Human History: Early Humans Had Stronger Bones Which Got Weaker As Farming Progressed
Before they discovered farming, our ancestors were like Usain Bolt. Their bones were well adapted to the strain of running and long-distance walking, just like those of a modern-day sportsman's would be. But new research has established that after the advent of farming, their bones became progressively weaker, according to a press release Monday.
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Alison Macintosh, a PhD candidate in Cambridge University's Department of Archaeology and Anthropology, came to this conclusion after investigating the bones of people living in the fertile soils of the Danube river valley, in Central Europe and comparing them to the bone density of present day Cambridge University students.
Human bones are very flexible and can respond quickly to change. When consistent force is applied to the bones through physical activity, tiny electrical currents are stimulated within the bone, which results in production of more bone tissue thus causing the bones to become denser and stronger. Hence athletes have stronger bones compared to non-athletes. Analysis of the bones of present day athletes show their remarkable adaptability to loading and intensity and direction of strains.
The bone size, shape, and markings left by muscles tell us a great deal about how early humans lived. And Macintosh found that the bones of humans who occupied the Danube valley from around 5300 BC became less strong over time, pointing to decline in mobility and lower limb loading in male agriculturalists, progressively and consistently through time.
Macintosh will present her study in the American Association of Physical Anthropologists in Calgary, Alberta on 8-12 April, 2014, where she will show that the bone strength decline occurred more in males than females, significantly due to culture change in Central Europe.
Macintosh used the data provided by biological anthropologist Dr. Colin Shaw, where he studied bone rigidity in modern Cambridge University students. A chronological analyses by Macintosh revealed that bone rigidity among the earliest farmers (around 7,300 years ago) was on average similar to today's students who lead active lives. But after just 3,000 years, average mobility had dropped to the level of those students rated as sedentary, after which the decline slowed.
Archaeologists have also found evidence that the start of the Iron Age coincided with intensification and diversion of different agricultural practices that resulted in extension of trade and exchange networks. "These developments are likely to have brought about changes in divisions of labour by sex and socioeconomic organisation as men and women began to specialise in certain tasks and activities - such as metalworking, pottery, crop production, tending and rearing livestock," said Macintosh.
Macintosh gathered evidence of bone structure across time by visiting cemeteries across Central Europe and conducting laser-scans of skeletons in Germany, Hungary, Austria, the Czech Republic, and Serbia. She applied cross-sectional geometric (CSG) properties on the lower limb bones of the skeletons to find out the effect of loading during a life-span. She measured skeletons as old as 5300 BC to 850 AD - a time span of 6,150 years.
Using a portable desktop 3D laser surface scanner to scan femora and tibiae, she found that male tibiae became less rigid and that bones in both males and females became less strengthened to loads in one direction more than another, such as front-to-back in walking. These findings indicate that these skeletons belong to generations who gradually became less active, probably walked lesser or carried out less demanding physical activities than the generations before them.
"Both sexes exhibited a decline in anteroposterior, or front-to-back, strengthening of the femur and tibia through time, while the ability of male tibiae to resist bending, twisting, and compression declined as well," said Macintosh. Although, analysis of bones of females, also showed some reduction in mobility, these were not consistent, giving rise to the theory that women during these times may have been involved in several other physical activities that needed less lower limb loading. There is evidence from two of the earliest cemeteries studied that females were using their teeth in processing activities to carry out tasks unlikely to have loaded their lower limbs much.
Comparisons between early human farming practices, gathered from archaeological evidence of Central European skeletons dating from around 7,300-1,150 years ago and present day farming populations in the rest of the world, throw up some interesting theories.
A study by Panter-Brick in 1996 found that the amount of work done by present day male and female farmers is more variable than foraging groups. And just like in early Central European farming communities, higher physical activity is recorded among males than females in Indian and Nepalese farming communities, but females have a higher relative workload than males in farming communities in the Upper Volta and the Gambia.
"This variability in the sexual division of labour in living agro-pastoralist groups shows the importance of context, ecology, and various cultural factors on sex differences in physical activity. So it is important when studying long-term trends in behavioural change between the sexes that the geographic region is kept small, to help control for some of this variability," said Macintosh.
Female skeletons showed a major change in femoral bending and torsional rigidity from the
Bronze Age into the Iron Age - between about 1450 BC and 850 BC in the samples studied-when women had the strongest femora of all the females examined in the study. This could be because the Iron Age sample included skeletons of Hungarian Scythians. Their chief occupation was animal husbandry and both male and females participated in horsemanship, and archery.
Macintosh concludes, "In Central Europe, adaptations in human leg bones spanning this time frame show that it was initially men who were performing the majority of high-mobility tasks, probably associated with tending crops and livestock. But with task specialisation, as more and more people began doing a wider variety of crafts and behaviours, fewer people needed to be highly mobile, and with technological innovation, physically strenuous tasks were likely made easier. The overall result is a reduction in mobility of the population as a whole, accompanied by a reduction in the strength of the lower limb bones."
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