As far as we know modern humans have been around for ~ 150,000-200,000 years. During this time until ~11,000 the Earth was in an Ice Age. Release from that Ice Age is correlated with the development of settled agricultural city-states, which dramatically increased our ability to ratchet. I believe, as Jared Diamond outlined in "Guns, Germs, and Steel" that the disproportionate ratcheting seen in different areas of the world was a product of several environmental factors. The most importan of those factors being a) domesticatable animals and plants, b) a continent w a large east-west axis (as opposed to north-south which impedes diffusion on domesticated plants and animals), and c) the development of a large network of civilizations which feed off of each others growth.
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.
Honestly, I can't say that there isn't some epigenetic factor that has contributed to development in ratcheting over the past 10,000 years, but it seems that a persons ability to continue this process is more dependent on socio-cultural factors, as opposed to ancestry. But there will probably need to be a lot of research to make the case that epigenetics played a role. Personally, I don't think it's possible that it played a larger role than environmental factors. How do you suppose you could test for that?
Certainly, it would be foolish to argue that epigenetics are a bigger piece of the puzzle than environment alone. But, I think that Lamarkian evolution has found a place in epigenetics, and Lamarkian evolution, while subtler, can work orders of magnitude faster than its Darwinian cousin. I would be surprised if epigenetics played no role in culture formation. It has been shown that epigentic changes can predispose rats to aggression. It stands to reason that the opposite could be true. The less war-like we become, the less-warlike our progeny may be. Hence, we can build bridges (literally and figuratively).