Jawbones are ‘shaped by diet’, a study finds

Diet has shaped human jaw bones; a result that could help explain why many people suffer with overcrowded teeth.

The study has shown that jaws grew shorter and broader as humans took on a more pastoral lifestyle.

Before this, developing mandibles were probably strengthened to give hunter-gatherers greater bite force.

The results were published in the Proceedings of the National Academy of Sciences.

“This is a fascinating study which challenges the common perception that there has been little recent change in the morphology of humans,” said anthropologist Jay Stock from the University of Cambridge.

Many scientists have suggested that the range of skull shapes that exist within our species is the result of exposure to different climates, while others have argued that chance played more of a role in creating the diversity we see in people’s profiles.

The new data, collected from over 300 skulls, across 11 populations, shows that jaws shortened and widened as humans moved from hunting and gathering to a more sedentary way of life.

The link between jaw morphology and diet held true irrespective of where people came from in the world, explained anthropologist Noreen von Cramon-Taubadel from the University of Kent.

Concurrently crooked

It would be tempting to conclude that this is evidence for concurrent evolutionary change – where jaw bones have evolve to be shorter and broader multiple, independent times, she told BBC News.

But the sole author of the paper suggested that the changes in human skulls are more likely driven by the decreasing bite forces required to chew the processed foods eaten once humans switch to growing different types of cereals, milking and herding animals about 10,000 years ago.

“As you are growing up… the amount that you are chewing, and the pressure that your chewing muscles and bone [are] under, will affect the way that the lower jaw is growing,” explained Dr von Cramon-Taubadel.

She thinks that the shorter jaws of farmers meant that they have less space for their teeth relative to hunter-gatherers, whose jaws are longer.

Teeth-pulling tale

“I have had four of my pre-molars pulled and that is the only reason that my teeth fit in my mouth,” said Dr von Cramon-Taubadel.

Ever since that time, she has wondered why so many people suffer with teeth-crowding.

“I think that’s the reason why this result resonates with people,” she said.

Dr Stock added: “[The finding] is particularly important in that it demonstrates that variation that we find in the modern human skeletal system is not solely driven by population history and genetics.”

These results fit with previous evidence of both a reduction in tooth and body size as humans moved to a more pastoral way of life.

It also helps explain why studies of captive primates have shown that animals tend to have more problems with teeth misalignment than wild individuals.

Further evidence comes from experimental studies that show that hyraxes – rotund, short-tailed rabbit-like creatures – have smaller jaws when fed on soft food compared to those fed on their normal diet.

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Primates leapt to social living

Scientists may be a step closer to understanding the origins of human social behaviour.

An analysis of over 200 primate species by a University of Oxford team suggests that our ancestors gave up their solitary existence when they shifted from being nocturnal creatures to those that are active during the day.

It is likely communal living was adopted to protect against day time predators, the researchers say.

The results are published in Nature.

From work on social insects and birds, some biologists have suggested that social groups begin to form when young do not leave their natal ground, but instead hang around and help raise their siblings.

Now, the latest evidence from primates suggests that this might not have been the case for our ancestors.

Leaping to sociality

By looking at whether closely related species share similar social structures, the Oxford team of evolutionary biologists shows that a common history is important in shaping the way animals behave in a group.

The team pinpointed the shift from non-social to social living to about 52 million years ago; a switch that appears to have happened in one step, and coincided with a move into daylight.

It did coincide with a change in family dynamics or female bonding, which emerged much later at about 16 million years ago.

“If you are a small animal active at night then your best strategy to avoid predation is to be difficult to detect,” explained Oxford’s Suzanne Shultz, who led the study.

“Once you switch to being active during the day, that strategy isn’t very effective, so an alternative strategy to reduce the risk of being eaten is to live in social groups,” she told BBC News.

Dr Shultz thinks that the move to day-time living in ancient primates allowed animals to find food more quickly, communicate better, and travel faster through the forest.

The link between sociality and a switch to daytime living might have been missed until now, she suspects, because biologists interested in this question have tended to work with Old World monkeys, like baboons, which are characterised by female bonded groups, which are not characteristic of many primate species.

Flexibly social

Human societies likely descended from similar large, loosely aggregated creatures, Dr Shultz explained, but the key difference, she pointed out, is that our closest cousins’ societies do not vary within a species, while humans’ do.

“In human societies we have polygyny… we have monogamy, and in some places we have females leaving the group they were born in, and in others males leave,” she said.

Why this difference exist is still unclear.

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Ancient horses’ spotted history reflected in cave art

Scientists have found evidence that leopard-spotted horses roamed Europe 25,000 years ago alongside humans.

Until now, studies had only recovered the DNA of black and brown coloured coats from fossil specimens.

New genetic evidence suggests “dappled” horses depicted in European cave art were inspired by real life, and are less symbolic than previously thought.

The findings are published in the Proceedings of the National Academy of Sciences.

Horses, which were the most abundant large mammal roaming Eurasia 25,000 years ago, were a key component of early European diets.

So it is not surprising that the cave art of this time had a certain equestrian flair – horses make up 30% of the animals depicted in European cave paintings from this era.

Biologists, interested in the diversity of European animals before the last Ice Age, are interested in how accurately these early artistic impressions portrayed the colouring of the horses that lived alongside the ancient humans.

“It was critical to ensure that the horse depictions from the cave paintings were based on real-life experiences rather than products of the imagination,” explained lead author Arne Ludwig from The Leibniz Institute for Zoo and Wildlife Research in Berlin.

In previous work, Dr Ludwig, and his colleagues, recovered only the DNA of black and brown coat colours from the prehistoric horse bones.

But the dappled coats of the 25,000 year horses depicted at the Pech Merle cave complex in France convinced the team to take a second look.

Fur coats

By revisiting the fossil DNA of 31 horse specimens collected from across Europe, from Siberia to the Iberian Peninsula, the researchers found that six of the animals carried a mutation that causes modern horses to have white and black spots.

Of the remaining 25 specimens, 18 were brown coloured and six were black.

Dr Ludwig explained that all three of the horse colours – black, brown and spotted – depicted in the cave paintings have now been found to exist as real coat-colours in the ancient horse populations.

The researchers say that these three colours probably provided enough variation for humans to create the diversity of coat colours and patterns seen in modern horses.

The domestication of horses, which produced modern breeds, is thought to have begun about 4,600 years ago in the steppe between modern Ukraine and Kazakhstan.

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Pioneers boast high fertility, say scientists

Scientists have shown that women who were first to settle in a new land had more children and grandchildren than those who followed.

Researchers analysed the family trees of French settlers who colonised Canada in the 17th and 18th centuries.

Their results could help to explain why some rare genetics diseases are common in communities established by migrations.

The findings have been published in the journal Science.

The team of researchers from Canada and Europe relied on data collected by the parish councils of Charlevoix and Saguenay Lac Saint-Jean, a region 170km north of Quebec, Canada.

The towns not only boast dairy farms, charming villages and sandy beaches but some of the best ever-kept marriage records – comprising more than a million people.

By building a picture of marriages and how many children the pairings produced, the researchers showed that woman who arrived as part of the first wave of immigration had 15% more children than those who arrived a generation later.

The pioneering woman married younger and benefited from scooping up the best local resources, they added.

But the study also found that the pioneering women’s children also had more children.

Lead author Laurent Excoffier, from the University of Bern in Switzerland, explained that the children of women at the front of the wave inherited their mother’s higher rate of fertility.

Yet, the researchers added, there was no such correlation between generations that arrived 30 years later behind the first wave.

Dr Excoffier drew parallels with cane toads. Scientists have observed that the toads at the edge of their range have bigger front legs and stronger back legs; all the better to invade new areas.

And when toads at the frontiers breed, their offspring inherit these longer, stronger limbs.

Such an effect is not unexpected, but until now no one has seen this phenomenon in humans.

“This was a rare chance to study a relatively recent human migration,” said co-author Damian Labuda, a geneticist from the University of Montreal, Canada.

Population geneticist Montgomery Slatkin from University of California, who was not involved in the work, called the study one of the “most interesting, detailed studies” he had seen.

“I think what happened [here] could easily have happened in other populations,” he added.

The findings suggest that families at the front of the wave of migration contributed more to the contemporary gene pool than those that were slower to arrive, explained Dr Labuda.

This could help explain why some rare genetic diseases are more common than expected in the Charlevoix and Saguenay Lac Saint-Jean regions.

That is because any disease causing mutations carried by people by the frontiers would be pass onto their descendents, who make up a large proportion of subsequent generations in the population.

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Icelandic rocks could have steered Vikings

Vikings used rocks from Iceland to navigate the high seas, suggests a new study.

In Norse legends, sunstones are said to have guided seafarers to North America.

Now an international team of scientists report in the journal the Proceedings of the Royal Society Athat the Icelandic spars behave like mythical sunstones and polarise light.

By holding the stones aloft, voyaging Vikings could have used them to find the sun in the sky.

The Vikings were skilled navigators and travelled thousand of kilometres between Northern Europe and North America.

But without a magnetic compass, which was not invented until the 13th Century, they must have relied on other navigational aids.

Without the stars, which would have been out of sight during the constant daylight of the summer months, the sun would have been their best bet to set their course by.

But on cloudy or foggy days the seafarers would have been left with only the direction of the wind and swell to guide their way.

Through the fog

Norse legends tell of seafarers lifting stones to the sky to spy the direction of the sun when it was hidden by cloud cover.

Earlier this year, a study in the Philosophical Transactions of the Royal Society B reviewed the evidence that naturally forming crystals can selectively block light of one polarisation – how waves of light can be restricted to certain directions of oscillation.

The new result shows that Icelandic spars, which are formed from crystallised calcium carbonate, are good polarisers and could have been the raw material of the mythical sunstones.

The spars can be easily cleaved and crafted into a rhombus shape required for the polarising effect, and the discovery of one on the wreck of an Elizabethan ship that sunk in 1592 “looks very promising” the authors report.

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Mothers of twins ‘have heavier single babies’

Single babies born to mothers of twins tend to be heavier, report scientists.

The report in the journal Biology Letters is based on a 40-year data set collected in The Gambia.

Mothers with twins were found to give birth to heavier babies, but the study found a similar trend even among single babies born before twins.

Twin pregnancies are risky for both mothers and offspring, and the study suggests heavier, healthier single children may offset those risks.

Worldwide only 13 in 1,000 babies are born a twin, although this rate is higher in developing countries.

Researchers interested in probing the twinning question further have had to rely on the few long-term data sets collected in parts of the world where birth rates are higher, and there are therefore more twinning events.

Evolutionary biologist Ian Rickard from the University of Sheffield in the UK, saw an opportunity to do just this when he learned of a long-term data set from The Gambia, which included not only birth weights of about 1,900 babies born to around 700 mothers, but also the number of twins.

Analysing all 40 years, Dr Rickard explained that he and his Gambian and London-based colleagues saw that women who produced twins gave birth to heavier non-twin babies.

Harvesting data

The exact differences, however, depended on when those single babies were born.

The Gambia experiences regular variations in food supply, from a “harvest season” between January and June, and a “hungry season” for the rest of the year.

Single babies born during the harvest season before twins were on average 226g heavier than those from non-twinned families; those born after the twins were 134g heavier.

However, single children born into twinned families in the hungry season showed no discernible difference in average weight from those of non-twinned families.

“We’ve known for quite a while that… if a [foetus] is exposed to a period of the year between about July and October during their third trimester, they tend to have lower birth weight,” said Dr Rickard.

The assumption is that the stress of food scarcity swamps the heavier-baby effect found in the harvest season.

Producing twins, Dr Rickard suggested, could be just a by-product of natural selection acting on birth weight.

However, he stressed the “importance of replicating this [finding] in another population to see if this pattern holds up”.

He suspects that a hormone called IGF, which has long been linked to birth weight in humans, could be responsible for this pattern.

IGF is known to influence the growth rate of foetuses, and is implicated in the “polyovulation” that leads to multiple births.

In cattle, IGF levels tend to be 1.5 times higher in the cows who give birth to twins, and in mice high levels of the hormone are linked to larger litters.

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Age-related brain shrinking is unique to humans

The brains of our closest relatives, unlike our own, do not shrink with age.

The findings suggest that humans are more vulnerable than chimpanzees to age-related diseases because we live relatively longer.

Our longer lifespan is probably an adaptation to having bigger brains, the team suggests in their Proceedings of the National Academy of Sciences paper.

Old age, the results indicate, has evolved to help meet the demands of raising smarter babies.

As we age, our brains get lighter. By 80, the average human brain has lost 15% of its original weight.

People suffering with age-related dementias, such as Alzheimer’s, experience even more shrinkage.

This weight loss is associated with a decline in the delicate finger-like structures of neurons, and in the connections between them.

Alongside this slow decline in its fabric, the brain’s ability to process thoughts and memories and signal to the rest of the body seems to diminish.

Researchers know that certain areas of the brain seem to fare worse; the cerebral cortex, which is involved in higher order thinking, experiences more shrinkage than the cerebellum, which is in charge of motor control.

Yet despite the universality of ageing, scientists do not fully understand why our brains experience this continuous loss of grey matter with age.

Intriguingly, the brains of monkeys do not seem to undergo the same weight loss, raising the question of whether it is a distinctively human condition.

Now, a team of neuroscientists, anthropologists, and primatologists have pooled their expertise and datasets to reveal the answer.

Comparing magnetic resonance images from more than 80 healthy humans between the ages of 22 and 88 with those of a similar number of captive-bred chimps, the researchers found that chimps’ brains do not shrink with age.

The results suggest that the estimated 5-8 million years of evolutionary history that separate chimps from humans have made all the difference in the way that the species age.

It takes a village…

Anthropologist Chet Sherwood from George Washington University in Washington DC, who led the study, thinks that humans live longer to “pay for” their larger-brained children.

Humans live relatively long compared to other great apes. The majority of this extended life is post-menopausal, while chimps are reproductively viable right up to their death.

A human brain is three times the size of chimpanzee’s.

And it is not such a stretch, Dr Sherwood suggests, to conclude that grandparents’ extended lives are in an evolutionary sense there to relieve mothers from being solely responsible for raising their big-brained, energetically costly infants.

“I say this right now, as my seven year old daughter is being looked after by my mother,” he told BBC News.

“Because neurons cannot regenerate, aging, he thinks, is just the stress of living long enough to lend a helping hand to some relatives.”

“[The study] provides very good evidence that the patterns of brain ageing in humans are quite different from other animals,” commented neuroscientist Tom Preuss from Emory University in Atlanta, US, who was not involved in the research.

However, Dr Preuss was clear that these differences do not make other animals useless as models for studying age-related diseases.

Instead, the differences could help to explain why humans suffer more from these diseases than other animals seem to.

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Early human fossils unearthed in Ukraine

Ancient remains uncovered in Ukraine represent some of the oldest evidence of modern people in Europe, experts have claimed.

Archaeologists found human bones and teeth, tools, ivory ornaments and animal remains at the Buran-Kaya cave site.

The 32,000-year-old fossils bear cut marks suggesting they were defleshed as part of a post-mortem ritual.

Details have been published in the journal PLoS One.

Archaeologist Dr Alexander Yanevich from the National Ukrainian Academy of Science in Kiev discovered the four Buran-Kaya caves in the Crimean mountains in 1991.

Since then, roughly two hundred human bone fragments have been unearthed at the site.

Among the shards of human bones and teeth, archaeologists have found ornaments fashioned from ivory, along with the abundant remains of animals.

The artefacts made by humans at the site allowed archaeologists to tie the ancient people to a cultural tradition known as the Gravettian.

This culture came to span the entire European continent and is named after the site of La Gravette in France, where this stone age culture was first studied.

Researchers were able to directly date the human fossils using radiocarbon techniques. The shape and form of the remains told the scientists they were dealing with modern humans (Homo sapiens sapiens).

Eastern promise

One thing that intrigued researchers was the scarcity of human long bones (bones from the limbs) in the caves.

The site yielded countless limb bones from antelope, foxes and hares.

But the human remains consisted of vertebrae, teeth and skull bones no larger than 12cm.

What is more, the positions of cut marks found on the human fragments were distinct from those found on the animal bones.

And while the bone marrow had been removed from butchered animals, it had been left alone in the case of the human remains at the site, explained co-author Sandrine Prat from the French National Centre for Scientific Research (CNRS) in Paris.

She suspects this demonstrates that human bones were processed differently from those of animals. Human flesh was removed as part of ritual “cleaning”, not to be eaten.

Defining culture

The finds offer anthropologists a glimpse into a very early and important human culture, said Professor Clive Finlayson, an evolutionary ecologist and director of the Gibraltar Museum.

“Gravettian culture is the culture that defines modern humans.

“These people had knives, lightweight tools, open air camps, they used mammoth bones to make tents,” he said, adding that this was the earliest example of the Gravettian cultural tradition.

Professor Finlayson said that uncovering evidence of this culture in Ukraine gave weight to the idea that early modern people spread into Europe from the Russian plains, not north through the Balkans from the Middle East.

“What has excited me is that we have found evidence of humans where I would expect them to be, exploiting foods that I would expect them to be exploiting,” Professor Finlayson told BBC News.

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Do Chimps Play With Dolls?

In the tropical rainforest of Uganda’s Kibale National Park, a young female chimpanzee seems to have adopted a stick. She’s holding it close to her abdomen and carrying it with her everywhere she goes. In a new study, the first to document this behavior in the wild, researchers argue that stick cradling may be akin to human children playing with dolls. And because the team observed it far more frequently in female chimps, the findings suggest that certain gender-specific behaviors are hard-wired.

Making the observations was no easy task. Harvard University primatologist Richard Wrangham and colleagues spent 12 hours a day—much of it crouched behind vegetation—tracking a group of 68 chimps through thick rainforest. During the study period, they observed about 300 instances of chimps picking up sticks. In 40% of cases, the chimps cradled the sticks in the crook of their arm or tucked between their abdomen and thigh (see picture), whereas the rest of the time they used sticks to probe trees and fight each other. More than three-quarters of the stick cradlers were female, the team reports online today in Current Biology. Females were also 10 times more likely to use the sticks as tools than males were—the first time such a large disparity has been reported.

Wrangham says stick cradling reminded him of doll play in girls. And because chimp mothers don’t play with sticks, young female chimps probably aren’t learning the behavior from watching their moms. Instead, it may be hard-wired. Given the close evolutionary relationship between chimps and humans, the implication is that doll playing and other gender-specific behaviors seen in young human children may be hard-wired as well, he says.

Rebecca Jordan-Young isn’t willing to go that far. A sociomedical scientist who studies sex, gender, and sexuality at Barnard College in New York City, Jordan-Young says she doesn’t think anyone should draw sweeping interpretations about innate differences between the sexes from this study. She says that the researchers cannot rule out that females carry sticks because they are mimicking the behavior of other adolescent females. It could also just be a cultural fad.

In addition, Jordan-Young questions the emphasis the authors placed on the doll-carrying observations. Just as intriguing, she says, is the fact that female chimps use tools much more often than males do. But those types of findings, she says, don’t grab headlines.

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