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Farming may have brought with it a host of benefits on diet and the economy, but it also caused us to become weak and puny. 

Research, covering a period of more than 7,000 years of human evolution, has revealed modern-day skeletons are lighter and more fragile than those belonging to our hunter-gatherer ancestors.

In fact, the bones of our early ancestors were comparable in strength to modern orangutans, but once farming spread, these bones became 20 per cent weaker.

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Research from the University of Cambridge, covering a period of more than 7,000 years of human evolution, has revealed modern-day skeletons (pictured bottom) are lighter and more fragile than those belonging to our hunter-gatherer ancestors (pictured top). They studied hip joints on ancient femurs

Researchers from the University of Cambridge used X-rays and CT scans to study ancient samples of human femur bones, along with femora from other primate species. 

In particular, they focused on the inside of the femoral head - the ball at the top of the femur which fits into the pelvis to form the hip joint.

This joint is one of the most load-bearing bone connections in the body.

There are two types of tissue that form bone. The cortical or 'hard' bone shell on the outside, and the trabecular or 'spongy' bone on the inside.

This trabecular bone is a honeycomb-like mesh inside the cortical shell that allows flexibility, but is also vulnerable to fracture.

The bones studied covered four distinct archaeological human populations representing mobile hunter-gatherers from 7,300 years ago, and more recent, sedentary agriculturalists. 

All were found in the same area of Illinois, and were therefore likely to be genetically similar. 

The trabecular structure was found to be very similar in all populations, but the hunter-gatherers had a much higher amount of actual bone relative to air.

'Trabecular bone has much greater plasticity than other bone, changing shape and direction depending on the loads imposed on it; it can change structure from being pin or rod-like to much thicker, almost plate-like. In the hunter-gatherer bones, everything was thickened,' said lead researcher Dr Colin Shaw.

This thickening is the result of constant loading on the bone from physical activity as hunter-gatherers roamed the landscape, seeking food.

This exertion would result in minor damage that caused the bone mesh to grow back stronger and thicker throughout life - building to a 'peak point' of bone strength, which counter-balanced the deterioration of bones with age.

Bone mass was around 20 per cent higher in the foragers - the equivalent to what an average person would lose after three months of weightlessness in space.

And after ruling out diet differences and changes in body size as possible causes, researchers concluded a drop in physical activity are the root cause of degradation in human bone strength across millennia.

They believe the findings support the idea that exercise, rather than diet, is the key to preventing heightened fracture risk and conditions, such as osteoporosis, in later life. 

CT scan shows how out bones have become more fragile

The bones studied covered four distinct archaeological human populations. The trabecular, mesh-like structure was found to be similar in all populations, but hunter-gatherers (left) from 7,000 years ago had a much higher amount of actual bone relative to air than agriculturalists (right) just 1,000 years later

Bone mass was found to be around 20 per cent higher in the foragers - the equivalent to what an average person would lose after three months of weightlessness in space.  Pictured is an early Neolithic (approximately 4000 - 5000 BC) 35 to 40-year-old male used to illustrate ancient skeletons

For example, more exercise in early life results in a higher peak of bone strength around the age of 30, meaning the inevitable weakening of bones with age is less detrimental. 

'Contemporary humans live in a cultural and technological milieu incompatible with our evolutionary adaptations. 

'There's seven million years of hominid evolution geared towards action and physical activity for survival, but it's only in the last say 50 to 100 years that we've been so sedentary - dangerously so,' said Dr Shaw from the university's Phenotypic Adaptability, Variation and Evolution (PAVE) Research Group.

'Sitting in a car or in front of a desk is not what we have evolved to do.' 

The bones of primates (orangutan pictured) were also studied to compare density and strength

Other theories for humans evolving a lighter, more fragile skeleton include changes in diet or selection for a more efficient, lighter skeleton, which was never reversed.

While the initial switch to farming did cause a dip in human health due to monoculture diets that lacked variety, the populations tested were unaffected by this.

'Of course we need a level of calcium to maintain bone heath, but beyond that level excess calcium isn't necessary,' added Dr Shaw.

The research also counters the theory that, at some point in human evolution, our bones just became lighter - perhaps because there wasn't enough food to support a denser skeleton. 

'If that was true, human skeletons would be entirely distinct from other living primates. We've shown that hunter-gatherers fall right in line with primates of a similar body size. 

'Modern human skeletons are not systemically fragile; we are not constrained by our anatomy,' Dr Shaw said.

'The fact is, we're human, we can be as strong as an orangutan - we're just not, because we are not challenging our bones with enough loading, predisposing us to have weaker bones so that, as we age, situations arise where bones are breaking when, previously, they would not have,'

While the 7,000-year-old foragers had vastly stronger bones than the 700-year-old farmers, Dr Shaw says that neither competes with even earlier hominids from around 150,000 years ago. 

'Something is going on in the distant past to create bone strength that outguns anything in the last 10,000 years.'

The next step for Dr Shaw's research team will be to look at how different types of loading and mobility shape bodies and bones by cross-referencing archaeological records with testing on modern ultra-marathon runners, who cover punishing distances over a range of terrains - from the Himalayas to the Namibian desert. 

The findings are published in the journal PNAS.  

The next step for Dr Shaw's research team will be to look at how different types of loading and mobility shape bodies and bones by cross-referencing archaeological records with testing on modern ultra-marathon runners, and athletes (Mo Farah pictured left). An ancient farmer is illustrated right

In a recent talk, the university also said it had compared ancient bones to that of its students, and found the leg bones of males living in 5,300 BC were just as good as those of highly-trained cross-country runners. Experts claim people today are 10 per cent smaller and shorter than their hunter-gatherer ancestors, too

He hopes this future work will provide insight into the kind of mobility that gave our ancient ancestors such powerful physical strength.

In a recent talk, Dr Shaw also said he had compared the ancient bones to that of Cambridge University students, and found the leg bones of males living in 5,300 BC were just as good as those of highly-trained cross-country runners.

But just 3,000 years later, the ancestors had leg bone structures closer to that of the Netflix-watching generation.

When our ancestors made the transition from hunter-gatherer societies to agricultural ones, their lower limb strength and overall mobility decreased.