December 9, 2008
Earlier this year a Turkish study reported that in a sample of 386 right handed students, body height was found to correlate negatively with the right- and left hand digit ratios (significant for the left hand in men, and the right hand in women). This implicates that in both males and females evidence was found that a ‘low digit ratio’ is more frequently found in people who has a long body height.
|SOME ADDITIONAL POPULATION EVIDENCE:
‘Finger Guru’ John T. Manning presented in his first book Digit Ratio an overview of data related to the ‘digit ratio’ in various populations. This data (Manning, Barley, et al.; 2000) points out that e.g. in Spanish & British people (both populations for both men and women) a significant HIGHER ‘2D:4D digit ratio’ (the ratio between the index- and ring finger) was found, compared to for example the finger ratios in Finish & German people (again in both populations for both men and women).
Interestingly, especially Spanish people, and in a lesser degree British people as well, are known for their (relatively) short body height – while Germans & Fins are known for their moderelately longer body height (compared to the Spanish & British): see the figure below. This implicates that there appears to be a strong link between the Turkish study which was published in 2008, and the earlier population evidence mentioned by Manning!!
READ FURTHER ABOUT FINGER LENGTH & VARIOUS POPULATIONS:
October 1, 2008
The world’s most famous ‘digit ratio’ research, John T. Manning, has begun examining autism too. He teamed up with Simon Baron- Cohen and Svetlana Lutchmaya from the University of Cambridge, who have used samples of amniotic fluid to directly measure the levels of hormones that babies are exposed to in the womb.
|When the children reached their first birthday, the researchers measured their vocabularies and ability to make eye contact. Poor language skills and an unwillingness to make eye contact are early hallmarks of autism. They found that babies who’d been exposed to high levels of testosterone in the womb fared the worst.
“What we’re hoping to look at is whether finger ratios can be used as a proxy for hormones,” says Lutchmaya. Amniocentesis (sampling the amniotic fluic surrounding the unborn baby) is a risky procedure that only a few mothers choose to undergo, she says. But by measuring finger lengths instead, researchers can assess a random sample of children for possible early signs of impaired language and social skill development. Currently, they are checking the fingers of children for whom they have amniotic samples.
Meanwhile, Manning and Baron-Cohen have looked at the finger ratios of 49 children with firm diagnoses of autism, 23 with a mild form of the disorder called Asperger’s syndrome, and their families. The researchers found that autistic children tended to have very low 2D:4D ratios. Interestingly, children with Asperger’s syndrome had ratios that fell between those of autistics and unaffected children. “It fits exceptionally well with the theory,” says Manning.
Clearly genes play a role too in these conditions. But could fetal hormone levels explain other cognitive differences between the sexes? Janel Tortorice at Rutgers University in New Brunswick, New Jersey, thinks they may. She has measured finger ratios in 2D:4D ratio gay women and found that their hands were significantly different from those of heterosexual women-in fact, they tend to resemble those of heterosexual men.
But she has also found differences in the way these women’s brains work. “They have more masculine fingers and more masculine cognition,” she says. On tests of spatial and verbal ability, lesbian volunteers perform more like men than heterosexual women, she says. If this can be confirmed by further studies, perhaps Manning’s most recent suggestion is not as outrageous as it sounds. He claims that musical talent, too, is nurtured in the womb.
An overview of the scientific sources which have found a link between finger length (low ‘digit ratio’: 0.94) and autism:
* The 2th to 4th ratio and autism – 2001 (PDF)
* [Evaluation of the 2nd to 4th digit ratio in the patients with autism] – 2005 (Japanese study)