You don't have to kill them, you just stop them from reproducing. It is cheaper and easier (in the horrific brave new world sense) to just sterilize anyone below a desired IQ threshold and let them act as worker class. Because by the time you can accurately gage adult IQ you would have already invested a lot of resources into the child.
The whole premise is that "like produces like", which of course is nonsense. Dumb people have brilliant kids, ugly people produce beautiful children, and so on and so forth.
3. However - you are right in one respect. There is usually a 'pull to the mean'. That means that children of exceptional people tend to be closer to the average, thus they are not as gifted as the exceptional parent.
Would an individual have been chosen for sterilization if:
1) He was born with a markedly pointy head, which caused much consternation to his parents and relatives.
2) Was developmentally backward. Notably, he failed to acquire language skills for a significant period during his early childhood.
3) He was educationally subnormal, showing signs of what would now be diagnosed as ADHD,and drugged into a stupor.
4) Was bone lazy. I believe that 'schweinehunde' was the informal term used at the time for this condition.
5) Was disobedient and rebellious, or one of those 'malcontents' that perennially threaten to upset the applecart of society (the term 'hooligan' enjoyed a brief vogue for describing this condition).
6) Was Jewish. The eugenics movement designated Jews for mass sterilization, along with Blacks, Poles and the 'bloody Irish' (but then again, these were the same dolts who thought that sterilizing homosexuals would somehow serve to 'keep the race pure').
Albert Einstein was a prime candidate for this preemptive culling.
If anything, Jews (or more precisely Ashkenazi) are a poster child for eugenics - since really that's what they went through in the middle ages, which is used to explain their enormous achievement (see http://www.economist.com/node/4032638)
