My answer is “no”: In about 21% of identical (monozygotic or MZ) twin pairs, one twin is right-handed and the other is either left-handed or ambidextrous. Since identical twins share identical genes, this is evidence that handedness is not a totally genetic trait. … But about 17% of all twins are left-handed. Many of the Rh negative celebrities are also left-handed: The question is “why?”. What else do Rh negatives tend to have in common that might contribute to this?