So a functioning brain is one that forms accurate models about what it will actually see next. Such as a bushman on the Serengetiwhose brain predicts he will soon see the inside of a lion’s intestinal tract upon realizing one is in full sprint for his neck. This model is one likely to incentivize enthusiastic flight, and thus result in a bushman who lives to model another day. In contrast, inaccurate models about lion behavior tend to have a suppressive effect on bushman longevity.
Having been in the company of Bushmen for extended periods, and having been in lion country on many occasions, I’m here to tell you, that’s not a bad analogy! (Of course, there are no Bushmen left in or near the Serengeti – that’s spread across northern Tanzania and southern Kenya, while today they are concentrated in Botswana – but what’s a couple of thousand miles between friends?)