The skeletons of human beings have changed over the past two million years becoming less robust or more gracile. Older people suffer more broken bones because the mass and strength of bone decrease with age. Age-related changes in bone result from interactions between environmental and genetic factors. The high incidence of broken bones late in life is a recent development for Homo sapiens based from an evolutionary perspective. The vast majority of bone-aging studies have concentrated on the bone's mass, volume, density or a combination of these. Scientists can compare bone adaptations in dominant and nondominant arms of people with differing activity levels. Adult skeletons remain responsive to increased exercise but they respond more slowly and less completely than those of children. The gracilization of the modern human skeleton is probably a direct result of the consistently advancing technology.
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