Reply #43: There are many ways for this to happen. [View All]

Here's an easy way to look at it. Since the effects of the seven skin color genes are cumulative, the more "black" genes you have, the darker the person is. A purely back person would be:

BBBBBBB

A purely white person would be:

WWWWWWW

Most of us are:

WBBWWWW, BBBWBBB, BBWWBBW, or some random combination thereof.

Now, our skin color genes are a random combination of our parents genes. If BBBBBBB and BBBBBBB have a baby, the only option is BBBBBBB...which is why blacks don't typically have white babies, and vice versa. If WBBBBBB and BBBBBBB have a baby, the genes will be one of the two.

When races mix, things get interesting. If WWWWWWW and BBBBBBB have a child, the skin color is 100% random. But that's not the ONLY possibly random combination. Lets say this is mom: WWBBWWB and this is dad: BBWWBBW. Because the two combined still contain the complete set of possibilities, it's still possible for them to have a baby that is either purely white or purely black. The odds of that happening are amazingly small (one in a million), but it does happen. The odds of this PPARTICULAR set of twins having different skin tones really wasn't all that small, because the genes don't even need to be purely one or the other to cause the difference in tone. BBWWWWW would look white, while BBWWWBB would look black. Even though all but two genes are identical, the difference between those two is enough to create an apparent difference between their races.