Review of 'Sexuality and Crime' by Anthony Walsh

Walsh incorporates insights from behaviour genetics, documenting how variants of one particular gene can affect people’s criminal propensities.

Written by Lipton Matthews.

Can evolutionary theory help us understand crime? Professor Anthony Walsh of Boise State University argues that it can. His recent book Sexuality and Crime: A Neo-Darwinian Perspective explores how social and biological factors relating to human sexuality contribute to criminal behaviour in modern society. It draws upon life history theory, sex ratio dynamics, behavioural genetics, studies of racial differences, and analyses of the personality traits associated with high reproductive effort. In this review, I will outline Walsh’s key arguments and critically evaluate their implications.

Central to Sexuality and Crime is life history theory, a framework within evolutionary biology that concerns how organisms allocate energy between growth, reproduction and survival. Life history strategies exist on a spectrum from “r-selected” (fast) to “K-selected” (slow). Individuals who follow a fast life history strategy prioritize present reproduction over reproduction in the future, often exhibiting impulsivity, risk-taking and reduced parental investment—traits that Walsh correctly identifies as predictors of criminal behavior.

Walsh emphasizes that fast life history strategies can be adaptive in environments characterized by high unpredictability, mortality rates and resource scarcity. In such environments, individuals who reproduce early and invest minimally in offspring increase the likelihood of passing on their genes before facing potential threats to their survival. While impulsivity and risk-taking may enhance reproductive success in these environments, they often conflict with societal norms and laws in modern nation states, resulting in criminal punishment. For example, the same impulsiveness that drives someone to pursue multiple sexual partners may lead them to engage in theft or violence as a means of acquiring resources.

Diving into the literature, Walsh cites research showing that traits linked to higher reproductive output are often associated with anti-social behaviour and criminality. A case in point is the 2018 study by Tielbeek and colleagues, which provides evidence for the shared genetic origins of reproductive effort and antisocial behaviour.

Using genome-wide association study (GWAS) data on up to 318,863 people, the researchers examined genetic correlations through the lens of life history theory. They found that alleles associated with higher reproductive output (an indicator of faster life history strategies) were positively correlated with those linked to antisocial behaviour (with a genetic correlation of 0.50). Conversely, alleles associated with later childbirth (a characteristic of slower life history strategies) were negatively correlated with those linked to antisocial behaviour (with a genetic correlation of –0.64).

It’s important to note that Walsh is not guilty of biological determinism. He acknowledges the role of environmental and cultural factors in shaping deviant behaviour. For example, supportive family structures, community cohesion, and access to education can all mitigate the impact of criminal predispositions. Individual propensities always interact with the environment.

Walsh’s discussion of the sex ratio provides further insight into the evolutionary basis of crime. He notes that imbalanced sex ratios disrupt mating markets, shaping male behaviour in ways that elevate the risk of criminality.

In societies where there is a surplus of males, married men tend to guard their spouses jealously and show stronger commitment to parenting. Such societies are characterized by higher levels of family stability and pro-social tendencies. However, male-skewed sex ratios also increase the proportion of unmarried men, who may channel their testosterone-fueled energy into antisocial activities. Women tend to pacify the men to whom they are married, so when women are in short supply, levels of violence are sometimes higher. (Think of the Wild West, for example—an environment often characterized by male-skewed sex ratios.)

Interestingly, levels of violence can also be higher when women are in a surplus (as compared to when the sex ratio is balanced or male-skewed). In these circumstances, men exploit the increased availability of mates, engage in sexual promiscuity and neglect their long-term parental investments. This dynamic contributes to family instability and thereby fosters criminal behaviour. For instance, a 2016 study by Ryan Schacht and colleagues found that rates of homicides and other violent crimes were higher in American counties where women outnumbered men.

In one of the most provocative sections of the book, Walsh addresses the extremely high rates of violent crime in America’s black community. He notes that black neighborhoods are often characterized by a surplus of females relative to males, driven in part by higher rates of incarceration and mortality among black men. This demographic imbalance, he argues, exacerbates social instability and violent crime. It should be noted that while Walsh’s analysis is rooted in evolutionary theory, he is cognizant of historical and social realities within black communities.

In another provocative section, Walsh incorporates insights from behaviour genetics, documenting how variants of one particular gene can potentially affect people’s criminal propensities. For example, the androgen-receptor gene (ARG) is a polymorphic gene that contains a trinucleotide CAG repeat, with the normal range spanning 11 to 30 repeats. Studies show that low numbers of repeats are associated with greater binding affinity for all androgens. And this may lead to heightened criminal proclivities.

A review by Kevin Nelson and John Witte of studies examining racial differences in the AR gene found that 76% of African Americans, 62% of whites and 55% of Asian Americans carried short alleles. These alleles are associated with heightened sensitivity to testosterone, which is known to cause aggression, impulsivity and an increased number of sexual partners. For example, a 2013 study by Marin Butovskaya and colleagues revealed that Tanzanian men with shorter ARG repeats exhibited higher levels of aggression, anger, and hostility, and had fathered more children than those with longer repeats. Likewise, Daniel Cheng and colleagues compared violent criminals with non-criminals in China, and found that the criminals were significantly more likely to have a small number of ARG repeats (to be specific, less than 17) than the non-criminals.

Walsh’s book offers valuable insights into the nature, nurture and evolutionary roots of crime. His integration of life history theory, sex ratio dynamics, and behaviour genetics provides a robust explanatory framework which is vastly superior to many vague sociological frameworks, and his willingness to address sensitive topics, such as race differences, demonstrates intellectual courage. However, two aspects of the book warrant further scrutiny.

First, Walsh’s evolutionary approach may understate the complexity of human motivations. In particular, one could argue that he risks absolving criminals of culpability by minimizing their agency. Clearly, exposure to unpredictable environments or imbalanced sex ratios does not lead all, or even most, individuals to engage in crime. Moral judgments and social norms play a crucial role. Second, Walsh could have given more attention to the role of women in all this. It’s obviously true that most crime – and nearly all violent crime – is committed by men. However, the book’s main thesis is that crime must be understood in the context of human sexual dynamics; therefore, it would have been nice to hear more about the female reproductive strategies that shape patterns of criminal offending.

Sexuality and Crime: A Neo-Darwinian Perspective offers an engaging and thought-provoking take on the evolutionary underpinnings of criminal behaviour. Its main strength is an interdisciplinary approach that combines relevant insights from both biology and sociology. While the book is not without limitations, it provides a much needed antidote to traditional criminological paradigms that overlook, or simply ignore, the evolutionary basis of human behaviour. Insofar as this is true, it constitutes a valuable resource for scholars and practitioners alike.

Lipton Matthews is a research professional and YouTuber. His work has been featured by the Mises Institute, The Epoch Times, Chronicles, Intellectual Takeout, American Thinker and other publications. His email address is: lo_matthews@yahoo.com

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