Righty or Lefty May Hinge on Genetic Throw

FREDERICK, Md. — A single gene may separate most right-handers from lefties.

Geneticist Amar J.S. Klar, who studied three generations of southpaws, says people with the gene are right-handed and those without it have a 50-50 chance of being either right- or left-handed.

While others debate his theory, Klar, a researcher at the National Cancer Institute’s genetics laboratory in Frederick, is plunging ahead with his next project: actually finding the gene.

Many studies suggest that handedness is primarily a learned trait. Genetic theories like Klar’s contend instead that people are hard-wired for handedness in the womb. His study was published last month along with other papers presented at the 1996 Cold Spring Harbor Symposium on Quantitative Biology.

He contends that those who inherit the gene, from either parent or both, are born right-handed. Those who lack the gene altogether have a random chance of being either right- or left-handed.

Klar calculates that 82% of people have at least one copy of the gene, making them right-handed, while 18% lack it. Half of those lacking the gene are right-handed; the others are left-handed or ambidextrous, he said.

There is a precedent in genetics for such a theory. In mice, the normal placement of the heart and liver on the left side of the body is determined by a single gene. When the gene is disabled, half the mice are born with their organs on the left side and half with their organs on the right.

Earlier genetic theories don’t explain why 18% of identical twins--twins who have the same genetic makeup--have different hand preferences. The random element in Klar’s theory answers that question.

“The hallmark of great science is that it reduces complexity into simplicity, and this is one of the things I like about this model,” said Bruce Stillman, director of the Cold Spring Harbor Laboratory, a molecular biology lab in Cold Spring Harbor, N.Y.

Isolating the gene for handedness would end the debate over its cause and help end prejudice against southpaws, said Kim Kipers, managing editor of Lefthander Magazine.

“I hope he’s right,” she said, “and I think he makes a good case for it.”