July 8, 2001
SCIENCE
Is Our Fate Written in the Lengths
of Our Fingers?
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.
Psychology professor Marc Breedlove is not sure why the
results are clear with
women. His speculation, though, is that it's easier for a
little extra testosterone to
affect females. Males, who tend to have at least seven
times as much anyway, are
designed to tolerate higher levels of the hormone,
whereas females "normally see
pretty low levels, so even a modest increase might be
registered by the brain."
Breedlove doesn't believe that all lesbians are merely
whipped up by a little extra
hormone floating in the amniotic soup. Some women may
become lesbian because
of that exposure, he says cautiously, but not all.
Hormones may influence, but their
power varies from person to person.
Over the last year or so, other scientists have tested
that lesbian finger result and
confirmed it. The most recent study, presented at the
Western Psychological Assn.
in May, is by Richard Lippa and Michael Cassens of Cal
State Fullerton. Lippa has
been pulling together a larger test group, including
college students, attendees at the
Long Beach Gay Pride Festival and so on. He expects to
have surveyed about 2,000
people when his results are tallied. He consistently sees
the lesbian-versus-straight
woman difference, although he emphasizes that it is a
small statistical difference.
When a scientist raises the "statistical difference"
flag, it usually means that these
studies tell you nothing about the individual. They are
group differences: If we
compare hundreds of lesbians to hundreds of straight
women, there will be more
male pattern hands in the lesbian group. But person by
person, there will also be
many straight women with longer ring fingers, gay women
with the usual "female"
hand and so on. Lippa also finds ethnic exceptions.
Latinos seem to have, overall,
the more "masculine" hand pattern, Caucasians more
female. He suspects that this
may be another kind of group variation, not necessarily
hormonal, in the same way
that height varies among ethnic populations.
So the more we look at our fingers, the more complicated
this gets. The
finger-length ratios are fascinating, says Lippa, because
"they provide a possible
measure, even if it is a very indirect and 'noisy'
measure, of prenatal hormone
exposure. Human prenatal hormone levels are very
difficult to assess in any direct
fashion." So that, for him, the 2D:4D ratios become a
"messy proxy" for early
hormone exposure, and the ethnic variations are part of
the noisy background.
Consequently, cautions Lippa, "there's simply too much
variability" to draw
conclusions about a person from his or her fingers. "You
need large numbers of
participants to see these effects," he says.
Despite such caveats, I suspect that many people will
find finger evaluations
irresistible. I did. I also speak with the expertise of
someone who has mentioned
this work to friends, family and fellow science
writers--all of whom instantly
whipped out a hand for analysis. So far, all have seen
the entertainment value. But
what about those who might take a more serious view?
We reside in a society still judgmental about sexual
orientation. It could be more
than risky--downright dangerous--if people become
convinced that finger length is
a reliable guide to a person's sexual preference. Critics
have suggested that the
danger makes the science not worth the risk. On that
point, I think they are wrong.
Yes, this work can be misinterpreted, despite all the
scientific instructions and
disclaimers. But these studies may also help correct even
bigger mistakes and help
counter judgmental attitudes about sexual orientation.
The research strengthens the
evidence that preference can be set before birth and
remain beyond our control.
If finger-length studies are, yet, a messy probe into
biology of behavior, then we
should support research that refines them, that moves us
that slight and critical step
closer to a genuinely thoughtful exploration of human
behavior, sexual and
otherwise.
Until then, the rest of us can at least enjoy the fact
that the personal finger check
holds up pretty well as a gotcha joke. Made you look,
right?
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