Smaller, weaker, and less stiff bones evolve from changes in subsistence strategy

Abstract

Summary

We propose a computational model with which to examine the evolution of bone. Our results indicate that changes in subsistence strategy have influenced the evolution of bone growth and mechanoregulation, and predict that bone size, stiffness, and structural strength may decrease in future generations, bringing increased risk of fracture and prevalence of osteoporosis.

Introduction

Archeological data suggest that bone size and strength have decreased over evolution. We hypothesize that changing evolutionary pressures and levels of physical activity, both arising from changes in subsistence strategy, have affected the evolution of bone. We propose a computational model with which to examine the evolution of bone growth and mechanoregulation due to the transitions from hunter–gatherer to agricultural to modern lifestyles.

Methods

The evolution of genes governing growth and mechanoregulation in a population of bones is simulated, where each individual is represented by a 2-D bone cross-section. Genetic variability is assumed to modulate growth through mechanoregulatory factors that direct periosteal expansion, endosteal expansion/infilling, and ash content accretion in response to strains incurred during walking.

Results

The model predicts decreases in cortical area and section modulus (a measure of structural strength) and increases in maximum compressive strain over the course of the simulation, meaning evolution of smaller, less strong, and less stiff bones is predicted for the population average. The model predicts small but continued decreases in size, strength, and stiffness in modern populations, despite the absence of a strong evolutionary advantage to efficient bones during this phase.

Conclusion

In conclusion, our results show that changing loading regimes and evolutionary pressures may have influenced the evolution of bone growth and mechanoregulation, and predict that bone size and strength may continue to decrease in future generations, bringing increased risk of fracture and prevalence of osteoporosis.

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Acknowledgements

The authors would like to thank Professors Patrick Prendergast and Roberto Fajardo for their advice on this study.

Conflicts of interest

None.

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Correspondence to N. C. Nowlan.

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Funding Sources

NCN has received funding from the Fulbright Program and the Irish Research Council for Science, Engineering and Technology. This work was partially supported by the NIH (AR44927, AR56639).

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Nowlan, N.C., Jepsen, K.J. & Morgan, E.F. Smaller, weaker, and less stiff bones evolve from changes in subsistence strategy. Osteoporos Int 22, 1967–1980 (2011). https://doi.org/10.1007/s00198-010-1390-3

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Keywords

  • Bone adaptation
  • Bone fragility
  • Evolution simulation
  • Hunter–gatherer
  • Physical activity