The Gene: An Intimate History - Siddhartha Mukherjee Page 0,158

if this is what we mean by “race,” then the concept has not just survived the genomic era, it has been amplified by it.

The problem with racial discrimination, though, is not the inference of a person’s race from their genetic characteristics. It is quite the opposite: it is the inference of a person’s characteristics from their race. The question is not, can you, given an individual’s skin color, hair texture, or language, infer something about their ancestry or origin. That is a question of biological systematics—of lineage, of taxonomy, of racial geography, of biological discrimination. Of course you can—and genomics has vastly refined that inference. You can scan any individual genome and infer rather deep insights about a person’s ancestry, or place of origin. But the vastly more controversial question is the converse: Given a racial identity—African or Asian, say—can you infer anything about an individual’s characteristics: not just skin or hair color, but more complex features, such as intelligence, habits, personality, and aptitude? Genes can certainly tell us about race, but can race tell us anything about genes?

To answer this question, we need to measure how genetic variation is distributed across various racial categories. Is there more diversity within races or between races? Does knowing that someone is of African versus European descent, say, allow us to refine our understanding of their genetic traits, or their personal, physical, or intellectual attributes in a meaningful manner? Or is there so much variation within Africans and Europeans that intraracial diversity dominates the comparison, thereby making the category “African” or “European” moot?

We now know precise and quantitative answers to these questions. A number of studies have tried to quantify the level of genetic diversity of the human genome. The most recent estimates suggest that the vast proportion of genetic diversity (85 to 90 percent) occurs within so-called races (i.e., within Asians or Africans) and only a minor proportion (7 percent) between racial groups (the geneticist Richard Lewontin had estimated a similar distribution as early as 1972). Some genes certainly vary sharply between racial or ethnic groups—sickle-cell anemia is an Afro-Caribbean and Indian disease, and Tay-Sachs disease has a much higher frequency in Ashkenazi Jews—but for the most part, the genetic diversity within any racial group dominates the diversity between racial groups—not marginally, but by an enormous amount. This degree of intraracial variability makes “race” a poor surrogate for nearly any feature: in a genetic sense, an African man from Nigeria is so “different” from another man from Namibia that it makes little sense to lump them into the same category.

For race and genetics, then, the genome is a strictly one-way street. You can use genome to predict where X or Y came from. But, knowing where A or B came from, you can predict little about the person’s genome. Or: every genome carries a signature of an individual’s ancestry—but an individual’s racial ancestry predicts little about the person’s genome. You can sequence DNA from an African-American man and conclude that his ancestors came from Sierra Leone or Nigeria. But if you encounter a man whose great-grandparents came from Nigeria or Sierra Leone, you can say little about the features of this particular man. The geneticist goes home happy; the racist returns empty-handed.

As Marcus Feldman and Richard Lewontin put it, “Racial assignment loses any general biological interest. For the human species, racial assignment of individuals does not carry any general implication about genetic differentiation.” In his monumental study on human genetics, migration, and race published in 1994, Luigi Cavalli-Sforza, the Stanford geneticist, described the problem of racial classification as a “futile exercise” driven by cultural arbitration rather than genetic differentiation. “The level at which we stop our classification is completely arbitrary. . . . We can identify ‘clusters’ of populations . . . [but] since every level of clustering would determine a different partition . . . there is no biological reason to prefer a particular one.” Cavalli-Sforza continued, “The evolutionary explanation is simple. There is great genetic variation in populations, even in small ones. This individual variation has accumulated over long periods, because most [genetic variations] antedate the separation into continents, and perhaps even the origin of the species, less than half a million years ago. . . . There has therefore been too little time for the accumulation of substantial divergence.”

That extraordinary last statement was written to address the past: it is a measured scientific retort to Agassiz and Galton, to the American eugenicists of the nineteenth century, and to the