Early human ancestors spent eons testing their skeletons while jogging through untamed landscapes hunting and gathering food to survive. Life is significantly easier today, and evidence of a more leisurely lifestyle is showing up in our rested bones. Since the invention of agriculture, new research shows, human bones have grown lighter and far less dense than those of early humans and closely related primates. Researchers believe sedentary lifestyles — made possible by agriculture and technology — are the root cause of human bone degradation over the past 1,000 years. Their findings reinforce the idea that exercise, not diet, is key to preventing fractures and osteoporosis. Thin Bones Researchers in two different studies X-rayed samples of human bones from various points in the archaeological record, as well as bones from various modern primate species. In both studies, researchers were most interested in trabecular bone, which is the sponge-like internal structure of bones that gives them added strength. Trabecular bone is of particular interest because it can change its shape and structure depending on the loads that are imposed on it. Basically, more load stress yields higher bone density and fewer air pockets in spongy trabecular bone. The more we exercise in life the stronger our bones grow, until they hit peak strength around the age of 30. After that, the aging process degrades our bones. More via Discover Magazine.