Smaller, weaker, and less stiff bones evolve from changes in subsistence strategy
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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.
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.
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.
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.
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.
KeywordsBone adaptation Bone fragility Evolution simulation Hunter–gatherer Physical activity
The authors would like to thank Professors Patrick Prendergast and Roberto Fajardo for their advice on this study.
Conflicts of interest
- 3.Martin RB (2003) Functional adaptation and fragility of the skeleton. In: Agarwal SC, Stout SD (eds) Bone loss and osteoporosis: an anthropological perspective. Springer, New YorkGoogle Scholar
- 5.Giladi M, Milgrom C, Simkin A, Stein M, Kashtan H, Margulies J, Rand N, Chisin R, Steinberg R, Aharonson Z, Kedem R, Frankel V (1987) Stress fractures and tibial bone width. A risk factor. J Bone Jt Surg 69-B:326–329Google Scholar
- 9.Ruff CB (2006) Gracilization of the modern human skeleton—The latent strength in our slender bones teaches lessons about human lives, current and past. Am Sci 94:508–514Google Scholar
- 12.Roberts JAF, Pembrey ME (1985) An introduction to medical genetics. Oxford, New YorkGoogle Scholar
- 17.McCammon RW (1970) Human growth and development. Charles C Thomas, SpringfieldGoogle Scholar
- 19.Martin RB, Burr DB, Sharkey NA (1998) Skeletal tissue mechanics. Springer, New YorkGoogle Scholar
- 25.Garn SM (1970) The earlier gain and the later loss of cortical bone, in nutritional perspective. Charles C Thomas, SpringfieldGoogle Scholar
- 31.Bennike P, Bohr H (1990) Bone mineral content in the past and present. In: Christiansen C, Overgaard K (eds) Osteoporosis 1990: proceedings of the 3 rd international symposium on osteoporosis. Osteopress Aps, Copenhagen, pp 89–91Google Scholar