A genetics perspective on race

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21 March is International Day against Racial Discrimination, so it’s perfectly on theme that we talk about race, albeit a little late. Race is something that appears simple at first but is actually quite complex. Most scientists agree that race is entirely social, but what does it mean to be a social construct? It also infringes on the common assumption that race has a genetic component. If genes determine your skin colour, shouldn’t it determine your race?

Here’s the thing: two people from the same race don’t necessarily have more genes in common than people from different races. [1] Race is not shared genetically, it is shared culturally. While a black person can share a language, music and ceremonies with other black people, they can realistically have more in common genetically with a white person than another black person.

This strange scientific discovery was first discovered by American biologist Richard Lewontin in his paper The Apportionment of Human Diversity, [2] in which he studied genetic markers from seven distinct ‘races’ and noticed this palpable observation.

His work was later criticised (ineffectively) by A W F Edwards, thus birthing “Lewinton’s fallacy”, an argument heavily utilized by white supremacists [3] . During the 1970s, genetic technology was not as advanced as it is currently; it wasn’t possible at the time to sequence the entire human genome. It was much more prevalent to observe different phenotypes (like skin colour) and assume that stronger differences in phenotype equates to stronger differences in genes. Reality, however, is rarely as simple.

While skin colour is readily observable, other genetic differences don’t appear easily to the human eye. For example, it is difficult to observe, from a cursory view, whether a person possesses genes that make them lactose intolerant. It could be assumed that a White man doesn’t, but such assumption should not be construed as truth. Lactose tolerant Black people exist, and so do White lactose intolerant people. You can observe what a person looks like, but someone’s exact genes are never guesswork.

An assumption could be made in which two people of different races are tolerant to lactose. However, it cannot be said with certainty that the genes governing their tolerance to lactose are exactly the same. Genes govern biochemical processes in the body which can become very complex. They could have mutations in completely different locations in the lactase gene, or a separate gene altogether that has a contribution in the pathway. [4] While genetic differences could cause differences in phenotype, genetic differences could also make similarities in phenotype.

This phenomenon is called convergent evolution, in which a population evolves to become phenotypically similar to another population simply because their environment calls for it. An East African population has independently evolved lactase persistence due to herding cattle [5] , a hundred miles away from the European population. Thus, alt-right claims about milk digestion being an exclusively European trait is dishonest. [6,7] While geographically separated, African and European ancestries evolved to have similar phenotypes (i.e. milk digestion) [8] and this is not an isolated case. Arabic ancestries also evolved separately to be lactose tolerant. [9]

Convergent evolution does not always lead to similar gene sequences. Merely, the product of those genes are similar. Recall the complexity of biochemical processes: mutations in vastly different locations in the genome could lead to a few similarities in phenotype. [10] It is genetic convergence that refers to convergent evolution that does lead to similar genetic sequences. While lactose tolerance is not an example of genetic convergence, a vast majority of human traits do show genetic convergence. [11] For example, the genes for cholesterol appear to evolve similarly in all human populations around the globe. The strongest reason behind this is the adoption of farming, which acts as a selection pressure. [12]

The impact of farming to human genetics is huge: humans are evolving to become more similar. Even chimpanzees, which to our human eye look similar to each other, actually have more genetic diversity than humans. This was proven true in 2003; after the conclusion of the Human Genome Project (HGP). It found that 99.9% of the human genome is the same in all populations and that any differences per individual could be attributed to a mere 0.1% of the human genome. [13,14] This same study also affirmed Lewinton’ theory that there were more differences within a group than outside of it.

A clinal population model

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The human species follows a clinal distribution of genes. [15]
Clinal or cline may appear to be an unfamiliar word in isolation, but can be understood as a gradient distribution. Gradients typically describe the shape of a graph and indicate whether the shape is an incline or a decline. An example of gradient distribution is skin colour, which is clinally distributed: the greater the UV light penetration, the greater the skin colour. While both Southeast Asian, South Asians and East Asians are categorically under the Asian umbrella of race in Western countries, they have many variations in skin color depending on the UV penetration of the region they originate. Hence, populations become a more accurate terminology to use in genetic studies, as opposed to race.

Global skin colour distribution of native populations. The colours on the map are based on the 36-tone chromatic scale devised by Austrian anthropologist Felix von Luschan to assess the unexposed skin of human populations. The higher numbers represent darker skin colour. Original data compiled by Biasutti 1941s. doi:10.1371/journal.pone.0022103.g002

As time goes on, any organism with DNA will slowly accumulate mutations. Mutations are defined as random changes in the sequence of DNA. Mutations have a random chance of occurring, and paired with the knowledge that human genome exists in clinal variation, it could be safe to assume a probabilistic view. What is the possibility of two randomly sampled humans with no familial relation to have similar gene variants? Now, what about the possibility of two randomly sampled humans with no familial relation to have similar gene variants and be members of the same population?

To tackle this probabilistic problem, let us first define an allele. An allele is a gene variant, which we will denote as A.

An allele has a certain frequency within a population, which we define as p. p can also be defined as the probability of inheriting allele A. The probability of inheriting a different allele, or not inheriting this allele is 1-p, which we define as q. We will call this other allele a (lowercase). Let’s assume the value of p and q are both 0.5.

Let’s put this all into a table for easier viewing. Remember, p and q remain constant as both are sampled from the same population.

Since a person has two copies of genes, they have three possible genotypes: AA, Aa, aa.
The probabilities of each genotype is calculated below:

Hence, let’s calculate the probability that two random individuals from the same population have the same genotype.

Which adds up to 0.0625 + 0.25 + 0.0625 = 37.5%. There is a 37.5% chance two individuals from the same population share the same genotype, and a 62.5% chance two individuals do not share a genotype.

Out-of-Africa Theory

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When participating in a commercial DNA test, they will mention your ancestry as part of the results. This doesn’t mean they have a model human genome that represents a specific population. Rather, they identify alleles in your genome and attribute it to being alleles common to a specific population. The key word here is common: while alleles for blue eyes are common in Northern Europeans, it is not exclusive to it, and does not represent all Northern Europeans. Alleles can be common in certain populations but cannot represent those populations.

All ancestries descend from Africa. [16-18] It is hypothesized that the first humans came from Africa, and migrated to other parts of the globe, forming all varieties of populations. At least two major expansions of human populations occurred. [19] Not only is it a mistake to assume the premodern world had isolated civilisations that developed independently with genetic proof of migration; interbreeding between populations occurred during and after migration events. A Tibetan population could interbreed with the Han Chinese population, introducing new alleles into the gene pool. Once this allele is introduced, it spreads within the population, thus forming the clinal distribution.

By Saioa López, Lucy van Dorp and Garrett Hellenthal - López, S., van Dorp, L., & Hellenthal, G. (2015). Human Dispersal Out of Africa: A Lasting Debate. Evolutionary Bioinformatics Online, 11(Suppl 2), 57–68. http://doi.org/10.4137/EBO.S33489 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4844272/, CC BY 3.0

Older lineages tend to accumulate more mutations. As time advances into tens of thousand years, DNA makes more and more random changes to be passed down to offspring. The African lineage, being the eldest, will thus accumulate the most mutations compared to other lineages, and thus two people of African ancestry will have less in common than two people of European ancestry. In fact, it is entirely possible for a person of African ancestry to have more in common with a person of European ancestry than another person of African ancestry. This is because the European lineage descended from the African lineage, and thus is younger and has less time to accumulate mutations.

Race as shared culture

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Race does not work as a biological concept; it is a categorical social construct. It is the shared culture that makes race, not genetics. In fact, a study in the US reported that many self-reported racial identities do not match genetic ancestry. [20,21] The study found that there was a gradient of ancestral proportions within a race category, affected by the transatlantic slave trade, colonisation, and migration.

Historically, race was coined during European eras of exploration (now commonly referred to as colonisation) in which colonists identified different skin colours and speculated in differences of culture. In 1775, Blumenbach described 4 major races: Caucasian, Mongolian, Ethiopian and American. [22] Modern views have adapted Blumenbach’s classification into White, Asian, Black and Native/Indigenous.

Race was a construct used to justify exploitation such as slavery. [23] Modern views such as critical race theory posits that race is a construct to justify racism and is facilitated by the legal system to maintain inequality. [24] While systemic racism is beyond the scope of this article, it remains justified to consider race as a social construct and not a biological one, and that any that state otherwise is ignoring a decade of genomic analysis and population studies.