Correlational data reviewed in the previous chapters suggest that aggressive behaviour and presumably also aggressiveness in men and women are related to current endogenous testosterone levels - but they do not prove a cause-effect relationship. In addition to studies on prenatal hormone treatment, research on the effects of testosterone intake in the adult female and male could possibly clarify the question whether aggression is actually testosterone-dependent.
Testosterone replacement therapy for hypogonadal males (Finkelstein et al. 1997; Skakkebaek et al. 1981) or exogenous testosterone as potential hormonal male contraceptive (Anderson et al. 1992; Bagatell et al. 1994; Nieschlag 1992; see Chapter 23 by Nieschlag and Behre in this volume) failed to show such an effect (Table 4.3). In a double-blind study by Bjorkqvist et al. (1994) male university students were given either testosterone, placebo, or no treatment for one week. After treatment the placebo group scored higher than both the control and testosterone group on self-evaluated anger, irritability, and impulsivity. Unfortunately, the authors of this well-controlled study did not assess aggressiveness with any of the standardized aggression questionnaires. A double-blind, cross-over study (Sherwin and Gelfand 1985) provided further evidence of a positive effect on hostility scores in surgically menopausal women during testosterone replacement therapy.
With increasing anabolic-androgenic steroid abuse a new field of research opened up. Adverse behavioural effects such as increased irritability and aggressiveness have been reported in several field studies on men andwomen (Bahrke etal. 1992; Brower etal. 1991; Perry etal. 1990; Strauss et al. 1983; 1985). A double-blind study by Hannan et al. (1991) confirmed these findings. Increased aggressiveness (resentment, hostility, and aggression) occurred, even more so in high-dose anabolic steroid users. In a review of pertinent research Uzych (1992) concludes that the possibility of increased aggression after steroid abuse cannot be excluded, but claiming that aggression in anabolic-androgenic steroid users is only testosterone-dependent is too simple. Factors such as unstable personality may be the source of willingness
Table 4.3 Effects of exogenous testosterone on aggression in men and women
Nature of relationship between circulating Studies based on Studies based on testosterone and aggression behavioural measures self-ratings or interviews
Significant positive van Goozen etal. 1995aa Brower et al. 1991
Finkelstein et al. 1997
Hannan et al. 1991
Perry et al. 1990
Sherwin and Gelfand 1985a
Strauss et al. 1983, 1985a van Goozen etal. 1991, 1994a, 1995b
Insignificant positive - Anderson et al. 1992
Bagatell et al. 1994 Bahrke etal. 1990, 1992 Nieschlag 1992 Skakkebek et al. 1981
Insignificant negative - Anderson et al. 1992
Note:a These citations involved female subjects to abuse steroids, as well as of aggressiveness. Bahrke et al. (1990) observed that irritability was slightly increased in many male steroid users but that only in a few, who were premorbid, might steroid use have been sufficient "to push them over the edge" and contribute to irrational or violent behaviour. Bjorkqvist etal. (1994) also conclude that steroid abuse may, for some, be a mediating factor enhancing aggressive tendencies by producing states of elated emotionality.
Further support of testosterone influence on aggression was published by van Goozen et al. (1994a; 1995a; 1995b) who studied female-to-male and male-to-female transsexuals. After three months of cross-sex hormone treatment female-to-male transsexuals responded with more anger and aggression on a questionnaire describing hypothetical aversive situations. In male-to-female transsexuals anger and aggression proneness significantly decreased after androgen deprivation (van Goozen etal. 1995a; 1995b).
In order to understand the complexity of the relation between sex hormones and aggression one further aspect has to be considered: testosterone and aggression seem to be mutually dependent. In addition to sex hormone influences on human aggression, several studies have shown that assertive or aggressive behaviour (e.g., in sport competitions or game contests) followed by a rise in status leads to an increase in testosterone levels (Booth etal. 1989; Elias 1981; Gladue etal. 1989; Gonzalez-Bono etal. 2000; Mazur and Lamb 1980; Mazur etal. 1992; McCaul etal. 1992).
However, the rise in testosterone following a win seems to be associated with the subject's elevated mood of victory or elation. Active participation in a competition is not necessarily required: testosterone levels increased among spectators watching their favourite sports team win and decreased for fans of the losing teams (Bernardt et al. 1989). If the mood elevation is absent or subjects do not regard the win as important, than the rise in testosterone did not occur (Mazur etal. 1997; Salvadore et al. 1987). Booth et al. (1989) also found that testosterone rose in tennis players 15 minutes before the next match - if the individual had won the previous match and probably anticipated winning again. Thus, the experience of winning and of a rise in status seemed to produce a rise in testosterone or to maintain an already elevated level, sustaining the winner's activation and readiness to enter subsequent competitions for higher status. Mazur's "Biosocial theory of status" (1985) incorporates these findings by hypothesizing a feedback loop between an individual's testosterone level and his or her assertiveness in attempting to achieve or maintain interpersonal status or dominance rank. This feedback loop may account for winning and losing "streaks" because each win reinforces a high testosterone level, which in turn reinforces further assertiveness or aggression.
This model of reciprocal effects between sex hormones and environment, although being more complex than simple hormone or experiential factors, still does not fully explain the variation in aggressive behaviour between individuals. New research perspectives will be necessary and helpful. A recent study within the theoretical framework of evolutionary psychobiology by Neave and Wolfson (2003) set an example. They argued that human males are more dominant and activated, attacking more readily within a territory defined as their own - a typical behaviour shown by males (and females) of various species, including subhuman primates. As antagonistic behaviour is related to testosterone levels, with an invasion triggering a subsequent rise in this hormone, they investigated the hypothesis that territoriality in male soccer players is positively related to levels of testosterone. They found that salivary testosterone levels in soccer players were significantly higher before home games than away games. Moreover, testosterone levels were higher before playing against an extreme rival than a moderate rival which could be a reaction to the extent of the perceived threat. However, in this study the self-report mood rating before the matches (e.g., dominant, confident, anxious, aggressive) did not relate to the players' testosterone levels.
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