Africans were also used in large numbers for slavery because they were easier to buy. During the beginning of the Atlantic Slave Trade, Africans were willing to sell other Africans as slaves to Europeans because they had their own system of slavery.
You could have sex towards the end of your bleeding and then actually conceive 4 or 5 days later with your early ovulation. The probabilities of getting pregnant while on your period are low, but the possibilities are there. This is not the time to have sex if you are trying to get pregnant.
It's unlikely to get pregnant while you're on your period-but not impossible. All of this combined should make it tough-but it all comes down to in any situation (unless you have no uterus) if you're having sex.. you CAN get pregnant and no method of planning, timing or birth control is 100% effective.