Nature v Nuture

In his first five odd months of life I've been struck by the number of behaviors he exhibits that mirror something in his parents: he's quiet, he sleeps well, he seems to enjoy a variety of foods, he now seems to be sucking his thumb. What's interesting is that these similarities to one or both of his parents has parents has surprised me more that his physical similarities. I mean, I always understood the nature v nuture thing but I guess I suppose it was something abstract that manifested itself in he children in psychology theses. But it's so immediate to observe it in real practice with one's child.