Hormones and the Aggressiveness

of the Serial Murderer

Hormones are regulatory chemicals produced in the endocrine gland that are secreted into the blood stream and carried to target cells that respond to the hormone by an alteration in their metabolism. In this way, the endocrine system is the second largest communication system in the human body, next to the nervous system. Rather than by neural impulse, the endocrine system's mode of communication is by circulation in the blood stream. Hormones released by this system are critical for the activation and control of sex, emotion, response to stress, and regulation of basic functions such as energy use, metabolism, and growth.

The key to the function of hormones, including testosterone, is the hormone receptor sites, which are similar to neurotransmitter receptors in that they are hormone specific. The "master gland" of these sites, and of the endocrine system, is the hypothalamus. The hormones released by the hypothalamus are mainly small peptides. The one that we are most concerned about is the gonadotropin-releasing hormone (GnRH), because it is the only known hormone that activates the sex hormones of the pituitary gland: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These anterior pituitary sex hormones in turn target the gonads (sex organs).

Because all but one documented serial killers are males, we will only focus on the results of the release of male hormones. In males, LH causes the cells in the testes to produce and release testosterone, and FSH causes the development and growth of sperm cells. Testosterone is responsible for maintaining masculine characteristics, and systematically regulating the secretion of FSH and LH, called a negative feedback system. The FSH and LH regulation is accomplished in two ways: (1) blocking the GnRH stimulation of LSH and LH release at the pituitary level, and (2) inhibiting GnRH release at the hypothalamus level.



The male hormone testosterone has long been thought to be linked to aggressiveness, and thus, violent crimes. Previous studies have shown that in the male rat, aggression and dominance relations are testosterone-deppendent. Further, administration of testosterone to castrated rats increases aggression. In these rats, aggression is noted toward an unfamiliar conspecific, not mouse killing or shock induced fighting because those behaviors are not testosterone dependent. This leads to the problem with human studies...no evidence regarding testosterone-dependent aggression situations and those that are not. In spite of these limitation, or maybe because of, confounding results in human studies have been reported. An examination of correlations between human levels and aggression during adolescence, in prison populations, among rapists, weightlifters (steroid-taking). Overall, human testosterone studies seem to depend on when testoterone is measred, what samples are taken, and what behaviors are tested for.

Animal research has linked aggressiveness with the male hormone testosterone. The human studies, however, have been inconsistent because the results depend on when the hormone is measured, how it is studied, and what types of behaviors are observed. Despite these problems, correlation studies have shown links between hormone levels and aggressiveness during adolescence, in prison populations, and among certain rapists.

Radiolabeled hormones were used to detect the receptors for testosterone in the brain. The receptor sites found to be most stimulated by the sex hormones are located in certain nuclear regions of the hypothalamus. The fact that the limbic system is a specific target for testosterone, implies the direct relationship it has with aggression. In a experiment, testosterone was injected into a pregnant female monkey. The result was a genetically female animal with a prominent phallus and no testes. When measuring and comparing the dominance and aggression level of this young monkey, it rated as a male.


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