Our fragile bones may be a result of a long history of sedentary lifestyles. This goes back well beyond the advent of the couch potato: The bones of modern humans aren't as tough as those of our hunter-gatherer ancestors, and researchers are linking it to farming. "Modern human skeletons have shifted quite recently towards lighter—more fragile, if you like—bodies. It started when we adopted agriculture. Our diets changed. Our levels of activity changed," an expert tells the Smithsonian. His team, which looked at CT scans of primate bones, finds that the lighter bones developed about 12,000 years ago.
A separate study investigated the hip joints of several populations, including agriculturalists, foragers, and nonhuman primates, EurekAlert reports. The agriculturalists, these researchers found, showed lower bone mass than foragers, while the particularly active foragers' bones were comparable to those of nonhuman primates. "The key appears to be higher physical activity and mobility from a very young age that makes the bones of nonhuman primates and human foragers stronger," a researcher notes, though he adds that diet may also be a factor. (Bones also tell the story of human-neanderthal sex.)