It's an interesting question. However, scientific studies have shown fairly conclusively that there is no connection...it's entirely cultural. Far more nurture than nature.
Genetics plays a limited role, but people are far more likely to be similar to their parents than they are to be similar to other members of their race.
Then explain why races have been breed by oppressors to be stronger or weaker. Example : Slave owners often had "big boned" black women give birth to children of very strong/tall black men. It is obvious that genetic "pluses" can be built upon and weaknesses be bred out of humans.
