THE SEVEN DEADLY SINS: Are We Programmed for Vice?

Guy Leschziner is a professor of neurology and sleep medicine at the Institute of Psychiatry, Psychology & Neuroscience at King’s College London. He is actively engaged in research and education / theglobeandmail.com

The debate over human free will has been ongoing for centuries. Without it, how can a person make a truly free choice between moral and immoral actions? And if there is no free will, how can one be held accountable for their sins? For instance, the great Christian reformer John Calvin argued that after the Fall, humans lost their ability to choose good and were no longer free in their decisions. However, in his divine plan for salvation, God predestined some for heaven and others for damnation. Strangely enough, this perspective may have certain biological foundations. In this light, sin can be seen as a religious metaphor for certain scientific discoveries.

THE NEUROLOGICAL NATURE OF SIN

In his new book, Seven Deadly Sins: The Biology of Human Nature, neurologist Guy Leschziner explores immoral behavior and uncovers its neurological basis. But if «bad» behavior is preprogrammed, can it still be considered a sin? If not, that’s good news for the «sinners».

The bad news, however, is that this also challenges the very idea of free will. Using specific case studies gathered over decades of neurological research, Leschziner demonstrates how this works. According to him, the vices we recognize from the Bible exhibit characteristics typically associated with neurological and physiological disorders.

They can trigger gluttony, anger, lust, envy… Here, we will explore a few such examples.

GLUTTONY: FROM TRASH TO DOG FOOD

In the house where Alex lives with six others who share her condition, there is no accessible food. The kitchen resembles a bank vault hidden behind a locked door. Even the trash bin has a heavy-duty lock. Alex cannot eat whenever she wants — she is only fed carefully measured portions at designated times.

Though she was born underweight, by her teenage years, Alex could eat three full meals in one sitting. She consumed anything and everything in large quantities — even gorging on cat food. As a result, her small frame eventually reached 110 kg (242 lbs).

Leschziner challenges the traditional view promoted by diet marketers that obesity stems from a mere lack of willpower. Clearly, gluttony can result from a condition that triggers an uncontrollable appetite — one so intense that, in extreme cases, people have literally ruptured their stomachs from overeating.

This issue is driven less by willpower or moral factors and more by genetics, hormones, and gut microbiota.

ANGER: THE «WARRIOR GENE»

When examining anger, Leschziner introduces us to two men suffering from epilepsy. One experiences violent outbursts after seizures, leaving behind piles of shattered dishes. The other has uncontrollable fits of rage triggered by his medication. The drugs help control his condition, so stopping them entirely isn’t an option.

The neurobiology of their «sin» is linked to the amygdala — two structures in the brain responsible for regulating aggression and recognizing anger in others. There is also a specific gene that scientists have dubbed the «warrior gene». Individuals with certain mutations in this gene are predisposed to aggressive and antisocial behavior.

No amount of willpower can override this. That’s why courts in countries such as the U.S. and Italy take genetic predispositions into account when determining sentences. Today, murder defendants undergo genetic testing to assess whether they have a biological inclination toward violence.

LAZINESS: A HEREDITARY DISEASE

Laziness, according to Leschziner, is a rather peculiar sin. It’s unclear why it made the list of deadly sins in the first place. At first glance, laziness seems far less harmful than anger, envy, or lust. Yet, it can be profoundly destructive.

The neurologist illustrates this with the case of Becky and Rhett, a farming couple whose lives were turned upside down by Huntington’s disease. This genetic disorder leads to involuntary muscle spasms, deteriorating coordination, memory loss, and diminished self-control. When Becky’s father was diagnosed, she underwent genetic testing, which confirmed that she, too, would eventually develop the disease.

A few years later, Becky began to change. Once a caring wife and mother, she gradually became apathetic, passive, and emotionally distant. For Rhett and their children, it was a painful ordeal. Becky now spends most of her days in a state of near-constant disengagement, lacking both the desire and cognitive ability to interact with the world around her.

LUST: AN EXCESS OF DOPAMINE

When discussing the neurological basis of this sin, Leschziner recounts the story of a British Army soldier who suffered a brain injury during World War II. The damage affected the frontal part of his brain. When he returned home, he was a different man — he became obsessively preoccupied with talking about sex, a behavior that had never been part of his personality before the injury.

Another soldier with a similar brain injury developed exhibitionistic tendencies. Unaware of the neurological nature of his behavior, he was repeatedly arrested for exposing himself in public. But what was causing this change?

The frontal lobes of the brain play a crucial role in suppressing sexual impulses. When they are damaged, hypersexuality can skyrocket to extreme levels, potentially wreaking havoc on even the strongest relationships.

As we know, dopamine is responsible for our sense of pleasure. Interestingly, about 3% of Parkinson’s disease patients who take dopamine-enhancing medication experience a surge in sexual desire.

Conversely, antipsychotic medications, which suppress dopamine, can significantly reduce sexual drive. This side effect frightens many patients, often leading them to discontinue their medication — at the risk of a psychotic relapse.

SLAVES TO THE BRAIN: RETHINKING FREE WILL

Leschziner argues that his interpretation of the seven deadly sins as biologically hardwired traits necessitates a reevaluation of free will. He recalls how, as early as 1964, two neuroscientists asked 12 healthy volunteers to perform hundreds of simple tasks — pulling a rope, catching a ball, and so on — while their brain activity was monitored via electroencephalography (EEG).

They observed that an electrical signal consistently appeared about 1–1.5 seconds before the participants engaged their muscles for voluntary actions. However, this signal was absent when passive movements were made — such as when the researchers physically adjusted the participants’ fingers for them.

In the 1980s, further studies refined these findings: brain activity preceding movement was detected about 200–300 milliseconds before individuals consciously decided to act. According to some scientists, this suggests that decisions we perceive as voluntary are actually made by our brains long before we become aware of them.

This challenges the very notion of conscious choice and control over our actions.

CAN WE CONTROL OUR OWN BRAINS?

However, not all scientists agree with this interpretation. Some argue that while our brains may generate impulses automatically, we still have the ability to veto them. Furthermore, some researchers suspect that the electrical signals observed in these experiments might be mere artifacts of the experimental setup. If that’s the case, then what do these findings really say about free will?

The debate over whether we are merely slaves to our brains remains far from settled — and, at times, highly contentious. Yet the individuals described by Leschziner clearly exhibit little to no free will. At least in certain cases, factors such as genetics, developmental variations, medication effects, brain injuries, or neurological disorders can severely limit one’s ability to control their actions.

Does this mean we should reject the concept of free will altogether? Or do we still have the capacity for full control over our decisions? The question remains open…

BEYOND GOOD AND EVIL

Leschziner himself believes that the answer to personal responsibility lies somewhere in between. However, this does little to resolve the age-old philosophical and theological dilemma of free will versus determinism. Perhaps it’s worth heeding the words of Saint Augustine: «That which was not done voluntarily was neither sin nor virtue».

If we accept this perspective, then brain chemistry and genetic predispositions are not matters of morality or sin — they exist «beyond good and evil». The real question is: to what extent do our biological traits define us as individuals? And how much do they align with our sense of self?

This is where self-awareness and self-regulation become essential. That is, of course, if we truly value free will in the first place.

Original research: