Does the United States have a heterozygous advantage?

Heterozygosity is defined as follows:

related to heterozygous
adjective Biology.
having dissimilar pairs of genes for any hereditary characteristic.

In common parlance it means the genes you get from your mother are different from the genes you get from your father. This leads to something called the heterozygous advantage - plants, animals and humans who are heterozygous have fewer defects.

To explain why, you need to understand how genes work.

We get 23 chromosomes from each parent, and these are selected at random from the database of genes from each parent's ancestors. When you get a healthy gene from one parent and a recessive gene from the other, the healthy gene will dominate and manifest. The recessive gene will stay silent. It's only if the same recessive gene is passed down from both parents (homozygosity), that you get problems.

To understand why heterozygous people have an advantage you first need to see why homozygous people don't.

Consider an isolated small village somewhere in the world. Say it starts with seven families. Over the next couple of centuries, even though people are careful not to marry first or second cousins, everyone will end up related to everyone else. So the pool of genes that the 23 chromosomes are being selected from is the same for both parents - and you are likely to find the same gene coming through from both parents.

This will end up concentrating certain traits. If the founding population of seven families were all scientists, it is likely that intelligence is concentrated in their descendants. If more than half of them were carrying the gene for cystic fibrosis, then the probability of their descendants getting the disease rises. And so on.

Breeding of pets is often done by mating close relatives in order to concentrate characteristics.

So what's the problem, especially of the founding population was smart, healthy, beautiful and intelligent? The problem comes from the fact that mistakes are made as genes are passed on, because we are still subject to evolution.

A woman's eggs are formed while she is still in the womb. So mistakes in those eggs will depend on the health of her mother while pregnant. A boy's sperm is similarly affected by the environment at puberty. Famines, heavy metals in the environment, pollution of air and drinking water at these crucial points tend to result in mistakes being made as the genes are copied for the sperm and egg.

That means that if you have a small founding population, you are not only concentrating the characteristics of the founding population, you are also concentrating all the genetic mistakes that are accruing over time. If the population continues to be isolated, more and more new mistakes accrue, and propagate through the population (because the choice of marriage partners is limited). That eventually results in crippling diseases and inability to reproduce.

The most famous example in history is that of the Hapsburg dynasty. They hit on the idea of accruing territory by advantagous marriages instead of war. The first generation that did this was very successful. But then came the problem of holding onto all the territory they accrued. Other people marrying into the family might be trying to acquire their territory, so they started marrying cousins instead. A few generations of this resulted in the horror show that was Charles II of Spain - see his picture below:

He had an abnormal jaw and tongue so he could hardly speak, his intelligence was low and he couldn't reproduce. And he thus ended the dynasty and all the lands the Hapsburgs acrrued were then fought over in the War of Spanish Succession.

And you can also see this in animals that are overbred - they usually can hardly walk or eat properly and some concentrations of genes make them vicious and unpredictable.

The Heterozygous Advantage

The heterozygous advantage comes from the fact that the chromosomes that you get from your mother are quite different from the chromosomes that you get from your father. Therefore if there is a defective gene handed down from one parent, the probability that the same gene from the other parent is also defective, is very low. The heathy gene thus manifests. Heterozygous individuals tend to be symmetrical and beautiful because the defective genes that warp a feature are silenced and over-riden by the healthy genes.

The more distant the parents are from each other the more heterozygous the child will be.

This is where the American Melting Pot has an advantage.

Take an immigrant to the USA from Ireland in the 19th century. When they meet and marry an Italian they met at church and produce children, those genes will not have been combined for some 3000 years. If their child then goes onto marry an immigrant from Poland and have a child, those genes will be combining for the first time in 20,000 years. If their child marries someone from India and has a child, the genes will be combining for the first time in 60,000 years.

Each time they marry out, the database of ancestral genes grows. And the bigger the database, the lower the probability that a defective gene will be randomly selected in the 23 chromosomes you pass on. If both parents have big databases of genes, then the probability that a defective or recessive gene will present from both parents is even lower.

This gives rise to a healthy smart population. Lots of famous Americans have this advantage.

Grace Kelly was a combination of Irish and German (two sets of genes that very rarely combined before the 20th century). She was famous for how symmetrical her face was.

Steve Jobs was the combination of Swiss-German and Syrian. Both parents were academics, so both were passing on intelligence, but the genes that were combining hadn't met for 30,000 years.

Barack Obama is a combination of English American and Kenyan. Those genes hadn't combined in about 100,000 years. Both his parents were smart but plain-looking - but Obama was an improvement on them in how he looked.

Most American athletes are of mixed race. And a disproportional amount of American academics are a combination of Jewish and English American.

African Americans are particularly interesting as they usually have European and Native American genes as well as African genes. Their African genes likewise tend to come from different parts of Africa. Genes that don't mix in Africa due to vast geographical distance, mixed in African Americans. This has given rise to the African American voice. It's big and powerful and has dominated the music scene from the start of the 20th century. People tend to think of it as a "black" voice - but you don't find this voice in Africa. African musicians tend to be sopranos and baritones - the big altos and tenors tend to be a purely American phenomenon likely created by the unusual combination of genes.

All of this has given the United States a global advantage. Their innovations are more successful than those from other countries. Their music, which is dominated by African Americans, has cultural hegemony in the world. Their movies dominate world media. Their scientists hold more Nobel prizes than other countries,

The only country that comes close is the UK, which also has a history of absorbing people (the number of prominent Brits with an Indian ancestor thanks to the Raj is huge - Richard Branson, Sebastian Coe, Prince William among others). Western Europe from the 18th century onwards (especially the UK, France and the Netherlands) tends to be more heterozygous than Eastern Europe, with resulting disparities of wealth.

All of this suggests that the USA won't be toppled from it's position of world superpower any time soon. To be a superpower you need good institutions, a large number of people, and of those people, a high proportion who are intelligent.

Monocultures like the Soviet Union and China lack those advantages because they are homozygous. The only possible challenge might come from South American if countries there can sort out their institutions.