It's a tricky hypothesis because it's so easily taken to extremes, including deterministic or even racist ones. I don't think a proponent of this hypothesis needs to go to any such extreme. I'm interested in a modest form of the hypothesis.

It's true that I suggest we might be only "puppets" in certain respects, or that we're not as autonomous as we might imagine. I stand by that, but I wouldn't want to say that all ideas are only epiphenomenal, and that the environment determines everything in society. I'm not saying that people are just puppets and that freewill is an illusion. On the contrary, I think our freedom is crucial to our existential condition since it helps explain what's so anomalous about the history of our transformations of nature.

Mainly, I was trying here to point to one seemingly overlooked political factor.

The global correlation between climate and political structures is undeniable, as is the effect of excessive heat on human cognition. The extent of the environment's influence, though, is another matter since there are bound to be many relevant factors, and some may cancel out others under certain conditions.

I wasn't aware of Jefferson's theory. I'll look into that, but I suspect it might be a rationalization of racism. He had over 600 slaves over the course of his life.