oa Editorial (The 2D:4D Digit Ratio: A Biomarker of Alcohol and Drug Abuse?)

The desire to feel good expresses itself in pleasure seeking behavior. One way this can be achieved is via mood alteration caused by alcohol, nicotine and drugs. The fundamental question how the pursuit for pleasure can result in loss of control, dependence or addiction may be elucidated by looking at differences between hawk-type and dove-type personalities. Maynard Smith and Price [1, 2] proposed the Hawk-Dove model to explain the success of an individual's behavior in a population. The ‘ hawk’ initiates impulsive and aggressive behavior (not stopping until injured or until the opponent backs down). Hawk-types are characterized by high levels of risk-taking behavior and hostility (first do, than think). In contrast, dovetypes retreat immediately if the opponent initiates aggressive behavior and will not fight under any circumstances, i.e. behavior that is characterized by low levels of risk-taking behavior and hostility (first think, then do). Research suggests that high levels of aggression and risk taking behavior are associated with alcohol and drug abuse [3, 4]. Therefore, it can be hypothesized that hawk-types are more likely to develop alcohol and drug dependence than dove-types. Whereas dove-types are capable of adapting lifestyle to circumstances and environmental changes, hawk-types are much more likely to persist in stereotype behavior [5]. Given this difference, it might be further postulated that hawk-types are less likely to be successful in quitting or reducing alcohol and drug use. Research indeed showed that high risk takers are less likely to alter smoking behavior [6]. Prenatal testosterone is important in the development of masculine characteristics such as aggression and strength. Amnionic fluid sample analysis revealed a significant relationship between prenatal testosterone - produced by the fetus - and social behavior in young children [7], adult aggression and risk taking [8, 9]. Prenatal testosterone therefore seems an important factor in determining whether the individual becomes a hawk- or dove-type. If the hawk-dove type model is useful to distinguish between people who are at risk for alcohol and drug abuse, it is important to have an objective biomarker or other correlate of prenatal testosterone that can be measured after birth. One of these correlates can be the 2D:4D digit ratio, since it is thought that prenatal testosterone affects digit length during development in the womb (Manning 2002). Digit growth is controlled by Hox genes [10], which is influenced by testosterone levels. High levels of testosterone increase the length of the fourth digit (ring finger) to a greater extent than the second digit (index finger). Hence, the 2D:4D digit ratio was suggested as biological correlate for prenatal testosterone exposure [11]. Importantly, the 2D:4D digit ratio does not change after the age of 2 [12, 13]. Hence, when measured in adults it provides valuable information about prenatal exposure to testosterone. After measuring finger length (see Fig. 1), the 2D:4D digit ratio can be easily calculated. If the ratio is less than 1, its more likely to be a hawk-type, if the ratio is greater than 1 it is more likely to be a dovetype....