My German ancestry mother has a geneology created all the way back to the 11th Century predominantly in East Prussia. On the other hand my blond, ice blue eyed, red headed husband was astonished when his mother told him shortly before she died that he is 1/16th American Indian. Since there was Mongolian Tartar in my ancestry I then realized it made sense that one son has dark hair and swarthy coloring and definitely looked like he could have Indian blood. The other son with medium brown hair and fair skin has high cheekbones and almond eyes. He had an epicanthic fold when he was a baby. He is now married to a woman from Puerto Rico, who knows she has Taino Indian in her ancestry. Both their children look very Latino.
A number of the most vicious Nazis had a grandparent or great grandparent who was Jewish. Regarding the influence of environment, there is the fascinating new science of epigenetics, wherein they are discovering the affect of environmental factors on the expression of genes in such subjects as weight gain, cancer, etc. They have found environmental differences in twin studies with epigenetics.
You just reminded me of my favorite part line in Saving Private Ryan, where the Jewish soldier yells at the German voice on the megaphone: "Your father was circumcised by my rabbi!"