Perhaps during a long ice-age the desert belt turns green and there is so much food available people grow to be 'very large' and in that time the 'rules' are a small group that interbreeds and the elongation is a sign if 'incest at a national level and lasting centuries'. The insanity that come with that is why their kingdoms failed when the climate changed to the one we have today where we are small because there is not much food to go around.