Here's a crackpot thought (but a thought-provoking one, nonetheless). I was talking with a couple colleagues a few minutes ago about the role of epigenetics in the obesity epidemic in America, which is an unexplored, but certainly important dimension. But let's back up a minute. Wallace discovered natural selection independent of Darwin, and may have been the catalyst for Darwin to finally publish Origin of Species. But, one great difference between Wallace and Darwin was that Wallace was a God-fearing man. He held the view that God must actively intervene in the word to some extent, because human culture is evident, and could not have happened by natural selection. He held such a rigid view of selection that he believed that all traits of an organism must serve some biological purpose. Thus, he reasoned, that when you listen to the beauty of an aria, you are hearing the work of God, because there is no natural reason for a soprano to exist, in fact no reason one could exist.

Let's get back to obesity. There was an interesting study published several months ago wherein the authors showed that obese rats give birth to pups with distinct miRNA profiles that predispose the rats to being obese themselves. One wonders if there is a similar thing at work in cultural development. Agricultural societies are always the ones that developed cities and ratcheted cultures, the thinking being that people were more sedentary when fed, and therefore had more time to explore engineering, etc. But I wonder if there is a biological component to cultural proclivity. What if eating cultivated grains as a staple changes our epigenetics in a way that affects our ability to think and produce culture?

This is highly speculative, but I think worth investigating. Maybe a positive feed back exists between thinking and nutrition that has finally reached its point of collapse, as all positive feedback loops eventually do, given that nothing can grow infinitely.