Anyone trying to understand our origins soon realises that no one thing pushed our ape ancestors across the threshold of humanity. It is difficult to pin down what makes us human anyway. We walk upright on two legs, with disproportionately large brains held high, communicating in spoken languages, navigating the complexity of human social life, producing sophisticated tools and artefacts, and creating culture. The story of how we became human is woven from many strands.It has also been long thought that the evolution of humans from their primate ancestors took place during a cooling/drying trend in which the forests retreated. While the monkeys like baboons adapted to the savannah and chimpanzees and gorillas took to the jungles, humans exploited the forest/fringe area. Much of the story lies in changing behaviour:
[Michael] Plavcan points out that size dimorphism can only persist if the biggest males can monopolise females and so pass on their genes at the expense of smaller males. That cycle can be broken if females change their behaviour in a way that makes it more difficult for a single male to monopolise them. If that happens, more males become able to pass on their genes, reducing competition for females and removing some of the pressure to be big, leading to a reduction in size dimorphism. The decreasing size differences of our ancestors "tells us that the way females behave is changing", Plavcan says.Very interesting. Read the whole thing.