From the New York Times:

You Are Shaped by the Genes You Inherit. And Maybe by Those You Don’t.

Carl Zimmer

MATTER JAN. 25, 2018

For centuries, people have drawn the line between nature and nurture.

In the nineteenth century, the English polymath Francis Galton cast nature-versus-nurture in scientific terms. He envisioned a battle between heredity and experience that shapes each of us.

“When nature and nurture compete for supremacy…the former proves the stronger,” Galton wrote in 1874.

What’s striking about Galton is that he came up with all these epochal contributions to the history of thought very late in history, long after much more complicated questions had been answered. And yet Galton is clearly one of the most valuable thinkers in human history even though (although very smart) he probably wouldn’t rank among the most brilliant.

Today, scientists can do something Galton couldn’t imagine: they can track the genes we inherit from our parents. They are gaining clues to how that genetic legacy influences many aspects of our experience, from our risk of developing cancer to our tendency to take up smoking.

But determining exactly how any particular variation in DNA shapes the course of our life is proving far trickier than Galton would have guessed. There is no clean line between nature and nurture: How a particular variant acts, if at all, may depend on your environment.

A study published on Thursday offers a striking new demonstration of this complexity. Genes may help determine how long children stay in school, the researchers found, but some of those genes operate at a distance — by influencing parents. The study was published in Science.

The authors go on coin a new phrase for this effect: “genetic nurture.” To scientists accustomed to tracing the links between the genes you carry and the traits they govern, it’s a headspinning idea.

A genetic variant may shape you not because it directly influences you, but because it changes those around you, noted Paige Harden, a psychologist at the University of Texas who co-authored a commentary on the new study: “Something is happening outside your own skin.”

Long before scientists could easily read DNA, there were clues that genes influence how many years people stay in school. Researchers compared identical twins — who have virtually identical DNA — to fraternal twins, and in study after study the educational attainment of identical twins tended to be closer than that of fraternal twins.

The recent revolution in DNA sequencing gave researchers a new way to study the link. In 2016, for example, researchers in England surveyed hundreds of thousands of people and linked 74 different gene variants to how long the participants stayed in school.

Some of those variants were in genes active in the developing brain, perhaps influencing relevant traits — everything from how well people learn new words to how motivated they are by long-term goals.

Yet the connection between genes and education remains murky. Each gene variant, on average, accounts for just a few weeks of the total. And when researchers try to estimate how important these variations are in entire populations, they end up with different figures. Some researchers estimate the proportion at 21 percent; others have put it at as high as 40 percent.

Either figure means that a lot of variation cannot be accounted for by genetics. Factors in the environment may explain some of the variation: a family’s wealth, for example, or the quality of schools children go to, or their exposure to pollution.

When the first DNA-based studies of educational attainment came out in 2013, a geneticist named Albert Kong sifted through the results. At the time, Dr. Kong was working at DeCode, a genetics company based in Iceland, and so he was able to look for some of the variants in the company’s database of Icelandic DNA.

Dr. Kong wondered if other researchers had missed something very important. “It suddenly occurred to me that part of this effect could be coming through the parents,” he said. “And then I got obsessed with the idea.”

Children, after all, get their genes from their parents. It was possible, Dr. Kong reasoned, that genes could influence how far children got through school by influencing their parents’ behavior rather than the actions of the children themselves.

Here’s an example of this. Imagine two equally tall, athletic young guys who both have ambitions to play quarterback in the NFL. These days, successful NFL quarterbacks tend to have had a lot of Nurture as well as Nature going for them. It’s an incredibly competitive job, so the winners tend to be guys who are both tall and wide and had family help in learning their craft in vast detail. (Peyton and Eli Manning didn’t win four Super Bowls between them just because they inherited some of their NFL quarterback dad Archie Manning’s nature, but also Archie helped them by providing advanced nurture as well. But, what this article is saying is that Archie wouldn’t have had the experience at quarterback to be an expert quarterback nurturer if he hadn’t had good genes for playing quarterback.)

In our example, one kid’s father, however, was 6’4″ due to his genes and played quarterback in high school and was a second-stringer in college, and he coaches football. The other kid’s father was 5’7″ due to his genes and played soccer in high school and was a second-stringer in college, and he coaches soccer.

Which tall young fellow is more likely to get the most fatherly coaching in the advanced skills of playing quarterback: the one with the tall dad who indeed played quarterback or the one with the short dad who instead knows more about how to play soccer? …

But Dr. Kong and his colleagues focused their attention on variants carried by parents but not passed to their children. These variants, the researchers found, predicted how long the children stayed in school — even though the children had not inherited them.

… Their combined effect was about 30 percent as big as that of the genes that the children actually inherited.

… Dr. Kong speculated that the genes carried by parents influence the environment in which their children grow up.

Typical Galtonian reasoning would assign this effect to Nurture rather than Nature. Galtonites use twin and adoption studies to divvy influences up into Nature and Nurture, The two potential NFL quarterbacks could, conceivably, have swapped fathers for complicated adoption reasons and then the one with the adoptive tall father would get the environmental benefit.

Dr. Harden said that taking account of genetic nurture could improve research on the effects of poverty on how children do in school, as well as studies of methods to improve educational attainment.

On the other hand, this kind of reasoning shows even more limits to social engineering than in simpler Galtonian analyses, since the supply of parents with the more beneficial genes for optimal nurturing is not limitless. There might be tall guys out there who would have made it as an NFL quarterback if they had been adopted at birth by Archie Manning. But the supply of dads with the genes to get the experience playing NFL quarterback to pass along advanced quarterbacking tips to their sons, biological or adoptive, is highly limited.

For other traits beneficial in nurture, nature’s supply of genes among parents might not be as rare, but it is still less than infinite.

[Comment at Unz.com]