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  1. #1
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    Default 2D:4D Finger Ratio

    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?

  2. #2
    not to be trusted miss fortune's Avatar
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    does this come with cliffs notes?
    “Oh, we're always alright. You remember that. We happen to other people.” -Terry Pratchett

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    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.
    "Hey Capa -- We're only stardust." ~ "Sunshine"

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

  5. #5
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    Next time I'm having trouble sleeping, I'll just come on here and read that article....

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    What is, is. Arthur Schopenhauer's Avatar
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    So, homosexual women have perfectly designed fingers for pleasuring other women? 2D:4D...
    INTJ | 5w4 - Sp/Sx/So | 5-4-(9/1) | RLoEI | Melancholic-Choleric | Johari & Nohari

    This will not end well...
    But it will at least be poetic, I suppose...

    Hmm... But what if it does end well?
    Then I suppose it will be a different sort of poetry, a preferable sort...
    A sort I could become accustomed to...



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

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    Quote Originally Posted by FalseHeartDothKnow View Post
    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...
    "Hey Capa -- We're only stardust." ~ "Sunshine"

    “Pleasure to me is wonder—the unexplored, the unexpected, the thing that is hidden and the changeless thing that lurks behind superficial mutability. To trace the remote in the immediate; the eternal in the ephemeral; the past in the present; the infinite in the finite; these are to me the springs of delight and beauty.” ~ H.P. Lovecraft

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    Quote Originally Posted by Jennifer View Post
    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


    Last edited by Bellflower; 05-12-2010 at 01:47 PM. Reason: There ya go! :)

  10. #10
    Vaguely Precise Seymour's Avatar
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    Apparently the fraternal birth order effect holds true even for adopted children, so it seems like it's more than family dynamics:

    Quote Originally Posted by Wikipedia
    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.)

    Quote Originally Posted by Jennifer View Post
    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).

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