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state; the presence of the TDF protein (Testis Determining Factor) on the Y chromosome in male offspring triggers the developing testes to secrete massive doses of testosterone. This then sculpts the body and the brain in a male-typical direction, and at the same time suppresses femaletypical development. In the absence of this Nick Neave and Daryl B. O’Connor describe their research into the complex protein in the female fetus, development of effects of this hormone the body and the central nervous system proceeds along nature’s default setting (female). Later on, during puberty and The steroid hormone testosterone hink of testosterone and you beyond, the second ‘activational’ effect has long been associated with probably think of lust, violence and becomes apparent: those cells and various male-typical behaviours. machismo. Indeed, testosterone is structures in the body that have been This review first highlights key often labelled ‘the aggression hormone’ initially ‘organised’ along male or female issues in behavioural due to its presumed relationships with lines, are then ‘activated’ by the sex endocrinology, and then provides such negative, antisocial and principally steroids (Nelson, 2000). a brief summary of the authors’ male qualities. Animal models can be used to compare research into various associations Over the past decade or organisational between testosterone and male so our principal research versus behaviours. Some evidence in activities have investigated activational support of the assumption is found, the extent to which levels of effects, for but some critical issues regarding testosterone can be associated example by testosterone-behaviour with certain male-typical castrating a relationships are also raised. behaviours. As you might male before expect, the answer is by no or after fetal means straightforward. For sexual one thing, hormones do not differentiation directly change behaviour; has taken place, they influence the expression or castrating of a behaviour within him before or To what extent does testosterone appropriate environmental/ after pubertal influence aspects of male-typical social contexts. When differentiation behaviours? studying human behaviours, has taken place. identifying which Such males can How useful is the 2D:4D ratio in environmental/social contexts be compared determining links between prenatal Testosterone influences the might be important remains physically and steroid exposure and subsequent expression of many behaviours behaviourally with a significant challenge to physical/behavioural characteristics? researchers trying to identify other males who What role do social/environmental hormone–behaviour have been left factors play in hormone–behaviour relationships. gonadally intact; in interactions? In behavioural endocrinology animal addition these castrated males can then of Is testosterone related to variations models are routinely used to address such course have their testosterone levels in aspects of cognition? questions. The effects of any hormones on returned to normal (or even higher than behaviour are normally described in terms normal) via replacement therapy, and once of ‘organisational’ versus ‘activational’ again alterations in their Neave, N. (2008). Hormones and effects. In the former, it is known that physiology/behaviour noted. Such studies behaviour: A psychological approach. during early fetal development, levels of have provided significant information Cambridge: Cambridge University the sex steroids (principally testosterone) concerning the role of sex steroids in Press. play a pivotal role in sexual differentiation. certain animal behaviours. The sexes begin life in an undifferentiated In terms of organisational effects,
Testosterone and male behaviours
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vol 22 no 1
january 2008