[mikepurvis]

> ...strange to me how nobody questions why beavers only make damns a certain size, birds only make nests and don't go beyond that in complexity.

Isn't most of this kind of just a matter of fitness, same as why birds become flightless on islands where there are no predators which demand flight to escape from? Basically, building anything more than a minimally-viable nest or a dam requires using energy that could be invested elsewhere to greater evolutionary advantage.

Humans have gone beyond because for as long as we can remember, we've always had vast, vast surpluses of energy, initially through the cooking of meat and agriculture, then via animal labour, and then finally via fossil fuels.