Yes, it has to do with resources and conservatism, but IMO in a slightly different way. My working hypothesis is what I like to call “big dick theory”. Anecdotally, big penis is associated with dominance, and, as the story goes, Africans are at the top, followed by Europeans, and finally Asians. Now, in animal kingdom, when the resources get scarce, the “big shots” physically drive out the “small shots”.

Hence, those who left Africa were not adventurous, but in search of a living space because they were simply weaker. And those who left Europe and other regions for Asia even more so. Therefore, it would be expected that you will find violence as the primary solution to conflicts in African cultures (and their descendants), violence and outsmarting as the modus operandi of Europeans (and their progeny), and violence, outsmarting and heightened reliance on collective numbers further East. In other words, if it ain’t broke, there’s no need to fix it; if violence makes the job done, why bother with outsmarting or collectivism.

Now, there was only one study I'm aware of that measured the average size of penis across ethnicities and it found no correlations in this sense (I could not find the original study, but AFAICT, this table is based on it). However, we are already so intermixed that the original genetics may be lost, while the (local and inherited) cultures are still conserved and in place (not to mention that a general trend Africa->Europe->Asia as I described it is present even in that table). Furthermore, while there is no clear correlation between size of penis and dominance, studies have found that longer penises may ejaculate sperm inside the vagina in places that would be harder for a following penis to displace. So, that's that.

In any case, your "heat hypothesis" does not explain why e.g. even today "black" ghetos outside of Africa follow African modus operandi and are arguably more violent than "white" or Asian ones even though they are in the same climate zone.