December 27, 2011
Recently professor John T. Manning revised his theory about finger length ratio development. While he had already mentioned the role of prenatal sex steroids, now the ‘balance’ between sexe hormones (testosterone & oestrogen) has become a key-element in his theory.
Manning described his revision in the PNAS-article: ‘Resolving the role of prenatal sex steroids in the development of digit ratio‘.
Manning’s working hypothesis now includes the following 7 key elements:
1 – 2D:4D Finger ratio results from the balance between prental testosterone & prenatal estrogen;
2 – High 2D:4D finger ratio result from low testosterone concentrations OR high estrogen concentrations;
3 – Low 2D:4D finger ratio result from high testosterone concentrations OR low estrogen concentrations;
4 – The ring finger (4D) has much more hormone receptors than the index finger (2D), therefore the 2D:4D finger ratio is mostly driven by changes in the length of the ring finger (due to prenatal hormone concentrations);
5 – Studies in human & animals indicate that the link between prenatal hormones and 2D:4D finger ratio is generally stronger for the right hand;
6 – 2D:4D Finger ratio varies with sexe: males generally have longer fourth digits relative to second digits than females;
7 – 2D:4D Finger ratio varies with ethnicity.
“Armed with this list of skeletogenic genes linked to 2D:4D, we can now be more focused in our examination of the links between 2D:4D and the etiology of sexdependent behaviors and diseases of the immune system, cardiovascular disorders, and a number of cancers.”