The Macdonald triad refers to the idea that there are three signs that can indicate whether someone will grow up to be a serial killer or other kind of violent criminal:

  • being cruel or abusive to animals, especially pets
  • setting fire to objects or otherwise committing minor acts of arson
  • regularly wetting the bed

This idea first gained momentum when researcher and psychiatrist J.M. Macdonald published a controversial review in 1963 of earlier studies that suggested a link between these childhood behaviors and a tendency toward violence in adulthood.

But our understanding of human behavior and its link to our psychology has come a long way in the decades since.

Plenty of people can exhibit these behaviors in childhood and not grow up to be serial killers.

But why were these three singled out?

The Macdonald triad singles out three main predictors of serial violent behavior. Here’s what Macdonald’s study had to say about each act and its link to serial violent behavior.

Macdonald claimed many of his subjects had exhibited some form of these behaviors in their childhood that may have some link to their violent behavior as adults.

Animal cruelty

Macdonald believed cruelty to animals stemmed from children being humiliated by others for extended periods of time. This was especially true of abuse by older or authoritative adults who the children couldn’t retaliate against.

Children instead act out their frustrations on animals to vent their anger on something weaker and more defenseless.

This may allow the child to feel a sense of control over their environment because they’re not powerful enough to take violent action against the adult who may be causing them harm or humiliation.

Fire-setting

Macdonald suggested that setting fires may be used as a way for children to vent feelings of aggression and helplessness brought on by humiliation from adults who they feel they have no control over.

It’s often thought to be one of the earliest signs of violent behavior in adulthood.

Fire-setting doesn’t directly involve a living creature, but it can still provide a visible consequence that satisfies the unresolved feelings of aggression.

Bedwetting (enuresis)

Bedwetting that continues after 5 years old for a number of months was thought by Macdonald to be linked to the same feelings of humiliation that could bring on the other triad behaviors of animal cruelty and fire-setting.

Bedwetting is part of a cycle that may exacerbate feelings of humiliation when the child feels they’re in trouble for or embarrassed by wetting the bed.

The child may feel more and more anxious and helpless as they continue the behavior. This can contribute to them wetting the bed more often. Bedwetting is often linked to stress or anxiety.

It’s worth noting that Macdonald himself didn’t believe that his research found any definitive link between these behaviors and adult violence.

But that hasn’t stopped researchers from seeking to validate a connection between the Macdonald triad and violent behavior.

Extensive research has been done to test and validate whether Macdonald’s claims that these behaviors could predict violent behavior in adulthood had any merit.

Testing the findings

The research duo of psychiatrists Daniel Hellman and Nathan Blackman published a study looking closer at Macdonald’s claims.

This 1966 study examined 88 people convicted of violent acts or murder and claimed to have found similar results. This seemed to corroborate Macdonald’s findings.

But Hellman and Blackman only found the full triad in 31 of them. The other 57 only fulfilled the triad in part.

The authors suggested that abuse, rejection, or neglect by parents may have also played a role, but they didn’t look too deeply at this factor.

The social learning theory

A 2003 study looked closely at patterns of animal cruelty behavior in the childhoods of five people later convicted of serial murder in adulthood.

The researchers applied a psychological research technique known as social learning theory. This is the idea that behaviors can be learned by imitation or modeling on other behaviors.

This study suggested that cruelty to animals in childhood could lay the foundation for a child to graduate to being cruel or violent toward other people in adulthood. This is called the graduation hypothesis.

This influential study’s result is based on the very limited data of only five subjects. It’s wise to take its findings with a grain of salt. But there are other studies that seem to have corroborated its findings.

Repeated violence theory

A 2004 study found an even stronger predictor of violent behavior related to animal cruelty. If the subject has a history of repeated violent behavior toward animals, they may be more likely to commit violence toward humans.

The study also suggested that having siblings could increase the chance that repeated animal cruelty could escalate into violence against other people.

A more modern approach

A 2018 review of decades of literature on the Macdonald triad turned this theory on its head.

The researchers found that few convicted violent offenders had one or any combination of the triad. Researchers suggested that the triad was more reliable as a tool to indicate that the child had a dysfunctional home environment.

Even though Macdonald’s theory doesn’t really hold up to close research scrutiny, his ideas have been mentioned enough in the literature and in the media to have taken on a life of their own.

A 1988 bestselling book by FBI agents brought the triad into the wider public eye by linking some of these behaviors to sexually charged violence and murder.

And more recently, the Netflix series “Mindhunter,” based on the career of FBI agent and pioneering psychological profiler John Douglas, brought massive public attention back to the idea that certain violent behaviors could lead to murder itself.

It’s nearly impossible to claim that certain behaviors or environmental factors can be directly linked to violent or murderous behavior.

But after decades of research, some predictors of violence have been suggested as somewhat common patterns in those who commit violence or murder as adults.

This is especially true when it comes to people who exhibit the traits of antisocial personality disorder, which is more commonly known as sociopathy.

People who are deemed “sociopaths” don’t necessarily cause harm or commit violence to others. But many of the signs of sociopathy, especially when they appear in childhood as conduct disorder, can predict violent behavior in adulthood.

Here are some of those signs:

  • demonstrating no boundaries or regard for the rights of others
  • having no ability to tell between right and wrong
  • no signs of remorse or empathy when they’ve done something wrong
  • repeated or pathological lying
  • manipulating or harming others, especially for personal gain
  • repeatedly breaking the law with no remorse
  • no regard for rules around safety or personal responsibility
  • strong self-love, or narcissism
  • quick to anger or overly sensitive when criticized
  • displaying a superficial charm that quickly goes away when things aren’t going their way

The Macdonald triad idea is a little overblown.

There’s some research that suggests it may contain some shreds of truth. But it’s far from a reliable way to tell whether certain behaviors will lead to serial violence or murder as a child grows up.

Many behaviors described by the Macdonald triad and similar behavioral theories are the result of abuse or neglect that children feel powerless to fight back against.

A child may grow up to be violent or abusive if these behaviors are ignored or unaddressed.

But many other factors in their environment can also contribute, and children growing up in the same environment or with similar situations of abuse or violence can grow up without these proclivities.

And it’s just as likely not to happen that the triad leads to future violent behavior. None of these behaviors can be directly linked to future violence or murder.