Bone Functional Adaptation

What is bone functional adaptation?

Bones are living tissues that can dynamically adapt to their environment. Trabecular bone -the spongy bone found inside joints- can change the thickness and orientation of its struts to be better able to cope with the mechanical stresses placed upon them during day to day activities. This principle can be used to reconstruct the behaviours of extinct organisms.

My work investigates this relationship between form and function in living humans and other primates and applies findings to reconstruct behaviour in our fossil hominin relatives.

Variation in living people to understand variation in the past

If we want to use bone to reconstruct behaviour in the past, we have to have a good understanding of how bone adapts to different activities. In this paper we compare bone structure in athletes and compare this to a control group. Different sports were chosen to illustrate different types of loading conditions:

Distance runners: impacts in a single direction
Cricket and Hockey: impacts in multiple directions
Swimming: no impact but high muscle work

Saers et al. (2021) American Journal of Biological Anthropology

This image shows cross sections through the ankle joint of a cricket player and an age matched control. Unsurprisingly, the Cricket player has much denser bone than the control. However, the 3D plot shows that when we combine several mechanical properties of the lower leg bone (tibia), individuals who practice different sports tend to form distinct clusters. These results will help us to reconstruct the types of activities that were performed by people in the past.

Reconstructing mobility

Since bone dynamically adapts its structure to suit its mechanical needs, indviduals who lead more active lives tend to have stronger bones. This is illustrated on the right with little spheres of bone taken from the foot of an agriculturalist and a forager. Foragers tend to walk greater distances per day than agriculturalists. As a result, the trabeculae of foragers are thicker and more closely packed together, resulting in a denser trabecular structure overall.

Saers et al. (2016) Journal of Human Evolution

Saers et al. (2019) American Journal of Biological Anthropology

Recent gracilisation of the human skeleton

The human skeleton has, on average, become much weaker during the last few thousand years. The underlying cause is not fully understood and explanations range from reduction in physical activity, changes to fertility, diet, pathogen stress, self-domestication, and more.

To figure out which of these underlying factors (or interactions between them) are responsible, we set out to collect a large micro-CT scanned dataset of human skeletal variation through time and space, using both archaeological collections and living people including athletes.

The analyses are still a work in progress so stay tuned, below is a sneak peak at some results.

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