The FBI agent sits across from the convicted killer, reviewing case notes. “When did it start?” he asks. The reply comes matter-of-factly: “The cats were first. Then, the neighbor’s dog. People came later.” From Mindhunter to Criminal Minds, we’ve thought that animal cruelty is the proverbial canary in the coal mine for future violence.
But is it true? Let’s look at what the latest research tells us.
The Birth of the Violence Link: The Macdonald Triad
In 1963, psychiatrist John Macdonald was studying 100 homicidal patients at the Colorado Psychopathic Hospital. He was trying to figure out what these patients were like and track what happened to them. He soon started noticing a triad of behaviors present in his most disturbed patients: childhood animal cruelty, fire-setting, and bed-wetting (enuresis).
Macdonald’s observations were purely anecdotal. Nevertheless, his mention of these three markers in “the very sadistic patients” sparked something in the collective imagination of both professionals and the public. The “Macdonald triad” was born.
Four years later, Macdonald decided to see if his initial observations would hold up under scientific scrutiny. He compared rates of animal cruelty in 80 patients hospitalized for homicidal threats, 192 convicted murderers, and 80 control patients. He got mixed results.
On the one hand, there was no significant difference between the three groups in terms of their history of animal cruelty. But when he narrowed his focus to 20 matched pairs of those who threatened homicide and those who actually committed it, animal cruelty was the distinguisher. He started thinking that animal cruelty might predict the degree of sadism in a violent offender rather than violence itself.
Over the next several decades, research continued to yield murky results. More recently, Joubert and colleagues (2021) examined the Macdonald triad and found that only a small minority (11.6 percent) showed all three markers. However, about half of those who did had the highest levels of aggression, and they were more likely to show “aggressive-antisocial” traits across the board. Their findings suggest that while the full triad isn’t common, its presence is significant.
The scientific shortcomings had little impact on the traction the Macdonald triad gained in popular culture. It was reassuring to think there were simple predictors and early warning signs of dangerous individuals. The reality is far more complicated.
What Do We Know About Children Who Abuse Animals?
In general, the younger a child starts to abuse animals, the more worrisome it is. We naturally have to take into account a child’s development; children under age six often lack a mature understanding of animals as sentient beings. A preschooler pulling a cat’s tail may not understand they are causing pain; to them, it seems similar to banging a toy on a table.
This analogy is drastically different than intentionally inflicting suffering for pleasure or for emotional release or cruelty that persists despite a clear awareness that the behavior is causing the animal distress. In other words, it’s not the toddler who accidentally harms a pet we need to worry about, but the school-aged child who repeatedly and deliberately tortures animals with full awareness of causing suffering and continues despite intervention—especially when combined with callousness or enjoyment of the animal’s distress.
But How and Why?
It’s one thing to establish a link between animal cruelty and human violence; it’s another to understand it. As researchers began asking more sophisticated questions about the how and the why, two theories emerged. One, the violence graduation hypothesis, viewed animal cruelty as both a training ground and a gateway to hurting people; violent people practice on animals before “graduating” to human victims. Intuitively, this made sense.
Additional research, though, raised some doubts. One study found that while animal abusers did commit more violent interpersonal crimes, they committed more crimes in general. They were just as likely to start hurting animals after they hurt another person as before. Even studies that supported the graduation hypothesis could not explain why many people who abuse animals never become violent toward humans or why many violent criminals have no history of harming animals.
It was time for an alternative theory. Enter the deviance generalization hypothesis, which argues that, rather than a stepping stone to violence against humans, animal abuse is part of a larger pattern of antisocial behavior. Not only were the 1.8 percent of the population who admitted animal cruelty more likely to hurt humans, but they were also more likely to engage in a wide range of criminal behaviors from robbery to arson to drug possession to extortion.
What Are We Talking About?
Animal abuse takes different forms; which one should worry us? Do some types of animal abuse predict certain types of interpersonal violence? Recent research reveals some nuances that true crime narratives often miss.
A groundbreaking study by Merz-Perez and Heide (2004) not only found a higher rate of animal cruelty among violent offenders (56 percent versus 20 percent), but they also found that violent offenders were more likely to have engaged in hands-on physical violence—kicking, beating, drowning, stabbing, or stomping. These weren’t abusers who were neglecting to feed their animals or leaving them outside in the cold; these were abusers who were intentionally hurting them. This was especially true in the context of intimate partner violence. Women whose partners abused pets are 7.6 times more likely to be victims of intimate partner violence compared to women whose partners did not harm animals.
When it comes to foreshadowing human harm, sexual animal abuse is in a class by itself. People who engage in animal sexual abuse rarely limit their deviant sexual interests to animals alone. In fact, research has consistently identified connections between bestiality and nonsexual animal abuse, child sexual abuse, and the consumption of child pornography. One study found that nearly one-third of offenders convicted of bestiality-related arrests had either forced a child to observe or participate in sexual acts with animals or had sexually abused both children and animals or the abuse of both children and animals by the same perpetrator. These findings support a “paraphilic crossover”—the tendency for individuals with one atypical sexual interest to develop or express others as well.
The Bottom Line
The relationship between animal maltreatment and human violence is complicated. Many children who harm animals never become violent towards humans. Conversely, many individuals who commit serious violent crimes have no history of animal abuse.
But we also know that certain patterns of animal cruelty—especially repeated, hands-on, and sexually oriented abuse—are red flags of broader antisocial tendencies that increase the risk for interpersonal harm. And, at its core, the link reminds us that compassion and protection should extend to all vulnerable beings—human and animal alike—and that the boundaries we draw between different forms of violence may be more artificial than real.
