Some people are taller than others. Others have wider hips, lighter hair, longer toes, or flatter feet. No one disputes that our genes help determine how we look. But what about intelligence—is it an inherited trait?

And as our ability to tinker with the genomes of human embryos comes closer to reality, will creating babies with enhanced intelligence be far behind?

Before taking that leap, we would have to understand the genes that contribute to intelligence. Some scientists are on the hunt for such “smart genes,” and their research has come under fire. The two biggest specters: that the work could support racist notions of biological differences, and that it could make those designer smart babies a reality.

That’s why scientists are now being called upon to consider whether it’s ethical to study the genetics of intelligence. Researchers should think about “limits we should place or steps we can take to be sure we don't repeat historical errors,” such as forced sterilization of the “feeble-minded” in the early 20th century, said Mildred Solomon, president of the Hastings Center, a bioethics think tank.

In early December, the Hastings Center gathered a small group of scholars and ethicists in New York City to discuss the future of intelligence research. Earlier in the week, a more international gathering had debated the ethics of editing human genes—and both groups wondered whether some studies could lead so directly to dangerous applications that they shouldn't even be done in the first place.

Genomes of the Super-Smart

Hastings bioethicists got involved in this issue last year, when a noted behavioral geneticist approached the Johns Hopkins Center for Talented Youth hoping to study its alumni, who had been identified in their teens as highly gifted by scoring above 700 on the SAT in seventh grade.

The request made the Hopkins center’s administrators uncomfortable. The geneticist was searching specifically for intelligence genes by collecting and sifting through genomes of as many super-smart people as he could—including, he hoped, the high-scoring Hopkins participants.

Would the staff be doing something amiss if they helped him? Was there something just a little bit off about his request in the first place—and, indeed, maybe even about the very nature of his gene hunting?

Unsure how to proceed, the Center for Talented Youth sought guidance from the Hastings Center. Investigations into the genetics of intelligence, Solomon explained, could have many unintended consequences, such as altering the parent-child bond “as we gain more genetic control over the kind of children we can create.”

Too Hot to Handle?

The most critical speaker at the December meeting was Dorothy Roberts, professor of law and sociology at the University of Pennsylvania. She disagreed with some behavioral geneticists' claims that their work would help intellectually disadvantaged children, who she said would be better served simply by getting more resources. In fact, she said, any research that bolsters the hereditary concept of intelligence could actually hurt the disadvantaged, since it almost inevitably would be used to support “racist, classist, gendered notions of intelligence.”

The bottom line, to Roberts, is that studying the genetics of intelligence “cannot possibly be socially neutral—and in fact will intensify social inequities.”

In some ways, it's already too late to stop such findings. Twin studies from as far back as the 1970s have already shown that identical twins (who generally share 100% of their genes) are more similar in terms of general intelligence than are fraternal twins (who share roughly 50% of their genes).

According to Erik Parens, senior research scholar at Hastings, this has been taken to mean that general intelligence—that is, the ability to reason, plan, solve problems, comprehend ideas, learn quickly, and learn from experience—has a genetic component.

“But it's really, really important to realize that while twin studies can show us that genetics are making a difference as to why people are different in terms of intelligence,” Parens said, “it cannot tell us anything at all about which genetic differences are making a difference, or how.”

The “which” and “how” questions are now being asked by scientists looking for smart genes, most prominently the behavioral geneticist Robert Plomin of University College, London. “The ultimate test will be to find the genes” that affect the heritability of learning ability, Plomin said recently in a BBC Radio interview.

But that search is proving difficult because there is no single gene, or even handful of genes, specifically “for” intelligence. Even using today's most sophisticated tools of molecular genetics, Parens pointed out that just three genetic variants have been found so far, each explaining a mere .02 percent of the variation between control subjects and people with high IQs.

“We're talking about many, many genes, thousands perhaps, of very small effects,” Plomin said. He called himself a “truth seeker,” and expressed annoyance at people who say “we should shut up and not talk about this stuff.”

What's been learned to date about smart genes won't yet have much impact on the real world.

“If you take someone who has that best possible combination of those variants, the person with the best possible combination will have two IQ points more than the one with the worst possible combination,” said James Tabery, a philosopher at the University of Utah.

And the importance of those genes could easily be overblown, he warned. “If you give just a whiff of a genetic explanation, people latch on to that and think that is really the driver of differences.”

Proceed With Caution

Safeguards are needed so that research findings are not used to further marginalize already-marginalized populations, according to a new report by the Hastings Center and Columbia University’s Center for Research on Ethical, Legal & Social Implications of Psychiatric, Neurologic & Behavioral Genetics.

The report doesn’t issue any blanket prohibition on research into the genetics of intelligence. But it does urge caution.

Researchers must do more than “guard against hyperbole” about the significance of their results as portrayed in the popular press, the report editors write. They also have to take steps help ensure that the study of intelligence isn’t drawn into a “vortex of classism and racism.”