I've reread the textbook about 5 times now and I STILL don't understand this:

According to the text, what is the rather counterintuitive finding regarding adoptive families versus biological families?

Nature vs. Nurture, but how would I answer?

Since I don't know what the question is, I can't direct you to further reading. Does the text say that "nature" (the genetic) influences more than "nurture" (the way the child is raised by adoptive parents), or the other way around?