As noted at Ouroboros, evolution is a harsh designer. Benefits are front-loaded for optimal fitness in early life, with no regard to just how much damage, pain and suffering the underlying biological machinery will go on to cause later. Hence aging: "Oft-quoted examples include the prostate and breast, where robust proliferation improves early-life fitness (via effects on reproduction and child-rearing, respectively) but can increase cancer risk (and thereby mortality rate) in old age. One might, therefore, expect to find that gerontogenes (genes whose wildtype function promotes or accelerates aging) are enriched among what are sometimes referred to as 'housekeeping genes': genes with run-of-the-mill functions in metabolism, whose efficacy is intimately linked with the success of fundamental processes like cell division, protein production, etc. ... Unfortunately for this theory, it's particularly hard to identify mutations in these genes, where loss of function means loss of life. In order to investigate the hypothesis outlined above, one would need to allow these essential genes to function throughout development, and then turn them off at maturity." Which researchers can now accomplish - and are turning up interesting results.