In exploring what's next for research on identical twins, the cover story for this month's National Geographic also charts the past of twin studies.

A big chunk of that history happened at the University of Minnesota.

In the 1980s and 1990s, the U's Minnesota Study of Twins Reared Apart conducted medical and psychological tests on identical and fraternal twins separated early in life. The U researchers' conclusions -- one being that IQ is largely determined by heredity -- countered popular beliefs about nature versus nurture.

The (fascinating) National Geographic article, "A Thing or Two about Twins," calls the U's research "a surprising twist" in the story of twin studies. It tells of Thomas Bouchard, Jr., who came across the case of two brothers, both named Jim, adopted by different couples:

"As soon as he heard about the two Jims, Thomas Bouchard, Jr., a psychologist at the University of Minnesota, invited them to his lab in Minneapolis. There he and his team gave the brothers a series of tests that confirmed their similarities. Although each had charted his own course in life, the Jim twins, as they came to be known, seemed to have followed the same paths.

'I remember sitting at a table with them when they first arrived,' Bouchard says. 'They both had fingernails that were nibbled down to the end. And I thought, No psychologist asks about that, but here it is, staring you in the face.'

Bouchard's research was controversial, the story says. That got me wondering about what the Star Tribune wrote about the work at the time.

I found a couple articles in the late 1980s and early 1990s. One, published in September 1987, carried the headline "Findings about identical twins may inspire some double takes." A front-page story in 1990 -- "U research on twins says IQ is 70% genetic" -- noted that Bouchard's work was "highly controversial" at the time. That article described Bouchard as "careful to point out that the research has not concluded that people are born with a certain, genetically determined intelligence level." The story continues:

"He described the idea as a 'blended theory of environmental influence.'

'We think nature manifests itself through nurture," he said. 'It's nature via nurture, not nature versus nurture.' He referred to the long-standing debate over whether the development of intelligence is genetic or environmental."

The study's findings, which got international media attention, changed the way people thought about heredity. "Bouchard delights in pointing out how one researcher recently changed an updated edition of a textbook," the 1987 article notes, "substituting the Minnesota study for a previous assumption that twins raised apart would be products of their environment."

Bouchard is retired now, he wrote via e-mail, and living in Steamboat Springs, Colo.