Another digit ratio study has surfaced. Time to follow up on my Digit Ratio post. A quick refresher on digit ratio first though. Digit ratio is determined by comparing the length of the 2nd (index) and 4th (ring) finger. This ratio is referred to as 2D:4D. A low 2D:4D ratio (longer 4th finger) is associated with higher testosterone exposure in the uterus and typically male. A higher 2D:4D ratio (shorter 4th finger) means a lower exposure to testosterone in the uterus and typically female.

Researchers in Vienna measured digit ratio and took pictures of the faces of 17 boys, aged 4-11, who had not yet reached puberty. What they discovered is that the boys with a lower digit ratio were already exhibiting masculine features. Their work, revealed in the latest issue of Proceedings of the Royal Society B, is the first study of this kind on children.

Previous research on digit ratio revealed men with a lower ratio (shorter index finger, so a higher exposure to testosterone in utero), had more masculine facial features (i.e. wider jaw, shorter forehead, thicker eyebrows and wider, shorter nose). However, no one knew if this was also true for children, as no study linking facial shape and digit ratio had ever been conducted on children. Typically, after birth male testosterone levels decrease to the same range as female infants and remain low (the lowest levels in their life) until puberty. At puberty, testosterone levels in males rapidly and steeply rise. Previous research assumed the levels of in utero exposure to testosterone were activated during puberty resulting in the masculine adult facial characteristics. However, the researchers of this study saw that the digit ratio variations on the boys in the study accounted for 14.5% of the varieties in face shape, which is considered significant in this type of study.

The research team speculates in their paper that their work linking the 2D:4D to children’s facial features “raises a novel set of questions: are boys with high prenatal testosterone exposure already perceived as more dominant and masculine by children and adults? Do they acquire more resources in competition with peers, and what are their strategies? To what extent does this model apply to girls?”

I, for one, look forward to reading about and reporting on these studies. Now, excuse me as I have to race home to measure my son’s finger length.

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