In the category of things we already knew but it's interesting to have scientific proof for: (Young) men respond hormonally to (young) women almost immediately -- even ones they aren't particularly interested in:
Research involving a group of male students found that their levels of the hormone testosterone increased to the same extent whether they were talking to a young woman they found attractive – or to one they didn't fancy much at all.
After 300 seconds alone in the same room as a woman they had never met before, and in some cases did not find particularly attractive, the men's testosterone levels of the hormone had shot up by an average of around eight per cent.
The study's authors believe the rise in testosterone may be an automatic and unconscious reaction that has evolved in man when faced with a woman, to prepare him for possible mating opportunities.
Essentially, this is why you so very infrequently hear young men say "not if she were the last woman on Earth." Their minds are made up on that score even before the men know their minds are made up.
Mind you, this is one of those studies determined to create more questions than it answers. My questions: Do young women have the same sort of immediate hormonal response (and if so, is it triggered by the men attempting to act more "manly" as hormones steep through their systems)? Do gay men have the same hormonal response to women as straight men and/or do they have the same hormonal response to men and straight men do to women? And also, how long before some opportunistic lawyer tries to argue in front of a jury that a flush of hormones made his client attempt something stupid and criminal against a woman? Because you know one will. Grumble.
Being a guy, the finding of this study makes sense to me; I do notice that my internal reaction to meeting a new woman is ever-so-slightly different than to meeting a new guy. Of course, the hallmark of being civilized is keeping your involuntary hormonal reactions to yourself. Yes, yes. It's a skill to have, my friends.