Are women naturally monogamous? According to an article I have just read by F. Roger Devlin, it's more accurate to describe women as hypergamous - meaning that women wish to mate with the "top" male (the alpha male). The top male is the one who is the most handsome; who has the most resources; and who is socially dominant.
It's a thought provoking idea. It implies that women, if left to their own natures, would scorn average, decent men in order to hold out for a rare alpha male.
If this is true, then it's the average joe who will be dismissed as a "loser" and those few with the highest status and highest income who will fit the category of "real men".
This is not at all the message of recent Hollywood romantic films. There is a genre of Hollywood films (think Adam Sandler) in which a goofy, poor male meets a beautiful woman who is already attached to a wealthy, dominant male. Our underdog hero finally triumphs and wins the woman by being nicer, less arrogant and more faithful than his rival.
I watched a classic Hollywood film a few years ago which presented things very differently. The plot of "A Touch of Mink" (1962) is that the female lead (Doris Day) is a bachelorette working in a diner. She and her female friend scorn the average joes they associate with; the men are presented as uncouth and unglamorous. She then meets the male lead, played by Cary Grant. He is a wealthy businessman, a leader of a boardroom full of dignified, worthy men.
Grant is presented as the ideal alpha male. He is tall and handsome, wealthy, socially dominant (he addresses the UN) and popular with women (something of a playboy). The challenge for the Doris Day character is to get him to commit to her; no easy task, but she finally manages it.
If women do tend toward hypergamy, as presented in the 1962 film, it means that when women talk of "not settling" it really means that they are rejecting average men and holding out for a Cary Grant type alpha male - for the pack leader.
This can't work. It's not possible to build a civilisation in which women hold out for the pack leader, each woman expecting him to commit solely to her.
Men have long been expected to give up the promiscuous side of their sexuality and to commit to a woman in marriage. In a way, a woman deciding to "settle" is the equivalent of a man deciding to commit. It's what is needed for family formation and (generally) for the well-being of the individual.
So what does persuade a woman to settle? In the late teens and early twenties, it can be especially difficult to hold out. The need for romantic and sexual companionship is felt strongly. It's especially easy at this age to feel lonely without a partner.
Perhaps this helps to explain why women who do hold out emphasise so much the need for a circle of close female friends.
As you get older, and leave the angst-ridden teenage years behind, it's a little easier to cope with being single. Another speculation: this might be why women say they become not less choosy but more so as they advance in years. As they become habituated to being bachelorettes, they feel less intensely the temptation to "settle".
Another window of opportunity is when women start to become bored with their careers and/or when the biological clock makes itself heard (i.e. from the late twenties/early thirties).
Note that feminists are often reluctant to admit to the existence of a biological clock for women. As recently as 2002, the National Organization for Women in the US objected to an advertising campaign by the American Society for Reproductive Medicine. NOW objected to posters with the simple message that "Advancing age decreases your ability to have children" and the ad campaign was cancelled.
I've encountered strong resistance from feminists myself when trying to make the same point about fertility risks. It makes me wonder if feminists recognise that women who are aware of the biological clock are most likely to settle, and therefore to begin to identify with the interests of their families, including their husbands and sons - to the detriment of the feminist movement.
Then there are women who will settle because they are more down to earth, or more insecure, or living in smaller communities with a smaller pool of eligible men.
Admittedly what I've written is a speculative and incomplete picture of what happens in relationships. There are plenty of women who do end up marrying the average, decent man. Even so, recognising the existence of hypergamy in women does help to explain the characteristic way that women approach relationships with men.