SW got it almost right.

Nature AND Nuture.

Idiots usually raise idiots, but there are exceptions, just as smart folks sometimes end up with prodigal carbon units they wish they didn't have to lay claim to. Over time genetics incorporate nurture that is successful because, well . . ., it succeeds.

Makes a person wonder at times how certain people manage to get through life, unable to make a single intelligent decision. Sh!t house luck is amazing that way.

Sg