December 8, 2012
Prenatal testosterone exposure, as indicated by relative finger length, may be a marker of increased verbal aggression in adults, new research suggests.
In 2 studies, investigators measured the ratio of length of the second digit/index finger to length of the fourth digit/ring finger (2D:4D) of more than 600 young adult volunteers.
Those who had smaller 2D:4D ratios, which correlates with prenatal exposure to testosterone, reported more verbal aggression behaviors than did the participants with higher ratios. In addition, the male participants showed smaller 2D:4D ratios and higher levels of verbal aggression than their female counterparts.
“These findings are very promising,” lead author Allison Shaw, PhD, assistant professor in the Department of Communication at the University at Buffalo–State University of New York, told Medscape Medical News.
The investigators report that this is one of the first studies to use this method to examine prenatal testosterone exposure as a determinant of a communication trait.
Although verbal aggression may be beneficial in certain situations, such as when standing up for oneself if attacked, higher degrees of this behavior have been shown to be detrimental, they note.
“Understanding the causes of verbal aggression, both biological and social, will allow therapists to have a greater understanding of how to work with these individuals,” said Dr. Shaw.
“In terms of clinical practice, I think the take-home message is that there is a longer process that is involved with this. It’s not just a set of behaviors.”
The study is published in the October issue of the Journal of Communications.
Proxy for Sex Hormones
According to the researchers, the ratio of 2D:4D is an indicator of prenatal androgen exposure (PNAE).
“The endocrine literature indicates that the ratio of the length of 2D to 4D is smaller for men than for women and this difference is driven by PNAE,” they write.
“Most importantly, data indicate that 2D:4D is a proxy for sex hormones levels at the time of brain organization.”
Previous research has also shown a link between 2D:4D and mental rotation ability, courtship behaviors, dominance, athletics, memory, and physical aggression.
“I became very interested in understanding how prenatal hormones can affect adult behavior. And as a communications major, I was especially interested in looking at communication behaviors,” said Dr. Shaw.
She noted that a recent study suggested that 2D:4D could predict financial success over a lifetime, which then gave her the idea to apply this technique toward understanding communication behaviors “not just in a social context but also within a biological one as well.”
In the first study, 224 students from the University of Tennessee in Knoxville (52% women; mean age, 20.2 years) had each hand photocopied. From these images, measurements were taken of each finger from its tip to where it meets the palm of the hand.
Questionnaires that included Infante and Wigley’s verbal aggression measure were then administered to all participants.
The second study included 405 students from a large Midwestern university (49.6% women; mean age, 20.4 years). Investigators measured each of the participants’ fingers in person and from images of their hands.
These students filled out the same verbal aggression measure used in the first study as well as the self-reported Infante and Rancer’s Argumentativeness scale and the HEXACO Personality Inventory.
In the first study, the men’s 2D:4D ratio was significantly smaller than the women’s — but only on the right hand ( P = .005). The men also showed higher levels of verbal aggression than did the women ( P < .001).
In addition, there were statistically significant correlations between 2D:4D and verbal aggression for both hands in both the men and the women.
In the second study, the men had significantly smaller mean 2D:4D ratios than the women on both hands for both the in-person and the photocopied measures. These men were also statistically more verbally aggressive than the women, but they were less argumentative.
Finally, the higher the level of verbal aggression, the lower the 2D:4D ratio for both sexes for the live measure of the right hand and photocopies of both hands.
The ratio did not correlate with either argumentativeness or openness to other experiences.
“This second study showed that 2D:4D didn’t correlate with just any type of communication behavior. Instead, it was with a very specific behavior caused by prenatal testosterone exposure,” said Dr. Shaw.
“Future research would profit by attempting to explicate the mediating mechanisms that result in androgen exposure and differences in 2D:4D and psychological dispositions,” write the investigators.
Dr. Shaw noted that, even so, the difference between the second and fourth digits for everyone “is pretty small.”
“You can’t really look at your hand and know your ratio or know if you’re predisposed to be more verbally aggressive than someone else,” she said.
“Instead, this is a proxy. In human research, we don’t have the ability to measure things perfectly. So these indicators are very important.”
J Commun. 2012;62:778-793. Abstract - The Effect of Prenatal Sex Hormones on the Development of Verbal Aggression
Earlier reports about 2D:4D digit ratios and agressesion:
After various studies in the past had already suggested that 2D:4D digit ratio could be linked with the Big Five personality dimension Extraversion / Introversion, a new experimental study shows how the finger ratio combined with hand shape produces highly significant results.
The picture above displays a schematic presentation of the results: e.g. the ‘+’ and ‘-’ signs show the proportional tendencies in the hands of Extraverts and Introverts. Details regarding the underlying results are presented in the article:
October 16, 2012
Study in Namibia points out that males & females with a low 2D:4D digit ratio tend to get married at an early age:
The second to fourth digit ratio (2D:4D) is used as a potential marker for prenatal androgen exposure. It is associated with many behavioral and biological variables, including fertility and sexual behavior. However, direct association between 2D:4D and reproductive success—in populations where no contraceptives are used—has not been investigated. Here, we present a study conducted among the semi-nomad Himba population living in northern Namibia. 2D:4D ratios were calculated for a sample of this population (N = 99; 60 women, 39 men), and the results were correlated with age, marital status, age at first marriage, number of children, and number of marriages. As found in the majority of previous studies, males had lower 2D:4D ratios than females. The 2D:4D ratio did not correlate with number of children. Females and males with a more masculine 2D:4D were married earlier and were more likely to have a husband or wife. We suggest that mating preferences for females with masculine 2D:4D are related to masculinity of phenotypic and personality traits of such women, which are beneficial in harsh environmental conditions and/or higher facial masculinity, which influences the perceived age of an individual. At the same time, masculine (physically strong, dominant, and hardworking) males might gather resources necessary to marry their first wife earlier.
NOTICE: 2D:4D digit ratio is known to correlate with many aspects of marriage/relationships, including e.g. the age of the partner, the number of partners, the offspring & the wearing of wedding rings.
October 15, 2012
On october 9 (2012) Manning et.al. presented the very first 2D:4D digit ratio study in Klinefelter syndrome (XXY).
The results describe how Klinefelter syndrome is typically featured with a high 2D:4D digit ratio + short fingers.
The ratio of second to fourth digit length (2D:4D) is a correlate of prenatal testosterone. High 2D:4D is associated with low prenatal testosterone, and reduced sensitivity to testosterone. Klinefelter’s syndrome (KS; 47 XXY) affects the endocrine system, such that low testosterone levels are found in KS foetuses, new-borns and adults. To date, there are no published data regarding the pattern of 2D:4D in KS males. Here we consider 2D:4D in KS individuals (n = 51), their relatives (16 fathers and 15 mothers) and an unaffected control sample of 153 men and 153 women. Adult KS individuals were taller than their fathers and had shorter fingers than fathers and male controls. Compared with fathers, male controls and mothers, KS males had shorter fingers relative to height. With regard to 2D:4D, KS individuals had higher 2D:4D than fathers (right and left hands), male controls (right and left hands) and mothers (left hands). Among KS males older than 13 years there were 34 individuals currently prescribed testosterone and nine not prescribed. In comparison to the former, the latter individuals had higher right 2D:4D and higher right–left 2D:4D. We conclude that KS males have mean 2D:4D values similar to those found in female population norms. In addition, testosterone supplementation in KS males may be most common for individuals with low right 2D:4D.
- digit ratio;
- Klinefelter’s syndrome;
- prenatal testosterone;
- testosterone sensitivity
October 15, 2012
After various digit ratio studies found conflicting results related to Extraversion & sensation seeking (most pointed into the direction of a negative correlation), a new Dutch 2012 study suggest that other finger lengths require to be taken into account in order to find more clear results!
The (unpublished) results from a female only suggest that low 2D:4D digit ratio + long pinky finger are much more often found in the hands of ‘extroverts’ (8 out of 40 hands = 20%), while this combination is rarely seen in the hands of ‘introverts (0 out of 28 hands = 0%).
Additionally, a high 2D:4D digit ratio with short pinky finger is much more common in the hands of ‘introverts’ (5 out 28 hands = 18%), compared to the hands of ‘extroverts’ (3 out of 40 hands = 7.5%).
August 11, 2012
I had not looked at my right hand so closely since high school days when my friends and I tried to divine each other’s future. The middle finger stood tallest, followed by the ring finger and then the index. In my other hand, I held a science magazine with an illustration of a “masculine” hand. It looked like mine. Apparently, the index finger on a typical “feminine” hand is almost the same length as the ring finger.
The magazine went on to say what the implication of the long ring finger was: I had received more testosterone in my mother’s womb. Estrogen would have made my index finger longer. Finger lengths are obvious indicators of hormonal activity at a crucial time in fetal development.
There are hundreds of studies linking finger length ratio to pretty much everything: behaviour, cognition, personality traits, length and size of body parts, diseases, and more. According to one study, people with my kind of hand are more likely to show mental toughness, optimism and aggression. My “masculine” hand predisposed me towards drug or alcohol addiction, left-handedness, athleticism, and a disinterest in babies. My chances of landing in prison, going mad, or being murdered were high.
Another study suggested that people with male hands were less adept at gauging the moods of people in photographs. As a film editor, I had cut between shots of actors’ faces to accentuate drama, comedy, and pathos in innumerable scenes and episodes of television series. Had I done this without being able to read faces? Give me a break.
I researched where a feminine hand would take me: high risk of breast cancer, schizophrenia, eczema, and hay fever. A longer index finger also indicated the person had better verbal and literary skills. Did I blow my chance of being a good writer while still in my mother’s womb?
I measured the two offending fingers on my right hand since it is more sensitive to prenatal sex hormones than the left. Dividing the length of the index by the length of the ring finger gave me a ratio of 0.95, an average male hand. Women with feminine hands should have a ratio close to one since their index and ring fingers are close to equal length.
It even works in animals. Rats injected with testosterone produce babies with longer fourth digits in their right foot, which would correspond to ring fingers in our hands. High ranking female rhesus macaques had longer ring fingers than lower ranking ones, said one study.
Then came the surprise: long ring fingers make us a successful species. Besides using fire, humans are unique in their ability to throw missiles, such as spears and with slingshots. Having long ring fingers stabilises the middle finger, which provides greater accuracy in hitting the target, said one study. It’s possible that men with long ring fingers, who brought home the bacon more frequently, were preferred mates.
Our destiny is in our hands. But I remain unconvinced. Some studies were drawing conclusions from examining a few people. Many results were contested by others. The methodology was inconsistent: some measured left hands, while one got impossible ratios. It’s possible some of these traits, even finger length, could be inherited. Reading these studies was more entertaining than enlightening — like reading personality types according to zodiac signs.
When my eyes were bleary from reading too long, I said to Rom: “The finger ratio can tell two things — prenatal exposure to sex hormones and maybe sexual orientation.”
Rom asked: “And?”
“What’s your sexual orientation?”
“Possibly lesbianism,” my voice dropped a notch.
With a broad grin and a suggestive look, he commented: “That could be interesting.”
Unwilling to go down that path I pushed back: “In your case, your finger shows your stupidity.”
Rom held up his hand calling for a ceasefire. In the 1960s, he had been bitten by a prairie rattler and his index finger was obviously stunted.
A report by Janaki Lenin
In the two videos below are taken from a Korean TV program featuring Professor John Manning describing how he is able to ‘predict’ the talents in Korean children.
(Manning is talking about visuospatial skills vs. verbal skills)
December 27, 2011
Recently professor John T. Manning revised his theory about finger length ratio development. While he had already mentioned the role of prenatal sex steroids, now the ‘balance’ between sexe hormones (testosterone & oestrogen) has become a key-element in his theory.
Manning described his revision in the PNAS-article: ‘Resolving the role of prenatal sex steroids in the development of digit ratio‘.
Manning’s working hypothesis now includes the following 7 key elements:
1 – 2D:4D Finger ratio results from the balance between prental testosterone & prenatal estrogen;
2 – High 2D:4D finger ratio result from low testosterone concentrations OR high estrogen concentrations;
3 – Low 2D:4D finger ratio result from high testosterone concentrations OR low estrogen concentrations;
4 – The ring finger (4D) has much more hormone receptors than the index finger (2D), therefore the 2D:4D finger ratio is mostly driven by changes in the length of the ring finger (due to prenatal hormone concentrations);
5 – Studies in human & animals indicate that the link between prenatal hormones and 2D:4D finger ratio is generally stronger for the right hand;
6 – 2D:4D Finger ratio varies with sexe: males generally have longer fourth digits relative to second digits than females;
7 – 2D:4D Finger ratio varies with ethnicity.
“Armed with this list of skeletogenic genes linked to 2D:4D, we can now be more focused in our examination of the links between 2D:4D and the etiology of sexdependent behaviors and diseases of the immune system, cardiovascular disorders, and a number of cancers.”
September 6, 2011
For quite a few years researchers have assumed that finger length development and the 2D:4D digit ratio is directed by sex hormones. Nevertheless, until now direct experimental evidence was lacking. However, researchers from Florida have reported an important discovery. They discovered via a study of the limb buds in mice – which are known for having a digit length ratio similar to humans - that human fingers are likely to have likewise sex hormone receptors as seen in the paws of mice.
A few comments made by researchers Martin Cohn (one of the researchers from Florida) and ‘finger professor’ John Manning:
“The discovery that growth of the developing digits is controlled directly by androgen and estrogen receptor activity confirms that finger proportions are a lifelong signature of our early hormonal milieu,” Cohn said.
“I’ve been struggling to understand this trait since 1998,”said John T. Manning, Ph.D., a professor at Swansea University in the United Kingdom, who was not involved in the current research.“”When I read this study, I thought, thank goodness, we’ve attracted the attention of a developmental biologist with all the sophisticated techniques of molecular genetics and biology.” “When Zheng and Cohn blocked testosterone receptors, they got a female digit ratio,” Manning said. “I find this completely convincing and very useful,” Manning said.“We can now be more focused in our examination of the links between digit ratio and sex-dependent behaviors, diseases of the immune system, cardiovascular disorders and a number of cancers.” “He suggested that the 2D:4D ratio would be an interesting question, and I have to admit to being skeptical,” Cohn said. “When he came back with the initial results, I was blown away. We looked at each others hands, then got busy planning the next experiment.”
The new discovery provides a genetic explanation for a raft of studies that link finger proportions with traits ranging from sperm counts, aggression, musical ability, sexual orientation and sports prowess, to health problems such as autism, depression, heart attack and breast cancer.
The report about the new study appears in this week’s Proceedings of the National Academy of Sciences.
An overview of some key-reports about finger ratios:
July 5, 2011
JULY 4, 2011 – Finally… the long waited proof is now available: Korean researchers from the In Ho Choi of Gacheon University Gil Hospital, have pointed out that the popular ‘digit ratio‘ does correlate with penile length!
Finger professor John T. Manning had already pointed out in his second book ‘The Finger Book‘ (2008) that a Greek study in the Naval and Veteran’s Hospital of Athens (2002) had pointed out that the length of the index finger correlates with the length, glans & volume of the penis. Manning commented (in ‘The Finger Book’):
“Spyropoulos and his collegues did not measure the remaining fingers, so we cannot be sure of their relationship to penis length. My guess is that they would have found the ring finger the strongest predictor, and that long ring fingers in relation to index fingers would be associated with longer penises.”
The new Korean study shows that John Manning – the ‘finger professor’ - was right… again!
The researchers from Korea found that the ratio between the second and fourth digits on men’s right hand correlate to the length of his flaccid and stretched penis. A lower index-to-ring finger length ratio indicates a longer (stretched) penis.
NOTICE: The table below is taken from the scientific article; it e.g. illustrates that likewise results were found for body length and penis length - for the ‘flaccid condition’ the result for body length were slightly higher than for the 2D:4D digit ratio, but in the ‘stretched condition’ finger length ratio was a better predictor for penis length!
The key to this relationship may lie in the womb, a team member added:
“During the fetal period, high concentrations of testosterone lead to high testicular activity, resulting in a lower digit ratio, in the present study, patients with a lower digit ratio tended to have a longer stretched penile length.”
The researchers also added that the length of the stretched and flaccid penis does show “a strong correlation” with an erect penile length.
The Korean report was published on july 4 in the Asian Journal of Andrology, and the scientific article is available at Nature.com.
How can we understand this correlation between finger lenght and penis length?
Let’s take a look at the hands of one of the biggest ‘stars’ in the adult industry today: Ron Jeremy. Jeremy is today known as the ‘best performing’ male adult star ever, he is e.g. listed in the Guinness Book of World Records for “Most Appearances in Adult Films”, and he is noted for his 9.75-inch (~24.75 cm) penis (self-reported according Wikipedia).
How about his hands? His handprints are display at the entrence of Hustler’s Hollywood, at the ‘Porn Stars Walk of Fame’ in West Hollywood, California – see the picture below. His 2D:4D digit ratio is estimated at 0.85… which is exceptionally low for a caucasian male!
MORE FAMOUS HANDS AVAILABLE AT:
‘Hands of fame’ – The hands of 93 celebrities & famous people!