As early as 1680 the majority of the slave population was native-born. ... They found that the rates of return on a slave were quite high and that holding slaves was quite profitable. The average rate of return of a male or female slave was about the same, around ten percent. ... This was a blow to all the theories that slavery was unprofitable and that slaves had low rates of return. It also showed that the rates of return were higher and not below that of alternative investments. ...