While the desire to split people into discrete categories of those we love and those we can have sex with may seem a peculiarly male phenomenon, women are far from innocent on this score themselves.

Men’s relationships seemed to be less deeply affected by whether or not there were opportunities to interact amicably

strong theme: Can a man and woman ever really be friends?

Once a relationship has been established, it seems that the men lose interest long before the women do: their focus on the female partner lasts only a few years and then declines steadily down to a token level by middle age.