"Recent, copious and regional." These are three words, according to New York Times science correspondent Nicholas Wade, that describe human evolution. That is, our development as a species has continued to the present, has involved significant changes, and (at least until modern travel became available) proceeded separately in each part of the world.

Or, in other words: Your eyes aren't fooling you, and those sociology and cultural-anthropology professors you had in college were full of it. Human races exist.

Wade has been gently broaching this subject for a long time, regularly reporting new genetic findings on the pages of the Times and even including a chapter on race in his terrific 2006 book Before the Dawn. But in his new work, A Troublesome Inheritance: Genes, Race and Human History, he dives in head-first. He covers everything, from the hard facts that establish the biological reality of race to highly speculative theories about how, exactly, racial groups might differ from each other genetically.

It's an important book. It should demolish the idea that race is nothing whatsoever but a "social construct" and jumpstart a conversation about human history. But unfortunately, A Troublesome Inheritance does not equip readers to deal with the broader ramifications of the claims it makes: Though such concerns are arguably outside the realm of science, these theories have the potential to inflame racial prejudices, and Wade's attempts to address this fact leave much to be desired.

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The basics of Wade's story are, as they say, "settled science." At this point there is very little dispute that humans first emerged in Africa, and that a small group of people left the continent around 50,000 years ago. After that, humans spread throughout the globe -- creating new populations wherever they went. These populations were often separated from each other, and they encountered different environments that could drive evolutionary processes.

Some of this evolution involved completely new features. Early humans with light skin, for example, were at a disadvantage in Africa, so whenever a light-skin mutation occurred, natural selection weeded it out. But as human populations moved north, light skin became beneficial, so these mutations took hold. One skin-color mutation shows a particularly extreme trend, being present almost all the time in Europeans and almost never in Africans.

That's not how it usually worked, though -- evolution involving new mutations takes a long time. Not only are beneficial mutations rare, but it takes many generations for them to spread from a single individual to a whole population.

More typically, evolution acted to gently reshape the variation that already existed within humanity. Many parts of the human genome are not fixed through the entire population -- that's a big reason why people have different heights, facial features, personalities, etc. And for a lot of characteristics, there isn't a single gene at work, but rather countless genes working together, each exerting only a small influence on the final product. When environmental circumstances change and new traits become valuable, evolution can begin immediately, increasing the frequency of helpful gene variants until the balance is just right. Here's an illustrative example from Wade: If there are 500 different genetic variants that can each boost height by 2 millimeters, increasing the prevalence of those variants by just 10 percentage points would cause the average height to climb eight inches. (Those checking the math should note that each person has two copies of each chromosome, so the average person would get 100 more height-increasing variants.)

This can happen faster than you might think; deliberate breeding in animals can show significant results in fewer than ten generations and remarkable transformations in 30 or so. Evolution may happen more slowly, depending on how strong selection pressures are, but it certainly has been happening: Wade cites one estimate that in humans, 14 percent of genes exhibit signs of recent natural selection. And most of this selection affected different racial groups differently.

Because human races emerged through such subtle changes, it can be underwhelming to look at a single gene -- to borrow an example from Razib Khan of Gene Expression, a variant might be present 40 percent of the time in one racial group but 45 percent of the time in another. But as Wade notes, these small differences add up quickly, and scientists can use these "ancestry informative" DNA markers to easily sort humans into population clusters -- clusters that correspond almost perfectly to the casual classifications people have used since well before the genetic age.

One can debate how broadly or narrowly to define the clusters -- just how many races are there? -- but it's undeniable that human populations exhibit distinctive genetic patterns. Racial groupings are human decisions, and so is the social importance we attach to those groupings. But race, more broadly construed, is a feature of humanity itself.

The big question is what these genes do -- when natural selection acted, what exactly was being selected for? Researchers have figured some of it out; genetic differences account for racial differences in skin tone, resistance to malaria, etc. But for many genes that have apparently been subject to recent natural selection, all we have are vague indications of their function. Wade writes that these genes affect "fertilization and reproduction," "skeletal development," and "brain function" -- and no, "brain genes do not lie in some special category exempt from natural selection."

That's what we know to a reasonable degree of certainty. Anything further requires speculation, and Wade boldly goes there.

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If genetics cannot yet tell us what each gene does, perhaps we can get some clues by looking at history, and in several chapters in the second half of the book, Wade explores theories about the trajectories of different population groups. An overarching theme is that while institutions matter greatly -- just look at the difference between North and South Korea -- it is possible that some institutions are better able to take root if certain genetic adaptations have already taken place. If human populations in some parts of the world, but not others, evolved slightly higher levels of trust, a slightly greater tendency toward nonviolence, and so on -- perhaps because population density forced them to live in close proximity to each other, abandon tribalism, and develop states -- that might help to explain why some populations have become unusually peaceful, democratic, and economically productive.

Wade himself concedes that these chapters contain much that isn't proven, and his ideas have raised eyebrows even among experts who like much about the book and are not beholden to political correctness. Here's Bell Curve coauthor Charles Murray, in his Wall Street Journal review: "Mr. Wade chose to expose his readers to a broad range of speculative analyses, some of which are brilliant and some of which are weak." And here's a tweet from evolutionary psychologist Steven Pinker: "Disagree w much of Wade (goes beyond data, gets some wrong) but he explodes race-is-only-a-social-construction myth."

No doubt, these theories will be subjected to rigorous analyses by historians, population geneticists, and other high-caliber experts in the months ahead. Here's a sample of what they'll be discussing:

(1) Why did the Industrial Revolution occur first in England? Wade lays out evidence, collected by the economist Gregory Clark in A Farewell to Alms, that those in England's upper classes had been having more children than those in the lower classes -- possibly affecting traits including "interpersonal violence, literacy, the propensity to save and the propensity to work," and in turn transforming the population into one capable of immense economic output. An enormous population growth spurt starting around 1770 finally set the revolution off, and it quickly spread to other nations that were similarly situated.

(2) Wade says China had the right evolution but not the right institutions to take advantage of industry once it emerged, which is why its economy didn't take off until it adopted economic reforms. Wade notes the examination system that was in place in China starting in 124 B.C., which he says created a sort of meritocracy that allowed the best scorers to rise in society and have the most children.

(3) Did violent tendencies evolve differently in different places? Wade notes that, among the Yanomamo of South America, men who have killed in battle have 2 1/2 times as many children as those who don't. And he cites evidence that one gene that seems to contribute to violence -- "MAO-A" -- doesn't show up evenly across populations, with one evidently violence-promoting variant being present in 5 percent of African-Americans but only 0.1 percent of Caucasians. The "gracilization" of the skull -- the thinning that occurred as humans became less likely to try to bash each others' brains in -- shows a pattern too, but a very different one: It's "most pronounced in sub-Saharan Africans and East Asians, with Europeans retaining considerable robustness." Still another genetic variant, one related specifically to violence when drunk, has been found in Finns.

(4) Wade also digs into Jewish history, relaying theories that the religion's emphasis on literacy -- a skill with little practical value in a farming society -- may have driven the less intelligent to join Christianity instead, and that European Jews' being highly concentrated in intellectually demanding professions like moneylending may have further contributed to increased IQ.

Could these narratives hold the key to understanding important elements of human history? Maybe. But are they suitable for a book aimed at the general public? That's a dicier question. As Wade writes, scientific speculation is fine so long as it's labeled as such, but this isn't just any old topic. At the very least, one would hope an author presenting these theories at length would carefully explain how to stop this kind of information from causing great harm.

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At numerous points Wade tries to offer such an explanation, but his attempts are underwhelming. In one early chapter, Wade offers a history of eugenics and scientific racism, and he says scientists have a responsibility to "test rigorously the scientific ideas that are placed before the public." This is a rather striking claim considering the rest of the book -- and elsewhere he downplays these concerns, saying that "opposition to racism is now well entrenched, at least in the Western world. It is hard to conceive of any circumstance that would reverse or weaken this judgment, particularly any scientific evidence."

Wade should be more worried. There's really no telling what the future of racial tensions will look like or how science will factor in, even if we limit our discussion to the Western audience most likely to read A Troublesome Inheritance. The Cliven Bundys and Donald Sterlings of the world aside, we have seen dramatic improvements in racial attitudes in the last 50 years -- but there's no guarantee that our progress will be maintained or advanced in future generations as Western nations become increasingly diverse; as the horrors of slavery, colonialism, fascism, Soviet communism, and forced sterilization recede from national memories; and as attempts to root out lingering racism reach heights that many find ridiculous (see, for example, recent complaints about tiny slights called "microaggressions").

Certainly, it is illogical to draw conclusions about an individual from the racial group he belongs to, even if every last one of Wade's theories is true. Remember, evolution worked on human populations mainly by subtly shifting gene frequencies -- every race has individuals with all sorts of attributes, even if the averages turn out to be a little different. But not everyone has a solid grasp on these kinds of statistical concepts. For many, there is no difference between "genes that increase X are slightly more common in this racial group" and "members of this racial group are inherently high in X." When X is, for example, intelligence or propensity to violence, this perception can lead to serious societal problems.

Perhaps the solution is to do a better job of teaching this distinction to the public, but thus far the media and academy have been no help whatsoever. As Wade points out, instead of explaining that race is real but racism is wrong, they are presenting the assertion that race is imaginary as a reason that racism is wrong, and branding as a racist anyone who suggests that evolution might happen to humans too. Since human evolution has indeed been "recent, copious and regional," we are seeing that what we've been taught is "racist" is actually just true.

There are ramifications for public policy here, too. As Wade writes, some have already used the idea that racial differences in IQ scores might be partly genetic (those supporting this theory usually give an estimate around 50 percent genetic and 50 percent environmental) to argue against education programs that seek to narrow racial gaps. These folks are wrong -- if a gap is 50 percent environmental, there's still good we can do, even if we haven't figured out how yet -- but genetic differences could indeed force some of us to rethink gaps in general. Liberals have long assumed that all racial gaps result from discrimination, while conservatives have protested that there are important cultural factors at work too. Proof of a genetic contribution would demolish the Left's core assumptions and complicate the issue of when policies like affirmative action and "disparate impact" (a federal rule that makes it difficult for employers to use tests on which different racial groups have different pass rates) are defensible.

And what about foreign policy? Wade's theories can underpin arguments about, for example, how we should approach "nationbuilding" projects. These ideas could keep powerful countries from making huge mistakes in the developing world. Or they could make rich nations give up on helping poor ones out of a belief that it's pointless.

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The stakes here are high, and these topics deserve much more attention than they've been getting. A Troublesome Inheritance has more flaws than one would hope, given the incendiary topic and the brilliance Wade has demonstrated in his other writing. But it ought to serve as a catalyst for a much bigger conversation about new discoveries in genetics and their implications.