"Yet Clark suspects that our genes may also play a role. Perhaps some families are just carrying the DNA that helps them succeed, he says. "
Main genetic factor for success could be a very good memory, a genetic parental trait, which will allow to memorise all the material to become a family doctor for example. Other genetic traits helping being successful are perseverance, logical thinking, critical thinking, being social and easygoing, creativity, etc.
When I was a kid in Poland in 70s, where doctor didn't make much more than a factory worker, and intellectual class couldn't send kids to private schools or give them a better start for their money or lack of it, one could see immediate genetic effect even in kindergarten and elementary school. Kids of doctors, lawyers, engineers were learning faster, had better attention, and generally a better logic (though not by a lot). Needless to say they always had better marks than the rest of the class. Kidds of factory workers, simple physical jobs, and parents with social-economic problems, were at the bottom of the score. The effect was mostly genetic, with economic factor lagging far behind.
Such genetic determinism tends to be an unpopular idea among many scientists.
Example of scientists who had great memory to acquire knowledge to become one, but lack critical and logical thinking to understand complexity of human nature.
We are not going to see their names in scientific breakthroughs, nobel prizes or monumental works.