The lower the ratio is between the length of your second digit to the length of your fourth digit(i.e. index to ring), the more successful people are in highly competitive sports, such as soccer (i.e. football), rugby, basketball, and skiing.
The reasons for this strange correlation is suggested to be that prenatal androgenic steroids affect brain development in a way that the brain becomes more sensitive to the activational effects of testosterone. This may lead to increased confidence, higher risk taking, search persistence, and heightened vigilance and faster reaction times. All important things in some sports... and now also in financial trading, as has been shown in this study by researchers at Cambridge, UK. Because androgens also make the ring finger longer than the index finger, this ratio of finger lengths can thus be used to predict success among athletes and stockbrokers.
Care must always be taken to get the causal relationship correct, though in this case it doesn't take much to see that it goes like this (solid lines):
The researchers compared profit and loss (P&L) of 49 traders taken from the trading floor in the City of London, at which only three out of about 200 traders are female. P&L was used as the measure for how well the traders did compared to each other, and the 2D:4D (second-digit to fourth-digit ratio) as a proxy for prenatal exposure to androgen.
As we can see, the higher the P&L is (meaning higher profits), the lower digit ratio, meaning that the ring finger is longer compared to the index.
Digit growth and gonadal development are both affected by Hox genes, which is why there is a developmental link between the two. Shortening of digits and defects in the urogenital tract are both caused to loss of Hox function (HOXA13).
Word of caution. These findings are to be taken as general trends to which there are many exceptions, of course. We are talking on average. If you don't have a long ring finger, you may still be great at sports and trading stocks, of course, and vice versa. The authors of the study suggest an even split between contributions of biology and experience (i.e. nature vs. nurture) in explaining long-term success of traders.
On Wikipedia I learned that
Androgen is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics in vertebrates by binding to androgen receptors. (...) The primary and most well-known androgen is testosterone.Why do I mention that? Because testosterone is of course better known as the principal male sex hormone. Recall that most traders are men, so since trading is a highly competitive high-stress line of work, men generally do better at it. One could then argue that this is culturally based, and that might be the case if women in that profession are frowned upon, or if parents (knowingly or not) encourage only their boys to become traders, etc.
However, this study suggests that in occupations that require high risk-taking and quick reactions, such as the one studied, are better suited for people who were exposed to more testosterone in the womb. Men. This is in opposition to other kinds of trading where the approach to the market is more analytical and long-term. Here a higher and more "feminine" digit ratio have previously been found to be dominant.
J. M. Coates, M. Gurnell, A. Rustichini (2009). Second-to-fourth digit ratio predicts success among high-frequency financial traders Proceedings of the National Academy of Sciences, 106 (2), 623-628 DOI: 10.1073/pnas.0810907106