A Show of Hands Researcher's single-minded pursuit of what makes righties and lefties leads to an interesting hypothesis, no matter which side you're on.

December 11, 1997|By Linell Smith | Linell Smith,SUN STAFF

FORT DETRICK -- It almost seems like science fiction: A geneticist sets out to discover why identical sister cells of yeast develop differently -- and comes up with an explanation as to why most people are right-handed.

What's more: His answer may advance the search for a cure for cancer.

At the moment, however, the route is paved with controversy. The scientist -- Amar Klar, head of a basic research lab at the National Cancer Institute's Frederick campus -- is proposing that genetics causes right-handedness, while many scientists still believe it is environmentally determined.

These scientists argue that handedness could not be inherited because 18 percent of identical twins show different hand preferences. They point out that handedness can be taught, whereas genetically determined traits such as eye color are immutable.

The more people disagree, the better, Klar says. Science is as much about disproving ideas as about proving them.

So far, statistics from his multi-generational human studies have impressed his learned colleagues, and now he's taking his hypothesis to the streets. He has discussed handedness with people in bars, strangers in train stations and any unsuspecting athlete who happens to share a whirlpool with him.

"People don't have to have a Ph.D. to understand this stuff," the 50-year-old scientist says. "And everyone has a strong opinion about it."

So here is Amar Klar's Hypothesis of Handedness:

1. Just as there is a cellular mechanism that controls human sidedness -- your heart is on one side of your body, your liver on the other -- there is also a mechanism that controls handedness.

2. Klar proposes that the mechanism is a gene form. A single gene can have many variants, some of which are functional, others inactive. Klar believes the gene for handedness has essentially two forms.

3. Eighty-three percent of the population carries the form that makes them right-handed.

4. Here's where it gets really interesting: There is no equivalent form that ensures left-handedness. Instead, the remaining 17 percent of the population carry a form of the gene that allows the random determination of handedness. Half of these people will be right-handed, the others will be left-handed, based on the same 50-50 principle of chance that controls the flipping of a coin.

Explaining the differences

The existence of a gene for random handedness explains the fact that roughly one in 11 people is left-handed or ambidextrous. And it may be able to demystify family differences that have baffled observers for years, such as how two left-handed parents can have a right-handed child. Or how one identical twin can be left-handed while the other is right-handed.

For Klar, the clincher was a two-year study of 100 three-generation families that had two left-handed grandparents. In these families, the right-handed children of two left-handed parents turned out to be "special" right-handers -- those who may have the gene for random handedness -- who gave birth to as many left-handed offspring as any other left-handed parent would.

Now, he and colleague Joy Sabl are trying to map the handedness gene using blood samples.

Bruce Stillman, director of Cold Spring Harbor Laboratory, the world-renowned genetics research institution, calls Klar's hypothesis "fantastic."

"It's an extremely innovative synthesis of a lot of complicated data. It's by no means proven, but I think it is a very simple and elegant hypothesis that is very testable."

Like most basic research funded by cancer institutions, the handedness study relates only indirectly to the disease. The scientists hope it will bring them closer to understanding how cells decide where they are supposed to be; when cancer metastasizes, cells lose their basic orientation.

Studying handedness may also shed light on how the human brain is organized; left-right hand orientation can affect which hemisphere is responsible for language processing and cognition and which controls spatial and non-verbal tasks.

If brain surgeons knew which hemisphere their patients used for language, for instance, they could better plan operations for tumors or epilepsy. Such knowledge might also help physicians figure out how well people could recover from strokes.

Over the years, many researchers -- primarily mathematicians and psychologists -- have proposed both genetic and sociological explanations for handedness. So far, no other models have provided the kind of results as Klar's multi-generational study.

"We think handedness is a simpler problem than people have made out," the geneticist says. "The psychologists think it is a very complex thing with a big impact from environment. I believe the primary engine of handedness is simple. What happens later may be more complicated.

"I grew up in India and they tell you to use your right hand for a lot of things. The issue here is whether you are inherently predisposed to be using one hand or the other," says Klar, who is right-handed.

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