̽��ֱ�� of Cambridge - Biological anthropology

Revealed: face of 75,000-year-old female Neanderthal from cave where species buried their dead

fpjl2 — Thu, 02 May 2024 06:46:45 +0000

A new documentary has recreated the face of a 75,000-year-old female Neanderthal whose flattened skull was discovered and rebuilt from hundreds of bone fragments by a team of archaeologists and conservators led by the ̽��ֱ�� of Cambridge.

Chimpanzees use hilltops to conduct reconnaissance on rival groups

fpjl2 — Thu, 02 Nov 2023 15:58:40 +0000

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.

̽��ֱ��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.

̽��ֱ��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 ̽��ֱ�� 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.”

̽��ֱ��study was conducted at the Taï Chimpanzee Project, where Lemoine worked during his PhD. ̽��ֱ��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.

̽��ֱ��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. ̽��ֱ��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.

̽��ֱ��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. “ ̽��ֱ��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.

̽��ֱ��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. ̽��ֱ��animals go into an intimidating frenzy, screaming and defecating and gripping each other’s genitals.”

*Chimpanzees stopped on peripheral hills in 58% of movements heading towards the border, but in only 25% of the movements heading towards the centre of their territory.

Research on neighbouring chimpanzee communities in the forests of West Africa suggests a warfare tactic not previously seen beyond humans is regularly used by our closest evolutionary relatives.

Tactical warfare is considered a driver of human evolution

Sylvain Lemoine

Roman M Wittig/ Taï Chimpanzee Project

Chimpanzees are seen attentively listening to other chimpanzees heard at some distance in the West African forests of Côte d’Ivoire, studied as part of research by the Taï Chimpanzee Project

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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First hominin muscle reconstruction shows 3.2 million-year-old ‘Lucy’ could stand as erect as we can

fpjl2 — Wed, 14 Jun 2023 05:44:09 +0000

A Cambridge ̽��ֱ�� researcher has digitally reconstructed the missing soft tissue of an early human ancestor – or hominin – for the first time, revealing a capability to stand as erect as we do today.

Dr Ashleigh Wiseman has 3D-modelled the leg and pelvis muscles of the hominin Australopithecus afarensis using scans of ‘Lucy’: the famous fossil specimen discovered in Ethiopia in the mid-1970s.

Australopithecus afarensis was an early human species that lived in East Africa over three million years ago. Shorter than us, with an ape-like face and smaller brain, but able to walk on two legs, it adapted to both tree and savannah dwelling – helping the species survive for almost a million years.

Named for the Beatles classic ‘Lucy in the Sky with Diamonds’, Lucy is one of the most complete examples to be unearthed of any type of Australopithecus – with 40% of her skeleton recovered.

Wiseman was able to use recently published open source data on the Lucy fossil to create a digital model of the 3.2 million-year-old hominin’s lower body muscle structure. ̽��ֱ��study is published in the journal Royal Society Open Science.

̽��ֱ��research recreated 36 muscles in each leg, most of which were much larger in Lucy and occupied greater space in the legs compared to modern humans.

For example, major muscles in Lucy’s calves and thighs were over twice the size of those in modern humans, as we have a much higher fat to muscle ratio. Muscles made up 74% of the total mass in Lucy’s thigh, compared to just 50% in humans.

Paleoanthropologists agree that Lucy was bipedal, but disagree on how she walked. Some have argued that she moved in a crouching waddle, similar to chimpanzees – our common ancestor – when they walk on two legs. Others believe that her movement was closer to our own upright bipedalism.

Research in the last 20 years have seen a consensus begin to emerge for fully erect walking, and Wiseman’s work adds further weight to this. Lucy’s knee extensor muscles, and the leverage they would allow, confirm an ability to straighten the knee joints as much as a healthy person can today.

“Lucy’s ability to walk upright can only be known by reconstructing the path and space that a muscle occupies within the body,” said Wiseman, from Cambridge ̽��ֱ��’s McDonald Institute for Archaeological Research.

“We are now the only animal that can stand upright with straight knees. Lucy’s muscles suggest that she was as proficient at bipedalism as we are, while possibly also being at home in the trees. Lucy likely walked and moved in a way that we do not see in any living species today,” Wiseman said.

“Australopithecus afarensis would have roamed areas of open wooded grassland as well as more dense forests in East Africa around 3 to 4 million years ago. These reconstructions of Lucy’s muscles suggest that she would have been able to exploit both habitats effectively.”

Lucy was a young adult, who stood at just over one metre tall and probably weighed around 28kg. Lucy’s brain would have been roughly a third of the size of ours.

To recreate the muscles of this hominin, Wiseman started with some living humans. Using MRI and CT scans of the muscle and bone structures of a modern woman and man, she was able to map the “muscle paths” and build a digital musculoskeletal model.

Wiseman then used existing virtual models of Lucy’s skeleton to 'rearticulate' the joints – that is, put the skeleton back together. This work defined the axis from which each joint was able to move and rotate, replicating how they moved during life.

Finally, muscles were layered on top, based on pathways from modern human muscle maps, as well as what little “muscle scarring” was discernible (the traces of muscle connection detectable on the fossilised bones). “Without open access science, this research would not have been possible,” said Wiseman.

These reconstructions can now help scientists understand how this human ancestor walked. “Muscle reconstructions have already been used to gauge running speeds of a T-Rex, for example,” said Wiseman. “By applying similar techniques to ancestral humans, we want to reveal the spectrum of physical movement that propelled our evolution – including those capabilities we have lost.”

Reference:
Ashleigh L. A. Wiseman. 'Three-dimensional volumetric muscle reconstruction of the Australopithecus afarensis pelvis and limb, with estimations of limb leverage.' Royal Society Open Science (2023). DOI: 10.1098/rsos.230356

Digital modelling of legendary fossil’s soft tissue suggests Australopithecus afarensis had powerful leg and pelvic muscles suited to tree dwelling, but knee muscles that allowed fully erect walking.

Lucy’s muscles suggest that she was as proficient at bipedalism as we are

Dr Ashleigh Wiseman

A cross-section of the polygonal muscle modelling approach, guided by muscle scarring and MRI data.

Yes

Gorillas found to live in 'complex' societies, suggesting deep roots of human social evolution

fpjl2 — Wed, 10 Jul 2019 05:24:40 +0000

Algorithms reveal “social tiers” in gorillas seen in only a few other species, such as dolphins and humans. Researchers suggest that some of these social bonds may be analogous to “old friendships” and “tribes” in humans.

‘Believing you’re a winner’ gives men a testosterone boost and promiscuous disposition

fpjl2 — Thu, 09 Aug 2018 08:36:05 +0000

A new study shows that men only have to believe they’ve bested another man in competition to get raised testosterone levels and an inflated sense of their own value as a sexual prospect.

Scientists found that this hormonal and psychological shift made men more inclined to approach new potential partners.

̽��ֱ��research team measured hormone levels, as well as self-perceived attractiveness and confidence in approaching women, in 38 men in their twenties before and after competing in head-to-head battles on rowing machines.

Unbeknownst to participants, the competitions in the study were rigged to randomly declare the winner, regardless of who was the stronger rower.

While previous studies have shown that winning can affect male hormones, it was not known whether this was down to the efforts it takes to win or the belief that one is victorious.

̽��ֱ��latest study, led by biological anthropologists from the ̽��ֱ�� of Cambridge and published today in the journal Human Nature, reveals that just being convinced you have won, or indeed lost, is enough to cause male hormonal fluctuations that can influence sexual behaviour.

Researchers say this is an example of “plasticity”: the body adapting quickly – without altering genetic make-up – to suit a change in circumstance. In this case a perceived change in social status, due to the men believing they have defeated a rival.

̽��ֱ��body attempts to take advantage of this apparent status improvement by inducing chemical and consequently behavioural changes that promote a “short-term” approach to reproductive success, say the researchers. Namely, more sex with new and different partners.

“Much of evolution consists of trade-offs in energy investment,” said study lead author Dr Danny Longman, from Cambridge’s Department of Archaeology.

“A common trade-off for males both across and within species is between mating strategies. One reproductive approach is short-term, investing time and energy in attracting and pursuing many mates, and fighting off competition. Another approach is long-term, investing energy in raising offspring with a single mate.”

“We found that a perceived shift in social status can cause male physiology to adapt by preparing to shift mating strategies to optimise reproductive success.”

Longman points out that in many animal populations, male social hierarchies correspond with reproductive success, and social status is determined by competition between males.

̽��ֱ��study used a simple proxy for social and sexual competition by pitting athletic young men against each other to see who was the most powerful rower.

“Victory in a rowing contest strongly implies the possession of greater physical strength than the opponent, a trait found to be valued by women in our evolutionary past when choosing a mate,” said Longman.

He took saliva samples to test hormone levels before and after the races. A number of psychological questionnaires were also administered, designed to gauge self-esteem, ‘sociosexuality’ (willingness to engage in casual sex), ‘self-perceived mate value’ and mating behaviour (e.g. the likelihood of approaching attractive women). Crucially, Longman and colleagues then manipulated the results of the races.

̽��ֱ��men who believed they had won received an average testosterone increase of 4.92%, while those convinced they had lost dropped by an average of 7.24%. Overall, men who thought they were winners had testosterone levels 14.46% higher their deflated opponents.

̽��ֱ��men who thought they had lost showed no difference in their perceived value as a mate or confidence approaching women. However, the men who felt like winners had a ‘self-perceived mate value’ that was 6.53% higher, on average, than their rivals, and were 11.29% more likely to approach attractive women in an effort to instigate sexual relations.

“ ̽��ֱ��endocrine system that controls hormones is responsive to situational changes. Previous research has shown that testosterone is lower when men are in a committed relationship, or have children, to promote long-term mating strategies,” said Longman.

“Our results show that both testosterone and its corresponding psychological effects can fluctuate quickly and opportunistically, shifting towards short-term mating in response to a perceived change in status that may increase mating value.”

Male social status has less to do with physical strength in many modern societies, and Longman would be curious to see if similar results arise from intellectual challenges more familiar to the office-based culture many men now inhabit. There is always the issue of free will, however.

“Male physiology may shift to take advantage of certain situations, but ultimately a man’s decisions are up to him.”

New findings suggest that the male body tries to “optimise” self-perceived improvements in social status through hormonal shifts that promote “short-term mating”.

Our results show that both testosterone and its corresponding psychological effects can fluctuate quickly and opportunistically

Danny Longman

U.S. Army

U.S. Army World Class Athlete Program wrestler Spc. Jeremiah Davis (right) squares off against Sunkist Kids' Joe Betterman

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Licence type:

Attribution

'Selfish brain' wins out when competing with muscle power, study finds

fpjl2 — Fri, 20 Oct 2017 11:51:43 +0000

Human brains are expensive – metabolically speaking. It takes lot of energy to run our sophisticated grey matter, and that comes at an evolutionary cost.

Now, a new investigation into the immediate trade-off that occurs inside us when we have to think fast and work hard at the same time is the first to demonstrate that – while both are impaired – our mental ability is less affected than our physical capacity.

Researchers say that the findings suggest a "preferential allocation of glucose to the brain", which they argue is likely to be an evolved trait – as prioritising quick thinking over fast moving, for example, may have helped our species survive and thrive.

Scientists from the ̽��ֱ�� of Cambridge's PAVE (Phenotypic Adaptability, Variation and Evolution) research group tested 62 male students drawn from the ̽��ֱ��'s elite rowing crews. ̽��ֱ��participants had an average age of 21.

̽��ֱ��rowers performed two separate tasks: one memory, a three minute word recall test, and one physical, a three minute power test on a rowing machine.

They then performed both tasks at once, with individual scores compared to those from previous tests. As expected, the challenge of rowing and remembering at the same time reduced both physical and mental performance.

However, the research team found that change in recall was significantly less than the change in power output.

During the simultaneous challenge, recall fell by an average of 9.7%, while power fell by an average of 12.6%. Across all participants the drop in physical power was on average 29.8% greater than drop in cognitive function.

̽��ֱ��team say the results of their new study, published today in the journal Scientific Reports, add evidence to the 'selfish brain' hypothesis: that the brain has evolved to prioritise its own energy needs over those of peripheral organs, such as skeletal muscle.

"A well-fuelled brain may have offered us better survival odds than well-fuelled muscles when facing an environmental challenge," said Dr Danny Longman, the study's lead author from the PAVE team in Cambridge's Department of Archaeology.

" ̽��ֱ��development of an enlarged and elaborated brain is considered a defining characteristic of human evolution, but one that has come as a result of trade-offs.

"At the evolutionary level, our brains have arguably cost us decreased investment in muscle as well as a shrunken digestive system.

"Developmentally, human babies have more stored fat than other mammals, acting as an energy buffer that feeds our high cerebral requirements.

"On an acute level, we have now demonstrated that when humans simultaneously experience extremes of physical and mental exertion, our internal trade-off preserves cognitive function as the body's priority."

̽��ֱ��adult brain derives its energy almost exclusively from the metabolism of glucose. Yet skeletal muscle mass is also energetically expensive tissue, accounting for 20% of the human male 'basal metabolic rate' – the energy used when doing nothing.

Longman says a limited supply of blood glucose and oxygen means that, when active, skeletal muscle becomes a "powerful competitor" to the brain. "This is the potential mechanism for the fast-acting trade-off in brain and muscle function we see in just a three minute window."

"Trade-offs between organs and tissues allow many organisms to endure conditions of energy deficit through internal prioritising. However, this comes at a cost," said Longman.

He points to examples of this trade-off benefiting the brain in humans. " ̽��ֱ��selfish nature of the brain has been observed in the unique preservation of brain mass as bodies waste away in people suffering from long-term malnutrition or starvation, as well as in children born with growth restriction."

New research on our internal trade-off when physical and mental performance are put in direct competition has found that cognition takes less of a hit, suggesting more energy is diverted to the brain than body muscle. Researchers say the findings support the ‘selfish brain’ theory of human evolution.

A well-fuelled brain may have offered us better survival odds than well-fuelled muscles when facing an environmental challenge

Danny Longman

Lead researcher Dr Danny Longman rowing with the Cambridge ̽��ֱ�� Boat Club. This is an example of the type and standard of the sample population used in the study.

̽��ֱ��study

Protocol A – isolated power test:
Participants rowed at maximal effort for 3 minutes, and their average Wattage was recorded.

Protocol B – isolated recall test:
Participants performed a free recall word task in which they were shown 75 words from the Toronto Word Pool for a 3 minute period. They then had 5 minutes to recall and write as many words as possible. ̽��ֱ��number of words correctly recalled during a given time period was recorded.

Protocol C – combined 'trade-off' test:
Participants did both (but with a different word set), and their average Wattage and number of words correctly recalled was recorded. Researchers used 'paired samples t-tests' to compare power output between Protocols A and C, and for comparing free recall in Protocols B and C. They then compared the two differences, and found that the percentage change in free recall was significantly less than the percentage change in power output – an average of 29.8%.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Meet the hominin species that gave us genital herpes

fpjl2 — Sun, 01 Oct 2017 23:06:35 +0000

Two herpes simplex viruses infect primates from unknown evolutionary depths. In modern humans these manifest as cold sores (HSV1) and genital herpes (HSV2).

Unlike HSV1, however, the earliest proto-humans did not take HSV2 with them when our ancient lineage split from chimpanzee precursors around 7 million years ago. Humanity dodged the genital herpes bullet – almost.

Somewhere between 3 and 1.4 million years ago, HSV2 jumped the species barrier from African apes back into human ancestors – probably through an intermediate hominin species. Hominin is the zoological ‘tribe’ to which our species belongs.

Now, a team of scientists from Cambridge and Oxford Brookes universities believe they may have identified the culprit: Paranthropus boisei, a heavyset bipedal hominin with a smallish brain and dish-like face.

In a study published today in the journal Virus Evolution, they suggest that P.boisei most likely contracted HSV2 through scavenging ancestral chimp meat where savannah met forest – the infection seeping in via bites or open sores.

Hominins with HSV1 may have been initially protected from HSV2, which also occupied the mouth. That is until HSV2 “adapted to a different mucosal niche” say the scientists. A niche located in the genitals.

Close contact between P.boisei and our ancestor Homo erectus would have been fairly common around sources of water, such as Kenya’s Lake Turkana. This provided the opportunity for HSV2 to boomerang into our bloodline.

̽��ֱ��appearance of Homo erectus around 2 million years ago was accompanied by evidence of hunting and butchery. Once again, consuming “infected material” would have transmitted the virus – only this time it was P.boisei being devoured.

“Herpes infect everything from humans to coral, with each species having its own specific set of viruses,” said senior author Dr Charlotte Houldcroft, a virologist from Cambridge’s Department of Archaeology.

“For these viruses to jump species barriers they need a lucky genetic mutation combined with significant fluid exchange. In the case of early hominins, this means through consumption or intercourse – or possibly both.”

“By modelling the available data, from fossil records to viral genetics, we believe that Paranthropus boisei was the species in the right place at the right time to both contract HSV2 from ancestral chimpanzees, and transmit it to our earliest ancestors, probably Homo erectus.”

When researchers from ̽��ֱ�� of California, San Diego, published findings suggesting HSV2 had jumped between hominin species, Houldcroft became curious.

While discussing genital herpes over dinner at Kings College, Cambridge, with fellow academic Dr Krishna Kumar, an idea formed. Kumar, an engineer who uses Bayesian network modelling to predict city-scale infrastructure requirements, suggested applying his techniques to the question of ancient HSV2.

Houldcroft and her collaborator Dr Simon Underdown, a human evolution researcher from Oxford Brookes, collated data ranging from fossil finds to herpes DNA and ancient African climates. Using Kumar’s model, the team generated HSV2 transmission probabilities for the mosaic of hominin species that roamed Africa during “deep time”.

“Climate fluctuations over millennia caused forests and lakes to expand and contract,” said Underdown. “Layering climate data with fossil locations helped us determine the species most likely to come into contact with ancestral chimpanzees in the forests, as well as other hominins at water sources.”

Some promising leads turned out to be dead ends. Australopithecus afarensis had the highest probability of proximity to ancestral chimps, but geography also ruled it out of transmitting to human ancestors.

Ultimately, the researchers discovered the key player in all the scenarios with higher probabilities to be Paranthropus boisei. A genetic fit virally who was found in the right places to be the herpes intermediary, with Homo erectus – and eventually us – the unfortunate recipients.

“Once HSV2 gains entry to a species it stays, easily transferred from mother to baby, as well as through blood, saliva and sex,” said Houldcroft.

“HSV2 is ideally suited to low density populations. ̽��ֱ��genital herpes virus would have crept across Africa the way it creeps down nerve endings in our sex organs – slowly but surely.”

̽��ֱ��team believe their methodology can be used to unravel the transmission mysteries of other ancient diseases – such as human pubic lice, also introduced via an intermediate hominin from ancestral gorillas over 3 million years ago.

New research uses innovative data modelling to predict which species acted as an intermediary between our ancestors and those of chimpanzees to carry HSV2 – the genital herpes virus – across the species barrier.

Herpes infect everything from humans to coral, with each species having its own specific set of viruses

Charlotte Houldcroft

Left: a cast of a P.boisei skull used for teaching at Cambridge ̽��ֱ��. Right: a figure from the data analysis in the study.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Monkeys regulate metabolism to cope with environment and rigours of mating season

fpjl2 — Wed, 20 Apr 2016 08:28:06 +0000

New research on male Barbary macaques indicates that these primates have a flexible metabolic physiology which helps them survive by changing the speed of chemical reactions within their bodies, and consequently levels of energy, depending on temperature and availability of food.

̽��ֱ��study also suggests that the metabolic rate of male macaques spikes dramatically during mating season, potentially providing a higher "aerobic capacity" at a point when males mate with multiple females a day, as well as fight other males for mating opportunities.

Levels of thyroid hormones start to build around a month before mating season, with these metabolism-predicting hormones doubling in some animals at the peak of the season. This is only the second time that changes in metabolic physiology in the run up to mating season have been seen in a vertebrate, the first being in house sparrows.

̽��ֱ��natural habitat of Barbary macaques, in the mountains of Morocco and Algeria, is one of the most extreme environments in which any non-human primate lives.

Temperatures in winter drop as low as -5 degrees centigrade, with deep snow covering the ground for months at a time. Summer temperatures can reach 40 degrees, with food and water becoming scarce.

Researchers say that the metabolic flexibility they have observed in macaques may be an echo in one of our primate cousins of a vital physiological mechanism that has allowed humans to adapt to the planet's extreme climates – from Saharan deserts to the Arctic.

"Barbary macaques increase and decrease cellular activity and energy consumption in order to respond to challenges of climate, sustenance and reproduction. In a sense, what happens at a macro level – animal behaviour – is reflected at a micro, cellular level," said lead author Dr Jurgi Cristóbal-Azkarate of Cambridge's Division of Biological Anthropology, who conducted the research with colleagues from the universities of Roehampton and Lincoln.

"Understanding the rules and mechanisms that govern key decisions such as energy allocation in existing primates is important in gaining insight into how our ancestors were able to thrive outside tropical Africa," he said.

"Our knowledge of traits that allowed hominins to adapt to new climatic conditions is practically restricted to those that leave a traceable fossil record. We currently have a very limited understanding of the importance of physiological mechanisms in human evolution. ̽��ֱ��Barbary macaques in the Atlas Mountains are an ideal model to help address this knowledge gap."

̽��ֱ��new findings are published today in the journal Biology Letters.

By collecting faeces dropped by the animals and analysing the samples, the researchers were able to assess levels of the thyroid hormone T3, which is known to provide an indicator of the 'basal' metabolic rate: the amount of energy expended to keep a body at rest.

̽��ֱ��thyroid has been shown to affect metabolism across multiple species, including humans, in whom underactive thyroids slow metabolic rates and can cause tiredness, weight gain and depression.

Samples were taken across a nine month period from adult males in two groups – one which has nearly half their food supplied by tourists, and one which has to rely only on the natural diet of foraging for plants and insects.

On average, the monkeys fed by tourists had levels of T3 that were 10% higher, suggesting that those on the natural diet had to conserve energy as well as forage for food. T3 levels also increased the longer animals in both groups had to spend foraging for food. This is in line with other findings in vertebrates showing that they reduce secretion of thyroid hormones to reduce metabolic rates and save energy when "nutritionally stressed".

As the area's climate went through its dramatic seasonal shifts, so too did the macaque metabolism. T3 levels dropped markedly from June to August, then began to rise as mating season approached in the early Autumn. While T3 dropped again after mating season, the levels stayed much higher during the harsh winter months.

"All mammals, and even more so primates, share a common physiology," said Cristóbal-Azkarate. "As with humans, Barbary macaques increase T3 production in winter. Metabolic rates increase in response to lower temperatures as a mechanism to generate more energy and consequently more heat."

Even rain affected T3 and metabolic rates, which increased in wet weather. Researchers say this may show the "high thermoregulatory cost of wet fur".

̽��ֱ��effect of the mating season on the macaques' T3 levels, and consequently their metabolic rates, was highly significant. At the height of the season, T3 levels of the males increased by an average of 80% between both groups. ̽��ֱ��average T3 increase in the wild feeding group was 98%.

"This was an unexpected and interesting finding, suggesting that males boost their metabolism in preparation for the energetic challenges both of mating and of competing with other males for access to females," said Cristóbal-Azkarate.

"Thyroid hormones are essential for sexual development and reproductive function in mammals – there is an important increase in T3 production during puberty, for example.

"To date, studies of male reproductive competition have focused almost exclusively on testosterone and stress hormones. However, our study suggests that there is a new player in the field of male reproductive competition: the thyroid, and metabolic rate."

Added Cristóbal-Azkarate: "This is the first time in which the effects of climate, nutrition and reproductive competition on thyroid hormone physiology have been studied simultaneously, in a naturalistic setting.

"By doing this, we have been able to learn about the way in which the flexibility of the metabolic physiology of Barbary macaques allows these primates – and perhaps other species, including humans – to balance the multiple energetic demands of their harsh and highly variable environment, and cope with ecological and social challenges."

̽��ֱ��flexible physiology of Barbary macaques in responding to extreme environmental conditions of their natural habitat may help shed light on the mechanisms that allowed our ancestors to thrive outside Africa, say researchers. New study also presents the first evidence for male primates boosting their metabolic physiology for mating.

Understanding the rules and mechanisms that govern key decisions such as energy allocation in existing primates is important in gaining insight into how our ancestors were able to thrive outside tropical Africa

Jurgi Cristóbal-Azkarate

NHK photo by Michael J. Sanderson/Ateles Films

Barbary Macaques in their natural habitat of the Atlas Mountains

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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