The evolutionary neuroandrogenic (ENA) theory is a conceptual framework which seeks to explain trends in violent and criminal behavior from an evolutionary and biological perspective. It was first proposed by the sociologist Lee Ellis in 2005 in his paper "A Theory Explaining Biological Correlates of Criminality" published in the European Journal of Criminology. Since then, it has expanded into an interdisciplinary field that intersects biology, psychology, and sociology. The theory rests on two propositions. The first is that in human mating behavior, females prefer males that appear to be more competent providers of resources, and so males exhibit increased competitive behavior than females to obtain access to those resources. The second is that biological mechanisms (namely increased presence of androgens) lead to differential development in the male brain which then mediates the increased competitive behaviors that cause criminality. Though it was originally intended to explain high rates of criminality in young men, it has since been used as a framework to explain gang behavior, terrorism, and the rise of the criminal justice system.
Some have called into question the validity ENA theory, citing mixed literature on the effect of prenatal androgen exposure on later aggressive behavior.
Background
Various sociological theories, such as the theory of differential association by Edwin Sutherland and the theory of anomie by Émile Durkheim, have sought to explain criminal behavior through the lens of socialization. However, such theories have been inadequate in explaining two trends: the rapid increase in criminality during puberty/young adulthood and the gender disparity in criminal behavior. In both cases, the trends are conserved between a variety of different societies, suggesting that these trends had a cause that was not culture-specific. Thus, researchers began looking for a biological explanation for such trends. During the 1980s, the modern field of evolutionary psychology took form with landmark studies such as David Buss' Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures. The scientific knowledge from developments in evolutionary psychology allowed Lee Ellis to formulate what is now known as the evolutionary neuroandrogenic theory.
Overview
Sexual selection
First, ENA theory posits that women value the social position and resources of a prospective partner more so than men. Therefore, there is a large evolutionary incentive for men to compete and obtain the aforementioned social status and resources. Thus, males have evolved greater competitive behavior, which could manifest itself in criminality depending on the behavior's position on the crude-sophistication scale.
Biological changes in males
Ellis hypothesized that the aforementioned selective pressures led to changes in the male brain that is mediated by a substantial increase in the presence of androgens (male sex hormones), particularly testosterone. During puberty, testosterone levels spike, producing three changes identified by ENA theory to play a crucial role in competitive behavior.
The first change is in lowering the sensitivity of the male brain to adverse environmental stimuli. This change has the dual role of decreasing sensitivity to pain and keeping the brain in a suboptimally aroused state. Thus, men will tend to seek more sensory stimulation while being more resistant to the pain that behavior might elicit. The second change caused by testosterone is alterations to the limbic system, increasing the likelihood of episodic dyscontrol, in which the person experiences a sudden, often violent negative outburst. Finally, Ellis believed that testosterone led to a change in the lateralization of the brain. That is, the left and right sides of the brain have been implicated in different mental processes with the left functioning more in language and moral reasoning while the right functioned more in calculation of risk and reward. Ellis suggests that testosterone shifted neocortical activity to the right hemisphere of the brain, thus decreasing moral reasoning in males.