“[M]ost people “know” that evolution is about “survival of the fittest” and that nature is red in tooth and claw. Therefore, it naturally stands to reason that when mortality declines evolution will be a weaker force. I think the problem here is that our conception of evolution is focused too greatly on proximate modes and large scale dynamics. That is, selective high mortality rates are a “common sense” way in which the “weak” can be weeded out from the “strong.” But what about the extremely high human spontaneous abortion rates? Evolutionary biologist Mark Ridley has argued that increased miscarriage rates will “balance” out the fact that more individuals with deleterious mutations are reproducing today than in the past. Selection therefore occurs in utero; we don’t observe it so it is not salient to us. But it is selection nonetheless.” (Gene Expression Blog)