What Galton could not see

When a child who had tutors, a stable home, early coaching and parents who knew how schools work turns out to be good at something, the result is usually described as talent. The preparation disappears into the person. Years later, the gap between that child and one who had none of it looks like a difference in what each was born with.

This conversion of nurture into nature has a founding text, and its author stated it plainly. In Hereditary Genius, published in 1869, Francis Galton made two claims about eminence: that "social hindrances cannot impede men of high ability, from becoming eminent", and that "social advantages are incompetent to give that status, to a man of moderate ability."¹ If both were true, the people at the top would be there by nature, and the advantages around them would be decoration. The story is also the more comfortable one for the people it describes, since it makes a position look earned rather than inherited.

How often people talk this way is hard to count. Where the conversion happens is easier to find, and the evidence gathered since Galton contradicts both of his claims, most strikingly in the instruments built to measure nature in the first place. Advantage turns into apparent ability at specific places: the early selection points that measure what a child can do now and treat it as what the child is. And even genetic measures, which seem to be the cleanest test of the nature side, turn out to carry a share of upbringing inside them.

Galton was not careless about this. He saw the obvious objection: "much which I should ascribe to breed, others might ascribe to parental encouragement and example." His answer was to compare the sons of eminent men with the adopted "nephews" of popes, who received every advantage of patronage without the inheritance.¹ He tried to separate nature from nurture with the data available in his time. What he could not see was how much of the separation happens at the point of selection itself.

At the point of selection

Gifted programs are a clean case, because they claim to find a fixed trait. In the early 2000s, a large Florida school district identified gifted children mainly through referrals by parents and teachers, and its gifted classes were mostly White children from higher-income neighbourhoods: only 28% of third-grade gifted students were Black or Hispanic, against 60% of all students. When the district began screening every second grader instead, with no change in the standard for giftedness, the odds of being identified as gifted rose by 174% among disadvantaged students, by 118% for Hispanic students and by 74% for Black students. The newly found gifted children were disproportionately poor, Black, Hispanic, learning English, and girls. When the screening was suspended in 2011, gifted rates returned to their old levels.²

The children's abilities did not change when the district changed its procedure. What changed was who was looked at. A referral system measures, along with ability, whether someone in a child's life thinks to make the referral, and it recorded the result as a property of the child.

A study of 1.2 million American inventors, linking patents to tax records, shows the same divergence over a longer stretch. Children from families in the top 1% of income were ten times as likely to become inventors as children from families below the median. Third-grade math scores, highly predictive of patenting, accounted for less than a third of that gap: children from lower-income families were much less likely to become inventors even when they had been at the top of their third-grade class. By eighth grade, test scores accounted for about half of the gap. The authors read this as low-income children starting on "relatively even footing" and falling behind, while cautioning that test scores are an imperfect measure of ability.³ Between the third and eighth grades, an environmental gap appears to become a test-score gap, and a test-score gap is what later observers call ability.

Birth dates do the same in sport. Youth teams are grouped by calendar year, so a child born just after the cutoff can be nearly a year older than a teammate born just before it. A review of rugby studies found male players born in the first quarter of the selection year outnumber those born in the last by about two to one (34.8% against 16.9%), with the effect stronger in youth categories than in senior ones.⁴ A coach choosing the best eight-year-olds is partly choosing the oldest, then giving them better coaching, better opponents and more confidence.

Galton's second claim fails for a related reason. The inventor study found that exposure matters causally: children who grow up around people inventing in a particular technology are more likely to patent in exactly that technology, and girls are more likely to invent in a technology if they grew up where more women invented in it. If women, minorities and children from low-income families invented at the rate of white men from high-income families, the authors estimate, the United States would have four times as many inventors.³ Advantage does not only remove obstacles. It supplies a direction.

Inside the measure

The obvious reply is genetics. If ability is partly heritable, and it is, then some of the gap between classes should be inherited, and genetic studies should be able to say how much. They can say something, but the measurements turn out to be entangled with the environment they are meant to exclude.

First, heritability itself depends on circumstances. A meta-analysis of studies on intelligence and school achievement found that in the United States genetic influences are larger in richer families and suppressed in poorer ones; in Western Europe and Australia, where access to good schooling and health care is more uniform, the effect was zero or reversed.⁵ A heritability figure is a property of a population in a given environment, not a fixed fact about a trait.

Second, parents' genes act on children through the home as well as through inheritance. An Icelandic study computed a genetic score for educational attainment from the parental gene variants that a child did not inherit. Those untransmitted variants still predicted the child's education, with an effect about 30% the size of the variants the child did inherit, because they shape the parents and therefore the household. The authors called it "genetic nurture", while acknowledging that part of the signal could reflect how parents pair up rather than how they raise children.⁶

Third, the usual genetic estimates shrink when compared within families. Studies of siblings, who share parents and upbringing, find that genetic associations with educational attainment and cognitive ability are smaller within families than across the population; an earlier study the authors cite put the reduction for educational attainment at around 40%.⁷ Part of what population studies attribute to genes is the family and social setting that tends to come with them.

None of this says that ability does not vary between people or that it is not partly inherited. It says that the instruments best placed to isolate nature carry upbringing inside them, so a visible gap between social classes cannot be read as a gap in nature without first removing what came with the class.

What the conversion costs

The conversion is not always permanent. In rugby, the birth-date advantage weakens from youth to senior levels and in some studies reverses: late-born players who survive early selection go on to do relatively well, an explanation researchers have proposed as the underdog hypothesis.⁴ The gifted gap in Florida narrowed as soon as the district looked at every child.²

That points to where the real cost lies. The children a selection point passes over do not usually reappear later to correct the record. They leave the team, skip the advanced track, never meet the inventor, and their missing development leaves no trace, while the selected children's development is credited to their nature. Galton's claim that hindrances cannot impede ability was untestable in his time because the people it impeded were invisible to him. They are still hard to see, but where institutions have stopped relying on referral and first impressions and looked at everyone, many of them have turned up.