Finger Length and Personality, Part 3: Q&A

I must admit, I have been smitten with curiosity about the so-called 2D:4D ratio. I find its implications for improved self-awareness and appreciation of diversity to be compelling. This is the third post on the subject, the previous ones having to do with the Higher Perspective article and then my attempt to more accurately measure the 2D:4D ratio. 

I also dedicated a whole edition of L.I.N.K.S. to the subject, and I published a related inquiry on facial symmetry--a feature that, like ring finger length, tends to increase in response to pre-natal androgen exposure. 

That is a lot of exploration and investigation already. But, being the curious sort, I feel one really good question usually inspires two or three dozen more. And so I have prepared for you a list of additional questions (and some preliminary answers). It's my hope that this Q&A monologue will engage readers and inspire something more like a dialog. If you share my interest in this topic and would like to advance the conversation, please feel free to chime in--via comments.

Here we go!

• Does it matter if you measure the ratio on your left hand or your right hand? If the measurements are different, which one is more accurate? 

Higher Perspective said simply to look at the back of your left hand. Most scientific studies I have seen cited have used calipers to accurately measure the digit lengths on the palm side. The copy machine works well enough for practical purposes as any errors are proportional. Some studies specify the right hand for increased accuracy, though I have yet to see why that should be the case. I suspect it's because "most people" are right-hand dominant. I suggest either using the hand with the greatest variation, or, having measured both, averaging the two.

• If your instincts are hardwired, how much choice do you really have in the heat of the moment? Are people with low 2D:4D ratios more likely to be aggressive drivers? 

Studies have shown a positive correlation between longer ring fingers and increased risky behavior. Obviously, behavior can be learned (or unlearned) through training, but it is interesting to note that a certain amount of aggressiveness is apparently innate. Studies have shown, for example, positive correlation between longer ring fingers and aggressive driving. 

• Is there a correlation between finger length ratio and other measures of personality, such as the MBTI profile? Are certain ratios disproportionately represented among Es or Is, for example? 

Low 2D:4D ratios are correlated with increased confidence, risk preference, search persistence, and vigilance. However, these traits are not unique to introverts or extroverts, so there does not appear to be a strong positive correlation between finger length ratios and personality type indicators such as the Jungian Meyers-Briggs Type Indicator (MBTI). It's worth noting that behavior and preference are different. 

• Is there a correlation between finger length ratio and a person's sex (male, female, or intersex), sexual orientation (i.e., gender identity, e.g., male, female, trans, queer), or sexual preference (asexual, heterosexual, bisexual, homosexual)?

The sex difference in digit ratios is unrelated to the Y-chromosome. Estrogen in utero does not produce larger ratios. The presence or absence of testosterone explains all the difference. 

• What are the ranges of ratios that have been measured?

Bailey and Hurd (March 2005) has a sample of 134 people. The distribution of men's finger length ratios has a mean of 0.947 and a standard deviation of 0.029. For women, the statistics are 0.965 and 0.026. 

• Are there any published studies correlating the effects of pre-natal androgens? For example, to what degree are finger length ratios and facial symmetry correlated?

There must be a study correlating finger length ratio and facial symmetry, but I have not found it yet. I did find a study that found a positive correlation between finger length ratio and penile length. Apparently, the researchers took measurements of male subjects while they were under general anesthesia 

• To what extent should finger length ratio influence your choice of  a potential mate? Should the ratio matter more or less than, say, a zodiac sign? In other words, is the finger length ratio merely a persistent but meaningless bit of pop psychology, or is it a window into serious insight?

No, those jeans fit you perfectly! 

• What, if anything, do these topics have in common? How are they related if at all? 
• Numerology
• Tarot
• Astrology (signs of the zodiac)
• Parapsychology (hypnosis, extra-sensory perception, telepathy, etc.)  
• Phrenology (reading the bumps on a person's skull for insights into brain structure and function)
• Chiromancy (reading the proportions of a persons hands and fingers for predictions of future health and well-being)
• Finger Length Ratio
• Positive Psychology
• Myers-Briggs Type Indicator
• Abnormal Psychology

You are looking at a list of 10 topics ranging from parapsychology to pop psychology to main stream psychology. They are listed in order of my estimation of their relative seriousness, beginning with topics that require the most skepticism and progressing to the topics that are relatively more sound. I conclude the Q&A with this point to show that I think the finger length ratio is more useful and more reliable than most of the other topics, but still less accepted in academic circles.

Send or post your responses to the questions posed, your additional questions, more links as you find them, and your own answers as you think of them.

L.I.N.K.S. that Lure, Intrigue, Nurture, Kindle, or Stimulate, Part 10: Finger Length Ratio and Personality

L.I.N.K.S. that Lure, Intrigue, Nurture, Kindle, or Stimulate, Part 10:

Finger Length Ratio and Personality

This 10th edition of L.I.N.K.S. is inspired by my recent pop psychology post on Finger Length Ratio and Personality which observed that the length of your ring finger was determined before you were even born. That post concluded with the open-ended observation that many other aspects of your appearance and even your personality may be in-born, and thus largely out of your direct control.

Coming as I do from the "Leaders are made, not born" school, the realization that I find the thought that some behavior is inborn a tad unsettling. I wanted to follow-up with some links (10 links, as a matter of fact--in honor of the 10th edition of L.I.N.K.S.!) to additional reading on the subject for those of you curious enough to explore this topic in a bit more detail. I welcome your comments.

Ten annotated L.I.N.K.S.

1. Five Things a Man's Finger Length Says About Him. The ratio of digits' lengths could hint at everything from personality to intellect to physiology to propensity for disease. http://www.livescience.com/49883-finger-length-in-men.html 
2. Finger length ratio can predict aggressive behavior and risk of disease. Researchers continue to study what sparks these hormonal changes and have begun looking at environmental chemical exposure, stress levels and diet during pregnancy. http://discovermagazine.com/2013/may/04-finger-length-ratio-can-predict-aggressive-behavior-and-risk-of-disease 
3. Polite, promiscuous... gay? What does your ring finger say about you? The longer your ring finger is is compared to your index finger, the greater chance you will be polite and happy, straight, rich or handsome, with a long penis. But, on the down side, you will have a much higher than average chance of developing prostate cancer. http://www.telegraph.co.uk/men/the-filter/11424695/Polite-promiscuous...-gay-What-does-your-ring-finger-say-about-you.html 
4. How the length of a woman's fingers reveals her Career: Short index finger hints that she's more likely to be in high-powered role. The idea is that a low 2D:4D ratio is associated with more aggressive behavior. Contrast this with the findings in article #10. http://www.dailymail.co.uk/sciencetech/article-2965316/How-length-woman-s-fingers-reveals-CAREER-Short-index-finger-hints-s-likely-high-powered-role.html 
5. Study: Finger length a tell-tale sign of a cheater? A study of 1,300 men and women in England and the United States found that those with same-length ring and index fingers are more likely to “stay” with a committed partner. Those whose ring fingers are longer than their index fingers may be more likely to “stray,” as the authors of the study put it. http://www.hlntv.com/article/2015/02/06/oxford-study-ring-finger-length-cheater-faithful
6. Can you judge a man by his fingers? Examining the link between relative lengths of index and ring fingers in men and their behavior towards women. Men with short index fingers and long ring fingers are on average nicer towards women. This phenomenon stems from their fetal life, and the hormones these men have been exposed to in their mother's womb. The findings might help explain why these men have more children. http://www.sciencedaily.com/releases/2015/02/150218122110.htm
7. Personality Isn't Random. A large component of a child's personality in inherited from that child's parents, and siblings tend to have far more in common with each other than two people their age in the general population. This article came close to making a connection between finger length and MBTI. http://washparkprophet.blogspot.com/2013/02/personality-isnt-random.html 
8. Penis Size: It May Be Written in the Length of His Fingers. Long ring fingers are associated with larger penile length in males and enlarged clitorises an shallow vaginas in women. http://healthland.time.com/2011/07/06/penis-size-it-may-be-written-in-the-length-of-his-fingers/
9. Human 2D (index) and 4D (ring) finger lengths and ratios: cross-sectional data on linear growth patterns, sexual dimorphism and lateral asymmetry from 4 to 60 years of age. The study examines how absolute and relative digit lengths vary over a wide range of postnatal ages, and tests whether these variables are influenced by gender, laterality and handedness effects. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2732043/
10. Finger length ratio (2D:4D) correlates with physical aggression in men but not in women. Finger length ratio (2D:4D) is a sexually dimorphic trait. Men have relatively shorter second digits (index fingers) than fourth digits (ring fingers). Smaller, more masculine, digit ratios are thought to be associated with either higher prenatal testosterone levels or greater sensitivity to androgens, or both. http://www.ncbi.nlm.nih.gov/pubmed/15620791

Incidentally, there is a lot of junk science out there, too, and plenty of bad or misleading links. Here is an example of a link that did not make the list. Anytime I see the word "THIS" or lots of ALL CAPS or exclamation points (!!) in the title of an article, I dismiss the article, the author, and the source.

• Assessing Masculinity / Femininity via various Finger Length and Hand Shape Ratios. Discover your MASCULINITY/FEMININITY hand factor by combining your digit ratio with your hand shape ratios! Ugh, the all-caps, the exclamation points, the bold claims... Smells like click bait. http://www.handresearch.com/diagnostics/finger-length-masculinity-femininity-factor-hands.htm

Finger Length Ratio and Personality, Part 2: Getting Specific

Here is a follow-up to my recent post on Finger Length Ratio and Personality in which we attempt to get more accurate about measuring the ratios, a bit more descriptive about the differences between men and women (on average) and slightly more detailed about what any of this might mean. 

Figure 1. A technique for more accurately measuring and calculating the 2D:4D ratio

Don't just look at the back of your left hand, as suggested in the popular Higher Perspectives article. Put both hands palms down on a copier and make a life-sized photocopy. Then, on the copy, mark the base and the tip of the 2nd and 4th digits of both hands as shown in the example. Measure and tabulate the length of all four fingers. Calculate the finger length ratios by dividing 2D by 4D.

Perhaps your left and right hands are symmetrical, as they appear to be in the above example. In this case, the left- and right-hand ratios will be identical. If your subject's hands are not symmetrical, use the ratio with the largest absolute distance from 1. Some studies suggest that the right hand is more accurate, but I suspect that this is because most people are right-hand dominant. Use which ever hand has the more pronounced effect.

I used data from Bailey and Hurd (March 2005) to make the figure below. In a sample of  134 people, the distribution of men's finger length ratios has a mean of 0.947 and a standard deviation of 0.029. For women, the statistics are 0.965 and 0.026.

Figure 2. Finger Length Ratios of Men and Women

Given these probability density functions, I set out to construct the corresponding cumulative distribution functions, so that we could more accurately estimate the percentages of men and women who have a 2D:4D ratio in defined ranges. Recall that in our previous study, Group A had a ratio less than 1, Group B had a ratio greater than 1, and Group C had a ratio equal to 1.

Fig. 3. The Higher Perspectives categories

To operationalize the Higher Perspectives model, I define Group A as less than 0.98, Group B will have ratios over 1.02, and those in Group C will have ratios that fall between 0.98 and 1.02.

Figure 3. Cumulative density functions of the Bailey and Hurd data for men and women

Using the cumulative density functions of the Bailey and Hurd data for men and women, I made the table shown below.  Approximately 85% of men and 70% of women will fall into Group A with a finger length ration less than 0.98. Twice as many women (28%) as men (14.4%) will have approximately equal ring and index fingers, placing them in Group B. Only a very small percentage of the population (2% of women and only 0.6% of men) will have longer index fingers, indicating very little androgen exposure in utero, and landing them in Group C.

Table 1. Groups A, B, and C Defined in terms of Finger Length Ratios for Men and Women

Obviously, we could opt to make Group C wider at the expense of Groups A and B and then adjust the population proportions. However, any difference between 2D and 4D that is perceptible to the unaided eye will cause a reasonable person to place the result into Group A or B. Group C should be narrowly defined within the limits of human perception, or the group divisions lack credibility. The eye can easily detect an eighth of an inch of difference at arm's length, but 1/16th is tough. Increasing the subject's index finger by 1/16th of an inch changes the ratio to 3.1875:3.25 or 0.9808--apparently equal to the unaided eye and nearly equal in real terms.

OK, now you are asking, "So what? Where are we going with this?"

I am glad you asked. The finger length ratio is determined in the womb, based on the amount of the androgen testosterone present in utero. Men are more likely to have longer ring fingers and a 2D:4D ratio less than 1. A lower 2D;4D ratio is associated with exaggerated masculine traits in both men and women. I wondered myself, is this useful information, or just some sort of genetic parlor trick like seeing who among your friends can curl their tongue or cross only one eye? A longer ring finger is no excuse for inappropriate behavior, but it may help explain why some folks are more naturally aggressive and risk-seeking than others. Simple markers such as finger length ratios may help us identify people who will need additional training and reinforcement to, for example, remain calm while driving.

And speaking only for myself, I find that kind of information very useful.



Reference:

Bailey, A,A,, and Hurd, P.L.. (March 2005). "Finger length ratio (2D:4D) correlates with physical aggression in men but not in women." Biological Psychology. 68 (3): 215–22.