The only way a group can subvert this much over the time scale they have is through race and religion, and the two must be so inextricably linked that they are the same. If it were just a religion there wouldn't be any pay off long term knowing the benefits could go to someone else's offspring, if it were just race at some point some of the group could expose their family for spiritual reasons. It has to be both and there is only one group that fits that description