Long ring fingers have been linked to increased risk of autism and attention deficit hyperactivity disorder (ADHD), a lower risk of a heart attack at a young age, a reduced risk of early breast cancer in women, greater fertility and aggression in men, as well as depression and neuroticism.But digit ratio is not the only dimension that has an effect on health.Those hairs are dependent on testosterone and suggests that receptors have been on the ring finger rather than the index.'' Since the first research on digit ratio, more than 200 studies have found links between it and myriad diseases and personality traits.Exposure to hormones may impact on body and brain development and on future behaviour.
One theory is that for a certain time in foetal development, there are testosterone receptors on the fingers, and that the ring finger may have more of these receptors and therefore more likely to grow faster when exposed to higher levels of the hormone.
In some cases, the dimensions are markers of the kind of womb environment that the growing foetus was exposed to, while in others they are a visible sign of the early afterbirth environment, including nutrition and family wealth.
Some of the most intriguing research centres on the so-called digit ratio theory put forward by evolutionary psychologist Professor John Manning, now attached to Swansea and Southampton universities, and author of The Finger Ratio, due to be published shortly by Faber & Faber.
They seem to appear around week eight, but by week 14 they have gone.
That is how testosterone has an effect on finger growth.