I find it interesting how it often seems to be the unusual or poorly adapted aspects of species that seem to give them serious health problems. For example, men’s reproductive systems have many glands and moving parts, which are prone to cancers, tears, and ruptures. Men’s storing fat mostly on their bellies (near the heart) may make the fat energy more easily accessible for vigorous activities (hunting, war, manual labor, sports, etc.), but also may increase men’s risk of fat clogging the arteries near their hearts, causing more heart attacks. The way that some women’s bodies store fat farther from the heart on the hips may be healthier, and the way that some women’s bodies store fat more in their chests might be unhealthier. Humans are the only species on Earth (to my knowledge) where the females have permanently enlarged breasts, and they are prone to breast cancer; in our species, it is a “secondary sex characteristic”. The first peoples to migrate from Africa to Europe may have suffered from weak bones, rickets, and cancers, because Europe is darker than Africa, and darker skin is less efficient at making vitamin D than lighter skin. Women’s widened hips make running/escape more difficult and might increase the risk of hip fracture, from which many elderly women don’t recover. Rabbits’ unusually big ears are prone to often-fatal ear infections, and, if they kick their unusually large back legs in the wrong way (e.g., when running, fighting, or being mis-held by humans) they can injure their spines and have paralysis. And some pure-bred dogs’ hips are prone to breaking.