According to the evolutionary theory of aging, why hasn't natural selection eliminated many harmful conditions and nonadaptive characteristics in older adults?

Evolutionary Theory of Aging describes t he view that natural selection has not eliminated many harmful conditions and nonadaptive characteristics in older adults. N atural selection is linked to reproductive fitness, which is present only in the earlier part of adulthood. According to evolutionary theory, possibly if some disease occurred earlier in development, it might have been eliminated many centuries ago.