Some animals (such as hydras and some jellyfish) can apparently live forever, but we humans are all going to die. Longevity is desirable, but aging—a slow process of deterioration—is not. Hearing declines (half of those older than seventy-five have disabling hearing loss), as does visual acuity (by age eighty, 70 percent of white Americans have cataracts [National Eye Institute 2019]). Reflexes are slower; reaction time increases. Strength declines, and bone density decreases. The skin thins and bruises more easily. Wrinkles develop; the hair turns gray and then white. Height decreases by one to thre inches. Dementia increases with age, affecting 19 percent of those between ages seventy-five and eighty-four and nearly half of those over eighty-five. Numerous diseases become more common, such as diabetes, cancer, and cardiovascular disease. If they live long enough, almost all men will develop prostate cancer although most of them will die with it rather than because of it.