@J.Chang We seem to get a lot of question that boil down to "nature versus nurture", like it was still the 17th Century, and everything was black and white. Humans have evolved to be mostly monogamous, despite being mammals, but there are huge social and cultural pressures that affect it - it isn't 100% nature and it isn't 100% nurture.

It's almost like we are NOT just reproducing robots.

I will ask around in psychology stackexchange. If you read the 3 books in the source it's very obvious. Some of the "source" are "jokes" and it seems that people are attacking those straw man. The 3 books I quote are very strong sources. The thing is you can't know it unless you read the book and I expect most people not to bother and say it's not.