Nature has widely enhanced brain functions. There is variation in intelligence. But since traits are selected for against usefulness and not toward an abstract

Nature has widely enhanced brain functions. There is variation in intelligence. But since traits are selected for against usefulness and not toward an abstract goal or destination you don't see much variation above or beyond that needed to promote the trait. Even today most people do not need much more abstract reasoning power than the median to survive and reproduce. (By "today" I mean within the last 10,000 years or so.) But in normal healthy people we see enough variation in abstract reasoning to have a profound effect on their performance in our brand spanking new technological environment of the last couple of thousand years; less than an eyeblink in evolutionary terms. And not just in competitive terms, but in absolute ability. A lot of that advancement can be simply be attributed to better nutrition and better mental and language models. I have little trouble believing that fiddling and tuning up the brain's electrical environment might might have some comparatively striking effects. (I can also see it possible to do great damage as well)