Geneticist John Stanford (who invented the gene gun) has showed that the human genome is deteriorating, and that the human race will last at most some 200 generations before dying of accumulating mutations, mostly passed on from father to son. This is because most mutations are harmful, but also so slight that they cant be detected and thus acted upon by natural selection - either survival of the strongest or sexual selection. Very harmful mutations can be eliminated from the genome by natural selection. Very few mutations are actually beneficial, and they aren't enough to counter the harmful ones.

This claim is of course incredibly controversial. Few have even heard of it, which is understandable. I read his book and found the arguments compelling.

He also points out that the maximum age of humans hasn't increased at all, only the median and average lifespan.

We are lucky to be living in an age where too much harm hasn't yet happened, but where we have good treatments for diseases and technology to make life comfortable.