Fatigue failure and skeletal evolution

The skeleton is primarily a mechanical organ that must resist deformation when loaded. Consequently, bone is mineralized and twice as heavy as other tissues, making it metabolically expensive. In addition, bone must overcome two other challenges. First, for geometric reasons loads on bones increase disproportionately with the animal’s size. Secondly, like other structural materials, calcified bone tissue contains flaws that, under load, can precipitate cracks leading to failure. The evolutionary solution to these fundamental problems is the process of bone remodeling in concert with the ability of osteocytes to sense both insufficient loading and mechanical damage caused by overloading, and to activate remodeling to correct the resulting problems.