Forager-to-farmer transition 'may have weakened our bones'

Date: Jan-16-2015 There is no biological reason why today's humans could not develop skeletons as strong

as those of our hunter-gatherer ancestors or modern orangutan cousins. An analysis of

prehistoric bones of foraging and agricultural populations shows the move toward farming reduced

the activity through life that helps build bone strength.

The hunter-gatherers' bone mass

was found to be 20% higher than that of their farming descendants.
Image credit: Timothy Ryan.

These were the findings of a new study published in the Proceedings of the National

Academy of Sciences by Timothy Ryan, associate professor of Anthropology at the

Pennsylvania State University, and Dr. Colin Shaw from the Phenotypic Adaptability, Variation

and Evolution Research Group at the University of Cambridge in the UK.

The study shows that while our hunter-gatherer ancestors who lived around 7,000 years ago had

skeletons as strong as today's orangutans, farmers living in the same area some 6,000 years

later had much lighter and weaker bones that would have been more vulnerable to fracture.

The researchers found that the foragers' bone mass was around 20% higher than that of their farming

descendants.

This difference is about the same as the bone loss seen in astronauts after 3

months of living in space in zero gravity.

For their study, the researchers examined X-rays of femurs from individuals who lived in four

distinct archaeological populations - including sedentary farmers and mobile foragers - in the

same area of the US state of Illinois. They also examined samples from other primate

species.

The part of the femur they focused on was the inside of the ball where it fits into the

pelvis to form the hip joint. This is one of the most load-bearing joints in the body.

After ruling out other factors that could have an effect on reducing bone density - such as

changes in body size and differences in diet - the researchers conclude that the main reason

behind the decrease in bone density between our foraging ancestors and our more recent farming

forefathers is reduction in physical activity.

They believe their findings support the idea that it is exercise rather than diet that

protects us from conditions like osteoporosis that make us vulnerable to fractures.

Commenting on what this means for us today, Dr. Shaw says modern humans live in a cultural

and technological world that is incompatible with our evolutionary heritage:

"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."

"Sitting in a car or in front of a desk is not what we have evolved to do," he adds.

Trabecular bone in hunter-gatherers was much denser

Our bones are made from two types of tissue: a hard outer shell known as "cortical" tissue,

and a spongy inside known as "trabecular" tissue. Trabecular bone has a honeycomb-like structure

that allows the bone to flex but also makes it vulnerable to fracture.

The researchers found that the trabecular structures of the samples they examined were very

similar, except in one respect - within the honeycomb structure, the hunter-gatherer samples

showed a much higher amount of bone relative to air.

Dr. Shaw says compared to other types of bone, trabecular bone has much greater plasticity.

It can change shape and direction depending on the load it bears. It can change structure from

pin-like to almost plate-like.

"In the hunter-gatherer bones, everything was thickened," he notes.

Dr. Shaw suggests the constant loading in the bone that occurs as a result of fierce exertion

over the lifespan of hunter-gatherers would lead to an accumulation of minor damage to the

trabecular bone.

He says the minor damage causes the bone to grow back stronger and thicker each time,

building to a peak strength that compensates for the deterioration that comes with age.

Dr. Shaw believes if you build your bone strength in early life, you could avoid hip

fractures later on - because then your bone strength would never dip to the level where

fractures can easily occur.

The researchers now plan to investigate how different types of load and mobility affect our

bodies and bones. They are going to compare archeological records with new measures taken from

today's ultra-marathon runners who cover punishing distances over varied terrains. The idea is

to discover what kind of mobility helped our ancestors develop such powerful bodies.

Meanwhile, Medical News Today recently learned that researchers from the Japanese

Aerospace Exploration Agency are using the International Space Station to investigate roundworms in outer space to help develop new treatments for

bone and muscle loss in humans living in space.

Written by Catharine Paddock PhD

Not to be reproduced without permission.

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Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.