mistermack wrote:Humans must have had a very unusual factor driving our evolution. Individuals who were a tiny bit more intelligent than others must have had a real survival advantage, for five million years continuously, because the brain size grew steadily and constantly for all of that period, whereas Chimpanzees and Gorillas etc hardly changed at all.
I have a personal speculation on that.
Wild chimps use tools at a very basic level, such as breaking open nuts between two rocks.
My speculation is that the human ancestral line split off because it started to make use of tools (and weapons) to a far greater amount. Imagine, for example, an early pre-human finding a rock that was accidentally ideal for digging out grubs, and deciding to keep it. This pre-human now runs around with a rock in one hand. It is only a matter of time before it finds other uses for it, like whacking the alpha male over the head....
Once the whole pre-human tribe get into the act, and this behaviour passes down through generations, suddenly a whole lot of changes become adaptive advantages. Upright stance. Stronger legs. Hands better able to manipulate. Bigger brains etc. The adoption of simple technology will suddenly stimulate a whole raft of evolutionary change.
For every human action, there is a rationalisation and a reason. Only sometimes do they coincide.