One thing I noticed looking back over my own life, and reading the experiences of other adoptees, is that while the adults are more than ready to bond with and actively, lovingly, and diligently parent a child that isn't biologically theirs, the babies have a much harder time bonding with their new moms. I guess there's a whole lot more instinct and a whole lot less higher brain functions at work there.
Nod. It's there. There's all kinds of information, historically, anthropologically, biologically... how we've evolved... we're having kids now, not as a necessity, but as a preference... you should look into it... you sound rather fascinated by it.