More Evidence That 2D:4D Correlates w/ Sexual Orientation
For the past two decades I have been following and writing about the 2D:4D digit ratio. At first, the data was suggestive, but not conclusive. We have reached the point that it can be concluded that it does indeed correlate with sexual orientation, as this recent study now shows:

Reference:
Schultheiss, O.C., Gebhardt, D., Meier, E. et al. Deconstructing Kinsey’s Scale: Digit Ratio Correlates Negatively with Gynephilia and Positively with Androphilia in Both Sexes. Hum Nat (2026). https://doi.org/10.1007/s12110-026-09518-z
More 2D:4D Evidence for Multiple Etiology of Homosexuality
For last few years, evidence has been accumulating that there is more than one etiology for male androphilia. This also reads upon the issue of the separate etiological origin of Homosexual Transsexuals (HSTS). We now have another paper looking at the 2D:4D ratio, the length of the index finger to ring finger, which has been found to be mildly sexually dimorphic and to be different in “tops” vs. “bottom” gay men and different in HSTS vs. AGP MTF transsexuals.
One of the leading researchers in this field is John Manning. He has a new paper published on the subject. Fortunately, NOT behind a paywall. Please do take a moment to read it.
The key take away is that there are two phenotypes for the 2D:4D ratio found in gay men, one that is feminized, and one that is not. The hypothesis is that one group was exposed to low testosterone / high estrogen in utero to feminize the hand and the brain, to become feminine homosexuals (and HSTS?) while the other group is exposed to HIGH testosterone / low estrogen to become masculine homosexuals. This fits with the earlier data that shows that bottoms and tops have different 2D:4D ratios, on par with the difference between men and women.
Further Reading:
Reference:
Manning, J.T., Fink, B. & Trivers, R. Digit Ratio (2D:4D; Right-Left 2D:4D) and Multiple Phenotypes for Same-Sex Attraction: The BBC Internet Study Revisited. Arch Sex Behav (2023). https://doi.org/10.1007/s10508-023-02703-6
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What The Fingers of Women With Complete Androgen Insensitivity (CAIS) Tell Us
There is still an ongoing debate as to whether the 2D:4D finger ratio actually indicates the influence of androgens, testosterone, on the developing fetus. So, a few researchers have turned to those women with Complete Androgen Insensitivity Syndrome (CAIS) to disentangle the influence of androgens and chromosomes / genes on the adult 2D:4D phenotype. A reminder to my readers; Women with CAIS are 46XY w/ normal testes, but because their bodies have a “broken” androgen receptor gene, their bodies do not respond to testosterone and thus they develop in mostly female typical fashion.
So, onto the studies of their fingers. We have three studies that all point to the same conclusion, that like women with 46XX karyotype, show a sexually dimorphic tendency to higher 2D:4D digit length ratios than men w/ 46XY, ON AVERAGE. This last point is important. The variability of all three populations is fairly high, so that it is only possible to see a statistical effect when looking at enough people. However, it does point to the conclusion that androgen exposure DOES influence the 2D:4D ratio and that karyotype alone does NOT explain the sexual dimorphism.
Further Reading:
https://sillyolme.wordpress.com/?s=2D%3A4D
References:
Sheri A. Berenbaum, Kristina Korman Bryk, Nicole Nowak, Charmian A. Quigley, Scott Moffat, Fingers as a Marker of Prenatal Androgen Exposure, Endocrinology, Volume 150, Issue 11, 1 November 2009, Pages 5119–5124, https://doi.org/10.1210/en.2009-0774
van Hemmen J, Cohen-Kettenis PT, Steensma TD, Veltman DJ, Bakker J. Do sex differences in CEOAEs and 2D:4D ratios reflect androgen exposure? A study in women with complete androgen insensitivity syndrome. Biol Sex Differ. 2017 Apr 12;8:11. doi: 10.1186/s13293-017-0132-z. PMID: 28413602; PMCID: PMC5389183.
de Sanctis V, Soliman AT, Elsedfy H, Soliman N, Elalaily R, Di Maio S. Is the Second to Fourth Digit Ratio (2D:4D) a Biomarker of Sex-Steroids Activity? Pediatr Endocrinol Rev. 2017 Jun;14(4):378-386. doi: 10.17458/per.vol14.2017.SSE.SexSteroids. PMID: 28613048.
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Gay Men’s Hands Tell Us About Their Erotic Role
Thirteen years ago, I wrote an essay on how scientists had been frustrated using the 2D:4D digit ratio to demonstrate that gays and transsexuals had anomalous pre-natal exposure to androgens. They had gotten very confusing, contradictory results. I’ve been following the research hoping that some headway would be made. Well, maybe we have.
First was the confusion of not segregating and analyzing transsexual subjects data based on etiology / sexual orientation. We may now have found a similar issue with looking at gay men. There is strong evidence that there is an etiological difference between subsets of androphilic males that has correlates with preferred erotic role, specifically, preferring receptive anal sex vs. everything else.
There have also had some scientists questioning whether the 2D:4D is really about androgen exposure at all. Some data suggests that the differences within, but not across the sexes, may be due to other factors such as stress induced cortisol exposure, etc. But for our purposes, that does not matter. What matters is that when we see data that differentiates between populations and correlates with other markers for those populations, we have something interesting to note and explore. Such is the case with the Swift-Gallant paper on 2D:4D difference between tops and bottoms.
“A growing body of work indicates that anal sex role (ASR) preferences may serve as a proxy for subgroups of gay men who differ in development and gender conformity. Thus, in the present study we asked whether gay men with different ASR preferences may differ in 2D:4D. We hypothesized that gay men with a Bottom ASR (receptive), who tend to be more gender nonconforming (GNC), would have a higher (more female-typical) average digit ratio than ASR Tops (insertive), who tend to be more gender conforming. We predicted that gay men with a Versatile ASR preference (i.e., preference for insertive and receptive) would be intermediate between these two groups in both GNC and 2D:4D.”
The data they gathered is remarkable. The statistical difference between the tops and bottoms was d=0.63 for their right hands. Compare this to the difference between control men and women (from another study) at d=0.76. Thus the difference is nearly as large as that between men and women. This is a dramatic result!
They found that versatiles, those that both top and bottom were intermediate between the two. There are two hypotheses that would explain this. One is that this is a dimensional trait that smoothly varies between tops and bottoms. The other is that this is in fact, taxonic, and those that self-labeled as “versatile” were in fact an admixture of the taxonomically distinct tops and bottoms. The data presented does not allow us to determine this.
I’m predicting that the later hypothesis is correct, based on the fact that earlier work supported that, especially since the obligate bottoms appear to be the only subset of androphilic males who exhibit the Fraternal Birth Order Effect.
Further Reading:
2010 Essay on 2D:4D frustrations
Essay on Etiological Differences between Tops & Bottoms
Essay on Socio-Economic Status effecting 2D:4D differences
Essay on 2D:4D study that supports transsexual taxonomy.
References:
Swift-Gallant, A., Di Rita, V., Major, C.A. et al. Differences in digit ratios between gay men who prefer receptive versus insertive sex roles indicate a role for prenatal androgen. Sci Rep 11, 8102 (2021). https://doi.org/10.1038/s41598-021-87338-0
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The Effect Of Socio Economic Status On Transsexuals
There have been many who have commented upon, and even some actual data, to suggest that there is a correlation between Socio Economic Status and etiology found in MTF transsexuals. However, many have made silly and unsupported suppositions as to why this should be. Most mistake the arrow of causation.
For “late onset” (autogynephilic) transwomen, the arrow of causation is very straight forward. Transition is socially, financially, and personally expensive. It often entails loss of career opportunities, loss of income, loss of family connections, divorce, child custody and ensuing child support payment obligations, etc. The very process of transition also entails costly medical and other “gender affirming” procedures (therapy, facial hair removal, hair transplants, etc.) Thus, an individual contemplating transition naturally weighs their ability to “afford” these social and financial costs. This means that the higher one’s personal Socio Economic Status, the more likely an autogynephilic male will transition.
Note that is their status AT THE TIME OF TRANSITION !
The arrow of causation is reversed for an HSTS. If she has risen to some level of career success or not, it is an effect of having experienced the visicitudes of being gender atypical, homosexual, and transsexual. It is NOT the cause of her being transsexual and certainly not of having chosen to transition.
For a teenager in transition, an “early onset” Homosexual Transsexual (HSTS), their future SES is an unknown country on the one hand, and likely NOT to become very great, given statistical and cultural realities on the other, especially if their family has already or is very likely to disown them. (I’ve written on this issue before.) If an HSTS works very hard, has a few lucky breaks, and becomes socially and financially stable, even “successful”, this cannot have had a retroactive influence upon her decision to transition. And certainly NOT upon her sexuality.
There have been, and will continue to be, HSTS who achieve some degree of success, even of considerable success in business or industry. Being hungry, cold, and homeless as a teenager and early 20 something often has the effect of driving one’s ambition to never be so again. And if they take advantage of their early education and social connections in a given industry, this cannot be seen as evidence of their sexuality or etiology, only of their “invisible knapsack” of knowledge, packed by their early experiences.
On the other hand, there are many HSTS who never do become financially stable, much less attain notable social, business, or career success, often trapped in a vicious cycle of poverty from an early age. But again, this too is a result, not a cause of their transsexuality.
However, there is a correlation with family of origin’s SES and HSTS, as has been noted by various observers and found in some of the datasets (e.g. Nuttbrock). J. Michael Bailey in his book, The Man Who Would Be Queen, speculated that feminine androphilic males that come from better SES would work harder to “normalize their gender identity”, to be a desister. To be honest, this notion felt wrong somehow.
Consider that desisters always do so BEFORE puberty. This smacks of biology, not sociology. Frankly, I doubt many pre-pubescent children think very deeply about their future careers and their chances of success as gay men vs. HSTS.
One interesting data point is that there are more HSTS transkids raised in middle and upper-middle-class families after adoption than would be expected. Similarly it has been noted that there are more HSTS in foster care than random chance would account. If the issue was low SES in the family that was raising them to persist to become HSTS instead of desisting to become gay men, they should have been desisters per Bailey’s speculation. But they didn’t desist.

We may now have another working hypothesis. It comes from all places, research on 2D:4D ratio of fingers. As I’ve pointed out before, there is some evidence that 2D:4D ratio is both sexually dimorphic and is correlated with both sexual orientation and gender atypicality, including being HSTS. This new data shows a correlation between the mother’s SES during pregnancy and a feminized 2D:4D ratio. That is to say, it suggests that women, without their conscious control, adjust their own hormones to favor masculinity if they are well off, and femininity if they are poor. How one’s SES causes this is as yet unknown, but the data is there.

There is a linear correlation between the 2D:4D ratio and SES as shown in this graph. Poor families have children with more feminized hands due to hormones in the womb. Since the 2D:4D ratio is stable from birth, the effect is only from prenatal exposure to hormones. While this effect is likely not enough on its own, in combination with other factors such as genetics / epigenetics (androphilia and HSTS “running in families”), the Fraternal Birth Order Effect, perinatal hormones, and perhaps other influences yet to be discovered, this maternal SES effect on hormones may be enough to cause the noted statistical finding of more HSTS coming from low SES households.
It is important to note that this SES effect would ONLY be operable prenatally. If the child is adopted, fostered, or if the mother should experience a dramatic increase in SES while she was raising her feminized male child, that child’s then experienced SES would have no bearing on that child’s sexual orientation, gender atypicality, or gender dysphoria. The SES effect would have already done it’s work, causing a locked-in effect. In this case, we would see a SES effected HSTS, but one who grows up in a much more privileged environment and thus much more likely to face the adversities thrown at such teenaged transsexuals and able to overcome them.
These findings have a personal resonance. My own 2D:4D, at 1.06 is literally off the chart feminized, one could describe it as hyperfeminized, not just hypomasculine. Given that we also know that such ratios are found to anti-correlate with sports performance, one would expect that I would be a very poor athlete, which was true. But, as many who know me (or think they do) have no doubt observed, I came from a fairly well off family. But what they don’t realize is that was only true of the second half of my childhood.
My father grew up in Port Arthur, Texas, a dirty, smelly, working class petroleum refining town on the Gulf Coast. He was born in the fall of 1929, right as the economy crashed. He grew up poor as poor can be. He shared stories of how he and his brothers would fish and hunt for crawdads in the Gulf waters to put food on the table. But he and his siblings were very smart and managed to get into college in spite of this lack of funds or legacy, partly on the GI Bill from serving during the Korean War. Even his gay brother climbed out of that poverty through study and hard work, largely because of their father (my grandfather) insisting upon it.
My mother grew up in a tiny farm town in the middle of nowhere on the boarder of Texas and Oklahoma. Her family was a little better off than my father’s, mostly by dint of hard work farming and ranching. (I have childhood memories of collecting eggs from the hen house and of feeding hay to the cows on their farm.) My mother too was very smart, graduated from high school at age 16 to attend college to earn a teacher’s credentials at age 19, graduating as a married woman with a baby in her arms, me. My father worked at a bowling alley, between classes, to support his young wife and child. My siblings came along in rapid succession. Thus, while my mother was carrying me, my parents were dirt poor students from working class families. Things must have been rough for my parents at first. Me? I don’t remember.
My father was proud to have worked his way out of the poverty he grew up in… earning his place in middle and even upper-middle-class professional circles, but always carried a bit of baggage from his childhood, especially around the topic of food. He would become enraged at food waste for example, remembering days of hunger. There was never the entitled expectation in our household that other well off families taught their kids. Instead, my father was constantly exhorting us to study hard, especially math and science, just as his father before him, fearing we would slip down the socio-economic ladder, saying, “You want to be a ditch digger when you grow up?” He not only helped us with homework, but independently tutored us in science, setting up experiments and demonstrations, from basic physics, chemistry, to biology, while our mother pushed us in reading, writing, and arithmetic (she had a teacher’s credential after all). I learned that same lesson about hunger when I was disowned and become a homeless street tranny. But my father’s lessons of hard work and study lifted me out of poverty, just as it had for him.
Further Reading:
2D:4D Evidence Supports Transexual Taxonomy
Autogynephilic Transwomen Have Higher IQs; A Selection Effect on Higher SES
Reference:
J.T. Manning, et al, “Parental income inequality and children’s digit ratio (2D:4D): a ‘Trivers-Willard’ effect on prenatal androgenization?”, Journal of Biosocial Science, 2021, https://doi.org/10.1017/S0021932021000043
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2D:4D Evidence Supports Transsexual Taxonomy
A new paper provided both new direct evidence and a meta-analysis of measurements of 2D:4D finger ratios in transsexuals, both FtM and MTF. Such measurements are interesting because it is known to be influenced by testosterone levels in utero and thus an indirect measure of testosterone exposure that might influence brain sexual dimorphism.
What is doubly exciting about this paper is that the authors fully comprehend the overwhelming evidence for the two type taxonomy and of the (mild) scientific controversy regarding sexual orientation vs. age of onset as the best clinical markers for the two taxons. The study is open access so I highly recommend following the link to it and reading it for yourself. The study is also interesting because of where it was conducted; Iran.
Iran is a Muslim country which while being extremely homophobic, both culturally and legally, treats transsexuals fairly well, at least legally and medically. Make no mistake, culturally, it is far from truly accepting. Further, Iran is considered a “Collectivist Society” according to the Hofstede Individualism vs. Collectivism Index. Lawrence has shown that this index highly correlates with the percentage of non-androphilic (and thus likely autogynephilic / late onset) transwomen transitioning in a given culture. Thus, we would expect that there were fewer such transwomen in the study and the reported data bear this out.
Let’s look at the new data they provide:
Table 1
Means (and SD) for 2D:4D in the left and right hand for transmen, transwomen, control women, and control men
|
Transmen |
Control women |
Transwomen |
Control men |
|
|---|---|---|---|---|
|
Left 2D:4D |
0.991 (0.034) |
0.991 (0.032) |
0.981 (0.033) |
0.974 (0.029) |
|
n = 104 |
n = 53 |
n = 88 |
n = 56 |
|
|
Right 2D:4D |
0.981 (0.030) |
0.983 (0.033) |
0.972 (0.029) |
0.959 (0.033) |
|
n = 104 |
n = 53 |
n = 89 |
n = 56 |
Table 2
Means (and SD) for 2D:4D in transsexuals’ left and right hand as a function of early or late onset of gender dysphoria
|
Transwomen |
Transmen |
|||
|---|---|---|---|---|
|
Early onset |
Late onset |
Early onset |
Late onset |
|
|
Left 2D:4D |
0.982 (0.034) |
0.975 (0.022) |
0.988 (0.033) |
1.009 (0.031) |
|
n = 80 |
n = 8 |
n = 92 |
n = 12 |
|
|
Right 2D:4D |
0.973 (0.029) |
0.963 (0.026) |
0.977 (0.028) |
1.007 (0.027) |
|
n = 81 |
n = 8 |
n = 92 |
n = 12 |
|
Before the analysis of transfolk, it would be a good idea to scale the effect by looking at the effect size between the controls. The difference between control women and men is d= 0.56 for the left hand and d= 0.76 for the right. This is only a moderate effect size.
Although the number of late onset is small, and thus must be viewed with caution, the analysis is still very interesting and would seem to confirm (agree) with the two type hypothesis. Consider that the two MTF types have a small but distinct difference of d= 0.24 for the left hand and d= 0.22 for the right. When we compare early onset type to the male controls we get d= 0.25 and d= 0.45 for the right.  When we compare early onset to female controls we get d= -0.27 for the left and d= -0.32 on the right. This shows that early onset transwomen are roughly halfway between the controls, and if anything a bit closer to the female controls.
But even more intriguing, and the reason for trusting this interpretation is that when we compare the late onset population to the male controls we see that it exactly agrees with the hypothesis that the late onset type is essentially like the majority heterosexual male population and not at all feminized, with effect sizes that are, statistically speaking, non-existent at d= 0.04 and d= 0.12 for the left and right hands respectively.
This shows that early onset MTF type has notably hypomasculine (feminized) hands while the late onset MTF type does not, and thus in agreement with other data that supports the two type MTF taxonomy.
But what about the FtM transmen? Here we see an even more intriguing set of data.
The two FtM types have a moderate to substantial, very notable, difference of d= -0.66 for the left hand and d = -1.07 for the right, indicating that early onset transmen are far more masculine than late onset. When we compare the early onset FtM to female controls we find effect sizes of d= -0.09 for the left hand and d= -0.20 for the right indicating a non-existent to small masculinization signal.
However when we compare the late onset FtM to female controls we see a very different pattern with effect sizes of d= 0.57 for the left and d= 0.80 for the right. The positive sign indicates that late onset transmen have a more feminine 2D:4D ratio than control women (!!). And the effect size difference between early and late onset transmen is far greater than the difference between control men and women (!!!).
This, if replicated, is very big news. It would support the notion that transmen also exhibit two taxons as has long been suspected, one that is masculinized in both behavior, sexual orientation, and very mildly in appearance, the other that is very feminine, androphilic, and autoandrophilic, the mirror image of late onset transwomen.
Further Reading:
Essay on Cultural Difference in Percentage of HSTS vs. AGP Transwomen
Reference:
Sadr, M., Khorashad, B.S., Talaei, A. et al. “2D:4D Suggests a Role of Prenatal Testosterone in Gender Dysphoria” Archives of Sexual Behavior (2020)
https://doi.org/10.1007/s10508-020-01630-0
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