Why do men and women have different psychology?
Evolution led to differences between men and women[edit]
In the very distant past - and even in the present in less modern societies - there was a very distinct difference in the roles of men and women. The very nature of our biology demands that women spent a lot of time being pregnant - and that made them the obvious choice for subsequent child-rearing. Since it's tough to be hunting wild animals while 8 months pregnant - that role fell to the males.
Humans are not like most mammals - or indeed most animals of every kind. With most mammals, a newborn is at least somewhat functional within hours - and able to fully fend for itself after a year or two. Humans need more time - a child is not fully mature and able to function in society for one to two decades.
The investment in time and energy for a female of our species in raising one or more children is absolutely enormous...a large fraction of a lifetime.
However, in principle, the male of our species may have a very brief role. Impregnate - move on.
Evolution favors those who reproduce most often and most successfully. So logically, males should impregnate as many females as possible to maximize their chances of passing their genes on into the future. But for females, this is a disastrous strategy because in order for their genes to pass on to the following generations, they have to invest heavily in child-rearing.
This produces an interesting result. Women have to select mates who are least likely to do exactly that. They must be highly selective and pick only males who are not going to do the evolutionarily most obvious thing. They need males who are going to look after them and their offspring. They need "pair-bonding" that's going to last for at least decades.
Evolution helps them in this regard - giving them better abilities to figure out which males are best at that kind of thing - and evolution helps the males by making them more able to exhibit the needed characteristics.
However: That a was then - and this is now![edit]
Our world has changed - dramatically - we now have a society where both males and females can provide for their children. Where even tiny babies can be reared by men using 'formula' milk and so forth. Evolution now favors a more neutral situation - where both males and females need to seek relationships that will last for decades - and both need to find mates who are both good child-rearers and good providers.
Evolution would ordinarily catch on to this - and over many generations, we'd evolve such that male and female psychology would become more similar.
But humans are a new paradigm here. We have (in effect) taken over our own evolution - we do all sorts of things like helping out the reproductive success of couples who'd otherwise fail to conceive - by providing things like infant formula, day care services, schools and so forth.
Males no longer need to be able to run fast or throw a good spear - providing they are good at computer programming or something. We have machines that allow most jobs to be done better by those with a brain than those with big muscles and lightning reflexes. "The Revenge of the Nerds" if you like.
These changes happened so fast that biological evolution is going to need a thousand years or more to catch up. But evolution is relentless - so it will.
Quite how this will play out over the very long term - is hard to say. Never in all of pre-history has a species been able to take control of nature to the degree that we're doing.
What's clear though is that people with a more 'gender-neutral' attitude are the ones who will be a part of the future.