2D:4D Finger Ratio

[FalseHeartDothKnow]

Animal models have indicated that androgenic steroids acting before birth might influence the sexual orientation of adult humans. Here we examine the androgen-sensitive pattern of finger lengths [1], and find evidence that homosexual women are exposed to more prenatal androgen than heterosexual women are; also, men with more than one older brother, who are more likely than first-born males to be homosexual in adulthood[2], are exposed to more prenatal androgen than eldest sons. Prenatal androgens may therefore influence adult human sexual orientation in both sexes, and a mother's body appears to "remember" previously carried sons, altering the fœtal development of subsequent sons and increasing the likelihood of homosexuality in adulthood.

In women, the index finger (2D, second digit) is almost the same length as the ring finger, the fourth digit (4D), although it may be slightly longer or shorter; in men, the index finger is more often shorter than the fourth. The greater 2D:4D ratio in females is established in two-year-olds[1] . Because all non-gonadal somatic sex differences in humans appear to be the result of fœtal androgens that masculinise males[3], the sex difference in the 2D:4D ratio probably reflects the prenatal influence of androgen on males[4].

In an anonymous survey, 720 adults who were attending public street fairs in the San Francisco area were asked their gender, age, sexual orientation, handedness, and the number and gender of children their mother had carried before them. As expected, men have significantly longer fingers than women (P < 0.001), and we confirmed reports that the 2D:4D ratio is greater in women than it is in men.

This sex difference in 2D:4D is greater on the right hand than on the left (see figure 1a below), indicating that the right-hand 2D:4D is more sensitive to fetal androgens than the left-hand ratio. The right-hand 2D:4D ratio of homosexual women was significantly more masculine (that is, smaller) than that of heterosexual women, and did not differ significantly from that of heterosexual men. Thus finger ratios, like otoacoustic emissions[5], suggest that at least some homosexual women were exposed to greater levels of fetal androgen than heterosexual women.

The 2D:4D ratio of homosexual men was not significantly different from that of heterosexual men for either hand (P > 0.09). However, segregating male subjects based on birth order provided support for the role of fetal androgens in male sexual orientation. The more older brothers a boy has, the more likely he is to develop a homosexual orientation[2]. Confirming these reports, we also found that only homosexual men had a greater than expected proportion of brothers (P < 0.01) among their older siblings (229 brothers: 163 sisters) compared with the general population (106 males: 100 females [6].

We found that the male 2D:4D ratio, which is unlikely to be influenced by social factors, also varies with the number of older brothers. The ratio was significantly more masculine in men with two or more older brothers than in men with no older brothers (Figure 1b). There is also a significant correlation (r = -0.104; p < 0.05) between the number of older brothers and the right-hand 2D:4D ratio in men. If male subjects are divided by sexual orientation, the same pattern of later-born men displaying a more masculine 2D:4D is seen. Having older sisters has no apparent influence on male sexual orientation[2], or on the 2D:4D ratio in men. No effect of older brothers or sisters on 2D:4D in women was observed, consonant with reports that older siblings exert no effect on female sexual orientation[7].

Our results suggest that events before birth (or even before conception in the case of older brothers) influence human sexual orientation. The masculinised right-hand 2D:4D ratio in homosexual women may reflect fœtal androgen levels that are slightly higher than in heterosexual women. Homosexual men without older brothers have 2D:4D ratios indistinguishable from heterosexual eldest sons, indicating that factors other than fœtal androgen (such as genetic influences[8,][9] also contribute to sexual orientation. Finger measures indicate that men with more elder brothers, including those men who develop a homosexual orientation, might be exposed to greater than normal levels of prenatal androgen.

Although hyper-androgenisation of homosexual men might not fit some cultural expectations[10], homosexual men display several hyper-masculine characteristics, including a greater mean number of sexual partners in a lifetime than heterosexual men, who in turn report more sexual partners than do women of either orientation.

Furthermore, reports that adult homosexual men have more circulating androgens (refer to [11], but see ref. [12]), larger genitalia[13], and more "masculine" auditory evoked potentials than heterosexual men[14], are consistent with at least some homosexual men being hyper-androgenised.

Although it is possible that the maternal influence on finger growth of subsequent sons occurs after birth, a prenatal influence seems more likely because of the extensive physiological pairing of mother and fœtus. The locus of the maternal "memory" for previous sons, and the mechanisms by which fœtal development of subsequent sons is altered, remain unknown.

Terrance J WIlliams, Michelle E Pepitone, Scott F Christensen, Bradley M Cooke, Andrew D Hubennan, Nicholas J Breedlove, Tessa J Breedlove, Cynthia L Jordan, S Marc Breedlove Department of Psychology and Graduate Groups Neuroscience, Endocrinology, 3210 Tolman Hall, MC 1650, University of California, Berkeley, California 94720-1630 USA

Thoughts on this?

 

[miss fortune]

does this come with cliffs notes?

 

[Totenkindly]

I think we've already discussed it a few times, in testing threads and whatever else... just probably not to this level of detail.

(Anyone wanna call Wonderpets to help out Whatever?)

In an anonymous survey, 720 adults who were attending public street fairs in the San Francisco area were asked their gender, age, sexual orientation, handedness, and the number and gender of children their mother had carried before them. As expected, men have significantly longer fingers than women (P < 0.001), and we confirmed reports that the 2D:4D ratio is greater in women than it is in men.

Was this sample of population compared to an actual random sampling among the wider US population? I have trouble accepting that the "SF street fair" population actually is a fair representation of gender and preference among US citizens without some sort of scaling/calibrating.

The 2D:4D ratio of homosexual men was not significantly different from that of heterosexual men for either hand (P > 0.09). However, segregating male subjects based on birth order provided support for the role of fetal androgens in male sexual orientation. The more older brothers a boy has, the more likely he is to develop a homosexual orientation[2]. Confirming these reports, we also found that only homosexual men had a greater than expected proportion of brothers (P < 0.01) among their older siblings (229 brothers: 163 sisters) compared with the general population (106 males: 100 females [6].

What does Object Relations have to say about the potential influence of having more older brothers in a family, in terms of how a younger male might be positioned, influenced, etc., early in life? (Maybe nothing, but the question needs to be asked.)

Although hyper-androgenisation of homosexual men might not fit some cultural expectations[10], homosexual men display several hyper-masculine characteristics, including a greater mean number of sexual partners in a lifetime than heterosexual men, who in turn report more sexual partners than do women of either orientation.

If women typically have less sexual partners than men do, then het men (driven by a "spread your seed" bio imperative) are automatically being "reined" in by the comparative reluctance of their female partners (driven more by a "nesting" bio imperative). Gay men, however, will find it far easy to engage in sexual activity because both partners are men and thus not subject to the same restraints as het couples, they are both seed-spreaders. I would expect to see an increase in homosexual encounters with two men as the participants. Can standardized masculine sexuality be correlated to increased homosexual partnering vs het?

We ALSO have a cultural bias in that homosexuals are not legally permitted to be monogamous, and certain social influences in fact insist that homosexuals are not monogamous. This will have an influence on how people behave. Monogamy is not supported legally, nor socially... leaving a "why bother?" attitude.

 

[FalseHeartDothKnow]

I want to use an image example but they keep appearing as little red crosses

 

[figsfiggyfigs]

Next time I'm having trouble sleeping, I'll just come on here and read that article....

 

[Arthur Schopenhauer]

So, homosexual women have perfectly designed fingers for pleasuring other women? 2D:4D...

 

[FalseHeartDothKnow]

I know it turned out boring, sorry guys...All the pictures are failing Trying to find a decent link...

 

[Totenkindly]

I know it turned out boring, sorry guys...All the pictures are failing Trying to find a decent link...

Good thing it doesn't involve the middle finger.

Maybe you linked them incorrectly? I can't see them in your edits, so if you need help let me know...

 

[FalseHeartDothKnow]

Good thing it doesn't involve the middle finger.

Maybe you linked them incorrectly? I can't see them in your edits, so if you need help let me know...

Thanks so much, Jennifer...I'll try and add a picture to this one

 

[Seymour]

Apparently the fraternal birth order effect holds true even for adopted children, so it seems like it's more than family dynamics:

The effect has been found even in males not raised with their biological brothers, suggesting an in-utero environmental causation.[2] To explain this finding, a maternal immune response has been hypothesized.[14] Male fetuses produce H-Y antigens which may be involved in the sexual differentiation of vertebrates.[14] Other studies have suggested the influence of birth order was not due to a biological, but a social process.[15]

The above article claims that birth order accounts for about 1/7th of the prevalence of homosexuality in men. (Of course, I'm a gay identical twin with two straight older brothers and a straight twin brother... still don't know why I turned out gay and my twin turned out straight.)

If women typically have less sexual partners than men do, then het men (driven by a "spread your seed" bio imperative) are automatically being "reined" in by the comparative reluctance of their female partners (driven more by a "nesting" bio imperative). Gay men, however, will find it far easy to engage in sexual activity because both partners are men and thus not subject to the same restraints as het couples, they are both seed-spreaders. I would expect to see an increase in homosexual encounters with two men as the participants. Can standardized masculine sexuality be correlated to increased homosexual partnering vs het?

We ALSO have a cultural bias in that homosexuals are not legally permitted to be monogamous, and certain social influences in fact insist that homosexuals are not monogamous. This will have an influence on how people behave. Monogamy is not supported legally, nor socially... leaving a "why bother?" attitude.

I agree with both points. In some ways, gay men are like straight men without the counter-balancing effect of women (or marriage in most states). It's difficult to form stable relationships if they must be kept secret and must be maintained without societal support (which was mostly the case until relatively recently).

 

[FalseHeartDothKnow]

Thanks Jennifer, you're amazingly helpful, I really appreciate it...The fact I couldn't find one for men means that you might have to invert it if you're a man...but lots of scientists say that it is non-conclusive in men apparently so...Thoughts?

 

[Totenkindly]

Thanks Jennifer, you're amazingly helpful, I really appreciate it...The fact I couldn't find one for men means that you might have to invert it if you're a man...but lots of scientists say that it is non-conclusive in men apparently so...Thoughts?

Well, basically the ratio indicates the amount of androgens in the womb -- the taller the ring finger past the index finger, the more androgens. Androgens are dominant in male fetus development despite being produced by both sexes.

IOW, you're already showing the pictures for more "masculinized" men -- it's the right-hand image.

Here's another pic:

Since we are holistic in nature, with lots of influences on our development and at many different stages in our development, we can't totally predict a total one-to-one between psychology and finger length and androgen quantity in utero ... however, there is at least at least some level of correlation. Males typically produce far more androgens in utero, and the androgens push a particular type of differentiation. But hormone levels might differ widely per individual for each gender, with their own bell curves.

side note: My finger ratio resembles the middle image up in the earlier pic.

 

[Salomé]

There are 3 components of sexual identity:
core gender identity (do you feel like a man or a woman)
sexual orientation (which gender(s) are you sexually attracted to and
gender role (behaviours culturally associated with a certain gender).

There is a theory that the brain is masculinised in 3 stages (prenatally) by exposure to androgens. (The default brain is female).
Complications at any of these stages lead to "abnormal" sexual identity.
(eg XY individuals with androgen insensitivity may identify as female, XXs with adrenal dysfunction as male)

The finger length thing is a marker for prenatal androgen exposure.

PRENATAL AND PERINATAL ENVIRONMENT
The turning point in our understanding of the effect of environmental factors in sexual orientation was generated by the work of Gunter Dorner. Probably because Dorner was based in East Berlin his pioneering research in the 1970s was not widely noticed (Dorner, 1972; Dorner, 1976; Dorner, 1977). Before Dorner there had been unsuccessful attempts to compare the hormonal profiles of adults expressing different sexual orientations. Dorner’s studies revealed the importance of the critical period when the sexual differentiation of the brain happens. While this critical period may vary slightly from one species to another, it is always around the time of birth.
Dorner started with animal experiments. Male rats were castrated on the first day of life and were injected with male hormones when adults. These male rats expressed a complete inversion of sexual behaviour. In other words, being deprived of testosterone during the critical fetal period of sexual determination produced homosexual behaviour in their adult lives.

What we know now about the hormonal profile of homosexuals fits perfectly with the hypothesis of a transitory lack of testosterone during the critical period. Homosexuals usually have the same level of total testosterone as heterosexuals, but their level of ‘free testosterone’ (testosterone that is not combined with other chemicals) is lower. The levels of pituitary hormones, which control testicular functions, are relatively high and so are the levels of oestrogens. It is important to realize is that if this hormonal profile were to be artificially reproduced in an adult, it would not give rise to homosexual behavior. When a fetus is faced with a lack of testosterone at the end of pregnancy it compensates for this by increasing secretions of pituitary hormones. At the same time as the fetus tries to increase the level of male hormones by a feedback mechanism, it increases in parallel the level of oestrogens. In fact, oestrogens increase the binding capacity of sexual hormones with proteins and lower the level of free testosterone.
This raises the question of how and why some fetuses lack male hormones at the end of pregnancy. The answer could be that certain stressful situations at this time might trigger a high level of activity in the mother’s adrenal glands. The adrenal glands release male hormones the action of which is different from testosterone, but similar enough to compete with testosterone in the fetal brain to lower the amount of free testosterone. Furthermore, a complementary question is raised: Can prenatal stress play a causal role in human male homosexuality?

Primal Health
​

ETA. Most of which Jennifer just said.
Good book covering most research to date: Brain Gender - Google Books

 

[Oberon]

side note: My finger ratio resembles the middle image.

Mine looks like the pic you posted.

 

[Lark]

I've heard the biochemical developmental argument about sexuality determinism before. My thoughts on this go something like this:-

- I do wonder following Magic Porefin (spelling) mentioning it on another thread but corresponding to consideration of psychology and development that the discussion had moved toward sociobiological determinism vs. memetics determinism. I think this could be important in the consideration of the determinants of sexuality as much as determinants of other psychology or behaviour. Personally as a cultural theorist I think it has more to do with it than hard sociobiological determinism.

- I suspect that considering the determinants of sexuality will be more controversial than perhaps considering the determinants of criminality or deviance. Its a highly politicised topic now and totally a subject of kultur kampf. The mixed feelings of fans of homosexuality about origins or determinants of sexuality, ie innateness at one time affirmed at another condemned, can generally not be acknowledged.

- The argument that sexuality, particularly male or female homosexuality, is determined by the biochemistry of the womb, when I have heard it deployed in Northern Ireland, has generally been done in a manner which on the one hand exhonorates males and fathers of any "blame" for conceiving a homosexual son or daughter, or possible closet orientation. There's an implication there I'm sure that no one friendly to homosexuality or wishing to promote it as a norm would appreciate, it's pretty much still considered abnormal and its something that people accept provided they dont feel responsible for it.

- This has meant that campaigners who once affirmed biochemical or sociobiological explanations of innateness or "inborn" homosexual orientations in confronting "naturalistic fallacies" are having second thoughts. Innateness or biological explanations failing to result in approval, acceptance and support, arguably the real goal of the homosexual identity groups, they arent as useful.

 

[Lark]

Also, is this for real?

It didnt occur to me until I'd contributed already but there are lots of folk myths about digital lengths and abnormality or even "evil", vampires and werewolves in some stories where detectable by the measurement of digits.

Isnt this likely to result in prejudice and bullying? I know in NI there where problems in the schools when the folk myths about the space between eyes could be used to tell which faith community people belonged to became resurgent (I shit you not).

 

[Salomé]

Also, is this for real?

It didnt occur to me until I'd contributed already but there are lots of folk myths about digital lengths and abnormality or even "evil", vampires and werewolves in some stories where detectable by the measurement of digits.

Isnt this likely to result in prejudice and bullying? I know in NI there where problems in the schools when the folk myths about the space between eyes could be used to tell which faith community people belonged to became resurgent (I shit you not).

Science shouldn't get involved in politics (and vice versa).

 

[Arthur Schopenhauer]

Mine looks like the pic you posted.

Mine are opposite.

4D being slightly shorter than 2D.


Interesting stuff.

 

[Arthur Schopenhauer]

Science shouldn't get involved in politics (and vice versa).

I don't know about that.

 

[Lark]

Science shouldn't get involved in politics (and vice versa).

Really? How? What do you mean?