Why men's ring fingers are longer than their index fingers

Sep 05, 2011

Biologists at the University of Florida have found a reason why men's ring fingers are generally longer than their index fingers — and why the reverse usually holds true for women.

The finding could help medical professionals understand the origin of behavior and disease, which may be useful for customizing treatments or assessing risks in context with specific medical conditions.

Writing this week in the , developmental biologists Martin Cohn, Ph.D., and Zhengui Zheng, Ph.D., of the Howard Hughes Medical Institute and the department of molecular genetics and microbiology at the UF College of Medicine, show that male and female digit proportions are determined by the balance of sex hormones during early embryonic development. Differences in how these hormones activate receptors in males and females affect the growth of specific digits.

The 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.

It has long been suspected that the digit ratio is influenced by sex hormones, but until now direct experimental evidence was lacking.

"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. "In addition to understanding the basis of one of the more bizarre differences between the sexes, it's exciting to think that our fingers can tell us something about the signals that we were exposed to during a short period of our time in the womb. There is growing evidence that a number of adult diseases have fetal origins. With the new data, we've shown that that the digit ratio reflects one's prenatal androgen and estrogen activity, and that could have some explanatory power."

Cohn and Zheng, also members of the UF Genetics Institute, found that the developing digits of male and female mouse embryos are packed with receptors for sex hormones. By following the prenatal development of the limb buds of mice, which have a digit length ratio similar to humans, the scientists controlled the gene signaling effects of androgen — also known as testosterone — and estrogen.

Essentially, more androgen equated to a proportionally longer fourth digit. More estrogen resulted in a feminized appearance. The study uncovered how these hormonal signals govern the rate at which skeletal precursor cells divide, and showed that different finger bones have different levels of sensitivity to androgen and estrogen.

Since Roman times, people have associated the hand's fourth digit with the wearing of rings. In many cultures, a proportionally longer ring finger in has been taken as a sign of fertility.

"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."

In dozens of papers and two books, including the seminal "Digit Ratio" in 2002, Manning has studied the meaning of the relative lengths of second and fourth digits in humans, known to scientists as the 2D:4D ratio.

"When Zheng and Cohn blocked testosterone receptors, they got a female digit ratio," Manning said. "When they added testosterone they got super male ratios, and when they added estrogen, super female ratios. And they've provided us with a list of 19 genes that are sensitive to prenatal testosterone and prenatal estrogen.

"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."

Cohn, whose uses the tools of genetics, genomics and molecular biology to study limb development, said his lab began studying the digit ratios after Zheng became determined to find an explanation.

"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."

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User comments : 28

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Deadbolt
2.9 / 5 (10) Sep 05, 2011
This is very probably the explanation for homosexuality - there is no "gay gene", it's a birth hormone thing.
Callippo
2.6 / 5 (5) Sep 05, 2011
This is very probably the explanation for homosexuality - there is no "gay gene", it's a birth hormone thing.
The both theories may be true at the same moment, as many hormones (or even biologically active chemicals) influent the expression of various genes.
Birthmark
5 / 5 (5) Sep 05, 2011
Homosexuality may be hormonal but also a little environmental. Homosexuals brains are shaped more like their heterosexual counter-sexes, thus proving it's genetic/hormonal. The more older brothers you have, the more likely you (general sense of a male) will be gay. That could be environmental, but it could also mean something changes in the woman's body after carrying so many males.

There's no one definitive answer, it's poly-situational.

Aside from the top posters, interesting article! Why would hormones affect digit ratio? Is it just a side-effect or is there some evolutionary basis to it?
virtualist
5 / 5 (3) Sep 05, 2011
There should be a corresponding relationship to the 'size' of the clitoris, ... I would think !
Lordjavathe3rd
3.3 / 5 (4) Sep 05, 2011
Alan Turing was allegedly homosexual. I say allegedly because I think it's possible for there to be different types of homosexuality. One form might be cultural confusion, another might be attraction to intellectual similarity, a third might be due to being continually dominated, while another might be due to a significant amount of hormonal influence. Of course I don't know, but I'm highly skeptical of definitive assertions.
macsglen
4.8 / 5 (4) Sep 05, 2011
Maybe someone could now look at finger length of transgender candidates. It could be interesting if there were a correlation between finger proportions and a person feeling they were born the wrong gender and wanting to change it.
sherriffwoody
1 / 5 (2) Sep 05, 2011
I thought males had longer ring fingers to get the g
Beard
5 / 5 (2) Sep 06, 2011
Just in case someone looked at their ring finger and was disappointed, it has no bearing on your hormone levels as an adult. This only alters your brain patterning as a fetus.
theskepticalpsychic
4.3 / 5 (6) Sep 06, 2011
I had no idea there was a male-female difference in ring and index ratios. I looked at my fingers and discovered my ring fingers are approximately 1/3rd of an inch shorter than my index fingers, a supposedly "female" fetal trait. Now, I am a hirsute older male with no obvious physical sexual anomalies. But I am homosexual; a physical therapist has told me I have "gyneform hips," and for a brief time at puberty I lactated. Is there a pattern here that points to possible fetal gender blurring?
feralblue
4 / 5 (4) Sep 06, 2011
my ring finger is longer than my index finger - i am so female, i can't tell you.
i'm 65 and i still love men - they are incredible 'creatures'. i also have a curvy figure. go figure it again !!! LOL
jibbles
not rated yet Sep 06, 2011
wow!
Bob_Kob
not rated yet Sep 06, 2011
Both are the same length. Wtf does that mean?
gmurphy
not rated yet Sep 06, 2011
The digit ratio is tied to a lot of characteristics: http://en.wikiped...it_ratio My 2D:4D ratio is 0.935, which indicates relatively high exposure to testosterone in the uterus. Very little besides that can be deduced reliably from the digit ratio
Beard
5 / 5 (4) Sep 06, 2011
I looked at my fingers and discovered my ring fingers are approximately 1/3rd of an inch shorter than my index fingers, a supposedly "female" fetal trait. Now, I am a hirsute older male with no obvious physical sexual anomalies. But I am homosexual


It's very likely that your brain was patterned toward female while in the uterus. This has no bearing on your hormone levels as an adult. This is also one of the best explanations for homosexuality.
DavidMcC
3.7 / 5 (3) Sep 06, 2011
Why only look at the 2D:4D ratio when most of the skeleton is affected by gender?
bluehigh
1 / 5 (1) Sep 06, 2011
... when MOST of the skeleton is affected by gender?

The skeleton is affected by race, nutrition, age and gender among other factors. MOSTLY only the pelvis and to some extent the skull are related to gender.
Vendicar_Decarian
not rated yet Sep 06, 2011
Ya, well... My ring finger is longer and thicker than yours.
A_Paradox
5 / 5 (4) Sep 06, 2011
@Birthmark
Why would hormones affect digit ratio? Is it just a side-effect or is there some evolutionary basis to it?


That was my question also. I guess the simplest inference is that the index:ring fingers ratio is an emergent, arbitrary outcome that of itself has no evolutionarily selective relevance. However I understand that women's elbows flex/hinge at a slightly different angle from men's elbows in order to avoid impact with their wider hips. This feature would require gender correlated differences in the distribution of sex hormone sensitive receptors amongst bone growth cells within the limbs.
gmurphy
not rated yet Sep 06, 2011
@A_Paradox, that's a really elegant explanation!, internets "plus one" to you sir :)
DavidMcC
not rated yet Sep 12, 2011
... when MOST of the skeleton is affected by gender?

The skeleton is affected by race, nutrition, age and gender among other factors. MOSTLY only the pelvis and to some extent the skull are related to gender.


It is "most", because women are generally smaller than men. Of course, that does not mean a given bone can be "sexed" on that basis, but it does mean that gender has an effect on much of the skeleton.
bluehigh
1 / 5 (1) Sep 12, 2011
When determining male and female in a skeleton, anthropologists look at the skull and hip bones, as there lie clues to the sex of the skeleton. The skull has three points in determining gender. These are the ridges located above the eyes, the bone situated just below the ear and the occiput, the bone located at the lower back of the skull.

http://library.th...olgy.htm

Generally(!)- It is diet that determines bone size and, for example, to compare a male from an Asiatic lineage to that of a female from a Nordic lineage, you would find that your supposition on male/female size relationships does not hold true.

Crikey David, you have solved seemingly intractable cosmological conundrums and you are an expert anthropologist too.

What other tricks can you do?

DavidMcC
not rated yet Sep 12, 2011
Bluehigh, I never said that gender was the ONLY factor affecting bone size, nor that I was an "expert" on anthropology. Only that there is unlikely only to be one anatomical feature affected by gender.

My specialism has been optics (and other branches of physics) in biology, but I do, indeed, have other tricks.

I haven't noticed you make many constructive contributions on certain subjects, that's all, such as with your posts on matter-antimatter interactions.

BTW, clear thinking is something you might learn to do better.
bluehigh
1 / 5 (1) Sep 12, 2011
David, flights of fantasy and unsubstantiated guesswork seems to be yet another trick of yours. I understand your concerns about clear thinking because it must be difficult for you to come down to earth from your multi-dimensional black hole.

In the meanwhile use your optics skill and cast your eyeballs around so as to learn that most of the skeleton is not substantially affected by gender alone.

What you suggested (in case you have memory failure as well as a lack of cognitive skills) is ...

Why only look at the 2D:4D ratio when most of the skeleton is affected by gender?


The answer, as I have attempted to explain is that some parts of the skeleton are substantially affected by gender and not most of the skeleton as you suggested. That is why an examination the 2D:4D ratio is significant.

Maybe theres a human sub-class for boneheads like you.
bluehigh
1 / 5 (1) Sep 12, 2011
To re-visit my suggestion that it is a logical mistake to discuss the interaction between two 'classes'; I stand by my original query as to the precise interaction that occurs. To say that anti-matter and matter annihilate on contact fails to take into account the 'elements' concerned. My comments were intended to find out what reactions occur when different matter/antimatter elements come into contact. EG: a cloud of anti-hydrogen meets a lump of 'normal' carbon. The point being that just to say it annihilates begs the question of what might remain after the 'explosive' interaction, where the 'elemental' composition is unbalanced.

It was a fair query, that you just did not like. Suck it up.
DavidMcC
not rated yet Sep 12, 2011
To re-visit my suggestion that it is a logical mistake to discuss the interaction between two 'classes'; I stand by my original query as to the precise interaction that occurs. To say that anti-matter and matter annihilate on contact fails to take into account the 'elements' concerned. My comments were intended to find out what reactions occur when different matter/antimatter elements come into contact. EG: a cloud of anti-hydrogen meets a lump of 'normal' carbon. The point being that just to say it annihilates begs the question of what might remain after the 'explosive' interaction, where the 'elemental' composition is unbalanced.


No, you misunderstood the point. You incorrectly inferred that I was suggesting that there was lots of carbon in the big bang. The original questioner realised that I had answered correctly, but you went of on an angry flight of fancy, as is your wont, it seems.
DavidMcC
not rated yet Sep 12, 2011
"David, flights of fantasy and unsubstantiated guesswork seems to be yet another trick of yours."
You're still not getting it, are you. I have tried to help cosmology out of a "hole" of its own making, by showing that currently "inexplicable" observations actually make sense if the universe is a daughter black hole of a slightly earlier universe. It's a bit like realising that cellular life didn't pop into existence from non-living material - it almost certainly came via the "RNA world" hypothesis.

"The answer, as I have attempted to explain is that some parts of the skeleton are substantially affected by gender and not most of the skeleton as you suggested."

I didn't even suggest that. You misinterpreted, as usual, like a dog, barking up the wrong tree all day.
BTW, how many "boneheads" can claim to have discovered the importance of photo-oxidative damage in animal evolution?

bluehigh
1 / 5 (1) Sep 12, 2011
David, you are such an egocentric dill. You believe you have invaluable insight into cosmology and now claim to have an epiphany regarding the origin of cellular life and claim some important contribution to animal evolution. Then you pollute the current discussion with defensive claims of misunderstandings and hold a grudge like some psychotic punk. If I were a dog then pissing on you would be a valid sign of your worth. What a sad case you are!

Now if you dont mind, I am getting my finger nails cut and buffed at other taxpayers expense through the wonderful benefits of universal health care.

Oh and by the way Aussie Medicare provides no cost Psychiatric consultations that could help you. Ask Oliver along, you could both tilt at windmills, discuss black holes or neutron repulsion together and the medication is subsidized.

DavidMcC
not rated yet Sep 12, 2011
"David, you are such an egocentric dill. You believe you have invaluable insight into cosmology and now claim to have an epiphany regarding the origin of cellular life and claim some important contribution to animal evolution."

I never claimed the second point, it was only a convenient analogy. However, I am claiming the other two. Neither are wild guesses - they are both evidence based. It's just a matter of understanding the relevance of observations and "joining the dots". If I had missed something, particularly on vertebrate eyes, it would have been pointed out by now, I'm sure, as I have a thread of my own on that subject. Even on cosmology, no-one could dismiss the idea in the knee-jerk way that you did. No doubt you had read of previous, inadequate multiverse hypotheses involving multiverses, and this conditioned your response. Am I right?
PS, I'm only being a little "egocentric" about this because of your "upping the anti" language, which seems to be your trademark.

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