There actually have been studies of primitive tribes and cultures where it was showed that they just didn't realize pregnancy happens from a single man's sperm, so children were considered the entire tribe's or to have multiple fathers (with actual language terms for the various fathers). There's also some cultures where men first slept with men while growing up before settling down with women due to thinking sperm was a guy giving up his power and younger ones needing it to grow into warriors. So it wasn't really as clear cut as we know it to be today.
But evolution happens whether or not the creatures in question understand evolution or even heredity. (In fact, if they know nothing about it, that makes it easier for evolution to do its thing without interference.) The legendary "shape of the human penis designed to pull out the sperm of other men who have recently had sex with the same woman", if it worked, would do very well evolutionarily in the first kind of culture you describe. Likewise, if teenagers being awake at odd hours does cause them to have sex and reproduce more often, then (assuming the tribe will take care of the children) the genes that cause them to do this will be selected for, whether or not the teenagers or the adults realize it.
Exactly. If jealousy and mate-guarding behaviour evolved in some males, it might spread whether or not they understood what was going on or what the mechanisms are.
One could look at the animal kingdom to get more insight on this, though of course there is such huge variety there that it drives home the point that "it's complicated."
