Low 2D:4D Values Are Associated with Video Game Addiction

Abstract

Androgen-dependent signaling regulates the growth of the fingers on the human hand during embryogenesis. A higher androgen load results in lower 2D:4D (second digit to fourth digit) ratio values. Prenatal androgen exposure also impacts brain development. 2D:4D values are usually lower in males and are viewed as a proxy of male brain organization. Here, we quantified video gaming behavior in young males. We found lower mean 2D:4D values in subjects who were classified according to the CSAS-II as having at-risk/addicted behavior (n = 27) compared with individuals with unproblematic video gaming behavior (n = 27). Thus, prenatal androgen exposure and a hyper-male brain organization, as represented by low 2D:4D values, are associated with problematic video gaming behavior. These results may be used to improve the diagnosis, prediction, and prevention of video game addiction.

Full report is available here:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0079539

(This concerns a study from Germany: Funding for this study was provided by intramural grants from the University Hospital of the Friedrich-Alexander-University of Erlangen-Nuremberg and by the Ministry for Science and Culture of Lower Saxony.)

The illustrations provide an impression of the results:

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.

Important Indicators

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

Via: Medscape

Earlier reports about 2D:4D digit ratios and agressesion:

Aggression, testosterone and your finger length!

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.

SUMMARY:

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.

Keywords:

  • 2D:4D;
  • azoospermia;
  • digit ratio;
  • Klinefelter’s syndrome;
  • prenatal testosterone;
  • testosterone sensitivity

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.

 

Manning reports:

“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.”

 
Full report:
Professor John Manning  revised his 2D:4D finger ratio theory

 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:

http://www.handresearch.com/news/digit-ratio-finger-length.htm

Length of ring fingers & correlates with sexual attraction.

Various studies have shown that babies exposed to higher levels of testosterone when developing in the uterus have longer ring fingers as adults, and higher levels of oestrogen typically result in longer pointer fingers. However, testosterone & oestrogen levels also affect the rest of the body, including a person’s physical appearance. The ratio between the length of the index and ring fingers has been found to be a good indication for a variety of social and economic factors, thought to be directly or indirectly related to the effects of the prenatal testosterone. These photographs are part of a study on beauty and sexual attraction.

In 2010 a Meta-analysis studyby researchers from the University of Ontario, Penn State, and the Centre for Addiction and Mental Health found that the second to fourth finger length ratio (2D:4D) serves as an indicator of sexual orientation. The study included 1.618 heterosexual men, 1.693 heterosexual women, 1.503 gay men, and 1.014 lesbians.

In addition to identifying the normative heterosexual sex difference in 2D:4D for both hands, the researchers found that heterosexual women had higher (more feminine) left- and right-hand 2D:4D than did lesbians. However… the researchers found NO difference between heterosexual and gay men (though moderator analyses by the researchers suggested that ethnicity explained some between-studies variation in men).


MORE  FINGER & DIGIT RATIO REPORTS ARE AVAILABLE AT:

http://www.handresearch.com/news/hands-in-the-news.htm

Last year British researchers reported new confirmative findings for a link between index finger length (relative to ring finger length) and the risk of developing prostate cancer. Men featured with a longer index finger than ring finger, appear to have a 33% higher chance for not developing prostate cancer.

Often such studies are qualified by non-experts as “nonsense” – initially because of the association with classical palmistry. Usually a main argument of concern is the seize of the studied sample: many ‘2D:4D digit ratio’ studies have been focused relatively small samples, and usually with the statistics were simly not strong enough to be applied to individuals. But those arguments can not be used to the describe the new British study!

The new British research involves a study where the hands of 1,524 prostate cancer patients were examined, which were compared with a control group of 3,044 men.

It can also be noted that Professor John Manning described in his second book ‘The Finger Book‘ with great details the suspected link between the ‘2D:4D digit ratio’ and prostate cancer – a complex theory about of role glutamine chains in the sensitivity of hormone receptors, which in their turn play a role in the activation of testosterone in the body:

…The various forms of the androgen receptor have important consequences for our health and behaviour. For example, African-American men have shorter glutamine chains (high sensitivity to testosterone) than white men. Short glutamine chains are associated with an increased susceptibility to prostate cancer, and this may in part explain why the incidence of prostate cancer is higher in African-Americans than in white Americans. …”

In short, there seems to exist a triangular relationship between: 1) the high percentage of prostate cancer in Americans with African ancestry, 2) the length of the glutamine chains, and 3) the length ratio between index finger and ring finger.

The importance of the new British study can be recognized in the fact the use of preventive screening for prostate cancer – which is anno 2010 usually done through the use of a blood test – is still an object of confusion. Simply because the benefits of the screening devices are still very unclear. Meanwhile it is a fact that prostate cancer is known as the No. 1 cause of death from cancer in men (see picture below).

Therfore finger length assessment can become a new tool in prostate cancer screeing!

The British researchers therefore are speculating about how to add a practical application of their finger length study to the traditional methods of prostate cancer prevention screening!

RELATED SOURCES:
More finger length studies
How to read your own palm!

Researchers from England & Canada presented earlier this week brand new evidence that the neanderthals’ life was much more dominated by competition & promiscuity than our lifes today! Maybe more surprizing is the method that the researchers used to acquire their new findings: finger length ratio measurements!

The study, published in the Proceedings of the Royal Society B, draws upon a famous and controversial indicator of social behavior: the comparative length of the index finger and the ring finger, also known as the 2D:4D finger ratio. If the ring finger is longer than the index finger, that’s supposed to be correlated with higher prenatal exposure to androgens — resulting in a higher proclivity for aggressiveness and promiscuity.

A few numbers from the results: 

Modern humans averaged a 0.957 index-to-ring finger ratio, and were considered to be on the line between a “pair-bonded,” or monogamous, species and a middle-of-the-road species.
Chimps, gorillas and orangutans had index-to-ring ratios in the 0.90 to 0.92 range, and were classified as “non-pair-bonded,” or promiscuous.
• An early modern human from Israel’s Qafzeh Cave, thought to be about 95,000 years old, had an index-to-ring ratio of 0.935. Based on that statistic, the researchers surmised this individual would be more promiscuous than modern humans.
• The finger bones from five Neanderthals yielded a 0.928 ratio, associated with even greater competitiveness and promiscuity. Ardipithecus’ bones took it up another notch, to 0.899. Two even older primate ancestors, Hispanopithecus and Pierolapithecus, had ratios of 0.848 and 0.908, which means they would have been tough to live with as well.
• On the other end of the spectrum, the monogamous gibbons had a 1.009 ratio … and the australopith sample came in with a ratio higher than that of modern-day humans (0.979). The implication, then, is that australopiths were monogamous.

Neanderthals vs. humans today!

Scientists, in collaboration with researchers at the universities of Southampton and Calgary, used finger ratios from fossilised skeletal remains of early apes and extinct hominins, as indicators of the levels of exposure species had to prenatal androgens – a group of hormones that is important in the development of masculine characteristics such as aggression and promiscuity.

 It is thought that androgens, such as testosterone, affect finger length during development in the womb. High levels of the hormones increase the length of the fourth finger in comparison to the second finger, resulting in a low index to ring finger ratio (2D:4D digit ratio). Researchers analysed the fossil finger bone ratios of Neanderthals and early apes, as well as hominins, Ardipithecus ramidus and Australopithecus afarensis, to further understanding of their social behaviour.

The hand bones of an early hominid - fosile presented by Wesley Niewhoener.

The hand bones of an early hominid

 

The rigth hand of 'Neanderthal Qafzeh 9'.

The hand bones of a neanderthal

 

The team found that the fossil finger ratios of Neanderthals, and early members of the human species, were lower than most living humans, which suggests that they had been exposed to high levels of prenatal androgens. This indicates that early humans were likely to be more competitive and promiscuous than people today.

The results also suggest that early hominin, Australopithecus – dating from approximately three to four million years ago – was likely to be monogamous, whereas the earlier Ardipithecus appears to have been highly promiscuous and more similar to living great apes. The research suggests that more fossils are needed to fully understand the social behaviour of these two groups.

Dr Susanne Shultz, from the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford describes:

“Social behaviours are notoriously difficult to identify in the fossil record. Developing novel approaches, such as finger ratios, can help inform the current debate surrounding the social systems of the earliest human ancestors.”

And Dr Emma Nelson, an archaeologist from the University of Liverpool, argues that comparing the finger-length ratios of extinct and present-day species is a valid technique for making an indirect assessment of our long-gone ancestors’ social behavior. She said:

“It is believed that prenatal androgens (male sex hormones) affect the genes responsible for the development of the fingers, toes and the reproductive system. We have recently shown that promiscuous primate species have low index to ring finger ratios, while monogamous species have high ratios.”

“We used this information to estimate the social behaviour of extinct apes and hominins. Although the fossil record is limited for this period, and more fossils are needed to confirm our findings, this method could prove to be an exciting new way of understanding how our social behaviour has evolved.

READ MORE ABOUT EARLIER RESULTS:
• Primate finger length linked with social behavior
• Human finger length & sexual orientation
• Evolution of the human hand & palmar creases

Can finger length predict infidelity?

[tweetmeme source=”handresearch” only_single=false] Earlier this year Dr. Phil and his panel of medical experts discussed the new science behind a cheater’s brain and what can be done if your loved one is at a higher risk. Author of Change Your Brain, Change Your Body, Dr. Daniel Amen, author of Insatiable Wives, clinical psychologist Dr. David Ley, Claremont University’s Dr. Paul Zak and author of The Male Brain, neuro-psychiatrist Dr. Louann Brizendine explain how you can discern a man’s risk for infidelity and the treatment options to lower his risk. Studies have indicated that the ‘Casanova-type’ finger ratio (low 2d:4d) is often seen in polyandry + polygyny populations, and …men who cheat!

Dr.Phil.com presents a 4 item list of physiological indicators that your han is at a higher risk for cheating:

  • Length of ring finger compared to pointer finger: The length of a man’s ring finger is linked to testosterone in utero and during puberty. A longer ring finger means more testosterone, and the increased likelihood of a greater number of sex partners and a higher risk of cheating.

  • Facial symmetry and size of jaw: If one side of a man’s face matches the other side, is symmetrical, the more it is an indicator to women that that man has high genetic value. Men whose faces are more [symmetrical] are more likely to have more partners because more women want to have their children.
  • Size of penis: If a male is well-endowed, that means more testosterone and a higher risk of cheating.
  • Brain injuries: Men with a history of engaging in impact sports like football or martial arts, or men who’ve had a history of concussions are at a higher risk. Also, men with disorders like ADD or bipolar disorder have low pre-frontal cortex activity or hyper-frontal activity, which could mean less ability to stop impulsive behaviors, like cheating.

So, how surprising is it really that Casanova had as well the long ring finger !?

 SUGGESTION FOR FURTHER READING:
BBC Test: finger length & sex I.D.!
Finger length & Cupid’s science!
The science of gaydar: finger length & sexual preference!
What they say about men with long ring fingers!

Academic science has developed a new theory about how finger length is related to human biology & behavior. A significant part of theory is focussed on the so-called: ‘2D:4D digit ratio’, which concerns the full length ratio of only two fingers: index finger vs. ring finger. In women the length of both fingers is usuallly about equal, while in men the ring finger is usually slightly longer: a tiny sex difference.

NOTICE: This tiny sexe difference has been confirmed among many ethnic populations around the world, but one should also keep in mind that the finger length differences between ethnic populations are often larger than the finger length differences between males and females.

FINGER LENGTH & ATHLETIC ABILITY

Professor John T. Manning of the University of Liverpool (School of Biological Sciences, Liverpool, UK) explains the link between finger length & athletic ability as follows (see video: starting at 2m5s):

Professor John T. Manning explains how finger length relates to testosterone & athletic behavior.

“Our fingers have information about how much testosterone and how much oestrogen we’ve been exposed to in the whomb. So, the longer one’s ring finger relative to one’s index finger, the more testosterone you’ve had. And that testosterone has an effect on the brain, and on the body. If a boy has a large amount of testosterone before birth, he is likely to be born with a very efficient heart and vascular system.”

“So the longer one’s ring finger relative to one’s index finger, the faster one can run.”

The BBC’s “Secret of The Sexes” confronted the ‘finger Professor’ with six athletes – all 5000 meter specialists, and asked him to “predict” the outcome of the race based on finger length only. Actually, the BBC provided Manning photocopies of the athletes hands, and in return Professor Manning risked his reputation by providing the results of a race that had yet to be run.

The outcome of the experiment is unvealed “LIVE” in the video (starting at 5m10s). And surprizingly… the theory appeared to be pretty accurate in practice. After Manning & the athletes are controfonted with the results Manning summarizes:

“… We’ve got four out of six right, but the two that are wrong were kind a quite close.”

The winner of the 5000 meter race responds:

“I thought… that finger thing is bullox because there are so many variables… I am very impressed”.

Coincidence?

Manning’s theory was also confirmed by the results of various studies e.g. on endurance running & sprinting speed. And in another likewise experiment finger length correctly predicted the outcome of a 100 meters race with 5 young sprinters.

FINGER LENGTH & OTHER LIFE ISSUES

In his second book – titled ‘The Finger Book‘ – Professor Manning explains that because of the prental link with the androgens (testosterone & oestrogen), finger length studies have generally shown consequent sensible correlations with a rainbow of life issue. The tiny sex difference appears to be highly revealing, for hundreds of studies the ‘2D:4D digit ratio’ appears to correlate with a wide range of topics that are usually also known for a typical male-female difference, including: musical ability, personality, health, and even sexual preference.
More articles & reports are available at: finger length & digit ratio news.

The following two videos present other materials from the BBC’s “Secrets of The Sexes”: in the second video Manning explains how finger length is related to performance in spatial-visual tasks, and in the third video Manning demonstrates how finger length is related to another typical sexe-related aspect of personality: the ability to empathize!

HOW TO MEASURE DIGIT RATIO?

NOTICE: Measuring the ‘2D:4D digit ratio’ is really a matter of measuring the full length of both fingers. Two additional tips to avoid: 1 – don’t try to ‘judge’ the 2D:4D digit ratio with bare eyes only (conscientious measurment + calculation is a necessity) 2 – one can not find the ‘2D:4D digit ratio’ from the back of the hand, nor the tips of the fingers only.

Picture source: University of Cambridge.
University of Cambridge: how to measure the 2D:4D digit ratio.

IS THIS THE NEW ‘PALM READING’?

In 2008 Professor Chris McManus of the University College London (Psychology and Medical Education) characterized Manning’s finger research as follows:

“Chiromancy, the notorious pseudoscience that Sir Walter Scott bracketed with physiognomy, astrology and “other fantastic arts of prediction”, has for two decades been creeping back into scientific favour. And John Manning is its high priest. In The Finger Book, he [Manning] writes: “I believe that the pattern and nature of our decline in middle life and the disease which will eventually lead to our death, is dependent to a large extent on our experiences as a foetus”, a phrase that could almost have been written by Cheiro, the early 20th-century society palmist.”

Because of the obvious association with the divination aspect of palmistry (which is still very popular in various countries such as India & Pakistan), the issue of the ‘2D:4D digit ratio’ will probably continue to have a controversial status.

Looking for more ‘Next Nature’ reports? You can find them at: www.nextnature.net. More reports about finger length are available at: finger length & digit ratio news.