Bantu expansion shows that habitat alters the route and pace of human dispersals

About decade ago, I played engineering game written in Flash (I cannot remember it name), where player must solve various tasks, e.g lift ball or stop ball which is dropped from high altitude. Unique idea of that game was fixed amount of money for whole game, which player need to spend wisely to pass all levels, or redo some levels again but with better efficiency, to save money. My first implementations in this game were simple: I understood problem and implemented most obvious solution, to advance quickly. Second solutions were improvements or optimization, to save money, to advance further. I beat game, but then my brother started to play same game and beat my score, so we started competition. Third solutions, made during competition, were true innovations: they are non-obvious and highly efficient, but each of such innovative solution had "lightbulb" moment first, and then sometimes hours of tweaking to implement it. So my gradation is: understanding of problem leads to obvious non-optimal solution first, then understanding of problem with first solution leads to improved solution (local optimum), then "lightbulb" moment leads to non-obvious efficient solution (global optimum).