Variability of the mechanical properties of bone, and its evolutionary consequences

Currey, J. D., Pitchford, J. W., & Baxter, P. D.

The relative variabilities (coefficients of variation; CV) of ten different mechanical properties of compact bone were determined from 2166 measurements. The unit of measurement was the individual bone, and all measures of variability were made on a minimum of four specimens from any bone. Three `pre-yield' properties had a CV of about 12%. Six post-yield properties had CVs varying from 24% to 46%. Pre-yield properties increase as a function of mineral content, post-yield properties decrease. These differences give insight into mechanical phenomena occurring at different stages during loading. Furthermore, the fact that some properties are more tightly determined than others has implications for the optimum values set by natural selection. In general the optimum will be biased in favour of the more tightly determined properties than would be the case if all properties had the same CV.

Keywords: bone; variability; mechanical properties; evolutionary optima