posted by Bla .
In terms of ultimate causes, why is it that genetic conditions that lead to mortality or disability in older individuals (post fifty years old) are much more common than genetic conditions that cause death or disability in young people?
Genetic conditions that cause death or disability in young people would be more likely to be selected against (from an evolutionary standpoint) because those genetic conditions would get in the way of the person being able to reproduce and would therefore reduce the person’s fitness. Genetic conditions that cause death or disability in older people would not be selected against because it did not affect their abilities to reproduce in anyway and therefore would get passed on from generation to generation. Ultimately, if the genetic condition gets in the way of reproduction, then it won’t get passed on to the next generation and will therefore occur less often in the population.