digit ratio 2D:4D ratio 2D:4D ratios A digit ratio calculated by dividing the length of the index finger of a given hand by the length of the ring finger of the same hand. In 1983, Glenn Wilson of King's College London would publish an odd paper entitled "Finger-length as an index of assertiveness in women" which somehow found that women with a lower 2D:4D ratio reported greater assertiveness. Wilson’s hypothesis was that skeletal structure and personality were simultaneously affected by sex hormone levels in utero, despite a marked lack of evidence to support the idea. In 1998, John T. Manning et al further developed this idea, asserting that the 2D:4D ratio was "a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen". In the 20 years since Manning et al's publication, more than 1,400 papers on 2D:4D ratio were published, linking the ratio to "attributes such as personality, cognitive abilities, and sexual orientation as well as to risk of illnesses such as cardiovascular disease, cancer, and amyotrophic lateral sclerosis". Unfortunately, few, if any, were ultimately replicable, including animal studies which purported to showcase the importance of the 2D:4D ratio. Because of the uncertainty of the link between prenatal hormone exposure of the 2D:4D ratio, Kim Wallen, editor of the journal Hormones and Behavior, decided to stop accepting papers on the topic, saying "I’m not saying androgen is not at all important for human behavior. It is… I just don’t think that finger ratios are a scientifically reliable measure of the early hormone environment". In 2021, a publication by Nave et al appeared to debunk the 2D:4D ratio and prenatal androgen exposure idea. The team looked at 2D:4D ratios of persons with congenital adrenal hyperplasia due to 21-hydroxylase deficiency, i.e. individuals with a condition defined by excessive prenatal exposure to androgens. While the group did find that 2D:4D correlated with sex (lower 2D:4D in males) and age (increase of 2D:4D through development), there was no evidence for differences in relation to prenatal androgen exposure in comparison to controls.