really true.

Despite your speculation, the fact is that in many societies people do discriminate based on kinship. As just one example I recently came across, from the Wikipedia article on the Fa'afafine of Samoa - men who take on women's roles, including caring for children - "They are markedly more willing to help raise their nieces and nephews than typical Samoan uncles: theyre more willing to baby-sit, help pay school and medical expenses and so on. This heightened altruism and affection is focused only on the faafafines nieces and nephews." (emphasis added)

Along similar lines, a friend who has spent time in Japan once informed me that the Japanese don't quite understand the notion that Americans would adopt an unrelated child.

There is a marked difference in Western culture, even going back to the Romans IIRC, where adoption of unrelated children is far more common than in other cultures - nor will I suggest that persons from other cultures could never bond with an unrelated child. Still, there is abundant evidence that family ties do make a large difference for many, or even most people.

Of course, I believe that many pedophiles have the capacity for a similar connection to most children as most people have only to their own children. I couldn't say yet what the biological mechanism for that could be, but maybe we will find out some day.