If you observe the residents of Japan and compare them to residents of the rural southern United States, you’ll note some differences. Some differences will be stark, others less so, yet they will not be isolated to religious and cultural practices. The differences that emerge will bleed into psychological and temperamental traits that also vary in noticeable ways across populations.

The reason for the existence of these differences, though, admits of no simple answer. Prevailing wisdom holds that the cultural and psychological differences that exist across human population groups were shaped largely by a confluence of history, sociological forces, and pure chance. This is likely true to some degree, but the prevailing wisdom — from my point of view — is incomplete. In Part I, we argued that human races exist, meaning that humans can be meaningfully classified into coherent groups based on genetic ancestry. If we’re going to take seriously the existence of meaningful racial variation we also have to at least consider that the genetic differences that exist across racial and ethnic groups also contribute to psychological and ultimately cultural differences across those same groups.

To suggest that races might possess slightly different temperamental, cognitive, and other psychological traits, and that some of these differences are partly genetic in origin, is to violate a powerful — perhaps the most powerful — academic taboo. The incendiary nature of the subject seems to flow largely from the fear that discussing biological group differences will foster racial prejudice among the general public. Indeed, people bent on quantifying human worth have erected racial hierarchies, propped them up with pseudo-scientific theories and folk understandings about group differences, and conscripted them into service towards reprehensible ends. History, in places, is a wasteland of tragedy when it comes to the treatment of minority individuals. Yet, the reprehensible treatment of minority groups currently, or in the past, does not constitute empirical evidence that race is a fiction, or that differences in the psychological constitutions across racial groups are purely environmental in origin.

Just as we argued in our first essay, a cosmopolitan society that assumes all individuals are equivalent in their worth should not be built on an assumption of human biological sameness. Whether human races are biologically, and even psychologically, identical is subject to puncture from empirical research; it might be true, or it might not be true. Our notions of human worth must reside on their own foundation; one separate from the need for racial groups to be biologically and psychologically indistinguishable. Any other approach is a textbook example of the moralistic fallacy — a misguided assumption that conflates how we think the world “ought” to be with how it “is” — and is thus a worldview vulnerable to demolition by scientific research.

Insuring the liberty and dignity of individual humans is morally laudable, regardless of whether race differences across any trait are the result of culture, biology, or some combination of the two. Human worth should never be tethered to the belief that human groups are identical in their biological constitutions. Human worth should never be attached to the belief that differences across groups must be the product of culture and nothing else. Group differences, and their causes, are questions that scientific inquiry can tackle. Whether those differences should have any bearing on how we treat individual humans is a moral question. The current essay is an attempt to deal with both topics.

Evolution, The Unity of Human Psychology, & The Ability to Drink Milk

It is important to first spend a moment providing a brief (simplified) overview of how evolution works. Toward this purpose, it seems reasonable to distill evolution by natural selection down to three principles (for the same points presented in a more wonderfully rich way, there is no one better to read than Richard Dawkins).

Principle 1: individual organisms (and their genes) are different from one another; there’s variation in nature.

Principle 2: in some cases, these differences produce advantages in the ability of an organism to survive and reproduce. This is especially important because the environment is fraught with challenges — everything from finding a mate (and persuading them to mate with you) to avoiding pathogens that can kill you.

Principle 3: the traits that confer these advantages are passed on via genes (the specific targets of natural selection); traits that harm reproduction are not. With this in mind, we can shift to why these principles matter so much for human evolution and differences that exist across groups.

As others have described previously, somewhere in the neighborhood of 150,000 to 200,000 years ago, modern humans (Homo sapiens) evolved in Africa. Roughly 50,000 years ago, we began migrating away from our original homeland to various other parts of the world (though some details are still debated). The “prevailing wisdom” was that up until that point, biological evolution had been sculpting not only a universal human physiology, but also a universal psychology. Though some evolutionary changes (diseases resistance, etc.) occurred post migration, our psychological constitution was thought to have remained largely unchanged. Put another way, biological evolution ceased for human psychological faculties. In some respects, this is true. No human being — regardless of his or her culture — is unfamiliar with the emotions of love, jealousy, or anger. Males are more impulsive, violent, and aggressive than females the world over; it’s not a pattern unique to Western society or to modernity. Evolutionary scholars have gone to great lengths documenting the host of “human universals” that exist the world over.

Why would there be such unity in the psychological repertoire of humans? Recall the principles of evolution discussed earlier. Our “humanness” (which is to say, most of our psychological traits) was largely shaped in Africa, and despite large-scale migration, humans all over the world faced very similar selection pressures. Like other animals, humans (regardless of where they happen to migrate) faced the challenges of finding food, finding mates, caring for offspring, and a host of other hurdles. It’s reasonable to expect that many of the traits — physiological, cognitive, and psychological — that helped us survive and reproduce in Africa did the same in Europe. In most important respects, there was no need for a large overhaul from natural selection.

Keep in mind, though, that once we began migrating and spreading out, different groups of humans lived (for tens of thousands of years) in sometimes radically different environments from one another. Some areas were hot, some were cold, and some were replete with certain pathogens, while others were not. Despite living in ecologies that were often quite different from one another, most researchers maintain that evolution simply works too slowly for any of this to matter (i.e., for natural selection to sculpt differences [especially psychological differences] across groups). It is true that evolution is a slow process, yet “slow” is a relative term. A stretch of 10,000 years (for example) is pretty brief evolutionarily, but is it enough time to make noticeable evolutionary changes in a population of humans?

Yes, it is.

The example most often trotted out to make this point has to do with the seemingly banal topic of dairy consumption; specifically, the ability to digest milk from birth until death. Many humans cannot, in fact, do this, as it requires the continued production of an enzyme beyond early childhood. The mutation that enabled lactose tolerance across the life span seems to have appeared sometime in the last 10,000 years. Natural selection would end up favoring the mutation; individuals who carried the gene were more reproductively successful (on average) than those who did not. Thus, the gene became more prevalent in some populations of humans relative to others. This type of rapid biological adaptation is important for a host of reasons; but in this case, it’s relevant because it pushes around our notions of what natural selection can do in a given (short) stretch of time.

The “Looming Crisis” That Lies Beyond the Dairy Cow

Make no mistake, evolutionary changes like the capability for lifetime dairy consumption are important occurrences in their own right, but these changes beg an obvious question. Should we assume that natural selection has only affected genes related to drinking milk (or skin pigmentation and resistance to certain types of disease)? For this to be true, it would have to mean that natural selection somehow managed to ignore our central nervous system (CNS) and, by extension, genes that are connected (directly and indirectly) to human personality and temperament. Temperamental and psychological traits are strongly related to survival and reproductive success in humans, moreover. Even slight differences in psychological propensities (being slightly more or less impulsive, or slightly more of less inclined to seek out new experiences, for example) might have had large effects on the survival and reproduction of our ancestors in the different environments they encountered.

What would be convenient at this point is if I could point you to five traits—or even one—and be able to say with a high degree of certainty that this trait differs across racial or ethnic groups because those groups encountered different selection pressures across the history of our species. One could certainly try and speak definitively, but it would still only amount to informed speculation, as the empirical jury is still out at this juncture. Some titillating possibilities exist, nonetheless, including the cognitive differences between Ashkenazi Jewish individuals and other ethnic groups. Some researchers have argued that the high IQ of Ashkenazi Jewish people — relative to other groups — is at least partially genetically caused, owing to intense selection pressures for intellectual capacity over the last several thousand years. Gregory Cochran, Jason Hardy, and Henry Harpending, specifically, have written on the topic. Yet, much more research is required.

As good fortune would have it, the technology available to ask and answer questions like these is rapidly advancing. The evolutionary psychologist Geoffrey Miller, some years back, wrote about the advances being made, for example, in gene sequencing technology. These “quantum leaps” forward are allowing researchers to resequence large portions of the genome rapidly, and for not much money. Miller, of course, was completely aware of what this meant for research into the sources of human differences, thus the “looming crisis” that the title of his article alludes to. Miller notes:

We will also identify the many genes that create physical and mental differences across populations, and we will be able to estimate when those genes arose. Some of those differences probably occurred very recently, within recorded history. Gregory Cochran and Henry Harpending argued in “The 10,000 Year Explosion” that some human groups experienced a vastly accelerated rate of evolutionary change within the past few thousand years, benefiting from the new genetic diversity created within far larger populations, and in response to the new survival, social and reproductive challenges of agriculture, cities, divisions of labour and social classes. Others did not experience these changes until the past few hundred years when they were subject to contact, colonisation and, all too often, extermination.

Given the rapid pace with which we know biological evolution can take place, the vastly different environments that humans encountered across the course of our history, and the unlikelihood that natural selection would skip over traits that were psychological and temperamental in nature, it’s simply a reasonable bet that some of the differences that emerge across human groups have been at least partly shaped by natural selection. Miller makes a final point, however, that resonates with a theme embedded in the start of the essay, and in part I.

He observes:

If the shift from GWAS [genome wide association studies] to sequencing studies finds evidence of such politically awkward and morally perplexing facts, we can expect the usual range of ideological reactions, including nationalistic retro-racism from conservatives and outraged denial from blank-slate liberals. The few who really understand the genetics will gain a more enlightened, live-and-let-live recognition of the biodiversity within our extraordinary species — including a clearer view of likely comparative advantages between the world’s different economies.

Miller’s essay ends on a decidedly upbeat note, but what if he’s wrong about something? What if people fail to adopt a “live-and-let-live” type of response? There is a human side of human biodiversity to worry about, and it is this topic that we turn our attention to next (Prior work offers arguments that dovetail generally with those presented here, and which offer far more detail than can be covered in a short, informal essay).

The Human Side of Human Biodiversity

It is interesting to consider that had the previous essay been about any organism other than humans there would be no need for this section. Whether or not natural selection shaped differences (psychological or otherwise) in a population of lizards is uninteresting to most people. But we’re not talking about lizards; we’re talking about people. The same people that we have to share this planet with on a daily basis. Can we trust ourselves, as a species prone to tribalism and xenophobia, to handle this type of information responsibly? As the psychologist Steven Pinker observes, the fear that is ever circling this topic comes in the form of a disconcerting possibility:

But if they [races] are not identical, it would be rational to take those differences into account.” He goes on, “If races or sexes are different on average, racial profiling or gender stereotyping would be actuarially sound, it would be naïve to expect information about race and sex not to be used to prejudicial ends.

Perhaps this is right. And after further thought and consideration, we—as a community of concerned scientists and members of society—ultimately decide that the risk is just too high. We cannot trust ourselves with information that could ignite a race war. As the neuroscientist Sam Harris recently observed, we may know precisely how to weaponize smallpox, but no good can come from making that information widely available. Many, perhaps even most, people wouldn’t act on it. Yet, all it takes is a few twisted souls to spark a holocaust. Better to err on the side of caution. Professional researchers, scholars, and philosophers, then, may reach a détente, agreeing to avoid discussions of the most incendiary traits that might differ across races (measures of general intelligence, for example), in effect declaring a moratorium on the issue.

We should ask ourselves, though, if scientists are not talking about race, who is likely to fill the airwaves with chatter? Individuals who have the inclination toward racial divisiveness are not likely to govern their speech about the topic as judiciously as scientists might. They will not call a moratorium, no matter how much we might like them to. When coupled with an unflinching, unscientific view of the world, an agenda is a powerful motivator. For someone like David Duke, for example, the silence of researchers only creates a vacuum that he can fill. Beholden to no ethics panel, or human subjects committee, people who would misuse information about race are likely to do so whether scientists study and discuss these questions or not.

Equally important, many in the academy would be motivated to rebut the claims of those seeking to foment racial unrest, moratorium or not, but how are they to do that? Canned retorts such as “there is no such thing as race” or “race differences are only a product of discrimination” are currently a preferred strategy. The trouble is both of these are empirical questions. You have to actually do the studies to know whether they are true. So a moratorium on race research only handcuffs our ability to counter bad arguments with better ones. This, of course, presents us with a catch-22: we could lift the self-imposed moratorium and do the research. But that brings with it the possibility that the findings don’t align with what we might hope (i.e., that there are no real race differences for psychological traits). Should such findings emerge, researchers could simply bury them. Not ideal, but if scholars protect the dignity of a group of humans by sitting on a finding or two, surely it’s a minor sin? You can only sit on so much, though, before the cauldron of findings overflows and you’re left to deal with it openly. This can be avoided with a moratorium, but then we’re back to square one. This sparks a near infinite regress of bad options.

This brings us back to the point made early in this discussion, and in Part I. Unless we’re prepared to engage in censorship, we should be prepared to learn about the potential existence of group differences, as well as their sources. Instead of moratoriums and canned retorts, however, we should instead shield human dignity entirely from assaults based on human differences. The best way to do that is to totally uncouple human worth from biological diversity. If a particular worldview is absolutely contingent on a particular truth claim, then it is subject to being falsified. If treating all humans as equal before the law requires that racial groups are identical in their temperamental tendencies, then it is a social value vulnerable to empirical findings. If all humans simply are equal before the law regardless of race or ethnicity (because we proclaim it as such), then no empirical finding about their biological differences could ever matter.

We concluded Part I by suggesting that “race exists, but racism doesn’t have to.” Nothing has changed. Different racial groups may have evolved slightly different psychological tendencies (or they may not have). Yet, if human worth rests on a foundation far removed from the fault line of human differences, then we have nothing to fear from a science of human biodiversity.