evolution is NOT driven by ‘survival of the fittest’.
it’s driven by ‘removal of the least fit’.
‘fitness’ is determined by breeding success (number of kids).
and ‘removal’ means death. – nothing will stop you having kids quite so effectively as being dead…
(you don’t have to be the fastest lion to catch a zebra, you just don’t want to be slower than the slowest zebra)
(you don’t have to be the fastest zebra to escape from the lions, you just don’t want to be the slowest)
and remember, there is no ‘momentum’ with evolution, humans may have got taller/more intelligent over time, but that’s no reason to think we will continue to get taller/more intelligent.
for evolution to have a ‘direction’ – you need constant selective pressure.
So, in a nutshell; what’s killing us before we have kids? – we’ll adapt to suit that.