Here's a problem to which no one has ever provided a satisfactory answer, or any answer at all, apparently: Which came first, mammals, specifically humans, or mammalian pregnancy?
Throughout the development of the human fetus it's constantly interacting with the mother via chemical signals and feedback systems, but until and unless all these interactions are in place and operational a fetus could never develop and there would be no next generation.
Yet Darwinian evolution holds that biological development occurs gradually, step by step, over eons of time with neither guidance nor foresight, but how could this be if all these systems have to be in place simultaneously and fully operational in order for the fetus to be viable?
So, either there's a gradual evolutionary pathway that mammalian pregnancy followed that has so far eluded all attempts to elucidate or all of the systems between mother and child were set in place from the beginning.
Believing the latter is at least as rational as believing the former, unless one has a priori ruled it out because it would require an intelligent, purposeful engineer at the outset of life and the skeptic has concluded that no such being has ever existed.
But why conclude that? It's simply a metaphysical preference lacking any evidential warrant.
The co-author of the book Your Designed Body, engineer Steve Laufmann, addresses the pregnancy problem in this short video: