Digit Ratio

Testosterone shows two peaks of production during a person’s development. The first occurs in the foetus at the end of the first trimester of development. The second occurs at puberty. It is thought that the prenatal peak affects “organizational” changes to the foetus, and these changes sensitize the individual to the effects of testosterone at puberty.

Digit ratio (2D:4D) is the ratio between the length of the 2nd or index finger and the 4th or ring finger. It is thought to be a marker of foetal levels of testosterone. If the index finger is relative long compared to the ring finger this indicates low foetal testosterone. The opposite indicates higher foetal testosterone. If this is correct we would expect KS individuals to have long index fingers relative to their ring fingers.

Professor Manning ran a study involving many members of the KSA in his sample group. Images of fingers (from photocopies of the palm of the hand) were measured in order to quantify the typical 2D:4D. The results for those with KS were compared to those of other adults.

It was found that although KS adults did have a higher digit ratio than would be expected for a non-KS male, the difference was too small to make it a realistic indicator.

Photocopy hands

Photocopies of hands were sent to Professor Manning who measured the length of both fingers measuring from the lower crease to the finger tip.

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