Inbreeding and Genetic Diversity – Will there soon be an American Super Race?

It’s common knowledge that some Kings and Queens married their own cousins or even siblings in order to “keep the crown within the family”. However, what was little known at the time was that such inbreeding was actually killing off entire dynasties. In the beginning of the 18th century, inbreeding caused the extinction of an entire line of Spanish Kings  with the death of Charles II of Spain, who was disabled, mentally retarded and disfigured. Known as “the Bewitched”, his speech was incomprehensible, he had epileptic seizures, became senile very early on in life, and was impotent. The reason? 16 generations of inbreeding.

CharlesCharles II of Spain. Source: Alchetron

These sexually sacrilegious spaniards make the Lannisters from Game of Thrones seem positively incest free.

Inbreeding vs Incest

Right. Time for some terminology. Firstly, incest and inbreeding are not the same thing. You don’t need to get explicit with relatives for inbreeding to occur – if a population is highly inbred, then individuals who are not “related” according to “social norms” may still be genetically similar enough that the pairing can not credibly be stated as a genetic outcross. This means that inbreeding can be a real threat for small communities who breed only amongst themselves.

So what’s the science behind it? Why exactly does inbreeding cause such problems? A look at the DNA

You’ve all heard about DNA. Discovered in the pubs of Cambridge, DNA is a long molecule that contains all our genetic code. This molecule is packaged into worm-like structures called chromosomes.


Wiggly worm like structures called chromosomes

Now every chromosome in human DNA is present in two copies (except for the sex chromosome in males, which come in two different kinds called X and Y).

Since genes are located on these chromosomes, we also have two copies of almost every gene. Some of these genes, however can be mutated.

What is a mutation?

Genetic mutations occur when information in a gene is changed in some way. Mutations can be inherited from a parent or acquired in certain cells throughout a lifetime.

These mutations can carry genetic disease. However, and here’s where it gets interesting – the principles of recessive inheritance state that both genes in the pair must be defective in the exact same way in order to cause the disease.

It takes two to mess up

This means that for these particular genetic diseases, having one recessive gene is OK. As long as we have one healthy gene, the recessive gene won’t cause any problems. However, if both copies are affected, the deleterious effect of the mutation shows, since there is no more healthy back up.



So what has this got to do with inbreeding? People who are related to each other share much more of their genetic code than unrelated people. Therefore, they will also share more mutations, making it more likely that the child will pick up two copies of the recessive gene.  

This is especially true for closely related people (siblings on average share 50% of their DNA). Between other types of relationships, the chances of getting two recessive genes due to inbreeding varies, and depends on how much the population has been inbred in previous generations. This chance is measured using an inbreeding coefficient.

The Inbreeding Coefficient

If there’s one thing scientists have shown, it’s that you can put numbers to just about anything. Many anthropologists calculate what is known as an “inbreeding coefficient”, symbolised by the letter F. This coefficient measures the probability that a person with two identical copies of a gene inherited both from the same ancestor. For example, a child born to cousins will have an F value of 0.0625. For Charles II of Spain, however, he was not simply the offspring of a first cousin marriage, he was the culmination of repeated instances of cousin marriage over several generations, and hence had an F value of 0.254. The higher the value, the greater the degree of inbreeding in that lineage.

Ethics and dangerous diseases like sickle cell anemia

This means that mating with your sibling isn’t just gross, it’s dangerous.

Even if you believe that consenting adults should be able to have sex with whoever they like, let’s not forget there’s a third person at risk who has no say in the matter. As shown above, Inbreeding is dangerous because it drastically increases the offspring’s chances of picking up a matching pair of recessive genes, and thus they have a significantly higher risk of inheriting a genetic disorder of some sort.

These genetic disorders are known as autosomal recessive disorders—conditions that are inherited through recessive genes. Even though they may not manifest themselves as unbounded, messed up evil like in King Joffrey (Game of Thrones), they are lifelong and pretty awful. Some examples of such diseases are cystic fibrosis, sickle cell anemia, and albinism.

No attraction for siblings – does that mean this is evolutionary?

Fortunately, mother nature does have her own methods for preventing inbreeding. According to evolutionary psychologists, simply observing your mother care for another baby signals that the other child is a sibling and discourages sexual attraction. This means that social norms aside, there is an evolutionary reason why we don’t usually tend towards finding adopted siblings sexually attractive. How inconvenient and awkward would that be!

Outbreeding – does the opposite for genetic inbreeding apply?

Okay, so one thing we know for sure now is that the more closely related a child’s parents, the more at risk they’ll be of developing genetic defects. What’s still unclear though, is whether this means the reverse is true. Is it true that the more distantly related a child’s parents are, the more likely they’ll be to possess advantageous genetic traits? A study published in the journal Nature, showed an increase in height and intelligence throughout evolution may be linked to the genetic diversity of offspring’s parents.  

We’re getting smarter

These results may also play a role in explaining the ‘Flynn Effect’ – the increase in intelligence from one generation to the next first discovered in the 20th century.

While most people believe that socio-economic factors such as increased schooling education and better nutrition take the front seat, increased genetic diversity could also play a small role. The increase in intelligence due to the Flynn is too big to be explained by genetic diversity alone, but it could be a contributing factor.

Again, nature may be on our side in encouraging women to choose genetically different mates. The role of pheromones has long been known in encouraging sexual attraction. A “smelly t-shirt” from 1994 showed that women might actually be able to smell the best genetic mate to father their babies, preferring the scents of the men who were most genetically different from them. Turns out “opposites attract” does actually have a scientific basis.

So is that why some people believe mixed race children are genetically superior?

While many people DO believe that mixed race children are genetically superior to their racially pure counterparts, such a notion is difficult to investigate scientifically, because science does not go well with the concept of separating humans biologically by race.

Some of our genes (a very small 7 per cent) DO vary between continental populations along the lines of “races”. However the map of the human genome has shown that the DNA of human populations across the globe is a continuum, and not segmented with national boundaries. On the whole, however, parents from different parts of the globe have a higher probability of being genetically dissimilar, and hence are less likely to carry the same defective genes. So while it is hard to scientifically test that mixed-race children are genetically superior, the chances of them having the same recessive mutations are definitely reduced.

And finally… does this lead to the American super race?

As our world gets increasingly more global and social taboos against interracial marriages fade, mixed race babies are on the rise. 1.2 million people across Britain describe themselves as “mixed”, making mixed race the third-largest and fastest-growing ethnic minority group. This phenomenon is especially pronounced in the United States – The Wall Street Journal reported a few years back that 15% of new marriages in 2010 were between individuals of different races, more than double what it was 25 years ago.


After all, the United States is a racially diverse country that started off with immigrants from all over the world. As mixed race marriages are on the rise, the gene pool is getting increasingly diversified, which may lead to stronger, smarter, and healthier kids. This has led some scientists to predict that within the next 50 years, mixed race children will grow up to have distinct genetic advantages, and continued racial mixing will lead to to America forming some kind of “super race”.

Count Richard Nikolaus von Coudenhove-Kalergi in 1925 in Practical Idealism predicted: “The man of the future will be of mixed race. Today’s races and classes will gradually disappear owing to the vanishing of space, time, and prejudice. The EurasianNegroid race of the future will replace the diversity of peoples with a diversity of individuals.


Want to learn more?

A good explanation of genetic mutations.
A paper on the Role of Inbreeding in the Extinction of a European Royal Dynasty.


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