New research published in Frontiers in Psychology provides evidence that personality traits associated with malevolence have contrasting relationships with reproductive success. The study suggests that while psychopathy is linked to having more children at a younger age, sadism is associated with having fewer children and starting a family later in life.
Behavioral scientists have spent decades categorizing dark personality traits. The most prominent model is known as the Dark Triad. This model includes psychopathy, narcissism, and Machiavellianism. Psychopathy involves a lack of empathy and high impulsivity. Narcissism is defined by grandiosity and entitlement. Machiavellianism is characterized by strategic manipulation.
Scholars later proposed expanding this model to the Dark Tetrad. This newer framework adds sadism to the list. Sadism is distinct because it involves deriving pleasure from inflicting pain or watching others suffer. A major question in psychology is whether sadism and psychopathy are truly different traits. Their definitions overlap significantly, leading some to argue they are the same construct.
Evolutionary psychologists are interested in these traits to see if they offer survival or reproductive advantages. Traits that lead to higher reproduction rates tend to persist in the gene pool. This concept is known as evolutionary fitness.
Prior research has suggested that psychopathy might be an adaptive strategy. It may allow individuals to exploit others for resources or mating opportunities.
Sadism has received less attention in this evolutionary context. It is often viewed as a more severe and dysfunctional form of aggression.
“This study was primarily motivated by an ongoing debate regarding whether dark personality traits – particularly psychopathy and sadism – reflect evolutionarily adaptive strategies or maladaptive by-products,” explained study author Ivana Hromatko, a professor of biological psychology at the University of Zagreb.
“The evolutionary interpretations of psychopathy are well developed, but the direct evidence linking Dark Tetrad traits to core fitness indicators (such as the number of children and age of first reproduction) remains scarce and inconsistent. We had the opportunity to examine these associations in a demographically representative sample, so we aimed to provide clearer evidence on the evolutionary relevance and potential selection pressures acting on dark personality traits.”
The study utilized a sample of 690 citizens from Croatia. The researchers used a stratified sampling method. This ensured the group represented the national population in terms of region and settlement size. The sample was also balanced for age and education level.
The participants were recruited through an online panel managed by the research agency Ipsos. The data collection took place in March 2025. The sample included 348 women and 342 men. The average age of the participants was approximately 48 years old.
The participants varied widely in their educational backgrounds. About 55 percent had completed vocational school. Roughly 12 percent held a bachelor’s degree. The participants’ average income aligned with the national median wage. This diversity helps ensure the findings apply to the general public rather than just university students.
Participants completed the Short Dark Tetrad scale. This psychological assessment consists of 28 items. It includes seven statements for each of the four dark traits. Participants rated their agreement with each statement on a 5-point scale.
The researchers also asked participants about their reproductive history. They reported the total number of children they had. They also reported their age when their first child was born. These two metrics served as the primary indicators of fertility.
The researchers analyzed the data using regression models. These statistical tools allow scientists to predict an outcome while controlling for other factors. The models accounted for sex, age, education, socioeconomic status, and the size of the community where the participant lived.
The results showed a positive connection between psychopathy and fertility. Individuals with higher psychopathy scores tended to have more children. This relationship held true even after adjusting for demographic factors.
The researchers also found a link between psychopathy and the timing of parenthood. Higher levels of psychopathy predicted a younger age of first reproduction. This suggests that impulsive or risk-taking behaviors associated with psychopathy may lead to earlier mating.
Sadism showed the exact opposite pattern. Higher scores in sadism predicted having fewer children. This trait was also associated with a delayed start to reproduction. Individuals with high sadism scores tended to have their first child at an older age than those with low scores.
Mediation analysis provided further insight into these patterns. This statistical method helps identify the potential mechanism behind a relationship. The analysis revealed that the age of first reproduction explains the link between personality and the number of children.
For psychopathy, the tendency to reproduce earlier leads to a higher total number of offspring. For sadism, the tendency to delay reproduction results in fewer offspring. This mechanism was consistent in the final path analysis.
The researchers also tested for associations with narcissism and Machiavellianism. In the initial correlations, these traits appeared to have negative links to fertility. However, these effects disappeared in the more rigorous regression models. Once the researchers controlled for other variables, narcissism and Machiavellianism did not significantly predict the number of children.
The study also explored whether biological sex influenced these relationships. Previous theories suggested that dark traits might be more adaptive for males than females. The data from this study did not support that hypothesis. The relationships between dark traits and fertility were similar for both men and women.
These findings contribute to the debate regarding the redundancy of sadism and psychopathy. If the two traits were merely different names for the same thing, they should relate to fertility in the same way. The fact that they have opposite effects suggests they are distinct behavioral dispositions.
“The main takeaway is that traits often grouped together as ‘dark’ differ substantially in their real-world consequences,” Hromatko told PsyPost. “Psychopathy and sadism, despite appearing similar, show opposite associations with reproduction, indicating that they may have very different long-term implications for individuals and populations.”
The results support the idea that psychopathy fits a “fast life history strategy.” In evolutionary biology, this strategy involves prioritizing rapid reproduction over long-term stability. The data suggests psychopathy facilitates this approach through earlier childbearing.
Sadism appears to be evolutionarily maladaptive in this context. The pleasure derived from harming others does not seem to translate into reproductive benefits. Instead, it correlates with a slower and less successful reproductive trajectory. It may be that the socially repellent nature of sadism hinders mating opportunities.
There are some limitations to this study that warrant consideration. The data was cross-sectional. This means it was collected at a single point in time. It is impossible to determine strict causality with this type of design. Longitudinal research that follows people over their lifetimes would provide more definitive evidence.
This research highlights that not all “dark” traits function the same way in an evolutionary sense. Psychopathy appears to carry certain reproductive advantages in the current environment. Sadism appears to come with reproductive costs. But these biological associations do not imply moral justification.
“We would like to stress that evolutionary associations do not imply social desirability or moral value,” Hromatko noted. “The fact that a trait is associated with higher fertility does not mean it is beneficial, admirable, or advisable at the individual or societal level. Moreover, these findings reflect probabilistic, population-level tendencies rather than deterministic outcomes for individuals.”
The study, “Adaptiveness of dark personalities: psychopathy and sadism have opposite associations with fertility,” was authored by Janko Međedović and Ivana Hromatko.
