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Is Our Fate Written in the Lengths of Our Fingers?

July 08, 2001|DEBORAH BLUM | Deborah Blum is a Pulitzer Prize-winning science writer and author of "Sex on the Brain: The Biological Differences Between Men and Women."

MADISON, Wis. — From my childhood, I remember one particularly goofy joke. It started like this: "What's the first sign of insanity? Hair growing on your knuckles." Then, just as the victim checked his or her own knuckles, came the punchline: "What's the second sign? Looking for it." The teller and any lurking observers would crack up, and we'd all troop off to try the joke on our siblings.

When the first reports linking finger length to behavior appeared, I had a sudden flashback to those days of checking for hairy knuckles. Scientists have now measured hundreds of people's hands and linked their finger structure to an extraordinary array of behaviors--musical talent, athletic ability, spatial skills, dyslexia, stuttering, sexual orientation. In March, British researchers added autism to the list.

It sounds like a gotcha joke--but one with potentially troublesome consequences. I can envision the scenarios: couples peering at each other's hands on the first date; parents checking their children's hands for signs of trouble; gloves becoming popular again as those of us with the "wrong" fingers (mine are, of course, "normal") seek to hide them,

Except, of course, that it's hard to keep a joke going in the face of reasonable science. When you really start exploring the connections between finger length and behavior, they turn out to be less hilarious than we joke lovers might hope. What they provide is a window on the ways scientists try to figure out who we are--and the ways that human biology, beautifully complex, gorgeously convoluted, makes that so hard.

All of this is really about the length difference between two fingers, the index finger (second) and the ring finger (fourth, counting from the thumb). Biologists call this the 2D:4D ratio. It appears that in the first trimester of pregnancy, as hormones are pitching in to help build the body, exposure to testosterone can result in a difference in lengths of these two fingers. Why? Unclear, although biologists have known for a long time that testosterone helps shape some bone growth--high, chiseled cheekbones, for instance. Now it appears that those of us exposed to a little more prenatal androgen tend to have a ring finger that's longer than the index finger.

It means, not surprisingly, that men--the testosterone heavies in our species--usually have longer ring fingers than index fingers. British researcher John Manning, at the University of Liverpool, sees testosterone as a potent force here. He did the recent autism work and is considering the role of hormones in that disorder. He's also done studies suggesting that exceptional athletes and math whizzes may have gotten an early high dose of testosterone. Manning has found, for instance, that some of Britain's best soccer players tend to have extra-long ring fingers compared to the index.

I'm wary of any finding that fully associates the size of a body part with a laundry list of behaviors and abilities. Those mistakes have been made in science before, to our cost, as with the 19th-century belief that because women have slightly smaller skulls than men they are dumber. And, even if there is a statistical correlation between the 2D:4D ratio and male athletes, that still doesn't make testosterone the sole source of athletic prowess. And it doesn't say much about female athletes at all. In women, overall, the finger ratio is different. Index and ring tend to be closer to the same length, the index maybe a little longer.

The exception to that, for women, seems to be regarding sexual orientation, which then begs a couple of questions. Is orientation set before birth? If testosterone shapes fingers prenatally, could it shape sexual behavior as well? When scientists at UC Berkeley decided to look into this last year, they were unsure what they would find.

The Berkeley study is one of those lovely examples of scientific reasoning. How do you get a diverse sampling of finger lengths? Researchers went to street fairs in Berkeley with a portable photocopier and copied 720 fairgoers' hands, while asking them pointed questions about their sex lives. What the Berkeley group found, published in the journal Nature, was that lesbians' finger lengths tend to resemble the more classic male hands. Do male homosexuals have hands in the so-called female pattern? It's not that easy, naturally, and those results have been contradictory.

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