Race is a word with an ugly history. Powerful countries have often used supposed differences between “races” as an excuse to conquer and enslave nations with technology less advanced than their own. In the 18th and 19th centuries, European scholars tried to disguise racism as science in order to justify exploitation and slavery. The eugenics movement of the early 20th century followed in their footsteps, and the Nazis likewise borrowed from 19th-century pseudoscience in their efforts to legitimize their deranged ideology.
With a history like this, it’s no surprise that among those who study human genetics, the word “race” still has the power to provoke controversy. Just last week, for example, the magazine American Scientist ran a review by Jan Sapp about two new books which argue race is a myth:
Although biologists and cultural anthropologists long supposed that human races—genetically distinct populations within the same species—have a true existence in nature, many social scientists and geneticists maintain today that there simply is no valid biological basis for the concept. The consensus among Western researchers today is that human races are sociocultural constructs.
Jerry Coyne, an evolutionary biologist at the University of Chicago, disagreed and said so:
Well, if that’s the consensus, I am an outlier. I do think that human races exist in the sense that biologists apply the term to animals, though I don’t think the genetic differences between those races are profound, nor do I think there is a finite and easily delimitable number of human races.
It sounds a lot like a quibble over definitions — and in fact, that’s exactly what it is. But tempting as it is to dismiss it as mere semantics, it matters, because as history illustrates, words like these shape the way we see the world.
So does this concept we call “race” have any basis in reality? Or is it a myth?
If you asked the average American to explain what “race” means, they’d probably mention skin color, because skin color is the most obvious difference between human populations. There are of course some other physical differences too. One interesting example is ethanol.
If you’re Asian-American or have Asian-American friends/colleagues etc., you may have heard of or experienced the so-called “Asian flush” or “Asian glow”. It’s not unique to people of Asian descent by any means, but this swift rosy-cheeked reaction to even small amounts of ethanol is far more common among East Asians than among those of Caucasian descent. I’ve known folks who would flush red after drinking less than half a beer — which isn’t a lot of alcohol, at least not for me.
The origins of the “Asian flush” lie in the way your liver metabolizes ethanol. When you drink wine (or beer, or a Jack and coke, or a vodka Red Bull, or whatever), the ethanol is absorbed into your bloodstream through the lining of your small intestine and your liver gradually breaks it down through a two-step process. In the first step, ethanol is converted to acetaldehyde in a reaction catalyzed by an enzyme called alcohol dehydrogenase.
Ethanol is on the left, acetaldehyde on the right. Another molecule called NAD+ takes part in this reaction but I’ve omitted it here.
Acetaldehyde is significantly more toxic than ethanol; here in California, in fact, it’s classified as “a chemical known to the state of California to cause cancer”. To keep the State of California happy, your liver converts the acetaldehyde into acetate, just like the acetic acid in vinegar. This second reaction is catalyzed by enzymes called aldehyde dehydrogenases. The most important of these for our purposes is called ALDH2.
The gene for ALDH2 lies on chromosome 12 (the full sequence of the gene is here). About 4/5 of the way through the gene (position 42421 in the GenBank file at the link above) you have the following DNA sequence:
In the ALDH2*1 version of the protein those first three letters — GAA — code for an amino acid called glutamate. In the “Asian flush” version of the gene (we’ll call it ALDH2-flush), a mutation has swapped out the G for an A, and the “AAA” triplet codes for an amino acid called lysine instead. The resulting enzyme is ineffective. If you inherit two copies of ALDH2-flush (one from each parent), your liver will still convert ethanol into acetaldehyde, but getting rid of the acetaldehyde is a slower process. After you drink, you temporarily end up with higher levels of acetaldehyde in your bloodstream — hence the flushed red face and other accompanying symptoms.
But it gets worse. The ALDH2 enzyme doesn’t work alone; 4 ALDH2 molecules clump together to form a single enzyme complex with four subunits*. Any time some of these subunits are ALDH2-flush, the resulting enzyme complex has reduced activity. So let’s say, for example, you inherit ALDH2*1 from your mom and ALDH2-flush from your dad. Now half of the ALDH2 protein produced in your liver cells is ALDH2*1, while the other half is ALDH2-flush. Most of the enzyme complexes that form will contain at least one ALDH2-flush subunit. Consequently, even if you inherit just one copy of the ALDH2-flush gene, the level of ALDH2 activity decreases by a much greater amount than you’d expect, given that you still have one “active” copy of the gene.
That’s why even people with just one copy of the ALDH2-flush variant still exhibit alcohol flush (albeit with less severe symptoms than those who have two copies). The young man in the “before-and-after” picture below, for example, inherited one copy of the ALDH2-flush gene. (This picture is from the PLoS article under ).
Now we come to the truly strange part of this story. ALDH2-flush is comparatively rare in European and African populations, but somewhere over a third of East Asians (Japan, Korea, China) have one or two copies of the ALDH2-flush gene, so through some bizarre quirk of our evolutionary history the “flush” variant of the gene has become fairly common in the East Asian population. And nobody really knows for sure why that might be.
Nor is this the only peculiarity of ethanol metabolism, because there are some interesting variations in other genes, most notably ADH1B. But I’ve wandered a little far off topic, so I’m going to come back around to this idea of different populations.
Clearly there are some interesting genetic differences between populations from different regions of the globe. Skin color, hair color and facial features are the most obvious, but there are others like ethanol metabolism and lactose intolerance too. So is it fair to call these different populations “races” on the basis of these genetic differences? Which is really another way to ask the question: what does the word “race” actually mean, anyway?
When I look up “race” in the Concise Oxford English Dictionary, I get the following not-very-concise definition:
1. Each of the major divisions of humankind, having distinct physical characteristics.
2. A group of people or things with a common feature.
3. A distinct population within a species; a subspecies.
The first definition is the one that’s been used historically, and I think it’s what most people have in mind when you say “race”. It’s a useless definition, because it assumes there are “major divisions” of humankind which are fundamentally different from each other, and that’s a completely incorrect assumption. The second definition is so vague it’s meaningless; by this definition, I could call candy bars a “race” because they contain sugar. And the third definition won’t work, because there is more genetic variation within these populations than between them. I like the way Jan Sapp puts it:
race is little more than skin deep in biological terms, and individuals are frequently more genetically similar to members of other so-called races than they are to their own said race.
So yes, there are interesting genetic differences between populations like skin color, hair color, ethanol metabolism and lactose intolerance, and ultimately the explanation for each of these lies in our evolutionary history. But while this genetic variation between human populations seems striking to us, it’s actually fairly trivial compared to the amount of genetic variation within human populations. These genetic differences are superficial and of relatively recent origin. And in the modern world, populations that were once kept relatively isolated from each other by geography are now mingling to an ever-increasing extent, such that the concept of “race” is becoming ever more meaningless.
You could of course define “race” another way. In his post, Jerry Coyne defines “race” thus:
In my own field of evolutionary biology, races of animals (also called “subspecies” or “ecotypes”) are morphologically distinguishable populations that live in allopatry (i.e. are geographically separated). There is no firm criterion on how much morphological difference it takes to delimit a race. Races of mice, for example, are described solely on the basis of difference in coat color, which could involve only one or two genes.
Coyne is right in a way. If you want to define “race” as a way to classify humans based on an arbitrarily-chosen morphological feature I suppose you could do that. But that makes nonsense of the word, because that’s not historically how race has been defined. Unless you redefine it to mean something it didn’t mean until now, I personally think the word “race” as applied to humans is basically meaningless (and loaded with a ton of ugly historical baggage into the bargain). If you want to describe a particular group, say people of East Asian ancestry, there’s no reason why you can’t use the word “population” instead.
We humans have a mania for categorizing things — classifying objects into discrete categories based on similarities and differences. It helps us to spot patterns and make sense of our world, so it’s often a useful habit. We have to be very careful, however, to make sure that the categories we use 1) are useful and 2) a reflection of the underlying reality.
A good example is the concept of species. If two organisms can mate and produce fertile offspring, we say they belong to the same species. But what about organisms that don’t reproduce sexually like bacteria? Pretty much any large population of bacteria will have some genetic diversity, and different populations of, say, E. coli could be genetically different from each other in lots of interesting ways. How different do they have to be from each other before you say, “These are now different species”? The problem here is that when it comes to bacteria, “species” is a category we invented, not a fundamental feature of the underlying reality. And Nature doesn’t care about our categories. The bacteria in a given population are what they are, regardless of how we categorize them. Nonetheless, we continue to classify bacteria into species because it’s a useful way for us to study them.
Similar considerations apply to the word “race” as applied to human populations. Does it reflect some fundamental underlying feature of reality? In the way it has conventionally been defined, no, it does not. Is it a useful categorization? No, not at all — in fact, throughout history this ill-defined, ridiculous concept has served as an excuse for exploitation and bloodshed. We are all members of the same subspecies, Homo sapiens sapiens. I agree with Sapp’s take: rather than redefining the word “race” in a futile effort to pretend it has some remaining utility, I think it’s high time we send the myth of “race” to its long-overdue end.
*i.e., a homotetramer.
 Nathalie Druesne-Pecollo, Bertrand Tehard, Yann Mallet, Mariette Gerber, Teresa Norat, Serge Hercberg, Paule Latino-Martel, Alcohol and genetic polymorphisms: effect on risk of alcohol-related cancer, The Lancet Oncology, Volume 10, Issue 2, February 2009, Pages 173-180, ISSN 1470-2045, 10.1016/S1470-2045(09)70019-1.
 Brooks PJ, Enoch MA, Goldman D, Li TK, & Yokoyama A (2009). The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption. PLoS medicine, 6 (3) PMID: 19320537