversations are structured with fast-paced turns of just 200 milliseconds on average," said Catherine Hobaiter  at the University of St Andrews, UK. "But it was an open question whether this was uniquely human, or if other animals share this structure."

"We found that the timing of chimpanzee gesture and human conversational turn-taking is similar and very fast, which suggests that similar evolutionary mechanisms are driving these social, communicative interactions," says Gal Badihi, the study's first author.

The researchers knew that human conversations follow a similar pattern across people living in places and cultures all over the world. They wanted to know if the same communicative structure also exists in chimpanzees even though they communicate through gestures rather than through speech. To find out, they collected data on chimpanzee "conversations" across five wild communities in East Africa.

Altogether, they collected data on more than 8,500 gestures for 252 individuals. They measured the timing of turn-taking and conversational patterns. They found that 14% of communicative interactions included an exchange of gestures between two interacting individuals. Most of the exchanges included a two-part exchange, but some included up to seven parts.

Overall, the data reveal a similar timing to human conversation, with short pauses between a gesture and a gestural response at about 120 milliseconds. Behavioral responses to gestures were slower. "The similarities to human conversations reinforce the description of these interactions as true gestural exchanges, in which the gestures produced in response are contingent on those in the previous turn," the researchers write.

"We did see a little variation among different chimp communities, which again matches what we see in people where there are slight cultural variations in conversation pace: some cultures have slower or faster talkers," Badihi says.

"Fascinatingly, they seem to share both our universal timing, and subtle cultural differences," says Hobaiter. "In humans, it is the Danish who are 'slower' responders, and in Eastern chimpanzees that's the Sonso community in Uganda."

This correspondence between human and chimpanzee face-to-face communication points to shared underlying rules in communication, the researchers say. They note that these structures could trace back to shared ancestral mechanisms. It's also possible that chimpanzees and humans arrived at similar strategies to enhance coordinated interactions and manage competition for communicative "space." The findings suggest that human communication may not be as unique as one might think.

"It shows that other social species don't need language to engage in close-range communicative exchanges with quick response time," Badihi says. "Human conversations may share similar evolutionary history or trajectories to the communication systems of other species suggesting that this type of communication is not unique to humans but more widespread in social animals."

In future studies, the researchers say they want to explore why chimpanzees have these conversations to begin with. They think chimpanzees often rely on gestures to ask something of one another.

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Chimp moms play with their offspring through good times and bad

When it comes to nurturing their young, mother chimpanzees go the extra mile, according to a new study. Using 10 years of observational data on wild chimpanzees, researchers found that while adults often play, and young chimps play a lot, when food gets scarce, the adults put mutual play aside and focus on survival.

But in the meantime, mother chimps continue to be their offspring's primary playmate, tickling, chasing, playing 'airplane'. That suggests the mother chimps take on an indispensable role fostering their young's physical and social development even when they are under food stress.

The study observations took place in Kibale National Park in Uganda, and the study analysis, published in Current Biology, was led by Zarin Machanda, an assistant professor of anthropology and biology, and her former postdoctoral associate Kris Sabbi, who is currently a college fellow in human evolutionary biology at Harvard University.

Kibale is the most primate-dense forest in the world, with thirteen species living there including over 1,000 chimpanzees. Researchers started habituating the chimps to the presence of humans in 1987. Over the decades, teams of researchers took detailed field notes of almost every observable behavior -- including climbing, feeding, grooming, calling, aggression, and play.

Through their previous work, Machanda and Sabbi were familiar with the playfulness of chimpanzees and decided to look deeper into the patterns of play behavior. They expected seasonal variations in food availability would affect adult chimps' time spent playing.

For example, when supplies of quality fruits were low, the chimps focused on finding and gathering figs and leaves, and put play time aside. Surprisingly, although chimp mothers had the same challenge in finding food, they continued devoting a lot of their time to nurturing their offspring's development through play.

Learning Lessons from Play

"The research on play ties into an effort to understand the evolution of leadership among chimps," said Machanda. "We were trying to see whether chimps have only one pathway to leadership, which has always been assumed to be aggressiveness, or whether play and other behaviors build multiple dimensions of character that might make them more or less successful."

Play is not very common in the wild, at least among adult animals. Young mammals do play often, but mostly with each other, or at the expense of an exasperated and passive adult. Exceptions include dolphins, monkeys, and apes. Natural selection tends to suppress the costly exercise after it serves its purpose for development, and time comes to focus on finding food, watching out for predators, and mating. With chimps, however, adult play serves to cement social bonds.

Why do some primates play throughout life and other mammals don't? "I think what sets primates apart is that they spend more time growing up compared to other mammals," said Machanda. "They also have highly developed brains and live in structured groups, with very specific rules governing interactions between individuals. Play permits them to build not only physical skills, but also the skills of social interaction."

Social structure in the chimpanzee world may also explain why mother chimps sometimes become the primary play partners for their young. The chimpanzees have a very fluid social system called fission-fusion, which means a group of 60 chimps, for example, may have smaller groups break away for days or weeks, which then merge again while other groups break off.

When food becomes scarce, chimp mothers tend to break away into smaller groups or solo with their babies. "But when they're doing that, they are also limiting the ability of their young ones to play with others, and the moms become the primary playmates," said Sabbi. "They're trading off that lower feeding competition in the larger group for more time and energy being spent playing with their little ones."

By comparison, a troop of 60 baboons always sticks together, so baby baboons always have other baboons close to their age nearby to play with. Baboon mothers usually do not play with their babies.

Types of Play

Play among the chimps often divides depending on their sex. "It's not uncommon to see male chimps to engage in more aggressive types of play, while females are doing a type of play related to parenting," said Machanda. "You see them practice carrying things -- a kind of preparation for future maternal behavior. Males often size each other up, and when they hit their second birthday, play style changes and can get rougher."

Mothers are often the ones that juveniles and older infants come back to. "If they're playing with somebody and it starts to get a little bit too rough, they'll switch it up and go back to playing with mom, because at the end of the day it's a very safe place," said Sabbi.

"If we compare to humans, it's very easy to find lots of evidence in the child psychology literature for how important it is for human mothers and fathers to be playing with their children, especially at really young ages. Moms and dads are important first play partners before kids branch out into their own social networks," she said.

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Great apes playfully tease each other

Babies playfully tease others as young as eight months of age. Since language is not required for this behavior, similar kinds of playful teasing might be present in non-human animals. Now cognitive biologists and primatologists from the University of California Los Angeles (UCLA, US), the Max Planck Institute of Animal Behavior (MPI-AB, Germany), Indiana University (IU, US), and the University of California San Diego (UCSD, US) have documented playful teasing in four species of great apes. Like joking behavior in humans, ape teasing is provocative, persistent, and includes elements of surprise and play. Because all four great ape species used playful teasing, it is likely that the prerequisites for humor evolved in the human lineage at least 13 million years ago.

Joking is an important part of human interaction that draws on social intelligence, an ability to anticipate future actions, and an ability to recognize and appreciate the violation of others' expectations.

Teasing has much in common with joking, and playful teasing may be seen as a cognitive precursor to joking.

The first forms of playful teasing in humans emerge even before babies say their first words, as early as eight months of age.

The earliest forms of teasing are repetitive provocations often involving surprise.

Infants tease their parents by playfully offering and withdrawing objects, violating social rules (so-called provocative non-compliance), and disrupting others' activities.

In a study recently published in the Proceedings of the Royal Society B, scientists from the University of California Los Angeles, the Max Planck Institute of Animal Behavior, Indiana University, and the University of California San Diego(Isabelle Laumer, Sasha Winkler, Federico Rossano, and Erica Cartmill) report evidence of playful teasing in the four great ape species: orangutans, chimpanzees, bonobos and gorillas.

"Great apes are excellent candidates for playful teasing, as they are closely related to us, engage in social play, show laughter and display relatively sophisticated understandings of others' expectations," says Isabelle Laumer (UCLA/MPI-AB) a post-doctoral researcher and the first author of the study.

The team analyzed spontaneous social interactions that appeared to be playful, mildly harassing, or provocative.

During these interactions, the researchers observed the teaser's actions, bodily movements, facial expressions, and how the targets of the teasing responded in turn.

They also assessed the teaser's intentionality by looking for evidence that the behavior was directed at a specific target, that it persisted or intensified, and that teasers waited for a response from the target.

The researchers found that orangutans, chimpanzees, bonobos and gorillas all engaged in intentionally provocative behavior, frequently accompanied by characteristics of play.

They identified 18 distinct teasing behaviors. Many of these behaviors appeared to be used to provoke a response, or at least to attract the target's attention.

"It was common for teasers to repeatedly wave or swing a body part or object in the middle of the target's field of vision, hit or poke them, stare closely at their face, disrupt their movements, pull on their hair or perform other behaviors that were extremely difficult for the target to ignore," explains UCLA and IU professor Erica Cartmill, senior author of the study.

Although playful teasing took many forms, the authors note that it differed from play in several ways.

"Playful teasing in great apes is one-sided, very much coming from the teaser often throughout the entire interaction and rarely reciprocated," explains Cartmill.

"The animals also rarely use play signals like the primate 'playface', which is similar to what we would call a smile, or 'hold' gestures that signal their intent to play."

Playful teasing mainly occurred when apes were relaxed, and shared similarities with behaviors in humans.

"Similar to teasing in children, ape playful teasing involves one-sided provocation, response waiting in which the teaser looks towards the target's face directly after a teasing action, repetition, and elements of surprise," Laumer explains.

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Chimpanzees use hilltops to conduct reconnaissance on rival groups -- study

Chimpanzees use high ground to conduct reconnaissance on rival groups, often before making forays into enemy territory at times when there is reduced risk of confrontation, a new study suggests.

Tactical use of elevated terrain in warfare situations is considered unique to humans -- until now. For the first time, one of the oldest military strategies has been observed in our closest evolutionary relatives.

Researchers conducted a three-year study of two neighbouring chimpanzee groups in the West African forests of Côte d'Ivoire, tracking the primates as they traversed their respective territories, including an overlapping border area where skirmishes occasionally took place.

The team found that chimpanzees were more than twice as likely to climb hills when heading towards this contested frontier as when they were travelling into the heart of their own territory.*

While atop border hills, chimpanzees were more likely to refrain from noisily eating or foraging and spend time quietly resting -- enabling them to hear distant sounds of rival groups, say researchers.

The further away the location of hostile chimpanzees, the greater the likelihood of an advance into dangerous territory upon descending the hill. This suggests that chimpanzees on high ground gauge the distance of rivals, and act accordingly to make incursions while avoiding costly fights.

Other mammal species such as meerkats use high ground to keep watch for predators or call to mates. However, researchers say this is the first evidence for an animal other than humans making strategic use of elevation to assess the risks of "intergroup conflict."

"Tactical warfare is considered a driver of human evolution," said Dr Sylvain Lemoine, a biological anthropologist from the University of Cambridge's Department of Archaeology, and lead author of the study published in the journal PLOS Biology.

"This chimpanzee behaviour requires complex cognitive abilities that help to defend or expand their territories, and would be favoured by natural selection."

"Exploiting the landscape for territorial control is deeply rooted in our evolutionary history. In this use of war-like strategy by chimpanzees we are perhaps seeing traces of the small scale proto-warfare that probably existed in prehistoric hunter-gatherer populations."

The study was conducted at the Taï Chimpanzee Project, where Lemoine worked during his PhD. The project is currently led by study senior author Dr Roman Wittig from CNRS in France.**

Teams of researchers spend 8-12 hours a day following four groups that are "habituated" to the presence of humans. It is one of the few sites where data is collected simultaneously on multiple communities of wild chimpanzees.

The project researchers have GPS trackers, through which the study authors were able to reproduce maps of two chimpanzee territories that border each other, including elevation data. These were matched to old French colonial maps to confirm topography.

Each group consisted of 30-40 adult chimpanzees at any one time. The study used over 21,000 hours of track logs from a total of 58 animals recorded between 2013 and 2016.

To establish and protect their territory, chimpanzees perform regular tours of the periphery that form a sort of "border patrol," says Lemoine. "Patrols are often conducted in subgroups that stay close and limit noise. As an observer, you get a sense that patrolling has begun. They move and stop at the same time, a bit like a hunt," he said.

The type of hills near the border used for reconnaissance are known as "inselbergs": isolated rocky outcrops that break up the forest canopy.*** Chimpanzees repeatedly returned to some of these inselbergs, where time on the summit was passed in a more muted state.

"These aren't so much lookout points as listen-out points," said Lemoine. "Chimpanzees drum on tree trunks and make excitable vocalisations called pant-hoots to communicate with group members or assert their territory. These sounds can be heard over a kilometre away, even in dense forest."

"It may be that chimpanzees climb hilltops near the edge of their territory when they have yet to hear signs of rival groups. Resting quietly on an elevated rock formation is an ideal condition for the auditory detection of distant adversaries."

Researchers analysed tactical movements in the half an hour after a stop longer than five minutes on a hill near the border, and compared it to movements after stops in low-lying border areas.

Following a hilltop recce, the likelihood of advancing into enemy territory increased from 40% when rivals were 500 metres away, to 50% when rivals were at 1000m, to 60% when rivals were at 3000m.

"Chimpanzees often expand their territory by encroaching and patrolling in that of their neighbours. Hilltop information-gathering will help them to do this while reducing risks of encountering any enemies," said Lemoine. "The border zone between the two groups was in a state of flux."

More territory can boost food provision and mating chances, says Lemoine. His previous work suggests that larger chimpanzee groups live in bigger territories with reduced pressure from rivals, which in turn increases birth rates within communities.

The latest research suggests that chimpanzees use hilltop reconnaissance to avoid confrontation, and violence is relatively rare, says Lemoine. But fights, and even kidnappings and killings, did occur between rival group members.

"Occasionally, raiding parties of two or three males venture deep into enemy territory, which can lead to fighting. Confrontations between rival chimpanzees are extremely noisy. The animals go into an intimidating frenzy, screaming and defecating and gripping each other's genitals."

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Human shoulders and elbows first evolved as brakes for climbing apes

The rotating shoulders and extending elbows that allow humans to reach for a high shelf or toss a ball with friends may have first evolved as a natural braking system for our primate ancestors who simply needed to get out of trees without dying.

Dartmouth researchers report in the journal Royal Society Open Science that apes and early humans likely evolved free-moving shoulders and flexible elbows to slow their descent from trees as gravity pulled on their heavier bodies. When early humans left forests for the grassy savanna, the researchers say, their versatile appendages were essential for gathering food and deploying tools for hunting and defense.

The researchers used sports-analysis and statistical software to compare videos and still-frames they took of chimpanzees and small monkeys called mangabeys climbing in the wild. They found that chimps and mangabeys scaled trees similarly, with shoulders and elbows mostly bent close to the body. When climbing down, however, chimpanzees extended their arms above their heads to hold onto branches like a person going down a ladder as their greater weight pulled them downward rump-first.

Luke Fannin, first author of the study and a graduate student in Dartmouth's Ecology, Evolution, Environment and Society program, said the findings are among the first to identify the significance of "downclimbing" in the evolution of apes and early humans, which are more genetically related to each other than to monkeys. Existing research has observed chimps ascending and navigating trees -- usually in experimental setups -- but the researchers' extensive video from the wild allowed them to examine how the animals' bodies adapted to climbing down, Fannin said.

"Our study broaches the idea of downclimbing as an undervalued, yet incredibly important factor in the diverging anatomical differences between monkeys and apes that would eventually manifest in humans," Fannin said. "Downclimbing represented such a significant physical challenge given the size of apes and early humans that their morphology would have responded through natural selection because of the risk of falls."

"Our field has thought about apes climbing up trees for a long time -- what was essentially absent from the literature was any focus on them getting out of a tree. We've been ignoring the second half of this behavior," said study co-author Jeremy DeSilva, professor and chair of anthropology at Dartmouth.

"The first apes evolved 20 million years ago in the kind of dispersed forests where they would go up a tree to get their food, then come back down to move on to the next tree," DeSilva said.

"Getting out of a tree presents all kinds of new challenges. Big apes can't afford to fall because it could kill or badly injure them. Natural selection would have favored those anatomies that allowed them to descend safely."

Flexible shoulders and elbows passed on from ancestral apes would have allowed early humans such as Australopithecus to climb trees at night for safety and come down in the daylight unscathed, DeSilva said. Once Homo erectus could use fire to protect itself from nocturnal predators, the human form took on broader shoulders capable of a 90-degree angle that -- combined with free-moving shoulders and elbows -- made our ancestors excellent shots with a spear (apes cannot throw accurately).

"It's that same early-ape anatomy with a couple of tweaks. Now you have something that can throw a spear or rocks to protect itself from being eaten or to kill things to eat for itself. That's what evolution does -- it's a great tinkerer," DeSilva said.

"Climbing down out of a tree set the anatomical stage for something that evolved millions of years later," he said. "When an NFL quarterback throws a football, that movement is all thanks to our ape ancestors."

Despite chimps' lack of grace, Fannin said, their arms have adapted to ensure the animals reach the ground safely -- and their limbs are remarkably similar to those of modern humans.

"It's the template that we came from -- going down was probably far more of a challenge for our early ancestors, too," Fannin said. "Even once humans became upright, the ability to ascend, then descend, a tree would've been incredibly useful for safety and nourishment, which is the name of the game when it comes to survival.We're modified, but the hallmarks of our ape ancestry remain in our modern skeletons."

The researchers also studied the anatomical structure of chimp and mangabey arms using skeletal collections at Harvard University and The Ohio State University, respectively. Like people, chimps have a shallow ball-and-socket shoulder that -- while more easily dislocated -- allows for a greater range of movement, Fannin said. And like humans, chimps can fully extend their arms thanks to the reduced length of the bone just behind the elbow known as the olecranon process.

Mangabeys and other monkeys are built more like quadrupedal animals such as cats and dogs, with deep pear-shaped shoulder sockets and elbows with a protruding olecranon process that make the joint resemble the letter L. While these joints are more stable, they have a much more limited flexibility and range of movement.

The researchers' analysis showed that the angle of a chimp's shoulders was 14 degrees greater during descent than when climbing up. And their arm extended outward at the elbow 34 degrees more when coming down from a tree than going up. The angles at which mangabeys positioned their shoulders and elbows were only marginally different -- 4 degrees or less -- when they were ascending a tree versus downclimbing.

"If cats could talk, they would tell you that climbing down is trickier than climbing up and many human rock climbers would agree. But the question is why is it so hard," said study co-author Nathaniel Dominy, the Charles Hansen Professor of Anthropology and Fannin's adviser.

"The reason is that you're not only resisting the pull of gravity, but you also have to decelerate," Dominy said. "Our study is important for tackling a theoretical problem with formal measurements of how wild primates climb up and down. We found important differences between monkeys and chimpanzees that may explain why the shoulders and elbows of apes evolved greater flexibility."

Co-author Mary Joy, who led the study with Fannin for her undergraduate thesis and graduated from Dartmouth in 2021, was reviewing videos of chimps that DeSilva had filmed when she noticed the difference in how the animals descended trees than how they went up them.

"It was very erratic, just crashing down, everything's flying. It's very much a controlled fall," Joy said. "In the end, we concluded that the way chimps descend a tree is likely related to weight. Greater momentum potentially expends less energy and they're much more likely to reach the ground safely than by making small, restricted movements."

But as a trail runner, Joy knew the pained feeling of inching down an incline in short clips instead of just hurtling down the path with the pull of gravity, her legs extended forward to catch her at the end of each stride.

"When I'm moving downhill, the slower I'm going and restricting my movement, the more I'm fatiguing. It catches up to me very quickly. No one would think the speed and abandon with which chimps climb down from trees would be the preferred method for a heavier primate, but my experience tells me it's more energy efficient," she said.

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How orangutans respond to novelty in the wild

Humans like to discover. Presented with something we've never seen before, most of us will be compelled to explore and learn more about it. The same can't exactly be said for our closest living relatives -- the great apes. Although decades of studies have shown that captive chimpanzees, gorillas, and orangutans will eagerly explore unfamiliar objects in a laboratory, great apes have rarely been observed in these encounters in the wild. As such, almost nothing is known about how great apes respond to novelty in the natural habitats in which they evolved. Now, a team from the Max Planck Institute of Animal Behavior (MPI-AB) has succeeded in measuring the behavior of wild orangutans in their first encounter with an unfamiliar object. The experiments, conducted in an Indonesian rainforest, uncovered a mix of social, environmental, and age factors that made orangutans more likely to explore. Published in Scientific Reports, the study reveals the conditions that spark curiosity in orangutans, and sheds light on how our own curious natures might have evolved.

The team studied orangutans at a long-term monitoring site, Suaq Balimbing, in Sumatra. Orangutans at the site have been habituated over decades to the presence of humans, thus offering scientists a rare opportunity to observe wild great apes at close range. Caroline Schuppli, director of the Suaq Project and the study's first author, became interested in how wild orangutans would react when presented with something unfamiliar.

"Curiosity is a trait that has driven the exceptional ability of humans to learn and innovate," says Schuppli, a group leader at MPI-AB. "If we want to know how the trait evolved in us, we have to study it in our closest living relatives."

Curiosity, which describes an individual's motivation to learn about the unknown, has been studied before in great apes; however, due to the logistical difficulties of studying wild animals, almost all tests have occurred in captivity. "We know that apes are very curious to explore when they are in the safe and controlled conditions of a zoo," says Schuppli. "But these results tell us little about what really triggered or suppressed curiosity over our evolutionary history."

About ten years ago, Schuppli and collaborators first attempted to assess curiosity in wild orangutans with an experiment inspired by captive studies. They roamed Suaq, peppering the forest with foreign objects for the orangutans to find: a bright red flag; plastic flowers and fruits; a stuffed toy. The results were stark. "They hardly ever came near any of the items," she remembers. "You could see them making huge circles in the forest to avoid the experiment."

Schuppli realized that testing orangutans' reaction to novelty in nature would require reimagining the past paradigm. "The challenge was figuring out how to entice them with something that was novel, but also familiar enough not to scare them off," she says. Over the years Schuppli perfected just such an object: a piece of tree trunk with a natural hole filled with local forest honey. The tree hole and food were familiar, but deploying these in an unusual way represented a novel foraging situation. With a team of local and international scientists, Schuppli hoisted the experimental log into trees about 10 meters from orangutans -- and watched what happened.

During the trials, the orangutans spent on average 30 minutes in the vicinity of the novel log. During this time, they explored the novel log by intensively observing it over extended periods of time and approaching it closely. Overall, however, orangutans rarely touched the branch directly; and when they did, they often used a tool, such as a stick to do so. "The orangutans were pretty cautious," says Tri Rahmaeti, a team member from Universitas Nasional in Indonesia and co-author on the study. "The honey reward could have easily been scooped out of the log using a finger, but they still preferred to use a tool so they didn't have to make physical contact."

But there were significant differences in the behaviors. Using statistical techniques, the team uncovered traits of individuals and features in the environment that amplified exploration. Young orangutans were far more likely than adults to observe and approach. And, orangutans were more likely to approach the log if they saw another individual heading that way too. The habitat also seemed to play a role: in areas with abundant food, orangutans observed more but approached less.

Says Schuppli: "On the one hand, the results confirmed our hunch that orangutans in the wild are not that keen to explore new objects. This could be because in nature, orangutans live very long lives in stable habitats where novelty is rare. So, the potential risk of approaching something unknown doesn't outweigh the potential reward."

"On the other hand, the experiment showed that there is flexibility in the behavior. Orangutans have the potential to be curious about novelty in nature, but only under certain conditions. And by experimentally testing this in a wild population, we pinned down the conditions."

Of these conditions, Schuppli finds the social factor most illuminating. "Orangutans are the least social of all great apes, and yet we find that the presence of association partners increases their curiosity," she says.

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Focus on function helps identify the changes that made us human

Humans split away from our closest animal relatives, chimpanzees, and formed our own branch on the evolutionary tree about seven million years ago. In the time since -- brief, from an evolutionary perspective -- our ancestors evolved the traits that make us human, including a much bigger brain than chimpanzees and bodies that are better suited to walking on two feet. These physical differences are underpinned by subtle changes at the level of our DNA. However, it can be hard to tell which of the many small genetic differences between us and chimps have been significant to our evolution.

New research from Whitehead Institute Member Jonathan Weissman; University of California, San Francisco Assistant Professor Alex Pollen; Weissman lab postdoc Richard She; Pollen lab graduate student Tyler Fair; and colleagues uses cutting edge tools developed in the Weissman lab to narrow in on the key differences in how humans and chimps rely on certain genes. Their findings, published in the journal Cell on June 20th, may provide unique clues into how humans and chimps have evolved, including how humans became able to grow comparatively large brains.

Studying function rather than genetic code

Only a handful of genes are fundamentally different between humans and chimps; the rest of the two species' genes are typically nearly identical. Differences between the species often come down to when and how cells use those nearly identical genes. However, only some of the many differences in gene use between the two species underlie big changes in physical traits. The researchers developed an approach to narrow in on these impactful differences.

Their approach, using stem cells derived from human and chimp skin samples, relies on a tool called CRISPR interference (CRISPRi) that Weissman's lab developed. CRISPRi uses a modified version of the CRISPR/Cas9 gene editing system to effectively turn off individual genes. The researchers used CRISPRi to turn off each gene one at a time in a group of human stem cells and a group of chimp stem cells. Then they looked to see whether or not the cells multiplied at their normal rate. If the cells stopped multiplying as quickly or stopped altogether, then the gene that had been turned off was considered essential: a gene that the cells need to be active-producing a protein product-in order to thrive. The researchers looked for instances in which a gene was essential in one species but not the other as a way of exploring if and how there were fundamental differences in the basic ways that human and chimp cells function.

By looking for differences in how cells function with particular genes disabled, rather than looking at differences in the DNA sequence or expression of genes, the approach ignores differences that do not appear to impact cells. If a difference in gene use between species has a large, measurable effect at the level of the cell, this likely reflects a meaningful difference between the species at a larger physical scale, and so the genes identified in this way are likely to be relevant to the distinguishing features that have emerged over human and chimp evolution.

"The problem with looking at expression changes or changes in DNA sequences is that there are many of them and their functional importance is unclear," says Weissman, who is also a professor of biology at the Massachusetts Institute of Technology and an Investigator with the Howard Hughes Medical Institute. "This approach looks at changes in how genes interact to perform key biological processes, and what we see by doing that is that, even on the short timescale of human evolution, there has been fundamental rewiring of cells."

After the CRISPRi experiments were completed, She compiled a list of the genes that appeared to be essential in one species but not the other. Then he looked for patterns. Many of the 75 genes identified by the experiments clustered together in the same pathways, meaning the clusters were involved in the same biological processes. This is what the researchers hoped to see. Individual small changes in gene use may not have much of an effect, but when those changes accumulate in the same biological pathway or process, collectively they can cause a substantive change in the species. When the researchers' approach identified genes that cluster in the same processes, this suggested to them that their approach had worked and that the genes were likely involved in human and chimp evolution.

"Isolating the genetic changes that made us human has been compared to searching for needles in a haystack because there are millions of genetic differences, and most are likely to have negligible effects on traits," Pollen says. "However, we know that there are lots of small effect mutations that in aggregate may account for many species differences. This new approach allows us to study these aggregate effects, enabling us to weigh the impact of the haystack on cellular functions."

Researchers think bigger brains may rely on genes regulating how quickly cells divide

One cluster on the list stood out to the researchers: a group of genes essential to chimps, but not to humans, that help to control the cell cycle, which regulates when and how cells decide to divide. Cell cycle regulation has long been hypothesized to play a role in the evolution of humans' large brains. The hypothesis goes like this: Neural progenitors are the cells that will become neurons and other brain cells. Before becoming mature brain cells, neural progenitors divide multiple times to make more of themselves. The more divisions that the neural progenitors undergo, the more cells the brain will ultimately contain -- and so, the bigger it will be. Researchers think that something changed during human evolution to allow neural progenitors to spend less time in a non-dividing phase of the cell cycle and transition more quickly towards division. This simple difference would lead to additional divisions, each of which could essentially double the final number of brain cells.

Consistent with the popular hypothesis that human neural progenitors may undergo more divisions, resulting in a larger brain, the researchers found that several genes that help cells to transition more quickly through the cell cycle are essential in chimp neural progenitor cells but not in human cells. When chimp neural progenitor cells lose these genes, they linger in a non-dividing phase, but when human cells lose them, they keep cycling and dividing. These findings suggest that human neural progenitors may be better able to withstand stresses -- such as the loss of cell cycle genes -- that would limit the number of divisions the cells undergo, enabling humans to produce enough cells to build a larger brain.

"This hypothesis has been around for a long time, and I think our study is among the first to show that there is in fact a species difference in how the cell cycle is regulated in neural progenitors," She says. "We had no idea going in which genes our approach would highlight, and it was really exciting when we saw that one of our strongest findings matched and expanded on this existing hypothesis."

More subjects lead to more robust results

Research comparing chimps to humans often uses samples from only one or two individuals from each species, but this study used samples from six humans and six chimps. By making sure that the patterns they observed were consistent across multiple individuals of each species, the researchers could avoid mistaking the naturally occurring genetic variation between individuals as representative of the whole species. This allowed them to be confident that the differences they identified were truly differences between species.

The researchers also compared their findings for chimps and humans to orangutans, which split from the other species earlier in our shared evolutionary history. This allowed them to figure out where on the evolutionary tree a change in gene use most likely occurred. If a gene is essential in both chimps and orangutans, then it was likely essential in the shared ancestor of all three species; it's more likely for a particular difference to have evolved once, in a common ancestor, than to have evolved independently multiple times. If the same gene is no longer essential in humans, then its role most likely shifted after humans split from chimps. Using this system, the researchers showed that the changes in cell cycle regulation occurred during human evolution, consistent with the proposal that they contributed to the expansion of the brain in humans.

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Cockatoos know to bring along multiple tools when they fish for cashews

Goffin's cockatoos have been added to the short list of non-human animals that use and transport toolsets. In a study publishing in the journal Current Biology on February 10, researchers show that the cockatoos carry multiple tools to their worksite when the job calls for it. This behavior has only been previously reported in chimpanzees, our closest relatives.

Goffin's cockatoos are small white parrots that hail from the Tanimbar Islands archipelago in Indonesia. Captive Goffin's cockatoos use and manufacture tools, and a recent study of wild-caught cockatoos reported that they can use up to three different tools to extract seeds from a particular fruit. Up until now, though, it wasn't clear whether the cockatoos considered these tools as a "set"; it's possible that what may look like a toolset is instead nothing more than a chain of single tool uses, with the need for each new tool appearing to the animal as the task evolves.

Now, a team of researchers have used controlled experiments to clarify that the cockatoos do indeed recognize when a job requires more than one tool. "With this experiment we can say that, like chimpanzees, Goffin's cockatoos not only appear to be to using toolsets, but they know that they are using toolsets," says first author Antonio Osuna-Mascaró, an evolutionary biologist at the University of Veterinary Medicine Vienna. "Their flexibility of behavior is stunning."

Osuna-Mascaró was inspired by the termite-fishing Goualougo Triangle chimpanzees of northern Congo, the only other known non-human animal to use toolsets. These chimpanzees fish for termites via a two-step process: first, they use a blunt stick to break holes in the termite mound, and then they insert a long, flexible probe to "fish" the termites out of the holes. In this study, Osuna-Mascaró's team tasked the cockatoos with fishing for cashews instead of termites.

To mimic the termite-fishing set-up, the researchers presented the cockatoos with a box containing a cashew behind a transparent paper membrane. To reach the cashew, the cockatoos had to punch through the membrane and then "fish" the cashew out. They were provided with a short, pointy stick for punching holes and a vertically halved plastic straw for fishing.

Seven of the ten cockatoos tested taught themselves to extract cashews successfully by punching through the membrane, and two of the cockatoos (Figaro and Fini) completed the task within 35 seconds on their first attempt. The cockatoos don't have an equivalent foraging behavior in the wild, so there was no chance that their tool use was based on innate behaviors, and each cockatoo used a slightly different technique.

Next, the team tested the cockatoos' ability to change their tool use in a flexible manner depending on the situation. To do this, they presented each cockatoo with two different types of box: one with a membrane and one without. The cockatoos were given the same two tools, but they only needed the pointy stick when a membrane was in the way. "The cockatoos had to act according to the problem; sometimes the toolset was needed, and sometimes only one tool was enough," says Osuna-Mascaró.

All of the cockatoos mastered the test in a very short period of time and were able to recognize when a single tool was sufficient. However, the birds engaged in an interesting behavior during this choosing phase. "When making the choice between which tool to use first, they were picking one up, releasing it, then picking up the other one, releasing it, returning to the first one, and so on," says Osuna-Mascaró. The researchers found that when cockatoos did this switching, they performed better on the tests.

Next, the team tested the cockatoos' ability to transport the tools as a set on an as-needed basis. They put the cockatoos through a series of increasingly challenging trials to reach the boxes: first they had to climb a short ladder while carrying their tools; then they had to fly horizontally with them; and in the final test, they had to carry the tools while flying vertically. As before, the birds were only sometimes presented with a box with a membrane barrier, so they had to decide whether the problem required one or both tools.

Some cockatoos learned to carry the two tools together -- by inserting the short punching stick into the groove of the halved straw -- when they were presented with a box that required both. This meant they only had to make one trip, albeit while carrying a heavier toolset. Most of the cockatoos transported the toolset on an as-needed basis, further indicating that they knew ahead of time when two tools were required, though some made two trips when necessary. One cockatoo, Figaro, decided not to waste time thinking and instead carried both tools in almost every trial.

"We really did not know whether the cockatoos would transport two objects together," says Alice Auersperg, senior author on the study and a cognitive biologist at the University of Veterinary Medicine Vienna. "It was a little bit of a gamble because I have seen birds combining objects playfully, but they very rarely transport more than one object together in their normal behavior."

There's a lot more to be learned about cockatoo tool use, the researchers say. "We feel that, in terms of technical cognition and tool use, parrots have been underestimated and understudied," says Auersperg.

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Human evolution wasn't just the sheet music, but how it was played

A team of Duke researchers has identified a group of human DNA sequences driving changes in brain development, digestion and immunity that seem to have evolved rapidly after our family line split from that of the chimpanzees, but before we split with the Neanderthals.

Our brains are bigger, and are guts are shorter than our ape peers.

"A lot of the traits that we think of as uniquely human, and human-specific, probably appear during that time period," in the 7.5 million years since the split with the common ancestor we share with the chimpanzee, said Craig Lowe, Ph.D., an assistant professor of molecular genetics and microbiology in the Duke School of Medicine.

Specifically, the DNA sequences in question, which the researchers have dubbed Human Ancestor Quickly Evolved Regions (HAQERS), pronounced like hackers, regulate genes. They are the switches that tell nearby genes when to turn on and off. The findings appear Nov.23 in the journal Cell.

The rapid evolution of these regions of the genome seems to have served as a fine-tuning of regulatory control, Lowe said. More switches were added to the human operating system as sequences developed into regulatory regions, and they were more finely tuned to adapt to environmental or developmental cues. By and large, those changes were advantageous to our species.

"They seem especially specific in causing genes to turn on, we think just in certain cell types at certain times of development, or even genes that turn on when the environment changes in some way," Lowe said.

A lot of this genomic innovation was found in brain development and the GI tract. "We see lots of regulatory elements that are turning on in these tissues," Lowe said. "These are the tissues where humans are refining which genes are expressed and at what level."

Today, our brains are larger than other apes, and our guts are shorter. "People have hypothesized that those two are even linked, because they are two really expensive metabolic tissues to have around," Lowe said. "I think what we're seeing is that there wasn't really one mutation that gave you a large brain and one mutation that really struck the gut, it was probably many of these small changes over time."

To produce the new findings, Lowe's lab collaborated with Duke colleagues Tim Reddy, an associate professor of biostatistics and bioinformatics, and Debra Silver, an associate professor of molecular genetics and microbiology to tap their expertise. Reddy's lab is capable of looking at millions of genetic switches at once and Silver is watching switches in action in developing mouse brains.

"Our contribution was, if we could bring both of those technologies together, then we could look at hundreds of switches in this sort of complex developing tissue, which you can't really get from a cell line," Lowe said.

"We wanted to identify switches that were totally new in humans," Lowe said. Computationally, they were able to infer what the human-chimp ancestor's DNA would have been like, as well as the extinct Neanderthal and Denisovan lineages. The researchers were able to compare the genome sequences of these other post-chimpanzee relatives thanks to databases created from the pioneering work of 2022 Nobel laureate Svante Pääbo.

"So, we know the Neanderthal sequence, but let's test that Neanderthal sequence and see if it can really turn on genes or not," which they did dozens of times.

"And we showed that, whoa, this really is a switch that turns on and off genes," Lowe said. "It was really fun to see that new gene regulation came from totally new switches, rather than just sort of rewiring switches that already existed."

Along with the positive traits that HAQERs gave humans, they can also be implicated in some diseases.

Most of us have remarkably similar HAQER sequences, but there are some variances, "and we were able to show that those variants tend to correlate with certain diseases," Lowe said, namely hypertension, neuroblastoma, unipolar depression, bipolar depression and schizophrenia. The mechanisms of action aren't known yet, and more research will have to be done in these areas, Lowe said.

"Maybe human-specific diseases or human-specific susceptibilities to these diseases are going to be preferentially mapped back to these new genetic switches that only exist in humans," Lowe said.

Read more at Science Daily

Chimpanzees synchronize their steps just like humans

A new study by researchers at the University of St Andrews and the Central European University in Vienna has revealed that chimpanzees share a human tendency to unintentionally synchronise their steps when walking alongside one another.

Whilst it is already understood that chimpanzees can coordinate when working towards a goal, such as pulling a string to release food, much less is known about their propensity to coordinate spontaneously.

The study, led by Dr Manon Schweinfurth, Lecturer in the School of Psychology and Neuroscience at St Andrews and published in the journal Current Biology today (Thursday 20 October), recorded the walking behaviour of chimpanzees at the Chimfunshi Wildlife Orphanage Trust, a sanctuary in Zambia, under different conditions. The chimpanzees were observed when walking alone or when walking next to others.

Researchers observed that chimpanzees show unintentional synchronisation in their steps when walking next to one another, suggesting that human's strong tendency to coordinate simple actions is shared with our closest primate relative, and therefore might be an ancestral trait.

Dr Schweinfurth said: "Humans deliberately plan and coordinate actions with others during sport games, group dances, musical ensembles, or military actions. But it is also part of our daily life -- like carrying items together or getting a child dressed. Indeed, joint actions have been suggested to be crucial for our success as a species because much more can be achieved together than alone. In fact, we can't help it and coordinate actions even when it is not necessary to do so, such as falling into the same rhythm with someone walking next to us."

"In contrast, one of our closest living relatives, the chimpanzee, does not appear to show the same preference for rather complex joint actions. But little is known about simpler forms of joint action, such as a tendency to fall into inter-individual synchrony. Chimpanzees are particularly interesting here, as they are a good model for our last common ancestor with other African great apes."

"We investigated whether chimpanzees spontaneously coordinate their actions in a semi-natural environment when coordination was neither planned nor the goal of an interaction, i.e., when they were walking close to each other. For this, we recorded their undisturbed walking behaviour under different conditions. We found that chimpanzees show unintentional synchronisation in their steps when walking next to conspecifics."

The study involved both male and female chimpanzees of a variety of ages, some related and some unrelated. When the chimpanzees walked together, a step by one walker was followed by the same respective foot of the other walker in 79% of the cases within less than 0.5 seconds.

"This study provides evidence that chimpanzees temporally synchronise their body movements to the movements of their conspecifics. This interpersonal coordination of movements is often called entrainment and relies on perception-action links that become coupled. Understanding which mechanisms humans share with other species can help us understand the evolutionary origins of more sophisticated forms of joint action."

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Chimpanzee stone tool diversity

During fieldwork aimed at documenting the stone tool use of a group of wild chimpanzees in the Taï Forest in Cote d'Ivoire in early 2022, the researchers identified and 3D scanned a variety of stone tools used to crack different nut species.

It has long been shown that various chimpanzee groups possess different tool use cultures involving wooden and stone tools, however, only some groups in West Africa use stone tools to crack open nuts. By comparing the 3D models of different stone tools used by chimpanzees in the Taï Forest to those from another group in Guinea, the researchers showed that there exist notable differences between the two groups in terms of their material culture.

The study shows that this particular group of chimpanzees in Guinea uses stone hammers varying in the type of stone and sizes, and very large stone anvils, sometimes greater than one meter in length. These durable stone tools are widespread across the landscape; preserve different levels of damage related to their use and represent a lasting record of chimpanzee behaviours.

Stone tools used for nut cracking can differ between chimpanzee groups

This study highlights the fact that, although several groups of chimpanzees practice nut cracking, the tools they use can differ significantly from one another, potentially leading to group specific material signatures. These differences are driven by a combination of stone choice, stone availability, and the nut species eaten.

Previous research has shown, that by using stone tools, some groups of chimpanzees develop their own archaeological record dating to at least 4,300 years ago. "The ability to identify regional differences in stone tool material culture in primates opens up a range of possibilities for future primate archaeological studies," says Tomos Proffitt from the Max Planck Institute of Evolutionary Anthropology, who led the research.

It has been hypothesised that a simple technology, like nut cracking, was a precursor to more complex stone technologies during the early stages of our own evolution more than three million years ago. Proffitt continues, "by understanding what this simple stone tool technology looks like, and how it varies between groups, we can start to understand how to better identify this signature in the earliest hominin archaeological record."

From Science Daily

The gene to which we owe our big brain

ARHGAP11B -- this complex name is given to a gene that is unique to humans and plays an essential role in the development of the neocortex. The neocortex is the part of the brain to which we owe our high mental abilities. A team of researchers from the German Primate Center (DPZ) -- Leibniz Institute for Primate Research in Göttingen, the Max Planck Institute for Molecular Cell Biology and Genetics (MPI-CBG) in Dresden, and the Hector Institute for Translational Brain Research (HITBR) in Mannheim has investigated the importance of ARHGAP11B in neocortex development during human evolution.

To do this, the team introduced for the first time a gene that exists only in humans into laboratory-grown brain organoids from our closest living relatives, chimpanzees. In the chimpanzee brain organoid, the ARHGAP11B gene led to an increase in brain stem cells relevant to brain growth and an increase in those neurons that play a critical role in the extraordinary mental abilities of humans. If, on the other hand, the ARHGAP11B gene was switched off in human brain organoids, the quantity of these brain stem cells fell to the level of a chimpanzee. Thus, the research team was able to show that the ARGHAP11B gene played a crucial role in the evolution of the brain from our ancestors to modern humans.

Animal studies on great apes have long been banned in Europe for ethical reasons. For the question pursued here, so-called organoids, i.e. three-dimensional cell structures a few millimeters in size that are grown in the laboratory, are an alternative to animal experiments. These organoids can be produced from pluripotent stem cells, which then differentiate into specific cell types, such as nerve cells. In this way, the research team was able to produce both chimpanzee brain organoids and human brain organoids. "These brain organoids allowed us to investigate a central question concerning ARHGAP11B," says Wieland Huttner of the MPI-CBG, one of the three lead authors of the study.

"In a previous study we were able to show that ARHGAP11B can enlarge a primate brain. However, it was previously unclear whether ARHGAP11B had a major or minor role in the evolutionary enlargement of the human neocortex," says Wieland Huttner. To clarify this, the ARGHAP11B gene was first inserted into brain ventricle-like structures of chimpanzee organoids. Would the ARGHAP11B gene lead to the proliferation of those brain stem cells in the chimpanzee brain that are necessary for the enlargement of the neocortex? "Our study shows that the gene in chimpanzee organoids causes an increase in relevant brain stem cells and an increase in those neurons that play a crucial role in the extraordinary mental abilities of humans," said Michael Heide, the study's lead author, who is head of the Junior Research Group Brain Development and Evolution at the DPZ and employee at the MPI-CBG. When the ARGHAP11B gene was knocked out in human brain organoids or the function of the ARHGAP11B protein was inhibited, the amount of these brain stem cells decreased to the level of a chimpanzee. "We were thus able to show that ARHGAP11B plays a crucial role in neocortex development during human evolution," says Michael Heide. Julia Ladewig of HITBR, the third of the lead authors, adds: "Given this important role of ARHGAP11B, it is furthermore conceivable that certain maldevelopments of the neocortex may be caused by mutations in this gene."

From Science Daily

What oxytocin can tell us about the evolution of human prosociality

Modern humans are characterized by their prosociality, a broad term that encompasses intraspecies empathy, social tolerance, cooperation and altruism. These facets of social cognition have been associated with variations in the oxytocin and vasotocin genes (OT and VT) and their receptors (OTR and VTR).To shed light on the genetic basis of this behaviour, scientists from the University of Barcelona (UB) and Rockefeller University carried out a new study comparing the available genomic sequences of these genes between modern humans, non-human primate species (e.g., chimpanzees, bonobos, and macaques) and, for the first time, archaic humans, using all the available genomes of Neanderthals and Denisovans.

In the study, published in the journal Comprehensive Psychoneuroendocrinology, the researchers identified several sites in which modern humans differed from both archaic humans and non-human primates, and others where both modern and archaic humans differed from non-human primates.

"We used an interdisciplinary approach to understand the evolution of hominid prosociality through the lens of the oxytocin and vasotocin receptors, where we combined evidence from modern and archaic genomics, population genetics, transcriptomics, and behavioural and neuroscientific studies, among other methods. These results can shed light on the genetics underlying possible sociality differences identified between modern humans and archaic humans, as well as the similarities between the modern human and bonobo social behaviour," said first author Constantina Theofanopoulou. This research is part of her doctoral thesis carried out under the co-supervision of Cedric Boeckx, ICREA researcher at the Institute of Complex Systems at the UB (UBICS) and Erich D. Jarvis, professor at Rockefeller University.

Variants unique to modern humans in more than 70% of the population

Considering the evidence on modern human prosociality and on the involvement of the oxytocin and vasotocin genes in social behaviours, the researchers hypothesized that the evolution of these genes might elucidate the genetic basis of the evolution of hominin prosociality. With this aim in mind, the study explored the differences between modern humans, archaic humans and non-human primates in polymorphic heterozygous sites in the human genome -- locations where at least two alternative sequences are found in a population. "Past studies that compared the entire modern human genome with the Neanderthal or the chimpanzee genomes have focused on changes that are fixed or nearly fixed in modern humans. This has led to them identifying sites where, for example, all Neanderthals had Adenine (one of the four nucleotides that with guanine, cytosine and thymine form the DNA) and nearly all modern humans (say, 98%) have Guanine. In this study, we searched for differences on locations where, by definition, not all modern humans share the same nucleotide, namely on polymorphic sites, where for example, 70% of the modern human population has Adenine and 30% Cytosine," adds Theofanopoulou.

The researchers identified five sites in the oxytocin and vasotocin receptors where modern humans are unique in one of their two (or more) variants compared to archaic humans and non-human primates, and which are at the same time found in more than 70% of the modern human population. Next, they conducted functional and frequency analyses to establish whether the variants are relevant. They performed a range of analyses on the five sites and found that some of the variants are highly functional, indicating that they have an effect on the molecular function of the proteins activated by these genes.

The researchers also found that these sites are encountered in genome regions that are active in the brain, particularly in the cingulate gyrus, a brain region involved in social cognition-relevant pathways. Moreover, all these sites have been associated in other studies with a plethora of social behaviours or social deficits, such as autism, attention deficit hyperactivity disorder (ADHD), aggression, and so on.

These findings may help to explain some of the social differences between modern humans and what we presume to know about the social behaviours of Neanderthals and Denisovans. "For example, they might be relevant to the smaller social groups attributed to Neanderthals and Denisovans or to the decreased modern human androgenization. They might also be relevant to a different social structure, i.e., Neanderthals have been linked to a polygynous social structure and a higher level of male-male competition than most contemporary modern human populations," says Constantina Theofanopoulou.

Variants present only in modern and archaic humans

The study also found two sites on the oxytocin receptor under a positive selection in modern and archaic humans: that is to say, modern and archaic humans showed a variant that was not present in any other non-human primate. This means that these sites are found in very high percentages in the modern human population (in this case, more than 85%). These same sites have also been associated with a great many social behaviours or deficits, and one of them was predicted to be a highly functional site in their regulation analyses. "The sites that are unique in both us and archaic humans versus non-human primates can elucidate the genetic underpinnings of the progressive social tolerance needed for the intensive cultural transmission of technological innovations (e.g., fire use) in the evolution of humankind, as well as for the reduced aggression indicated by several markers in early hominid evolution, such as the reduction of male canine size and the accelerated demographic success," adds Theofanopoulou.

Convergent sites with bonobos

Lastly, the researchers found three sites where modern humans and bonobos, a primate species that shows convergence of prosocial behaviours with humans, have the same nucleotide. "The convergent sites in modern humans and bonobos could be insightful for understanding the posited similarities in prosociality, social tolerance and cooperation between us and bonobos, and the differences of both compared to chimpanzees. For example, bonobos outperform chimpanzees on tasks relevant to social causality or theory of mind and are more attentive to the face and eyes, suggestive of higher empathic sensitivity," notes the researcher.

All the sites identified in this study have also been independently associated with disorders that include social deficits, such as autism spectrum disorders (ASD). "Understanding developmental disorders through evolutionary lenses can aid into us achieving what we call an evo-devo (evolutionary and developmental biology) understanding of these disorders. If indeed "ontogeny recapitulates phylogeny," then deciphering our evolutionary trajectory may shed light to new genetic spots for clinical research that might, in turn, lead to earlier disorder diagnosis," highlights Constantina Theofanopoulou.

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Chimpanzees combine calls to form numerous vocal sequences

Compared to the complex use of human language, the way animals communicate with each other appears quite simple. How our language evolved from such a simple system, remains unclear. Researchers from the Max Planck Institutes for Evolutionary Anthropology (MPI-EVA) and for Cognitive and Brain Sciences (MPI-CBS) in Leipzig, Germany, and the CNRS Institute for Cognitive Sciences in Bron, Lyon, France, recorded thousands of vocalisations from wild chimpanzees in Taï, Ivory Coast. They found that the animals produced hundreds of different vocal sequences containing up to ten different call types. The order of calls in these sequences followed some rules, and calls were associated with each other in a structured manner. The researchers will now investigate if this structure may constitute a step towards human syntax and if chimpanzees use these sequences to communicate a wider range of meanings in their complex social environment.

Humans are the only species on earth known to use language. We do this by combining sounds to form words and words to form hierarchically structured sentences. The question, where this extraordinary capacity originates from, still remains to be answered. In order to retrace the evolutionary origins of human language, researchers often use a comparative approach -- they compare the vocal production of other animals, in particular of primates, to those of humans. In contrast to humans, non-human primates often use single calls -referred to as call types -- and rarely combine them with each other to form vocal sequences.

Consequently, vocal communication in non-human primates seems much less complex than human communication. However, human language complexity does not arise from the number of sounds we use when we speak, which is typically bellow 50 different sounds in most languages, but from the way we combine sounds in a structured manner to form words and hierarchically combine these words to form sentences to express an infinite number of meanings. In fact, non-human primates also use up to 38 different calls to communicate, but they rarely combine them with each other. However, since they have so far not been analysed in great detail, we may not have a full picture of the structure and diversity of vocal sequences produced by non-human primates.

Researchers recorded thousands of vocalisations

Researchers at MPI-EVA and MPI-CBS in Leipzig and from the Institute of Cognitive Sciences at the CNRS in Bron, Lyon, France, recorded thousands of vocalisations produced by the members of three groups of wild chimpanzees in the Taï National Park in Ivory Coast. They identified 12 different call types and assessed how chimpanzees combine them to form vocal sequences. "Observing animals in their natural social and ecological environment reveals a previously undiscovered complexity in the ways they communicate," says first author Cédric Girard-Buttoz. "Syntax is a hallmark of human language and in order to elucidate the origin of this human ability it is crucial to understand how non-human primate vocalisations are structured," adds Emiliano Zaccarella, another lead author of the study.

The study shows that chimpanzees communicate with each other using hundreds of different sequences, combining up to ten call types across the whole repertoire. This is the first documentation of such a diversity of vocal production in non-human primates. Furthermore, the researchers show that calls -- in combination with specific other calls -- predictably occurred in certain positions in the sequence, following adjacency rules. These adjacency rules applied also to sequences with three call types.

"Our findings highlight a vocal communication system in chimpanzees that is much more complex and structured than previously thought," says co-author Tatiana Bortolato who recorded the vocalisations in the forest. "This is the first study in a larger project. By studying the rich complexity of the vocal sequences of wild chimpanzees, a socially complex species like humans, we expect to bring fresh insight into understanding where we come from and how our unique language evolved," Catherine Crockford, senior author on the study, points out.

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Human fetuses evolved to slow shoulder growth for easier delivery

Why do human mothers have a much harder time giving birth compared to our evolutionary cousins, the chimpanzees and macaques?

The differences are a big head and wide shoulders. But it has made all the difference for safer births.

"The question is actually two-fold, " says study author Naoki Morimoto of Kyoto University. "What also makes childbirth difficult for women is the relatively narrow pelvis."

Morimoto's team discovered two central aspects of the female human skeletal anatomy that deserve attention when discussing the evolution of childbirth.

The first comes with its own set of points: initially, the growth of human shoulders slows down just before birth and speeds up thereafter; next, this phenomenon alleviates the problem of shoulder dystocia, where the shoulders interfere with safe passage of the fetus through the birth canal.

"It is important to note that the second point reconciles the incompatibility of wide shoulders with the narrow birth canal. The shoulders show an 'intelligent' modification in fetal development," notes lead author PhD candidate Mikaze Kawada.

What makes a human skeletal makeup 'human' in terms of the head and shoulders is size proportionality to the pelvis. Our largely developed brains have resulted in large heads, and our wide shoulders explain bipedal stability and an ability to throw objects far.

On the other hand, the need to make walking more efficient reduced the size of the pelvis as our ancestors treaded farther and more frequently.

Morimoto and his team used computed tomography to obtain cross-sectional representations of the clavicle in humans, chimpanzees, and Japanese macaques from fetal to adult samples.

The team then looked at different shoulder-width to birth-risk correlations between humans and the two other primates. Chimpanzees have proportionally large shoulders and yet, like macaques, fewer shoulder-related birth complications. Since chimpanzees move about less frequently on two feet, their pelvis -- and therefore their birth canal -- is larger than that of their human counterparts.

"We surmise that the wide shoulders, relative to the pelvis of our ancestors, emerged simultaneously with the narrower pelvis as we became fully bipedal," says Morimoto, "but before the brain evolved to today's size."

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Century-old malaria parasite puzzle solved as ape origin traced

Scientists have solved a 100-year-old mystery about the evolutionary links between malaria parasites that infect humans and chimpanzees.

They have discovered that the parasite P. malariae - one of six species that spreads malaria among humans - originated in African apes before evolving to infect people.

While it is often associated with mild disease, if untreated P. malariae can cause long-lasting, chronic infections that may last a lifetime, researchers say.

The evolutionary puzzle has its origins in the 1920s when scientists identified chimpanzees infected by parasites that appeared identical to P. malariae under a microscope.

It was thought both parasites belonged to the same species, but - until now - this could not be verified as the genetic make-up of the chimpanzee strain had never been studied.

Now, scientists at the University of Edinburgh, in collaboration with colleagues at the University of Pennsylvania, USA, have used leading edge techniques to study the parasites' DNA.

They have found that there are, in fact, three distinct species. One species - P. malariae - infects mainly humans, while the two others infect apes.

One of the two ape-infecting parasites was found in chimpanzees, gorillas and bonobos across Central and West Africa. This previously unknown species is only distantly related to the human parasite.

The other ape parasite is much more closely related to the one that infects humans. Knowing this enabled researchers to make detailed comparisons of the genetic diversity of the two species.

This revealed that the human malaria parasite population went through a genetic bottleneck, where its population temporarily shrank and most of its genetic variation was lost.

A likely explanation for this is that P. malariae was originally an ape parasite, but a small number of parasites switched hosts to begin infecting humans, the team says.

The study, published in the journal Nature Communications, was funded by the National Institutes of Health.

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Savannah chimpanzees, a model for the understanding of human evolution

To prosper, most great apes need lush forests in Africa (bonobos, chimpanzees, and gorillas) or Southeast Asia (orangutans), except for some groups of chimpanzees that live in savannahs, habitats characterised by high temperatures and very low seasonal rainfall.

Adriana Hernández, Serra Hunter professor at the Faculty of Psychology of the University of Barcelona, co-led the study conducted by an international team of primatologists who reviewed the existing research on the behaviour and ecology of savannah chimpanzees to understand how these apes adapt to extreme conditions.

According to the researchers, the environmental conditions of these places would lead to a specific type of behaviours and physiological responses in these chimpanzees -such as resting in caves or digging in order to get water- which are not observed in their counterparts that live in more forested areas, where they do not deal with these extreme environmental conditions.

"The study on savannah chimpanzees and what we call the landscape savannah effect have important implications for reconstructing the behaviour of the first hominis who lived in similar habitats and therefore, it helps us to better understand our own evolution," notes Adriana Hernández, who co-led the study, published in the journal Evolutionary Anthropology, together with Stacy Lindshield, from the University of Purdue (United States).

The genetically closest-to-humans evolutionary living relative

Chimpanzees (Pan troglodytes) are our closest living relatives, since they share 98.7% of their DNA with humans and have a common ancestor that lived between 4.5 and 6 million years ago. Despite this proximity, they lack some of the biological and cultural traits that humans possess to adapt to extreme heat, such as numerous eccrine sweat glands, relative lack of hair, or the ability to create artefacts such as water containers and sun hats to mitigate dehydration and sunstroke.

The chimpanzees that live in the savannah are taxonomically indistinguishable from other chimpanzees. For this reason, comparisons of behaviour, morphology and ecology with chimpanzees that live in more forested landscapes provide key information for hypothesising how early humans may have adapted millions of years ago while African forests were receding and gave place to savannahs.

"We know that early hominins adapted to savannah environments similar to those occupied by chimpanzees today, and researchers think that savannah conditions caused adaptations in our ancestors, such as brain expansion or tolerance to high temperatures," says Adriana Hernández, who is also the co-director of research at the Jane Goodall Institute Spain. "Therefore -she continues-, understanding how our genetically closest living relatives adapt to a dry, hot, seasonal and open environment, very similar to those where early hominins lived, helps us to model how our ancestors might have adapted and how the features that define us as humans might have emerged."

Strategies to adapt to high temperatures

Among the different characteristics of savannah chimpanzees described in the study, their strategies to deal with high temperatures stand out. "Understanding how they deal with heat can help us better understand what strategies human ancestors may have used to cope with high temperatures. Some strategies are probably the same for chimpanzees and hominins, such as the use of caves or going into water pools to cool down," notes the researcher. Another example the researcher highlights is the ways in which these chimpanzees try to hydrate themselves during the advanced dry season, such as digging for water when this resource is reduced to just a few spots in the landscape. "Early hominins also had to deal with low water availability during part of the year," Hernández adds.

Groups distributed over larger areas

The study also confirmed that chimpanzee social groups in the savannah are distributed over unusually large areas of around 100 km², while chimpanzees living in more forested areas have ranges between 3 and 30 km², approximately. "However, although group sizes are similar in different habitats, chimpanzees in the savannah have a much lower population density, which could be explained by the low availability of food in this habitat."

Despite the fact that we know much more about savannah chimpanzees now than ever before, their exact numbers are unknown, although according to the researchers "there are fewer than those living in the forest areas, as the total area they occupy is much smaller." In addition, because they have a lower population density, there are far fewer individuals in areas of the same size than in the forest. "It should be noted that there are far fewer sites where savannah chimpanzees have been studied, as there are only two study sites where savannah chimpanzees are habituated to humans and their behaviour can be observed directly. In contrast, there are many study sites where chimpanzees are fully habituated to researchers in the forest, a habitat where these primates have been studied for decades," explains Adriana Hernández.

Keys to understanding adaptation to climate change

Another important contribution of this study is that it helps to understand the potential effects of climate change on the species. "The adaptation of savannah chimpanzees to extreme climates can help us model how chimpanzees that currently inhabit forests might adapt to changes that climate studies project will make their environments drier and warmer. This is important, since the species is categorized as Endangered and the West African subspecies (Pan troglodytes verus) is Critically Endangered," says the expert.

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What makes us human? The answer may be found in overlooked DNA

Our DNA is very similar to that of the chimpanzee, which in evolutionary terms is our closest living relative. Stem cell researchers at Lund University in Sweden have now found a previously overlooked part of our DNA, so-called non-coded DNA, that appears to contribute to a difference which, despite all our similarities, may explain why our brains work differently. The study is published in the journal Cell Stem Cell.

The chimpanzee is our closest living relative in evolutionary terms and research suggests our kinship derives from a common ancestor. About five to six million years ago, our evolutionary paths separated, leading to the chimpanzee of today, and Homo Sapiens, humankind in the 21st century.

In a new study, stem cell researchers at Lund examined what it is in our DNA that makes human and chimpanzee brains different -- and they have found answers.

"Instead of studying living humans and chimpanzees, we used stem cells grown in a lab. The stem cells were reprogrammed from skin cells by our partners in Germany, the USA and Japan. Then we examined the stem cells that we had developed into brain cells," explains Johan Jakobsson, professor of neuroscience at Lund University, who led the study.

Using the stem cells, the researchers specifically grew brain cells from humans and chimpanzees and compared the two cell types. The researchers then found that humans and chimpanzees use a part of their DNA in different ways, which appears to play a considerable role in the development of our brains.

"The part of our DNA identified as different was unexpected. It was a so-called structural variant of DNA that were previously called "junk DNA," a long repetitive DNA string which has long been deemed to have no function. Previously, researchers have looked for answers in the part of the DNA where the protein-producing genes are -- which only makes up about two per cent of our entire DNA -- and examined the proteins themselves to find examples of differences."

The new findings thus indicate that the differences appear to lie outside the protein-coding genes in what has been labelled as "junk DNA," which was thought to have no function and which constitutes the majority of our DNA.

"This suggests that the basis for the human brain's evolution are genetic mechanisms that are probably a lot more complex than previously thought, as it was supposed that the answer was in those two per cent of the genetic DNA. Our results indicate that what has been significant for the brain's development is instead perhaps hidden in the overlooked 98 per cent, which appears to be important. This is a surprising finding."

The stem cell technique used by the researchers in Lund is revolutionary and has enabled this type of research. The technique was recognised by the 2012 Nobel Prize in Physiology or Medicine. It was the Japanese researcher Shinya Yamanaka who discovered that specialised cells can be reprogrammed and developed into all types of body tissue. And in the Lund researchers' case, into brain cells. Without this technique, it would not have been possible to study the differences between humans and chimpanzees using ethically defensible methods.

Why did the researchers want to investigate the difference between humans and chimpanzees?

"I believe that the brain is the key to understanding what it is that makes humans human. How did it come about that humans can use their brain in such a way that they can build societies, educate their children and develop advanced technology? It is fascinating!"

Johan Jakobsson believes that in the future the new findings may also contribute to genetically-based answers to questions about psychiatric disorders, such as schizophrenia, a disorder that appears to be unique to humans.

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Building bonds between males leads to more offspring for chimpanzees

If you're a male chimp looking for love -- or offspring -- it pays to make friends with other males.

A study led by the University of Michigan, in collaboration with Arizona State and Duke universities, examined why male chimpanzees form close relationships with each other, and found that male chimpanzees that build strong bonds with the alpha male of the group, or with a large network of other males, are more successful at siring offspring. The results are published in the journal iScience.

"One big question that biologists have had for a long time is why you see so many friendly behaviors such as cooperation and alliance in animals," said lead study author and U-M postdoctoral researcher Joseph Feldblum. "One would expect to see these social bonds -- or strong, friendly social relationships -- only if they provide some sort of fitness benefit to the individuals. Males wouldn't spend all this time grooming other males and forgoing trying to find females or food unless you get some kind of benefit from it."

One benefit would be the opportunity to sire more offspring, but no previous studies have looked at the link between social relationships and reproductive success in chimpanzees. Much of the research in this area has been done in female primates, who are primarily concerned with accessing resources in order to reproduce quickly. For males, the biggest task is getting reproductive access to females, says Feldblum, also an assistant professor in the U-M Department of Anthropology and member of the Michigan Society of Fellows.

"Chimps cooperate frequently, and often in these very dramatic ways: You see things like grooming, all kinds of complex alliance formation and group territorial defense," Feldblum said. "The question is: What do males get out of it and how?"

It turns out, they get babies.

One function of these social bonds, the researchers found, is to help males gain access to mating opportunities they wouldn't otherwise be able to get without help from their friends. To examine the link between sociality and paternity success, the researchers examined behavioral and genetic data from a population of chimpanzees living in western Tanzania. The group is part of the ongoing study of chimpanzees in Gombe Stream National Park, begun by Jane Goodall in 1960.

The researchers began by constructing a base model that captures the effects of male age, dominance rank and genetic relatedness to the mother on male siring success. They first used the model to look at 56 siring events with known paternity between 1980 and 2014. Then, they tested whether adding measures of male social bonds to the models improved their ability to predict which male would sire a given offspring.

They found that males with more strong association ties -- males with the highest number of social bonds with other males -- had a higher likelihood of siring offspring. In fact, two or more strong association ties meant a male chimpanzee was more than 50% more likely to sire a given offspring, after accounting for the chimp's age, relation to the mother and dominance rank score.

Next, the researchers wanted to understand how a chimp's relationship to the alpha male underpinned male reproductive success. To do this, they examined the role of strong bonds with the alpha male, looking at 45 siring events by non-alpha males. They generated the same base model, this time comparing the model with models that included several measures of bond strength with the alpha male, among other measures.

The model that fit best included what is called the composite sociality index, which includes grooming and association with the alpha male. It showed that subordinate males with strong bonds with the alpha male, as well as those with many strong association ties, were more likely to sire a given offspring.

"Sucking up to the boss is nothing new," said co-author Anne Pusey of Duke University. "We show that it's always paid off."

But the researchers also found that two factors -- a strong bond with the alpha male and many strong association ties -- both independently contributed to reproductive success.

In animal behavior, coalition formation is when two or more individuals jointly direct aggression toward a third or another group of individuals. According to previous research, individuals that are more central in the network of coalitions tend to rise in rank and sire more offspring.

In the current work, the researchers showed that males who form stronger ties are also more likely to form coalitions, and the researchers hypothesize that this larger alliance network helps males gain mating opportunities. They also found that forming these many strong bonds leads to chimps' improvement in rank within the group; those that made it to the alpha position were also more likely to sire offspring.

A clearer idea of the benefits of social relationships in chimpanzees provides clues about the evolution of friendship in humans.

"Together with bonobos, chimpanzees are our closest living relatives, and help us to identify which features of human social life are unique. This study suggests that strong bonds among males have deep evolutionary roots and provided the foundation for the more complex relationships that we see in humans," said senior author Ian Gilby, a researcher at ASU. "This research also highlights the value of long-term studies like these, which are essential for understanding the biology of a species that lives for many decades and is slow to reproduce."

Feldblum says more research is needed to tease out how coalition formations and these social bonds lead to siring success.

"Is it that if your ally is nearby, you're more likely to mate with an estrus female, or does having your allies around you protect you from harassment from other males?" Feldblum said. "Or because your ally will support you if a conflict erupts, your stress levels are lower and you can devote more energy to mating efforts? This last step we still don't know."

Gilby is an associate professor at the School of Human Evolution and Social Change at ASU, and a research affiliate in the Institute of Human Origins, which curates the data used in this study. Pusey, professor emerita at Duke, has spent the last 30 years of her career assembling, organizing and digitizing this unique dataset.

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Creativity and community: How modern humans overcame the Neanderthals

A new study is the first-ever to identify the genes for creativity in Homo sapiens that distinguish modern humans from chimpanzees and Neanderthals. The research identified 267 genes that are found only in modern humans and likely play an important role in the evolution of the behavioral characteristics that set apart Homo sapiens, including creativity, self-awareness, cooperativeness, and healthy longevity. The study, led by an international and interdisciplinary team of researchers from the American Museum of Natural History and Washington University among other institutions, is published today in the journal Molecular Psychiatry.

"One of the most fundamental questions about human nature is what sparked the explosive emergence of creativity in modern humans in the period just before and after their widespread dispersal from Africa and the related extinction of Neanderthals and other human relatives," said study co-author Ian Tattersall, curator emeritus in the American Museum of Natural History's Division of Anthropology. "Major controversies persist about the basis for human creativity in art and science, as well as about potential differences in cognition, language, and personality that distinguish modern humans from extinct hominids. This new study is the result of a truly pathbreaking use of genomic methodologies to enlighten us about the mechanisms underpinning our uniqueness."

Modern humans demonstrate remarkable creativity compared to their closest living relatives, the great apes (chimpanzees, gorillas, and orangutans and their immediate ancestors), including innovativeness, flexibility, depth of planning, and related cognitive abilities for symbolism and self-awareness that also enable spontaneous generation of narrative art and language. But the genetic basis for the emergence of creativity in modern humans remains a mystery, even after the recovery of full-genome data for both chimpanzees and our extinct close relatives the Neanderthals.

"It has been difficult to identify the genes that led to the emergence of human creativity before now because of the large number of changes in the human genome after it diverged from the common ancestor of humans and chimpanzees around 10 million years ago, as well as uncertainty about the functions of those changes," said Robert Cloninger, a psychiatrist and geneticist at Washington University in St. Louis, and the lead author of the study. "Therefore, we began our research by first identifying the way the genes that influence modern human personality are organized into coordinated systems of learning that have allowed us to adapt flexibly and creatively to changing life conditions."

The team led by Cloninger had previously identified 972 genes that regulate gene expression for human personality, which is comprised of three nearly separate networks for learning and memory. One, for regulating emotional reactivity -- emotional drives, habit learning, social attachment, conflict resolution -- emerged in monkeys and apes about 40 million years ago. The second, which regulates intentional self-control -- self-directedness and cooperation for mutual benefit -- emerged a little less than 2 million years ago. A third one, for creative self-awareness, emerged about 100,000 years ago.

In the latest study, the researchers discovered that 267 genes from this larger group are found only in modern humans and not in chimpanzees or Neanderthals. These uniquely human genes code for the self-awareness brain network and also regulate processes that allow Homo sapiens to be creative in narrative art and science, to be more prosocial, and to live longer lives through greater resistance to aging, injury, and illness than the now-extinct hominids they replaced.

Genes regulating emotional reactivity were nearly the same in humans, Neanderthals, and chimps. And Neanderthals were about midway between chimps and Homo sapiens in their genes for self-control and self-awareness.

"We found that the adaptability and well-being of Neanderthals was about 60 to 70 percent of that of Homo sapiens, which means that the difference in fitness between them was large," Cloninger said. "After the more creative, sociable, and physically resilient Homo sapiens migrated out of Africa between 65,000 and 55,000 years ago, they displaced Neanderthals and other hominids, who all became extinct soon after 40,000 years ago."

The genes that distinguish modern humans from Neanderthals and chimpanzees are nearly all regulatory genes made of RNA, not protein-coding genes made of DNA.

"The protein-coding genes of Homo sapiens, Neanderthals, and chimps are nearly all the same, and what distinguishes these species is the regulation of the expression of their protein-coding genes by the genes found only in humans," said co-author Igor Zwir, a computer scientist at Washington University School of Medicine and the University of Granada. "We found that the regulatory genes unique to modern humans were constituents of clusters together with particular protein-coding genes that are overexpressed in the human brain network for self-awareness. The self-awareness network is essential to the physical, mental, and social well-being of humans because it provides the insight to regulate our habits in accord with our goals and values."

The researchers determined that the genes unique to modern humans were selected because of advantages tied to greater creativity, prosocial behavior, and healthy longevity. Living longer, healthier lives and being more prosocial and altruistic allowed Homo sapiens to support their children, grandchildren, and others in their communities throughout their lives in diverse and sometimes harsh conditions. And being more innovative than other hominids allowed humans to adapt more flexibly to unpredictable climatic fluctuations.

"In the bigger picture, this study helps us understand how we can effectively respond to the challenges that modern humans currently face," Tattersall said. "Our behavior is not fixed or determined by our genes. Indeed, human creativity, prosociality, and healthy longevity emerged in the context of the need to adjust rapidly to harsh and diverse conditions and to communicate in large social groups."

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