How many grandmothers do you have to go back till you get to eve?

I was laying on my sofa today while my daughter was watching an extremely annoying kid's show, when I realized that it would not be hard to figure out how many generations back you have to count to get to the first homo sapiens. The answer shocked me and my wife.

If we say that on average there are 4 generations per 100 years, and human beings have been around for 200,000 years:

(200,000/100) * 4 = 8,000 generations

This can help explain why there isn't much diversity in human populations. In fact, there is more diversity in one small tribe of chimps in the jungles of Africa, than there is in our entire species. This is but one factor to take into account to explain our variation riddle, I'll save the rest for another post.