It is rumored that in the late 40's some people were born with a strand of dna that was quite self destructive.  If they had children, they would doubt the child was theirs. He would simply tell another relative that "...if the child is not mine, I will kill them."   If  the relative does not say anything, they would presume the child is not theirs in evident self doubt and they would kill the child slowly if not immediately. This was an expression of tremendous  self doubt and murderous ego.