The second-to-fourth digit ratio correlates with aggressive behavior in professional soccer players

We tested the hypothesis that high levels of testosterone during prenatal life, testified by a low second–to–fourth digit ratio (2D:4D), as well as in adulthood would influence the aggressive behavior of professional soccer players. On 18 male professional players from a first level Italian Soccer Team we calculated 1) the 2D:4D ratio of the right hand, 2) the number of yellow and red card per game, 3) the mean salivary testosterone concentration (Sal/T), and 4) the way of handling aggressive impulses assessed with the Picture Frustration Test (PFT).Soccer players with a lower 2D:4D had a higher number of fouls per game. Moreover, we observed a significant negative correlation between Sal/T and D2:D4 ratio. We also observed a significant negative correlation between 2D:4D ratio and their aggressiveness. Finally, we detected a significant positive correlation of Sal/T and fouls/game score and PFT test. No significant correlation was detected between D2:D4 or Sal/T and playing position of playersThis study shows that, in professional soccer players, an aggressive behavior, with the consequent increased risk of fouls during the game, is more likely in individuals having high testosterone levels not only in adulthood but also during their intrauterine life.