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quote:Look down at your right hand. Is your ring finger longer than your index finger? Or vice versa? To be certain, take a ruler and measure from the bottom crease of each finger to the tip.The measurements tell you something about the environment of your mother's womb just weeks after your conception, a time when your fingers, and more importantly, your brain, were developing. Because of the influx of sex hormones at this prenatal stage, men tend to have ring fingers that are slightly longer than their index fingers. In women, these fingers are usually the same length or the index digit is just a bit longer.Digits are subtly affected by testosterone and estrogen produced in the womb by the fetus (not by the mother). Between weeks 8 and 14, tiny fetal testes, ovaries and adrenal glands secrete the baby's own supply of sex hormones. These chemical messengers, particularly testosterone, cause chain reactions in the body, spurring the growth of the genitals, encouraging and inhibiting growth in brain regions and causing changes in the fingers. Many scientists believe relative finger length—or digit ratio—is a marker for brain differences molded by hormones. Like a bit of prenatal graffiti, a longer ring finger says, "Testosterone was here."John Manning, a biologist at the University of Liverpool, first identified digit length as a sign of prenatal hormones eight years ago. He believes digit ratio is an important, if indirect, tool for studying the fetal brain and the womb, an environment that's off-limits to scientists except for analysis by amniocentesis. (And even then, because sex hormones fluctuate hour by hour, amniocentesis is a poor indicator of testosterone exposure.)"Early sex hormones have an organizing effect on the brain that's permanent," Manning says. But the differences between the sexes aren't all that interesting to biologists. More telling are the variations within each sex. Females with masculine digit ratios have more masculine behaviors, he says. Likewise, males with a typically female ratio exhibit more typically feminine behaviors.A recent study of digit ratio in Scottish preschool children between the ages of 2 and 4 found strong relationships between digit ratio and gender-normative behavior. Girls with masculine-type finger ratios tend to have higher hyperactivity scores and more problems relating to their peers than do other girls. The same study, published in Early Human Development, found that boys with female-type finger lengths are on average more emotional than other boys. "They tended to be very sensitive," says Manning.Except for genitalia, relative finger length is the only physical trait fixed at birth that is sexually dimorphic—meaning males and females show typical gender differences. Other sexually dimorphic traits, such as height and waist-to-hip ratio, don't appear until puberty."Everything you see as far as sex differences in the behavior of toddlers is an aftereffect of prenatal testosterone," says Dennis McFadden, a psychology professor at the University of Texas at Austin. Manning and others have linked finger length ratios to aggression, left-handedness, heart disease, autism and attention deficit disorder, all traits that are more common in men. (Studies indicate they are most common in men with longer than average ring fingers.) A "masculine" finger pattern seems to similarly mark girls predisposed to hyperactivity and autism.Some scientists believe prenatal sex hormones are also part of the puzzle of homosexuality and that a high level of testosterone may wire the brain for attraction to the same sex. Intriguingly, research shows that a prenatal testosterone level is most strongly linked to homosexuality in women, according to a recent article in the Archives of Sexual Behavior. Lesbians are more likely than straight women to have a masculine finger ratio, says McFadden.
quote:It has been suggested that autism may arise as the result of exposure to highconcentrations of prenatal testosterone. There is evidence that the ratio of the lengthsof the 2nd and 4th digit (2D:4D) may be negatively correlated with prenataltestosterone. We measured the 2D:4D ratio in 95 families recruited via the NationalAutistic Society, U.K.. The sample included 72 children with autism (23 withAsperger’s syndrome, AS), 34 siblings, 88 fathers, 88 mothers and their controls. Wefound that the 2D:4D ratios of children with autism, their siblings, fathers and motherswere lower than population norms. Children with AS, who share the social andcommunicative symptoms of autism but have normal or even superior IQ, had higher2D:4D ratios than children with autism but lower ratios than population norms. Therewere positive associations between 2D:4D ratios of children with autism and theratios of their relatives. Children with autism had lower than expected 2D:4D ratiosand children with AS higher ratios than expected in relation to their father’s 2D:4Dratio. We conclude that 2D:4D ratio may be a possible marker for autism which couldimplicate prenatal testosterone in its aetiology.
quote:Canadian researchers say they’ve found a way to help ‘finger’ men with physically aggressive personalities.A University of Alberta study finds that measuring a man’s index finger length relative to his ring finger length predicts his predisposition to being physically aggressive.The shorter the index finger relative to the ring finger, the higher the amount of prenatal testosterone and the more likely the man will be physically aggressive, they researchers say.In a prepared statement, study co-author Dr. Peter Hurd admitted he initially thought the finger-aggression link was “a pile of hooey,” until he reviewed the data.According to the researchers, experts have known for a hundred years that the index-to-ring finger length ratio of men differs considerably from that seen in women. And more recently, research has suggested that the length of men’s fingers changes depending on their exposure to testosterone in the womb.
quote:Originally posted by geckoi didnt mean what i said about criminality, i was being overly dramatic, and it wasnt really needed.i actually would say that all studies of personality traits are invalid, or at least, have to have much more substantial proof than they already do. extraordinary claims need extraordinary evidence. and something like "people with long ringfingers are more agressive" is a pretty extraordinary claim.ive been pretty anti-psychiatry since i became aware of the "science"(guesswork) in treating peoples personality "disorders"(quirks). i know this is a position few agree with, so maybe i shouldnt bother bringing it out.