My cousin Sam is raising another man's child. His wife already had a young daughter when they met, and as Sam and his wife became closer and got married, the daughter gradually came under his care. Now she lives in his house and calls him Dad and pretty much adores him, and they're a happy little family. Sam is investing huge amounts of money and time into another man's daughter, giving up his chance to have any genetic children of his own, and he's happy about it.
My other cousin Lucy has a simpler story. She just doesn't have any children and never plans to have any.
So they're two out of millions of people who have voluntarily given up on evolutionary fitness. Sam and Lucy's genes are going nowhere because of the choices they've made. And they're what I think of when I read those "evolutionary psychology" articles about how everything humans do is all about maximizing our fitness and making sure our kids are ours and our seed is spread. (These articles, incidentally, and I'd provide links if I had a proper computer to type this on, have a charming tendency to think fitness consists of getting laid, rather than getting laid and conceiving a child and raising them to adulthood. Steps 2 and 3 there are actually pretty significant.) It seems ridiculous to me to suggest that Lucy is somehow subconciously attracted to men with good genes for her children, when she very consciously isn't using anyone's genes for anything. Or that Sam and his wife's relationship is based in ensuring the fatherhood of children, when they know damn well he's not the genetic father.
Obviously humans are evolved animals, and our history has selected for those who passed on their genes. But in our case selection has led us toward intelligence, and that complicates things. It means that human behavior really can't all be explained in terms of reproduction. It has to be seen in light of us being human.