I'm no biologist, but as I recall newborns have long DNA strands. As it says, each time cells split the strands shorten a bit eventually leading to age related

I'm no biologist, but as I recall newborns have long DNA strands. As it says, each time cells split the strands shorten a bit eventually leading to age related illnesses. AFAIK there are no benefits to telomere length shortening with time. As I understand it, after we've reproduced and raised children - which we generally do before age-related illnesses kick in - we only have limited evolutionary value and no longer face stringent selection pressures. So it's probably that there were few opportunities for evolution to correct age related illnesses, or few survival-of-the-fittest opportunities (since we've already reproduced by the time they occur). However, this theory ignores the ability for grandparents to look after children. I suppose it's only minor enough for us to have evolved to live to ~80 but doesn't require youthful health any more.