I'm a guy. I don't think any rules really apply. Since you know something about evolution you may know about all the cultural differences as well. What may be considered indecent in one place may be normal somewhere else. I read about one society where it was perfectly fine for women to go sleep with other guys when her husband was off on a hunting trip, then when he returned she did also, and there was no problem at all.
I know a woman who had sex with her husband on the first date, and they are still together after twenty years, so I guess he didn't respect her less. For me personally I would prefer to get to know someone before we have sex, because I am sensitive and to me sex does change things in the interaction. If the sex is good or she has a nice body it could blind me for a time to some qualities that don't work for me. Conversely if the sex does not seem good it may make me less inclined to notice some great qualities she may have. Also I have the notion that I want the sex to be special when we do have it, so I would rather see it as part of the experience of getting serious rather than treating it as a casual thing.
Having said all that, I'm a single guy and I do find it extremely hard to live without any sex. Masturbation is not enough. So while I would like someone special in my life I don't know how to satisfy that need in the meantime. I wish I could find women to have sex with until I get truly attached.