Psychopathy: An Introduction to Biological Findings (2014) is a research-based overview of the genetic, neurological, and physiological mechanisms behind psychopathy, written by two of the top experts in the field.

NOTES

About the Author:
Andrea L. Glenn is a psychologist and researcher known for her work on the biological and cognitive mechanisms underlying psychopathy and antisocial behavior.
Adrian Raine is a neurocriminologist whose research on brain structure, physiology, and genetics has shaped the modern understanding of antisocial and violent behavior.

Intro

Factor structure of psychopathy as defined by the Psychopathy Checklist–Revised (Hare, 2003).

Psychopathy vs. Antisocial Personality

ASPD is a broad and heterogeneous DSM diagnosis defined mainly by persistent antisocial and criminal behavior: law-breaking, aggression, deception, and impulsivity. It captures about 75% of inmates, far more than psychopathy, and most research on “antisocial” samples does not distinguish which individuals are actually psychopathic.

The key difference:

• Psychopathy includes the Interpersonal–Affective (Factor 1) traits—callousness, shallow affect, lack of empathy, manipulativeness.
• ASPD does not require these traits and largely overlaps only with the Lifestyle–Antisocial (Factor 2) aspects of psychopathy.

Aggression also differs:

• Psychopaths show instrumental (planned, goal-directed) aggression, in addition to some reactive aggression.
• Individuals with ASPD or other disorders linked to aggression tend to show more reactive aggression.

In sum: psychopathy is a narrower, more specific construct centered on interpersonal–affective deficits, not merely antisocial behavior or criminality. ASPD is broader and captures many individuals who are not psychopathic. Psychopathy can—but does not have to—include criminal behavior.

Subtypes of Psychopathy: Primary & Secondary

Research suggests that psychopathy is not a single uniform pattern but includes distinct subtypes. Early theorists proposed etiologically different forms of psychopathy (Lykken 1957; Karpman 1941), and modern studies support this view. Personality-based models consistently identify two groups among individuals with high psychopathy scores:

1. an emotionally stable, low-stress-reactive subgroup, and
2. a subgroup marked by negative emotionality, impulsivity, and hostility (Hicks et al. 2004; Hicks, Vaidyanathan, and Patrick 2010).

These are commonly referred to as primary and secondary psychopaths. Secondary psychopathy is linked to higher anxiety (e.g., Newman and Schmitt 1998; Skeem et al. 2007) and poorer interpersonal functioning—greater irritability, social withdrawal, and lower assertiveness—while both subtypes show similar levels of antisocial behavior (Skeem et al. 2007). Evidence also indicates that their developmental pathways differ (Kimonis et al. 2011; Skeem et al. 2003), and each group may involve distinct neurobiological abnormalities.

Chapter 1. Genetics

By analyzing twin and adoption studies, the authors conclude that psychopathy, like most personality disorders, has a significant genetic component, meaning a substantial portion of the variation in psychopathic traits is explained by inherited factors.

Key Findings:

• Substantial Heritability: the main findings from these studies are that psychopathic traits appear to be moderately to highly heritable and share some common genetic factors with antisocial behavior more generally, but they are also attributable to unique genetic factors
• Stability is also partially genetic: Genetic factors have also been found to contribute to the stability of psychopathic traits over time. Several studies have established that psychopathic personality is stable (Loney et al. 2007, Lynam et al. 2007). A study by Forsman et al. (2008) found that genetic factors contribute to this stability. In contrast, changes in psychopathic traits over time were found to result primarily from environmental factors
• Different facets of psychopathy share common genetic factors The finding that there are common genetic factors infuencing the distinct aspects of psychopathy suggests that it is indeed a unified construct. Two studies have found that some of the same genetic factors contribute to the different facets of psychopathy (Taylor et al. 2003, Larsson, Andershed, and Lichtenstein 2006), finding sizable genetic correlations between the different factors of psychopathy, including callous-unemotional features and impulsive-antisocial features. These studies suggest that there is a strong relationship among the genetic factors that are associated with the different aspects of psychopathy
  • But there are also unique genetic factors for different facets: Blonigen at al. (2005) found no genetic correlation between the Fearless Dominance and Impulsive Antisocial factors of psychopathy, suggesting that the two factors may derive from independent etiological processes. Also Taylor et al. (2003) and Larsson, Andershed, and Lichtenstein (2006) found that unique genetic effects that are important for the different psychopathy factors (i.e., there are unique genetic effects that influence the different psychopathy factors over and above the genetic influence from the latent psychopathy factor)
• Psychopathy shares common genetic factors with antisocial/externalizing behavior: Taken together, the results from behavioral genetics studies indicate that genetic and nonshared environmental factors account for individual differences in psychopathic traits from childhood through adulthood
• Nonshared rather than shared environment accounts for the rest of the variance: Studies of antisocial behavior have most often found that the environment that is shared between twins has an effect on antisocial behavior (Rhee and Waldman 2002, Larsson et al. 2007). However, across all the studies reviewed here on psychopathic personality traits, the influence of shared environmental factors was negligible
• Gender may play a role: For example, Fontaine et al. (2010) found that in youth with stable, high levels of callous-unemotional traits, boys demonstrated stronger genetic influences, whereas girls demonstrated stronger shared environmental influences <— 🙋🏼‍♂️Lucio’s note: could this be related to women’s higher interdependence?

Heritability studies provide averages
It is also important to keep in mind that this figure represents an average across a large number of people, and that in some individuals, genes may have a stronger influence on the development of psychopathic traits than the environment, and in other individuals, the opposite may be true

When it comes to specific genes or polymorphisms:

The additive effects of different genes:

Hoenicka et al. (2007).

Chapter 2. Hormones

The two primary hormones that have been associated with psychopathy are cortisol and testosterone

• Findings linking testosterone with psychopathy are inconsistent: Despite the strong theoretical evidence that psychopathy may be associated with high levels of testosterone, only a few studies have tested the hypothesis and results are inconsistent.
  • One study found testosterone levels to be associated with scores on the Lifestyle-Antisocial Factor 2 of the PCL-R in forensic psychiatric patients, although results may be confounded by comorbid substance abuse and other psychiatric disorders (Stalenheim et al. 1998).
  • A more recent study in a large sample of individuals recruited from temporary employment agencies found no relationship between psychopathy (or its factors) and testosterone (Glenn, Raine, Schug, et al. 2011). Similarly…
  • Another study found that testosterone levels were not different in boys with callous-unemotional traits compared to healthy controls (Loney et al. 2006).
  • In other antisocial and aggressive groups, higher testosterone levels have been observed in girls with conduct disorder (Pajer et al. 2006), adolescent boys with externalizing behaviors (Maras et al. 2003), young criminals (Kreuz and Rose 1972; Dabbs, Frady, and Carr 1987; Dabbs, Jurkovic
• Findings of lower cortisol are inconsistent: Low resting cortisol levels have been associated with impaired fear reactivity in young children (Kagan, Reznick, and Snidman 1988), increased sensation seeking in men (Rosenblitt et al. 2002), and increased monetary risk taking (van Honk et al. 2003). A few recent studies have found relationships between cortisol and psychopathy. However, others have failed to replicate this finding (van Honk et al. 2003; Glenn, Raine, Schug, et al. 2011)

• Hypothesis: T + other hormones: Although a direct link between testosterone and psychopathic traits has not been established, some evidence suggests that testosterone may interact with other hormones to predispose to psychopathy
  • The testosterone/cortisol ratio hypothesis: In a large sample of individuals Glenn, Raine, Schug, et al. (2011) found that psychopathy was associated with the ratio of baseline testosterone to cortisol reactivity to a stressor; this accounted for 5 percent of the variance in psychopathic traits. No significant relationships were observed between psychopathy and individual hormone measures, which included baseline testosterone and cortisol, and cortisol reactivity to a stressor; it appeared that only when both hormones were taken into consideration did a significant relationship emerge.
• Burnout hypothesis: One hypothesis is that there may be some type of “burnout” effect, where chronic stress or other environmental factors overwork the stress response system to the point that it no longer responds properly.

The similarities between testosterone and psychopathy

Chapter 3. Psychophysiology

Psychophysiological research involves the study of two overarching systems: the autonomic nervous system, which controls mostly visceral functions and is measured by skin conductance and heart rate, and the central nervous system, which consists of the brain and spinal cord and is measured by electroencephalogram (EEG)

• Lower response to cues of aversive stimuli, not the stimuli itself: When examining the startle refex, aversive conditioning, or the response to aversive stimuli, one interesting fnding is that psychopaths do not appear to have reduced physiological responses to the actual aversive stimulus such as the shock or loud noise blast (exceptions include Hare and Quinn 1971, Lykken 1957, Fung et al. 2005). Instead, the deficits appear to be primarily in the ability to respond to cues that signal that an aversive event will occur
• Impaired Fear Conditioning: Psychopathic individuals exhibit a deficit in fear conditioning. When exposed to a neutral stimulus (e.g., a tone) that is repeatedly paired with an aversive outcome (e.g., a shock), non-psychopathic individuals develop a fear response (measured by skin conductance/electrodermal activity). Psychopaths typically show a dramatically blunted or absent skin conductance response, demonstrating a fundamental deficit in learning to fear aversive consequences.
• Blunted Startle Response: They show reduced startle reflex potentiation when anticipating or viewing negative emotional stimuli (like threatening pictures or fearful faces). This suggests a failure to engage the normal, defensive physiological system, which contributes to their Boldness and lack of anxiety.
• Orienting Responses: Conversely, psychopaths sometimes show enhanced orienting responses to pleasant or reward-related stimuli, suggesting an imbalance where their attention is strongly biased toward reward but insensitive to punishment.

Chapter 4. Neuropsychology

This chapter links psychopathy to specific cognitive and executive function deficits, offering a bridge between brain structure and observable behavior.

• Avoidance as a goal works, but avoidance with a reward doesn’t: psychopathic individuals display normal abilities to avoid monetary punishment when this is their only goal. However, they exhibit deficits in the ability to avoid monetary punishment when the task also involves a goal of earning monetary rewards. It is suggested that when their primary goal is earning reward, they are unable to reallocate attention to cues of potential punishment (Newman and Kosson 1986)
• Both neurological case studies and neuropsychological testing suggest that psychopathy likely involves deficits in the ventromedial PFC and amygdala

Chapter 5. Brain Imaging

Brain imaging fndings, for the most part, have been able to confrm what has been hypothesized based on psychophysiological, neuropsychological, and behavioral data regarding the brain regions that are implicated in psychopathy. Tese regions include the amygdala and parts of the frontal lobe. In addition, brain imaging research has identifed several additional regions that may function diferently in psychopathic individuals, or that may indicate abnormal development of the brain.

• Amygdala Dysfunction: This is the most consistent finding, strongly linked to the Meanness/Callous-Unemotional traits. Studies show:
  • Structural Abnormalities: Reduced gray matter volume in the amygdala.
  • Functional Abnormalities: Hypoactivity (reduced activation) of the amygdala when processing fearful and sad facial expressions (distress cues) and during moral decision-making. This may explain the observed emotional blunting and lack of empathy.
• Ventromedial Prefrontal Cortex (vmPFC): This region, which is critical for integrating emotion into decision-making and regulating the amygdala, also shows:
  • Structural Abnormalities: Reduced gray matter volume and white matter integrity.
  • Functional Abnormalities: Reduced activity during tasks involving emotional regulation, moral judgment, and reversal learning (learning to switch responses after an outcome changes). This links to poor judgment and impulsivity (Disinhibition).
• Limbic System Connectivity: Psychopathy is also viewed not as a deficit in a single area but as a disconnection between the limbic system (emotion centers like the amygdala) and the frontal lobes (control centers like the PFC).

Chapter 6. Biosocial and Environmental Influences

This chapter moves from purely biological factors to the crucial interaction between biology and the environment (Biosocial perspective).

• Parenting matters: Numerous studies of antisocial behavior and crime have identified parenting practices such as harsh or erratic discipline, poor parental supervision, and distant, cold, and rejecting parenting styles as risk factors for antisocial behavior. In the Cambridge Study, poor parental supervision in youth significantly predicted psychopathy scores in adulthood, but this was true only for the Lifestyle-Antisocial
  • Fathers matter: One of the strongest predictors of the affective features of psychopathy was having an uninvolved father, although this is likely to be mediated by a number of other factors
  • Parents’ relationship quality matters: Family conflict is another factor that has been associated with psychopathy. The Cambridge Study found a significant relationship between having a disrupted family at age 8 and psychopathy scores at age 48
• Maternal smoking may matter: psychopathic traits were associated with maternal smoking during pregnancy (…) Controlling for these factors, in addition to genetic factors, the effects of maternal smoking were reduced by between 75 percent and 100 percent. Thus, it is not clear whether maternal smoking itself (as a toxin that may damage the fetus) actually predisposes for psychopathic traits
• Gene-Environment (GxE) Interaction: The expression of genetic vulnerabilities (e.g., MAOA low-activity allele) may depend on the level of environmental adversity experienced, such as childhood maltreatment. A high-risk genotype combined with a high-risk environment significantly amplifies the likelihood of psychopathic outcomes.

Chapter 7. Successful Psychopaths

This chapter addresses the controversial concept of “successful” psychopaths—individuals high in psychopathic traits but who avoid criminal detection and achieve societal success (e.g., in business or politics).

• Biological Comparison: Early research suggests that successful psychopaths may possess biological advantages that unsuccessful psychopaths lack. For example, they may have intact executive function and PFC activity, allowing them to regulate the expression of their antisocial impulses. They are better at engaging their frontal regions to control their amygdala-driven emotional deficits.
• Mask of sanity: This concept validates Cleckley’s original idea of the “mask of sanity,” where high intelligence and strategic control (functional biology) mask the core, underlying affective pathology.

Chapter 8. Ethical Issues

This chapter addresses the moral, legal, and societal implications of a biological model of psychopathy, including

• Free Will vs. Determinism & responsibility: If psychopathy is demonstrably linked to brain abnormalities (e.g., a damaged vmPFC), does this mitigate an individual’s criminal responsibility?
• Neuro-Prediction and Dangerousness: Using neurobiological or genetic markers to predict future violent or criminal behavior raises serious civil liberties concerns regarding preventative detention, especially for juveniles.
• Labeling Effects & Bias: The term “psychopath” is highly pejorative in forensic settings and can unfairly bias legal decisions (e.g., parole, death penalty sentencing), often leading to a presumption of incorrigibility, regardless of current evidence. <— 🙋🏼‍♂️ Lucio’s note: the opposite is also true, though. The correct diagnosis though also allows society to reduce the costs of crime and spare many innocent victims

Chapter 9. Prevention, Intervention, and Treatment

• Early Intervention: Treatment is most effective for youth high in CU traits because their brains are still developing. Interventions include specialized parent training to increase warmth and consistent reinforcement, and programs targeting emotional recognition (e.g., training children to recognize fear/sadness in others).
• Nutritional supplementation: Several studies have found that nutritional deficiencies predispose for antisocial behavior (…) Neugebauer, Hoek, and Susser (1999) found that male offspring of mothers who were severely malnourished during the first and second trimesters of pregnancy had 2.5 times the normal rate of antisocial personality disorder in adulthood. Poor nutrition in the first three years of life has also been associated with long-term antisocial behavior throughout childhood and late adolescence (Liu et al. 2004)
• Relieving maternal stress and depression: maternal stress and depression are factors that have been found to affect the developing brain and that are associated with psychopathic traits
  • Sleeping patterns: Another form of maternal stress is disrupted sleep patterns that result from shif work. Ramlau-Hansen et al. (2011) found that maternal shift work was associated with an 11 percent increase in testosterone levels in male offspring at ages 18 to 21
• Pharmacological Intervention: Future treatments may involve medications to target specific neurobiological deficits, such as:
  • Serotonin/Dopamine Agents: To reduce impulsivity and aggression (Disinhibition).
  • Oxytocin: To potentially enhance social cognition and empathy (Meanness).
• Neurobiological Intervention: Emerging, though speculative, methods like neurofeedback or transcranial magnetic stimulation (TMS) could one day be used to functionally “re-tune” dysfunctional brain regions (e.g., to increase vmPFC activity or connectivity).
• Treatment may also contribute: a review found that treatment results for adult psychopaths range from low-moderate to poor with three of eight studies demonstrating that psychopathic individuals benefited from treatment (Salekin, Worley, and Grimes 2010). But findings are mixed for psychological treatment like cognitive behavioral therapy, group therapy, family therapy,

SHARPEST INSIGHTS

These are the insights that struck us the most.
We use the authors’ quotes and research, but the titles and interpretations are our own—and may not reflect the authors’ intent.
Credit for the insight goes to them; blame for the interpretation is on us.

Is Successful Psychopathy Even A Thing?

A story described by Cleckley can make us reflect on what ‘successful’ truly means:

Cleckley describes a middle-aged man who came from a well-regarded family and who made his way through three years at a prestigious university by utilizing the work of his friends and cheating on exams.
He dressed in nice clothes and was popular at social gatherings. Although he had not paid his fraternity fees, he was tolerated because of his entertaining style and his ability to easily recruit new freshmen to join.
By age 50, a survey of his life revealed that he had consistently been supported by wealthy women who repeatedly loaned him money and would help him find new positions when he lost a job. He had no difficulty having several women at his beck and call. When one relationship would go sour, he had no trouble finding another woman to raise money for a new venture or find him a new position. He was also able to make valuable business associations by loitering at the country club, and these associations enabled him to make a good living for brief periods, but his ventures always failed. Such individuals are sometimes referred to as successful psychopaths—individuals with high levels of psychopathic traits who are able to get by in society, often taking advantage of others, without ever coming into contact with the law.

Look at this:

• Tolerated, not admired
• Possible lower value women that supported him, not quality ones
• No work/business success

This is certainly leagues above the psychopaths who languish in prison, but I wouldn’t call this ‘successful’ either.

QUOTES

The cost of psychopathy on society:

The prevalence of psychopathic personality traits takes a major toll on society. In criminal populations, offenders with psychopathic traits are responsible for a disproportionate amount of crime, particularly violent crime. In the rest of society, psychopathic traits are a driving force behind much of the corruption, exploitation, manipulation, and deception that occurs on both large and small scales. Psychopathy causes undue physical, emotional, and fnancial trauma in the lives of countless individuals

On ‘successful’ psychopathy being an even higher cost:

Much of the research we have discussed thus far has focused on psychopathic individuals in forensic populations and may not be generalizable to psychopaths in the general population. However, noninstitutionalized individuals with psychopathic traits not only may outnumber the institutionalized psychopathic population, but also may in the long run be more dangerous and destructive to society (Gao and Raine 2010

🙋🏼‍♂️ Lucio’s Analysis

I’d Like Less Defensive: Findings Over Morals

One reminder that ‘genes are not destiny’ is important, but many of them feel like defensiveness, and I felt there were too many.
A book for scholars and researchers should focus on findings, not on moral and ethical concerns.

Also, some passages feel defensively negative about what we may be able to do in the future, like this one:

There is no “crime gene.”
By no means is there a single gene, or even a small group of genes, that will enable us to predict which individuals will commit crime in the future
Genes confer risk for traits such as those observed in psychopathy, which may heighten the risk for criminal behavior, but we will never be able to use genes to predict which individuals will become psychopathic or persistent criminals. In reality, hundreds and maybe thousands of genes are involved, each of which makes a small contribution by coding for proteins and enzymes that in turn affect brain functioning, psychological processes, and ultimately behavior

There is no single gene, of course, but the tone feels like discounting the importance of genes. Or, worse, that mapping the hundreds or thousands of risk-related genes is a futile effort in terms of predictive power.
Instead, I believe that understanding these polygenic contributions could be extremely valuable for prevention, early intervention, and tailored corrective strategies.

There is no ‘single gene’ of course, but being able to map those hundreds or thousands may still be able to help with prevention and correction.

REVIEW

Psychopathy: An Introduction to Biological Findings is a valuable introductory text to understand the genetic, biological, but also cultural factors that contribute to psychopathy.

Since the book is meant for academics, it can be a bit dry at times, and you may have to dig or research separately to understand some concepts—but that’s an added opportunity to learn more.

Check the best books on psychopathy or our most recommended books.