I certainly don't believe that any "bigger, faster" mutations are novel to the slave population as they can occur within any group of people. But through breed

I certainly don't believe that any "bigger, faster" mutations are novel to the slave population as they can occur within any group of people. But through breeding these mutations are likely to be more prevalent in the target population. This explains why the 400m race can be dominated by blacks but Jeremy Wariner (white guy) can still be the fastest. If that were true you would see similar numbers of sprinters from West Africa. If your last point were true we would see world class sprinters coming out of one of the West African nations. I can't think of any.