Prenatal hormones and aggression

Animal studies generally indicate that the presence of androgens in early life is important in establishing a biological readiness for future aggressive behaviour (Archer 1988). Much of the pertinent research on psychological effects of sex hormones in human studies consists of naturally occurring syndromes which result either from spontaneous endocrine excess or deficiency during fetal and early postnatal life (e.g., congenital adrenal hyperplasia) or prenatal sex hormone treatment of the pregnant mother. It is important to emphasize that true experimental design is precluded when studying potentially harmful hormone treatments in humans. Therefore, the researchers had to rely almost exclusively on these "experiments of nature" or existing clinical conditions to investigate how early exposure to hormones influences the potential for aggressive behavior in humans.

Overall, the results of pertinent studies show a slight effect of exposure to testosterone, progesterone with androgenic potential or diethylstilbestrol (a synthetic, nonsteroidal estrogen which exerts organizational effects similar to those of androgens converted to estrogens): an increase in physical aggressiveness, play with fighting figures, and intense energy expenditure (e.g., vigorous play and athleticism) but not on verbal aggression during childhood years. The positive effects of early exposure to sex hormones are significant for both boys and girls, yet these influences seem subtle (Berenbaum and Hines 1992; Ehrhardt and Baker 1974; Ehrhardt and Meyer-Bahlburg 1981; Ehrhardt et al. 1989; Hines 1982; Jacklin et al. 1983; Nordenstrom et al. 2002; Reinisch 1981; Reinisch and Sanders 1984). In a recent study, Hines et al. (2002) found that the mothers' endogenous testosterone level measured once between gestational weeks 15 to 36 (mean 16th week) related linearly to masculine-typical gender role behaviour of their child during preschool age in girls but not in boys.

Exogenous estrogens, usually given in combination with progestagens and progestin-based progestagens can counteract endogenous androgenic effects and thus demasculinize certain aspects of aggressive behaviour in early childhood and adolescence (Ehrhardt etal. 1984; Meyer-Bahlburg and Ehrhardt 1982; Yalom etal. 1973;Zussman etal. 1975).

Archer (1991) explained the rather small or even insignificant effects of prenatal hormone excess with results obtained from animal studies. He suggests that

Table 4.2 Endogenous testosterone and aggression in men and women

Nature of relationship between circulating testosterone and aggression

Studies based on behavioural measures

Studies based on self-ratings

Significant positive

Insignificant positive

Insignificant negative Significant negative

Aromaki et al. 1997; Banks and Dabbs 1996a; Brooks and Reddon 1996; Christiansen and Winkler 1992; Dabbs and Hargrove 1997b; Dabbs etal. 1987, 1988b, 1991, 1995; Ehlers etal. 1980b; Ehrenkranz etal. 1974; Elias etal. 1981; Gladue etal. 1989; Inoff-Germain etal. 1998b; Kedenburg 1977; Kreuz and Rose 1972; Lindman et al. 1987; Mattson etal. 1980; Olweus etal. 1980, 1988; Rada et al. 1976; Scaramella and Brown 1978 Kedenburg 1977b; Lindman etal. 1992; Meyer-Bahlburg et al. 1974a, 1974b; Rada et al. 1983; Susman et al. 1987

Susman etal. 1987b

Aromaki et al. 1997; Cashdan 2003b; Christiansen and Knussmann 1987; Ehrenkranz et al. 1974; Gladue 1991b; Gray etal. 1991; Harris etal. 1996a; Houser 1979; Mattson et al. 1980; Olweus et al. 1980; Persky etal. 1971; Rada etal. 1983; Van Goozen et al. 1994b; von der Pahlen etal. 2002b

Bateup et al. 2002b; Campbell et al. 1997; Dabbs etal. 1991; Doering et al. 1975; Meyer-Bahlburg etal. 1974b; Persky etal. 1977; Rada etal. 1976; Udry andTalbert 1988a Kreuz and Rose 1972; Monti et al.

1977; Persky etal. 1982b Gladue 1991bb

Note:a These citations involved female and male subjects b These citations involved female subjects organizing effects may only be detected clearly after puberty in the presence of adult sex hormone levels. In human studies the possibility that pubertal sex hormones are required to detect hormonal influences on behaviour remained untested except for the study by Yalom et al. (1973). He found stronger correlations of prenatal anti-androgen exposure to behaviour in adolescents after reaching puberty.

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