Science has poked its nose into how men and women are attracted to each other, as outlined in an article in the Wall Street Journal, entitled "The Tricky Chemistry of Attraction
As it turns out, taking birth control pills can really screw up your attraction to the right kind of guy! The attraction is only for those days you should have been ovulating. So when you choose a life mate, and take a year and a half to do this, be aware real chemistry certainly is involved in the initial attraction:
The type of man a woman is drawn to is known to change during her monthly cycle - when a woman is fertile, for instance, she might look for a man with more masculine features. Taking the pill or another type of hormonal contraceptive upends this natural dynamic, making less masculine men seem more attractive....The findings have led researchers to wonder about the implications for partner choice, relationship quality, and even the health of the children produced by these partnerships....The study also showed that women seemed to prefer the scents of men whose immune systems were most different from the women's own immune-system genes....
Having two different immune systems would give the children better protection against bad germs. Supposedly, we ferret this out by using our sense of smell!
In the movie Species, a gorgeous female alien gets loose from a research laboratory and goes searching for a male. She picks up this one guy, he takes her home, and she starts kissing him ferociously. Then suddenly, she stops, sniffs him, and then kills him! She sniffed he had diabetes! She kills rather than mates with a man who is not going to pass on healthy chromosomes. It looks like some of this biology is built into us (short of the homicide part, that is).
When women ovulate, they give off subtle cues, and men tend to find them more attractive at this time. But when she's using hormonal birth control, she's no longer interested in masculine men, and masculine men are no longer interested in her:
Researchers speculate that women with less-masculine partners may become less interested in their partner when they come off birth control, contributing to relationship dissatisfaction....[and] and increased attraction for other men during their fertile phase. Women partnered with traditionally masculine partners didn't have such urges....
So the message is don't pick a guy when you're on the pill, 'cuz you're going to pick a wuss. And when you get off the pill and you're married with three kids, you'll look at him and think "I married a wuss," and the next time you're fertile, you'll get turned on to some macho dude.
I cannot argue that in attraction, there probably is a lot of biology and chemistry involved, because we're biological creatures. Human beings with their incredible gray matter, however, are complex and decisions are made for many different reasons having nothing to do with health or picking a good partner.