I chanced upon this very interesting point on the internet: the ratio in the length of your index and ring (2D:4D ratio) finger may be a good indication of the level of testosterone that you are exposed to at birth. Testosterone is a hormone that generally brings about masculine traits. And it was scientifically shown through a large sampling cohort that a higher exposure to testosterone will bring about a lower 2D:4D ratio (a ratio of 0.96 as an appropriate benchmark).
An obvious correlation between homosexuality and testosterone level can be formulated. Interestingly, a higher exposure to testosterone at birth may also be linked to medical conditions such as autism. In contrast, a lower exposure to testosterone at birth may be linked to anxiety disorders.
Abstract
Children with autism have a relatively shorter index finger (2D) compared with their ring finger (4D). It is often presumed that the 2D:4D ratio is associated with fetal testosterone levels and that high fetal testosterone levels could play a role in the aetiology of autism. It is unknown whether this effect is specific to autism. In this study, 2D:4D ratios of 144 males aged 6 to 14 years (mean age 9y 1mo [SD 1y 11mo]) with psychiatric disorders were compared with those of 96 males aged 6 to 13 years from the general population (mean age 9y 1mo [SD 1y 10mo]). Psychiatric disorders were divided into autism/Asperger syndrome (n=24), pervasive developmental disorder–not otherwise specified (PDD–NOS; n=26), attention-deficit–hyperactivity disorder (ADHD)/oppositional defiant disorder (ODD; n=68), and anxiety disorders (n=26). Males with autism/Asperger syndrome (p<0.05) and ADHD/ODD (p<0.05) had significantly lower (though not significantly; p=0.52) ratios than males with an anxiety disorder, and males with autism/Asperger syndrome had lower ratios than those in the comparison group. These results indicated that higher fetal testosterone levels may play a role, not only in the origin of autism, but also in the aetiology of PDD–NOS and of ADHD/ODD. Males with anxiety disorders might have been exposed to lower prenatal testosterone levels.
Furthermore, the testosterone level also seems to affect hand preference.
Abstract
The finger length ratio (2D:4D) is a biomarker for the prenatal levels of testosterone. The prenatal effects of testosterone on the development of brain hemispheres are considered as a key factor in the etiology of left-handedness. We tested whether 2D:4D correlates with the type of handedness in males (18 right-handers and 18 left-handers). Right hand 2D:4D, left hand 2D:4D, average 2D:4D, and the difference between right and left 2D:4D (D(r-l)) were compared. The value of D(r-l) in left-handers was significantly lower than D(r-l) in right-handers. This result can be interpreted as proof that left-handers were subjected to higher levels of testosterone in utero.
Clearly, I can go on forever….but before I knock you asleep, go measure your 2D:4D ratio and let me know your sexuality, your hand preference and social skill. You may opt out of declaring your sexuality if you prefer to remain in the closet.
