My theory is that when people have to leave a society it is the best (happiest) people who leave. People that I conclude have infantile personality have always in the past been the one's to dominate society, hence they had no reason to leave. This means that a society where people are emigrating there will be an increase in people with infantile personality. In a country receiving immigrants there will be a dilution of people with infantile personality in addition to the positive effect of getting fresh genetic material.
My theory says that the more recently a country has become populated the fewer people there will be with infantile personality. This means people in general are better, since I define people with infantile personality as bad (unhappy).
I'm no expert on ancient migration and one has to understand that people with infantile personality do not procreate very succesfully, which means they over time might recede to some equilibrium point.
Hinduism must be Nature's biggest breeding program. In this light Islam could be viewed primarily as a punishment and not a religion. Islam divides people in we and them (believers and infidels), which is based on prejudice. Teaching this kind of thinking is basically to make people into rascists. Maybe their is a lesson to be learned from this fact. Maybe Islam is the religion of choice for people with infantile personality? Can Islam easily be used to further the interest of an individual, group, or society? We know from history that religion in the past has been used to further the interest of individuals, groups, and societies. Is Islam still being used in this way? No prophet is accepted in his own country, except Muhammad. Muhammad is the only prohpet that has had a position of power within society, go figure. The institution of harem might have been Nature's way of trying to produce more offspring from people with infantile personality. USA should be populated with the best people mankind can offer, according to this theory. However, it is also possible that the opportunities offered in the USA has attracted people with infantile personality. Finally, I just want to say that Nature wants diversity. It makes us complex and beautiful. One doesn't have to like everything in this world, just try to accept it.