Biological Theories

The first theory of sexual murder, proposed by Krafft-Ebing (1886), was based on a biologi- cal/evolutionary perspective. Krafft-Ebing considered sexual murder to be atavistic, in that it is a throwback to behavior that was common at an earlier time in the evolutionary cycle.

The conquest over women takes place today in the social form of courting, in seduction and deception. From the history of civilization and anthropology we know that there have been times, as there are savages today that practice it, where brutal force, robbery, or even blows that made a woman powerless, were made use of to obtain love’s desire, (p. 60)

The author reasoned that primitive men would force themselves on women in an effort to propagate the species. “In the intercourse of the sexes, the active or aggressive role belongs to man; woman remains passive, defensive. It affords a man great pleasure to win a woman, to conquer her” (p. 59). Thus, contemporary sexual murderers have a pathological reservoir of aggression that has become “excessively developed, and express [es] itself in an impulse to subdue absolutely the object of desire, even to destroy or kill it” (p. 60).

MacLean (1962) offered a different biological/evolutionary theory involving the development of the psychosexual functions of the human brain. This researcher referred to the “animalistic” or lower brain centers, which involve “the primitive interplay of oral, aggressive and sexual behavior” (p. 289). This oldest or most primitive part of the brain (sometimes called the R-complex or the reptilian brain) and also the slightly more developed limbic structures of the brain (amygdala) are areas that control fear and aggression. These centers are closely connected to other limbic structures governing sexual functions (septum, hippocampus). MacLean referred to male squirrel monkeys’ natural display of their genitals during a fight as an example of this brain-behavior fusion occurring naturally in less advanced species. Such observations in the animal kingdom “appear to shed some light on psychiatric observations that the acts of mastering, devouring and procreating seem to be inextricably tied to one another” (p. 299). Thus, sexual murderers may have an anatomical connection between sex and aggression—in other words, a biological, rather than a psychogenic, fusion of these instincts.

Money (1990) supports a neurobiological explanation for all sexual aggression; in fact, he thinks all sexual offenders suffer from some type of nonspecific “brain disease.” This author agrees with MacLean that the problem most likely lies in the older centers of the brain, including the limbic system:

The limbic region of the brain is responsible ... for predation and attack in defense of both the self and the species. In the disease of sexual sadism, the brain becomes pathologically activated to transmit messages of attack simultaneously with messages of sexual arousal and mating behavior. This pathological mix up of these messages in the brain is brought into being by faulty functioning of the brain’s own chemistry. Faulty functioning may be triggered by something as grossly identifiable as brain damage resulting from the growth of a tumor, or from an open or closed head injury. Alternately, the trigger may be submicroscopic and too subtle to be easily identified on the basis of current brain scanning technology, (pp. 28-29)

Money also stresses the contribution of genetics, abnormal hormonal functioning, pathological relationships, sexual abuse, and the overlap of traditional psychiatric disorders.

Building on prior research and theory, Miller (2000) offers a neuropsycho-dynamic model of the compulsive murderer. He also contends that the problem lies in hyperactive temporal lobe/limbic mechanisms, which result from a combination of factors including biology and experience. “The predatory serial killer is literally a limbically kindled ‘engine of destruction.’ He won’t stop and doesn’t want to, because nothing in life could possibly replace the thrill of dominating and destroying another human being” (p. 158). Miller supports MacLean’s notion of a fusion in the limbic areas that govern sex and aggression, but Miller believes these two drives become melded as a result not only of biology but of an abusive, hypersexualized upbringing as well.

Reid (2017b) recently reviewed various biological theories of sexual murder, beginning with the nineteenth century to the present. Her review included research on genetics, head injuries, gross structural/functional abnormalities, chromosomal anomalies, as well as other factors such as the effects of illness and exposure to toxins. The author also discussed various methodological problems with all of the theories and research findings and concluded that serial sexual homicide “is the result of a complex interplay of various organic and environmental developmental factors and that biology represents only one small part of its pathogenesis” (p. 59).