Tag Archives: chimps

Apes signal ‘hello’ and ‘farewell’ when starting and exiting social interactions

Two bonobos grooming each other at the San Diego Zoo. Credit: Pixabay.

When it’s a simple “hi!”, a head nod, or a bow, humans across cultures signal acknowledgment of the person when engaging in conversation, acts of cooperation, or simply being in the presence of others. Likewise, we also signal disengagement with a gesture or vocalization signifying farewell. This complex social behavior has important implications beyond mere politeness, and apes seem to also purposefully signal the start and end of interactions, according to a new study.

“Investigating how humans and other primates use communication and gaze to coordinate joint action with others is fascinating! It is exciting because it happens on-the-fly – a spontaneous coordination process that bears witness of our sense of joint commitment. Watching two friends having lunch together tells much about how they value each other and their commitment to each other. We thought that, by looking at how apes get into and out of natural interaction of play and grooming, we might find a similar external structure of joint action as in humans; a way by which joint commitment could be studied naturally,” Raphaela Heesen, a postdoctoral researcher at Durham University in the United Kingdom, told ZME Science.

In order to act together to fulfill a common goal, whether it’s building a new house in their community or launching a rover on Mars, two or more people must be jointly committed to acting as a body. This mutual sense of obligation is known as joint commitment, and philosophers and scientists consider it integral to human cooperation, society at large, and the historical success of our species in shaping the world.

But is joint commitment unique to humans? Perhaps not. At least some aspects of it, such as signaling engagement and disengagement, may be shared by apes.

“In humans, joint commitment is not just a product (a mental state) but also a process, or “interactional achievement”. What it means is that, in order for us two to even establish a feeling of mutual obligation (a product of joint commitment) we have to go through an interactional process that requires mutual coordination (in the form of mutual gaze or exchange of communicative signals, in our case language). We first need to establish joint commitment in an entry phase, then maintain it, and later agree to dissolve it in an exit phase. Entry and exit phases of a joint action can thus be used as markers for joint commitment; therefore, entry and exit phases in non-human animal species can be analyzed to investigate joint commitment. In a species that doesn’t communicate before getting into an interaction and while getting out of it, this could mean that there is probably no commitment involved,” Heesen said.

Heesen and colleagues recorded interactions among chimpanzee and bonobo groups in order to investigate whether these closely related species also shared joint commitment features. They got the idea after considering anecdotal evidence that this may be the case. For instance, when two bonobos were interrupted during their grooming, they later used gestures to resume the interaction with each other. Was this a singular event? That’s what the researchers set out to investigate — and it turns out that both chimps and bonobos signal greetings and farewells.

“Our most important finding was that chimpanzees and bonobos do very frequently mutually gaze at each other and communicate when entering and exiting from joint actions.” Heesen said.

To arrive at these conclusions, the researchers analyzed more than 1,200 interactions within five different groups of bonobos and chimpanzees housed in zoos. Bonobos exchanged entry signals and mutual gaze prior to playing 90% of the time and chimps 69% of the time. Exit signals were even more common, with 92% of bonobo and 86% of chimpanzee interactions featuring them.

These greeting and farewell signals included gestures like touching each other, holding hands, butting heads, or gazing at each other.

This video shows two chimpanzees entering a social grooming activity. Madingo (male) approaches Macourie (female) and both mutually gaze at each other (start of the entry phase). Macourie then uses a series of gestures, first attempting to grab Madingo, then touching his shoulder and back (gestures), and finally, grab-pulling him at his hips (gesture). Macourie then starts grooming him on his shoulder once he is sitting in close proximity. The entry stops with the first grooming movements, upon which the main body starts. Credit: Raphaela Heesen and Emilie Genty.

Furthermore, when engaging in entry and exit phases, the apes took into consideration familiarity and power dynamics. Bonobos who were familiar with each other tended to have shorter entry and exit phases, if they existed at all. That’s pretty similar to how humans engage with close friends since they are not afraid to come off as rude or impolite. The shared social history allows them to more rapidly cut to the chase.

“The second most important finding was that, in bonobos, the phases seemed more affected by social dimensions, particularly social bond strength, compared to chimpanzees. Intriguingly, the pattern mirrored what we find in humans and what some people define as “social etiquette” or “politeness”: when interacting with a good friend, you are less likely to put effort into communicating politely. In bonobos, a similar pattern is evident in the structure of the joint action phases. Bonobos produce fewer and shorter entry and exit phases when initiating or terminating a joint action with a closely bonded conspecific as compared to when initiating or terminating a joint action with a weakly bonded one; this pattern was not apparent in chimpanzees by contrast,” Heesen explained, adding that this doesn’t necessarily mean that apes have notions of “politeness” or “social etiquette”, or at least not in the way humans perceive them. “It could also be explained by the fact that apes care about themselves and want to avoid risks with unfamiliar partners,” she added.

Interestingly, the degree of familiarity and strength of social bonds did not seem to have an impact on the social entries and exits among chimps. This may be owed to the strict hierarchical nature of chimp communities, whereas bonobos tend to be more egalitarian.

There are still many unknowns concerning the origin and evolution of joint commitment, but this study marks a step further in unraveling this behavior that’s so central to human society. Next, the researchers plan to investigate joint commitment in other great apes, such as orangutans and gorillas, as well as more distantly related species like wolves or dolphins.

“I think generally there is much to explore from the way in which primates communicate when coordinating joint action. And one way this can be done is by comparing how different species get into and out of social interactions with peers. There may well be differences in the complexity with which some species do so; perhaps other, more distantly related species do not even communicate when exiting from a social encounter; we advocate more studies to investigate this process,” Heesen concluded.

The findings appeared in the journal iScience.

Bands of chimps attacked and killed gorillas. It’s the first time we’ve witnessed anything like this

It’s the first time this type of distressing behavior has been seen among great apes.

Two male chimps of the Rekambo community in Gabon surveying their territory. Credit: LCP, Lara M. Southern.

Both chimpanzees and gorillas are known to be capable of great violence. But generally, their violent behavior is directed towards members of their own species during internal feuds for territory, resources, and mating rights. This is why recent reports of two fatal fights between chimps and gorillas at Loango National Park in Gabon have had scientists concerned. It’s the first time an inter-great-ape killing has been documented.

“Our observations provide the first evidence that the presence of chimpanzees can have a lethal impact on gorillas. We now want to investigate the factors triggering these surprisingly aggressive interactions,” says Tobias Deschner, a primatologist at the Max Planck Institute for Evolutionary Anthropology.

War of the apes

Researchers with the Loango Chimpanzee Project have been monitoring apes living in the park since 2005. The aim of this research project is to investigate tool use, hunting behavior, territoriality, communication, and diseases to gain a better understanding of the behavioral diversity and complexity in chimpanzees (Pan troglodytes troglodytes).

Between 2014 and 2018, the researchers observed nine episodes in which chimps and gorillas interacted. That's nothing out of the ordinary as these types of encounters are quite common in eastern and central Africa.

Up until recently, all chimp-gorilla encounters observed by researchers were peaceful and sometimes even playful. Imagine their surprise when, in 2019, they witnessed not one but two violent clashes between these apes, each leading to deaths.

In both instances, the male chimps ganged up on gorillas at the outer edge of the chimps' territory. Although gorillas are enormously stronger than chimps, they were heavily outnumbered in both instances. Researchers happened to be only 30 meters (100 ft) away when the violence erupted, which made these episodes even more harrowing.

"At first, we only noticed screams of chimpanzees and thought we were observing a typical encounter between individuals of neighboring chimpanzee communities. But then, we heard chest beats, a display characteristic for gorillas, and realized that the chimpanzees had encountered a group of five gorillas," said Lara M. Southern, Ph.D. student and first author of the study, recalling one of the lethal clashes from 2019.

Interspecies battles

The fights lasted between 50 and 80 minutes. The chimps formed coalitions of more than two dozen members and attacked two families of gorillas. Although two silverbacks (the leaders of the group) and the females resisted and fought back, two gorilla infants were separated from their mothers during the chaos and were killed. Several chimps were injured in battle, including a severe injury incurred by an adolescent female, but there was no fatality on their side.

The aggressive chimps acted in coordination, working together to isolate the weakest members of the gorilla groups. This is how they ultimately were able to separate the baby gorillas from their mothers.

These concerning events are clearly atypical and may be the result of dwindling shared resources. Fruit availability has been relatively low in tropical forests in Gabon in recent years, which may be due to climate change. If this turns out to be indeed the case, then we can add inter-ape warfare to the ignoble list of environmental damage caused by human activity.

"We are only at the beginning to understand the effects of competition on interactions between the two great ape species in Loango," says Simone Pika. "Our study shows that there is still a lot to explore and discover about our closest living relatives, and that Loango National Park with its unique mosaic habitat is a unique place to do so."

The distressing clashes between the apes were described in a study that appeared this week in the journal Scientific Reports.


Bonobo food-sharing points to evolutionary origin of human generosity


Credit: Wikimedia Commons.

Cooperation is the bedrock of human social behavior and arguably the main reason why our species has come to dominate this planet. It’s through forming very tight-knit communities and sharing — not just of resources but knowledge, too — that humans have managed to overcome their individual weaknesses and vulnerabilities. But where did this striking behavior originate? Evolutionary clues may lie in our closest relatives, the bonobos, which seem to be eager to share food with peers even when they could have easily kept it for themselves. Tool-sharing, however, is not part of their generosity repertoire.

What makes a generous ape?

Our species split from the lineage common to chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) roughly seven million years ago. Chimps and bonobos split from a common ancestor which they had shared two million years ago.

To the untrained eye, bonobos and chimps are hard to tell apart. However, the two differ in morphology, behavior, and perhaps even emotions and cognition in important ways.

Bonobos live in female-dominant social groups where the females form tight bonds against males through same-sex socio-sexual contact, an approach that some scientists believe is what limits aggression. Sex plays a vital role in bonobo society — the animals do not form permanent partnerships and making love is used both as a greeting and to resolve conflicts. The typical bonobo has red lips, neat little ears, and a distinctive hairdo. In the wild, they have not been seen to cooperatively hunt, use tools, and aggression is quite uncommon (the completely peaceful, hippie bonobo is a myth).

Chimps live in male-dominant groups, where intense — sometimes lethal — aggression is common. Chimps are so aggressive and competitive that they will even eat the infants of other chimpanzee groups. Unlike bonobos, chimps hunt in groups and use tools. Studies have shown that chimps also exhibit some features of generosity. In one experiment, chimps handed over a tool that was out of reach to another chimp and who was clearly requiring it.

But what about bonobos?

Christopher Krupenye, a primate behavior researcher at the University of St. Andrews in Scotland, repeated the experiment with bonobos that live in the Lola Ya Bonobo sanctuary in the Democratic Republic of Congo. Two individuals were placed in cages side by side with a narrow window in between. One individual had several palm nuts while the other individual had several rocks at his disposal — that are perfect for cracking palm nuts.

The bonobos showed very little intent in sharing the rocks but consistently shared the nuts (18% of the trials) even though they could have kept them for themselves with no repercussions. Because there was no pressure to share their nuts, the bonobos seem to have behaved this way out of generosity.

In the wild, chimps also sometimes share food, but only on certain occasions such as following a big hunt or to placate pestering beggars.

In most species, food sharing happens between parent and infant. But, when it comes to food, the findings show that bonobos are uniquely prosocial among non-human primates.

It’s not clear why the bonobos wouldn’t share tools. What’s truly striking is that the behavior is almost completely opposite of chimps, who would share tools but not food.

Perhaps the separate evolutionary paths that bonobos and chimps each took may have shaped their unique takes on generosity. Alternatively, since bonobos don’t really use tools, they may fail to grasp the tool’s utility to the other person. Bonobos, who live in forests where food is abundant, have never been observed to crack nuts with a rock or fish termites with a stick as chimps often do. 

But although their generosity isn’t fully rounded, the study suggests that bonobos share many traits with humans in this respect. Over millions of years, our lineage may have encouraged more sharing, leading to more versatile generosity. For instance, human children as young as five understand that generosity scores them social points among their group and are remarkably willing to do so (although some parents reading this article may beg to differ).

The findings appeared in the Proceedings of the Royal Society B.


Great apes abilities misunderstood in decades of research by human hubris


Credit: University of St Andrews.

Scientists are learning striking new features about nonhuman great apes on a yearly basis. Progress, however, is slow and some papers can actually be misleading as a result of some researchers’ skewed views and biases. In other words, our false sense of superiority leads us to perceive great apes such as chimps or orangutans are clever — just simply never as clever as humans.

In many respects, this approach mirrors inter-racial bias that was until not long ago prevalent. These are the conclusions of a recent paper published by leading development psychologists.

Can we understand great apes if we think we’re better than them?

The new paper published in the journal Animal Cognition was authored by Dr David Leavens, of the University of Sussex, with Professor Kim Bard, University of Portsmouth, and Professor Bill Hopkins, Georgia State University.

The trio combed through today’s available literature on great ape behavior spanning hundreds of studies over two decades. Their stark conclusion is that our knowledge of apes’ social intelligence is largely based on wishful thinking and flawed science.

“The fault underlying decades of research and our understanding of apes’ abilities is due to such a strongly-held belief in our own superiority, that scientists have come to believe that human babies are more socially capable than ape adults,” said Leavens in a statement.

“As humans, we see ourselves as top of the evolutionary tree. This had led to a systematic exaltation of the reasoning abilities of human infants, on the one hand, and biased research designs that discriminate against apes, on the other hand,” he added.

A prime example noted by the authors are those studies that discuss ‘joint attention’, a process whereby infants engage with one another about an object or event. This is a key indicator of brain development which can be communicated by pointing or shifting gaze from an object to an individual and back with the intention to direct the other individual to look at the same object.

Studies that focus on joint attention have always rated human infants as more developed than apes. Such findings, however, are somewhat silly simply because authors compare apples and oranges. Specifically, researchers would rate human abilities against apes reared in an orphanage.

Due to Western conventions of non-verbal communication, the human infants naturally outperformed apes on some tasks. What’s more, when a human infant points at distant objects, it’s clearly marked as a sign of cognitive sophistication but when a non-human ape does it, it’s marked as an ambiguous behavior.

Social interactions among bonobos - pointing gestures and pantomime, too, are deployed in communication. Credit: LuiKotale Bonobo Project/ Zana Clay.

Social interactions among bonobos – pointing gestures and pantomime, too, are deployed in communication. Credit: LuiKotale Bonobo Project/ Zana Clay.

Another study, for instance, compared 12-month-old human children with apes age, on average, 18-19 years old. This particular effort found that only humans could point towards an absent object. The authors of the present examination, however, claim that the study’s design took no consideration for the differences in human and ape age, life history, or environment. Case in point, more recent studies have shown that apes are indeed capable of communicating about absent objects, just like the human infants.

One 2013 study found striking similarities among chimpanzee, bonobo and human infant gestures and symbols suggesting language, as we know it, evolved from gesture-based communication first.

Studies have also shown great apes employ gestures in an intentional, flexible and goal-oriented ways and display them in various contexts like grooming, playing or feeding. For example, to request food, great apes usually use begging gestures in which they stretch their arms and open their hands towards other conspecific with food.

Furthermore, Amy Pollick and Frans de Waal reported that the gestural repertoire varies from group to group of the same species, in some kind of gestural dialect. Another researcher identified some gestures that sound us like “move away”, “please, groom me”, “stop that” or “follow me”.

chimp gestures

In 2015, scientists found that just like babies, bonobos exhibit a type of communication in which they use the same sound with different intonations to say different things. They use these high pitch “peeps” to express their emotions.

These are simply a couple of examples of complex gestures, evidence of high social intelligence, which were recently published.

“There is not one scientifically sound report of an essential species difference between apes and humans in their abilities to use and understand clues from gestures, for example. Not one,” Leavens said.

“This is not to say such a difference won’t be found in future, but much of the existing scientific research is deeply flawed.”

In many ways, this sort of flawed experimental design is reminiscent of the collapse of rigor from a hundred years ago when some psychologists would assert that Northern races were the most intelligent of all humans. We now know that this is not nearly the case. Instead, studies have shown that intelligence is highly sensitive to environmental input and that previous studies that claim otherwise used inadequate testing contexts. These were poor studies, in other words, and much of the same is happening with modern papers on great ape social intelligence.

“In examining the literature, we found a chasm between evidence and belief. This suggests a deep commitment to the idea that humans alone possess sophisticated social intelligence, a bias that is often not supported by the evidence,” Bard said.

Shifting the paradigm to more open mindedness

The authors would like to see a paradigm shift and a revisal of evolutionary theory. They propose several solutions.

One would be cross-fostering where apes are adopted by human families. Previously, studies have shown that foster-apes are capable of communicating in ways other apes can’t. However, this method has its limitations, ethically-wise none the least.

Dr. Leavens and colleagues say that comparative behavior studies ought to be grounded in variables which can be objectively measured. Many skills and features currently in comparative psychology research can’t be observed or measured.

Also, if apes and humans ought to be compared fairly, they ought to be trained. No human infant is raised without some minimal amount of training from table manners to how to behave when a stranger enters the home. Some scientists claim that many human infant behaviors are spontaneous but that’s extremely difficult to say for sure and open to speculation.

Poor sampling is another common problem the authors have encountered. Almost all studies compare human infants from Western, industrialized societies to orphaned apes or those raised in sterile institutions.

The bottom line is that even scientists can be biased and practice inter-species discrimination. It is understandable. It’s challenging to make a huge mental leap and objectively assess the capabilities of a non-human species. But we have to if were to paint a fair and accurate picture of how our closest relatives.

Chimps in the Taï National Park are dying at worrying rates from anthrax caused by a novel bacteria called Bacillus cereus biovar anthracis. Credit: MPI f. Evolutionary Anthropology/ L. Samuni.

New Anthrax variant is causing havoc in Africa threatening chimp populations

Chimps in the Taï National Park are dying at worrying rates from anthrax caused by a novel bacteria called Bacillus cereus biovar anthracis. Credit: MPI f. Evolutionary Anthropology/ L. Samuni.

Chimps in the Taï National Park are dying at worrying rates from anthrax caused by a novel bacteria called Bacillus cereus biovar anthracis. Credit: MPI f. Evolutionary Anthropology/ L. Samuni.

A somewhat benign bacteria related to the species that causes anthrax is now causing an alternative form of the disease in Africa. This new form of anthrax is different from the original on a couple of levels. For instance, it now not only strikes mainly hoofed mammals but also other animals. Chimps seem to be particularly vulnerable. Some 40 percent of all chimp deaths in Côte d’Ivoire’s Taï National Park can be attributed to the new anthrax and, if left unchecked, the chimp population there could be wiped out within 150 years.

“To our surprise, almost 40 percent of all animal deaths in Taï National Park we investigated were attributable to anthrax,” said virologist Emmanuel Couacy-Hymann from the Ivorian Animal Health Institute in a statement.

A worrying death toll

Fabien Leendertz of the Robert Koch Institute in Germany has been visiting the Taï National Park (TNP) for the past 16 years. The first time he and colleagues went there, they were surprised by the number of carcasses they could find. As the deaths piled up, the researchers decided to investigate. Since 2004, they took samples from 204 animal carcasses, and the bones of 75. They also tested 1,634 carrion flies in 2008, which are known to carry diseases.

Scientists knew there’s an alternative anthrax-causing bacteria for more than a decade. What Leendertz’s team was after were new clues that might tell them more about its effects on wildlife.

Anthrax is caused by Bacillus anthracis, a germ that lives in soil. When it spreads to animals, the bacteria causes infection in the skin, lung, and intestines. As such, the disease which has a kill rate of up to 85% can spread through cuts or open sores on the skin, by inhaling bacterial spores or after eating infected meat.

The bacteria infects animals such as cattle, sheep, and goats (ungulates, in general) more often than people. B. anthracis is also far more prevalent during certain seasons. But that doesn’t mean it’s not dangerous.

Many people know about it from the 2001 bioterror attacks when someone purposely spread anthrax through the U.S. mail. This killed five people and made 22 sick.

A hybrid killer

Scientists have known for more than a decade that there is another bacteria that’s causing identical anthrax disease symptoms.

B. anthracis has a cousin called B. cereus that also lives in the soil and food. It’s generally harmless, although some strains have been linked to food poisoning. One strain, however, seems to have come in contact with the virulence plasmids from B. anthracis resulting in an alternative anthrax bacteria called B. cereus bioar anthracis or Bcbva for short.

Data from the samples, some as old as 28 years, suggest Bcbva is present in 40 percent of carcasses, 35 percent of bones, and five percent of 1,089 fly samples that were collected to gauge disease prevalence.

The sampling and genetic screening suggest that Bcbva is already widespread, showing up in samples from 5 of 11 locations included in the study published in Nature. Moreover, unlike B. anthracis, Bcbva seems to be present all the time, not just in seasonal outbursts. This is very worrying because it means anthrax could cause havoc among populations in tropical rainforest environment, not just those found in arid conditions as was the norm.

Another notable distinction is that Bcbva seems to hit a wider variety of animals, not just ungulates. Some of the mammal species known to be infected by Bcbva include chimps, porcupines, six different monkey species, as well as a type of antelope called duikers.

Chimps are particularly hard hit by Bcbva, with  31 of the 55 sampled individuals having died from anthrax. Researchers from the Max-Planck Institute for Evolutionary Anthropology in Germany, who were among the international team of collaborators involved in this study, say that the data indicates chimps in the Taï National Park could be driven extinct.

There are so far no reported deaths from Bcbva infections in humans. However, reliable autopsy data is rare to find in this part of Africa, so this might be due to under-reporting. The strain could also mutate to infect humans at some point, which is why everyone is taking things very seriously. As for the chimps, the scientists are now investigating a possible vaccine solution.

Chimps, unlike humans, are more likely to choose genetically-dissimilar mates

A new study found that while chimps sleep around a lot, they’re pretty selective about who they make little chimps with. The team found that these primates are more likely to conceive with the individuals that most differ from them genetically.

Image credits Pascal Renet / Pexels.

A couple of days ago we’ve talked about how humans tend to pick their mates after similarities in genome — a practice called assortative mating. From a biological point of view, it gives couples a higher chance of passing on desirable traits to their offspring, such as height, intelligence, and so on. It does, however, also come with potential drawbacks.

So let’s take a look at the opposite mating strategy — negative assortative mating. Postdoc associate in evolutionary anthropology Kara Walker and her team at Duke University found that chimps, our closest living relatives, are more likely to reproduce with genetically-different mates.

They took DNA samples from roughly 150 adult chimps from the Gombe National Park in Tanzania, and examine between 8 to 11 variable sites in their genome. They used this data to estimate the genetic similarity between every possible pairing of mates.

Getting some strange

Chimps get down a lot. But their adventures don’t always lead to offspring. The team compared the pairings that produced infants to those that didn’t, and found that females conceived with males that were genetically less similar to them than the average male. They were somehow able to determine genetic similarity among unfamiliar mates who were far removed from them in the family tree, the team concluded.

The female chimps of Gombe NP usually leave their family group when they reach adolescence, seeking a new group (with new males) to reproduce with. These females, even though they had few or no male relatives in the community they immigrated to, showed an even stronger preference for genetically-dissimilar mates than the native females. The researchers say that the females’ mate choices are driven by inbreeding depression — which is the drawback I was referring to earlier.

When two genetically-similar individuals have offspring, they have a higher chance of passing on beneficial genes — but they also have a higher chance of passing on harmful one. In the absence of another gene version to override it, this harmful gene will become active. Over time, the process increases whole populations’ vulnerability to certain pathogens or environmental factors. That is inbreeding depression in a nutshell — a whole group sharing one or more Achilles’s heel because everyone is related to everyone else.

Gene-dar on the ready

Instinctually, this is what makes you and chimps not cool with parent-offspring or sibling-sibling pairing. Such pairings are rare in chimps, and when it occurs it’s less likely to produce individuals that survive to maturity than their peers.

However, while we can determine the genetic makeup of our mate through DNA tests (you should probably not suggest that on your first date), chimps can’t. The researchers are now trying to find out how the chimps can recognize genetically-distant mates. They suggest that the primates do more than simply avoid potential mates they grew up with, being able to distinguish even among unfamiliar partners. It’s not sure yet exactly how they discriminate but it might be a best guess based on appearance, smell, or sound, said professor of evolutionary anthropology at Duke and senior author of the paper Anne Pusey.

Timing could also play a factor. The females might be pickier about partners during their most fertile period. The team is also considering processes that take place after mating, such as a female unconsciously choosing some males’ sperm over others or influencing the outcome of a pregnancy, Walker said.

The full paper “Chimpanzees breed with genetically dissimilar mates” has been published in the journal Royal Society Open Science.


Male chimpanzees take an active interest in their offspring’s well-being, suggests early humans did the same

Male chimps take an active role in protecting their offspring, new research suggests, by prioritizing time and effort into the task rather than focusing only on future mating options. The study challenges our traditional view of the primates, that of a highly promiscuous species whose males may not even recognize their own offspring.

Image via Wikimedia.

A new study by George Washington University anthropologists looked at male chimps to try and answer why human fathers invest so much time and energy in offspring. The team used data acquired at the Gombe Stream National Park, Tanzania over a period of more than 25 years. They examined the behavioral patterns of 17 father chimpanzees and 49 mother-infant pairs to see if the males recognized their offspring and if they showed a difference in behavior around them.

The researchers found the males associated with mothers of their offspring early in infancy and interacted with their infants more than expected. The fact that the males spent time with nursing mothers even though this didn’t increase their chances of fathering the next infant supports the paternal effort hypothesis, according to which males associate more with mothers in order to protect their offspring, not for sexual gain.

“As anthropologists, we want to understand what patterns could have existed early in human evolution that help explain how human behavior evolved,” said Carson Murray, assistant professor of anthropology at the GWU and lead author of the paper.

“This research suggests that males may sometimes prioritize relationships with their offspring rather than with potential mates. For a species without pair-bonds where it was assumed fathers didn’t know which infants were their own, this is an important finding.”

The researchers also found that the males would spend time grooming and caring for their offspring. Chimpanzees are one of the closes living relatives modern humans have. Discovering that they not only have paternal recognition, but also take an interest in raising and caring for their offspring rather than only focusing on future mating opportunities, offers insight into how early human fathers behaved.

“Our findings are not only further evidence that chimpanzee fathers recognize their offspring in a promiscuous species, but also that fathers behave differently around their offspring,” said Margaret Stanton, postdoctoral scientist at GW’s Center for the Advanced Study of Human Paleobiology and co-author of the paper.

But, while the paper offers some valuable insight, it cannot answer the overall question of how human paternal behavior evolved by itself.

The full paper “Chimpanzee fathers bias their behaviour towards their offspring” has been published in the journal Royal Society Open Science.

The Red Light Forest – Prostitution in the Animal World


You know what’s awesome? Having sex.

We like it so much that it creeps into every corner of our lives. On a recent drive, I saw a huge billboard advertising a sporting bets website. It struck me as odd because this ad featured a pretty, scantily-clad young woman encouraging me to bet on sports — an activity that easily makes it onto my top 3 not-sexy-things list. Why were the two put together? Why does this lady want me to bet, and why do I feel compelled to do so?

Well, because sex sells.

It’s a fact that hasn’t escaped animals, either. All life is programmed to procreate, and sex is a great way to do it. It’s not the only way, but it’s certainly the most fun. Procreation is a very powerful instinct and organisms will go to great lengths to satisfy it — something which some species have learned to leverage to their advantage.

Chimp prostitution

In 2011, scientists inadvertently created prostitution among Capuchin monkeys during an experiment, but the history of monkey prostitution goes back even further.

Back in 2009, Christina Gomes and Christophe Boesch of the Max Planck Institute for Evolutionary Anthropology published a paper in support of the “meat-for-sex” behavior hypotheses in early human society. In a nutshell, the theory holds that the ladies would have been all over the best hunters among our ancestors because they had meat to share. This would benefit the males by providing more mating opportunities while allowing the females a method to widen their diet and intake more calories and nutrients via meat without having to hunt — which is both dangerous and energy intensive.

But since early humans are decidedly scarce, the team tested their theory on chimpanzees.

“Humans and chimpanzees are unusual among primates in that they frequently perform group hunts of mammalian prey and share meat with conspecifics,” the team writes.

Tit for meat

Just like humans, chimpanzee males have been observed to share meat with unrelated females, which seems strange from an evolutionary point of view. Hunting is dangerous and draining, so meat has a lot of value — in a sense, meat is expensive. As a species, chimps are also “highly promiscuous, […] have a certain degree of female choice,” and the hunters usually “control the sharing of their catch.”

That feel when you’ve got all this meat and she says she’s a vegetarian.
Image via Day Donaldson / Flickr.

So I think you can guess where this is going. The males have meat which they can decide to share or not, and they’re really horny. The females, on the other hand, aren’t as physically fit as the males so they can’t get as much meat, but they do have something the males want. Namely, themselves.

The team followed a group of wild chimpanzees in the Taï National Park, Côte d’Ivoire, between 2003 and 2006. The group consisted of five adult males and 14 adult females. Out of these 14, eight had been in estrus (in heat) at some point during the study period. As male chimpanzees only copulate with estrous females, the analysis was restricted to pairs formed by these females and the five adult males.

At least one estrous female was present in 64 of the total 90 successful observed hunts, and at least one anestrous female was present during 81 of the hunts. During this time, the team recorded 262 male to female meat transfers. How much and how often each male shared meat with each female varied considerably during the study, meaning each female received a different caloric benefit from each male. A total of 262 copulations were observed during the time the females were in estrus, in at least 30 different pairings.

A female generally didn’t copulate with all the males, and the time they spent with each male varied considerably. Out of the 30 pairs that were observed copulating, in nine cases (30%) the male did not share meat with the female, while in 21 cases (70%) the male shared meat with the female throughout the entire study period. The team accounted for factors such as social status or grooming, but meat sharing still remained a significant factor in mating success.

So while chimpanzees don’t follow the clear-cut “I will pay you this for sex” behavior humans employ, males considerably improved their chances of copulating by sharing meat.

Penguin chicks are all about location

While chimpanzee females trade sex for food, a real-estate shortage is powering Adelie penguin (Pygoscelis adeliae) females’ prostitution. The species builds nests out of the material available on the beaches they use to nest, but because there are so many penguins, there isn’t always enough to go around.

“This material is in the form of small stones used to create a platform on which the female lays her two eggs. Stones are in great demand in the colony and are collected by both males and females from the ground in the area surrounding the breeding group,” write F. M. Hunter and L. S. Davis in their paper.

Adelie penguins mate for life, but certain females have been observed to leave their nest and visit single males that are trying to build their own. There they copulate with the lucky fellows, take a stone, and then scamper off to their own nest. The duo observed ten cases of a female visiting a single male and note that the female is receptive to copulation, and in 8 out of 10 cases the act ended with successful insemination.

Not to brag but I have the biggest pebble on this beach.
Image credits Liam Quinn / Flickr.

They also write that after each attempt at copulation the male dismounts the female who takes a stone then leaves. In 5 out of the 10 cases, the female returned to the lone male to take another stone, but without further copulation. In one case, a female returned no less than 10 times to the extrapair male, taking a pebble each time. The females always returned to their mate after their adventures, depositing the pebble on their nest. The paired males didn’t seem to suspect anything fishy going on, and no extrapair male was observed to try and take the stones back from the females.

Tricky females…

Sometimes, however, the females outright trick the males — they take part in the courtship ritual, take a few stones, then leave the male alone. Dr. Fiona Hunter, a researcher in the Zoology Department at Cambridge University, who has spent five years observing the birds’ mating patterns, said that we don’t really understand why this happens.

“The female only takes one or two stones,” she said. “It takes hundreds to build the nest to get their eggs off the ground.”

“I think what they are doing is having copulation for another reason and just taking the stones as well. We don’t know exactly why, but they are using the males.”

One of her theories is that the females are on the look-out for potential future mates, in case they ever need one. Whatever it is that drives them, prostitution is much less widespread among penguin females than their chimpanzee counterparts.

“It’s probably only a few percent,” Dr. Hunter adds. “I was watching opportunistically, so I can’t give an exact figure of how common it really is.”

The humm of love

Being a hummingbird gal ain’t easy. Hummingbirds are fiercely territorial, and males usually have the upper hand. Being heavier and stronger than the females, they command the territories with better overall energetic value — the best turfs with plenty of flowers that produce nectar. The females, on the other hand, are usually forced to make due with less attractive territories — either those that are very large and hard to defend or those that yield less nectar. So, when the going gets tough because of droughts or loss of plants, the females must either make do with limited energy resources or find a way to sponge off of the males’ territory.

This my turf.
Image part of the public domain.

Emeritus Professor of Biology at the University of Syracuse Larry Wolf described in a paper in 1975 how the female Purple-throated Carib Hummingbird (Eulumpis jugularis) was observed to use sex to feed off of males’ territory during a time of drought. The specimens he collected during his study showed that because the birds’ mating season wasn’t yet in swing, the males’ testes weren’t yet fully enlarged (1-1,5 mm large in January compared to 6 mm by mid-April) and the females were not yet ready to lay eggs — in other words, there was no reproductive incentive behind the mating.

Power play

Wolf described the behavior in 5 steps, labeled A to E. These could all take place or just a number of them, for example straight from A to E. Wolf theorized that birds which wave interacted previously might skip the middle steps.

When a female first attempted to feed in a territory claimed by a male, he would chase her off, constituting stage A. Stage A would see repeated chasings-off of the female, with later-stage flights taking the male further away from his territory for longer periods of time. In stage B, the female would position herself in close proximity to the male with no aggression from him. He who would allow her to feed and would make token shows of dominance by making a “rocking display towards the female, who was usually more than five feet away at the time.” The male would also allow the female to displace him from perches he vigorously defended up to that point.

Stage C included performances by both birds, usually the male, with stage D being copulation. The females were responsive to the act, assuming a horizontal posture with the tail to one side. Wolf notes that up to stage D, the usually dominant males allowed the females to assume dominance, letting them feed on the best flowers and allowing them to perch unimpeded.

Stage E, the postcopulatory period, saw the males either standing a short distance away from the females or flying in circles above them. If the females attempted to feed again, the males would chase them off as soon as they became aware of it. Following the act, the males had re-established their dominance over the females.

Sex truly sells, but it also buys.

It seems to me that these female animals offer sex as a bargaining chip for things they can’t — or would be too difficult to — get for themselves. Be it food or shelter for their eggs, they look to males who have the resources they need and convince them to share by copulating with them. There’s betrayal, role reversal, and debauchery, but in the end everyone gets a meal and some love.

And isn’t that what we all want?


Three-dimensional models of chimpanzee and human skulls showing their endocranial casts (teal) and brains (purple). Credit: Jose Manual de la Cuetara/Aida Gomez-Robles Read more at: http://phys.org/news/2015-11-nature-nurture-human-brains-evolved.html#jCp

Human brain plasticity doesn’t seem to be shared by chimps – is this a unique gift?

It seems like evolution has fostered us humansto become the dominant species on planet Earth. We owe so many gifts to the tender processes that began millions of years ago and shaped us the way we are today. Gripping dexterous hands, social behavior and let’s not forget about those brains. It’s not enough to have a big brain, though. What makes us humans particularly successful is our ability to adapt constantly to our environment. Humans fair well in luxurious plains, but they seem to survive in the desert as well. Then look at the times we’re living in. Technology, networking, all our cultural heritage. It takes a lot to adapt to changing times, and no other species seems to be this good at it. While we owe a great deal to genetics, it’s brain plasticity – an inherent ability to mold our cerebral connections to fit our environment – that took us the extra mile.

Three-dimensional models of chimpanzee and human skulls showing their endocranial casts (teal) and brains (purple). Credit: Jose Manual de la Cuetara/Aida Gomez-Robles Read more at: http://phys.org/news/2015-11-nature-nurture-human-brains-evolved.html#jCp

Three-dimensional models of chimpanzee and human skulls showing their endocranial casts (teal) and brains (purple). Credit: Jose Manual de la Cuetara/Aida Gomez-Robles
Read more at: http://phys.org/news/2015-11-nature-nurture-human-brains-evolved.html#jCp

Chimps, our closest relatives along with Bonobos (we share 99% of our DNA), do not seem to share the same ability. A group of researchers performed brain scans to examine the heritability of brain organization in chimpanzees compared to humans. They performed MRI scans on 218 human brains and 206 chimpanzee brains. The humans involved in the study were either twins (identical and fraternal) or siblings, while the chimps had a variety of kinship relationships, including mothers and offspring or half siblings. Brain size in both humans and chimps was obviously directed by genes. In contrast, however,  chimpanzees’ brain organization is also highly heritable, but in humans this is not the case. In other words, while we take cues from the environment and restructure our brain patterns accordingly, chimps think in a certain way from birth. They may be incapable of adapting past what they’ve been used to for generations.

“The human brain appears to be much more responsive to environmental influences,” said Aida Gómez-Robles, postdoctoral scientist at the GW Center for the Advanced Study of Human Paleobiology and lead author on the paper. “It’s something that facilitates the constant adaptation of the and behavior to the changing environment, which includes our social and cultural context.”

“A major result of increased plasticity is that the development of neural circuits that underlie behavior is shaped by the environmental, social, and cultural context more intensively in humans than in other primate species,” concluded the researchers, who published the findings today in Proceedings of the National Academy of Sciences.

While chimps do live in communities, these are far less complex than human’s. Does human culture stem from brain plasticity? It may very seem likely. Just look at how human culture has changed over the millennia. Constantly morphing, always different, just like our brains. There’s a great deal of things we share with primates, but there also some unique traits to us humans. Much more work is required and many puzzles await. “We still have a very incomplete understanding of what is special about the human brain compared with the brains of our closest fossil and living relatives,” researchers wrote in a new study.

chimp language

Chimps ‘tell’ each other where the best fruit trees are found and how big these are

Chimps, our favorite primate cousins, communicate with each other through a complex gesture language, partially decoded by scientists. Depending on the situation and the gesture, chimps tell each other things like “Stop that,” “Climb on me,” or “Move away.” Now, an exciting new study found that chimps also communicate through vocalization. Researchers found that the primates would “speak” to their peers and relay what their favorite fruits are and where the best trees can be found.

chimp language

“Chimpanzees definitely have a very complex communication system that includes a variety of vocalisations, but also facial expressions and gestures,” says project leader Ammie Kalan of the Max Planck Institute for Evolutionary Anthropology.

“How much it resembles human language is still a matter of debate,” she says, “but at the very least, research shows that chimpanzees use vocalisations in a sophisticated manner, taking into account their social and environmental surroundings.”

The biologists closely followed chimpanzees for more than 750 hours in the Ivory Coast’s Taï Forest and analyzed their calls. When the chimps encountered fruits from Nauclea trees, they elicited high pitched calls. Further yet, when the trees were small the high pitch was kept, while bigger trees were relayed to peers with lower hums. In total, some  379 food calls produced for five different food species were analyzed, but higher pitched calls were produced for the Nauclea.

“I never tried these fruits myself, but they do smell very good in the forest,” Kalan says. “They are also quite big and easy to ingest, and we also know that they have a high energy content, which is important for wild animals.”

Granted, this is far from being a conclusive finding and the authors highlight further work is needed to determine whether variation in food call pitch can influence receiver foraging behaviour. Still, if this is true, then chimps communicate with fellows in their community which foods are of better quality and where these are found, which is impressive in itself and not that unlikely considering complex chimp behaviour. Besides a complex gesture language, chimps establish cultures and pass down skills to their peers. They even exhibit fashion-like behaviour.

Findings appear in Animal Behaviour.


Chimps Pass down Skills to Peers and Establish Cultures

Chimps, our closest relatives, can pass down knowledge and skills, like using a new tool for instance, and establish cultural communities, according to a recently study published in PLOS Biology. Communicating and passing down skills, inventions and knowledge is considering a pre-requisite to what we commonly refer to as human culture, and the findings suggest that this kind of behavior can be traced back to the common ancestry we share with other primates.

Chimp culture


A breathtaking shot of a fellow primate, enjoying a dip by the water. Photo: Capital Wired

Dr. Catherine Hobaiter from the University of St. Andrews was always fascinated that some chimp communities employ certain tools, while neighboring communities use other tools or no tool at all for a given task. This suggests that these various practices and habits suggest that there are different chimp cultures, and that these are passed down from other chimps. For instance, a community Hobaiter and colleagues studied uses leaf sponges – leafs folded in the chimp’s mouth – to dip the water and drink from them. Quite civilized. It’s almost impossible to tell when this technique was introduced or who the original inventor was.

The researchers, however, were fortunate enough to witness the introduction of a new tools before their very own eyes. Nick, a 29-year-old alpha male chimpanzee, made a sponge made of moss while being watched by Nambi, a dominant adult female. Soon enough, seven other chimps were found to make and use their own moss sponges in just six days following the invention. It’s a remarkable example of social learning, yet this is the first time it was witnessed in the wild!

“This study tells us that chimpanzee culture changes over time, little by little, by building on previous knowledge found within the community,” said Thibaud Gruber, one of the researchers. “This is probably how our early ancestors’ cultures also changed over time. In this respect, this is a great example of how studying chimpanzee culture can help us model the evolution of human culture. Nevertheless, something must have subsequently happened in our evolution that caused a qualitative shift in what we could transmit, rendering our culture much more complex than anything found in wild apes. Understanding this qualitative jump in our evolutionary history is what we need to investigate now.”

To demonstrate the inheritance of the sponge, the researchers build a complex static and a dynamic network model. The most conservative estimate of social transmission accounted for 85% of observed events, with an estimated 15-fold increase in learning rate for each time a novice observed an informed individual moss-sponging.

Chimps can be so amazing at adapting to their environments and are remarkable social creatures (I have a hunch they’re not the only primates capable of doing this either). Chimps use specific gesture language to communicate with their peers, a behavior which is most likely also culturally passed down. But maybe the most evident display of chimp culture is that they also embrace fashion fads. Yes, you’ve heard right – after following a group of chimps from the  Chimfunshi Wildlife Orphanage Trust, a sanctuary in Zambia, researchers found that after an individual was ‘parading’ around with a grass in his ear, other chimps began to do the same after a while.