Lex Friedman had an evolutionary biologist on his podcast, sometime in the last few months. The way he explained it was that the accumulation of simple mechanisms trend towards the more complex mechanisms via gradients, electron affinity, etc. I believe it was with Michael Levin, but I can’t play the audio to confirm right now.

I’ve had the opportunity to work with quite a few patients that were born with anatomical structures where they shouldn’t be or oriented abnormally (e.g. Apert syndrome and dextrocardia). It’s fascinating stuff from a biological standpoint.