"men are less selective about whom they’ll sleep with; men like casual sex more than women; and men have more sexual partners over a lifetime."
I always considered those assumptions to be pure bunk. Consider which sex is more likely to have a greater number of partners on average in a population with an equal amount of men to women in mated pairs. In any such a scenario, for one of the men to be promiscuous with more than one woman then one of the women would also have to be similarly as promiscuous with more than one man. And for each new partner a man acquires, one more of the women will have to take on a new partner.
Let's look at a scenario where there's a population of five men and five women where four of the women are totally monogamous with one partner each and the fifth is a hooker who had intercourse with all five of the males for figuring out which sex would have more partners over a lifetime. You would have four of the five men having two partners each and one of the five with only one partner for a total of nine different partners and divide by five for an average of 1.8 partners each over a lifetime. The women would be the one with five partners and four with just one partner each for the exact same average of 1.8 partners over a lifetime. So it's a wash and it always will be. It is impossible to conclude that men have more partners over a lifetime in a society with an equal population of each sex according to the math. Of course I'm limiting this strictly to heterosexual relationships or encounters because these studies deal with assumptions to support Darwinian theories of evolution affects our choices in mating and procreation.
Now where the assumption that men have more sexual partners holds true is that there are no populations in geographically defined areas where the populations of men to women are exactly equal. The real reason why women tend to have fewer partners on average than men in most modern societies has less to do with women being more selective or that men like casual sex more, but that there are generally more women than men at any given time because women live longer on average and despite that would give them more time to take on additional partners over a longer lifetime, they simply have less opportunity because there is a smaller pool for them to choose from for either prospective mates or casual sex partners. Thus women on average would by necessity have to be less selective or risk being left out of the mating game. It has more to do with numbers than the Darwinesque gene search for superior genes theories we're told it has to be. Sorry, ladies, the odds are just stacked against you. Similarly, in an isolated society where the men vastly outnumber the women, then one can expect women would on average have more sexual partners in a lifetime than the men and there they can afford to be much more selective.
It's very rarely really what it seems at face value no matter what the experts tell us. Consider the implications of the pure numbers game, carefully read that article again, and consider how you form your opinions in relation to what the experts are trying to sell us.