A review of Original Sin by Kathryn Paige Harden; 320 pages; Random House (March 2026)

The behavioural geneticist Kathryn Paige Harden opens her latest book with a line straight out of a Hunter S. Thompson novel: “It was a sweltering, tedious summer … when Travis and I decided to go to the West Texas desert to drop acid.” But what was supposed to be a psychedelic holiday to escape the monotony of the COVID lockdowns takes a dark turn when Harden’s boyfriend has a bad trip. He gets trapped in a hallucination that he has crashed his car and killed Harden and is racked by guilt for his imagined actions. “What,” Harden asks, “was the ghastly belief at the core of Travis’s waking nightmare? There’s nothing you can do about it, and you will be responsible.”

Harden uses this autobiographical episode as a springboard into deeper philosophical questions about what it means to be responsible in an era when science can predict who is more likely to commit a crime based purely on their DNA. She ponders whether we should take people’s genetics into account when deciding “whether and how they should be punished for the sins they commit.” She asks, “Does science let us off the hook … or is science, in the end, as accusatory as a bad acid trip…?” Importantly, she tackles these questions about causation and responsibility as someone who was “raised religious and fled the church as an adult,” addressing her book to “modern, enlightened” readers like herself who “don’t believe in God anymore.”

Harden made a first attempt to grapple with these questions in her previous book, The Genetic Lottery, in which she sought to put a progressive spin on the finding that current social inequalities are partly due to genetic differences between people. Unfortunately, both of Harden’s books fail to confront the hard choices that a naturalistic worldview presents us with, though each fails to meet this challenge in a different way. The naturalistic worldview implies that all human behaviour has non-supernatural causes of one kind or another. Insofar as that view is accepted, there are only two possibilities: either moral responsibility is compatible with the comprehensive causation of human behaviour or moral responsibility cannot exist. We might call this the “determinist’s dilemma.”

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In The Genetic Lottery, Harden dodges this dilemma by equivocating over whether all human behaviour has prior causes. She argues that we’re only responsible for our life outcomes to the extent that they aren’t explained by known genetic and environmental causes. “Should we consider genetic influences as a limitation [of] a person’s agency or control?” she asks. “Should we hold people less responsible for their highly heritable outcomes?” Her response is emphatic: “In my view the answer is yes—the extent to which someone’s life outcomes can be traced back to their starting point in life calls into question how much they could have acted differently.” Driving this point home, she adds, “After the joint outcomes of both the social and the natural lotteries are taken into account, the remaining unpredictability in psychological traits and socioeconomic positions is small,” leaving “remarkably little territory left for ‘personal responsibility.’”

This is a claim about responsibility and causation. Harden holds that, to the extent that our behaviour has prior genetic and environmental causes, we cannot be held responsible for it: a position that philosophers call “incompatibilism.” But The Genetic Lottery did not argue that moral responsibility does not exist, only that our genetic and environmental circumstances greatly diminish our responsibility for our actions and outcomes. This raises an obvious question: if all of our behaviour is caused, why should the causes that we know about diminish our responsibility while the causes that we don’t know about do not? After all, ignorance cannot plausibly be a source of human agency. In effect, Harden unwittingly flirts with the idea that some aspects of our behaviour are miraculously uncaused and self-caused—a god-of-the-gaps theory of free will, which holds that moral responsibility lurks in some dark corner of human behavioural variation that science is yet to explain. But there is nowhere for supernatural sources of human agency to hide in a naturalistic worldview that has lost all faith in miracles.

In her new book, Original Sin, Harden seems to have spotted this fatal flaw in the position she defended in The Genetic Lottery. She acknowledges that it’s “universally true of all humans” that our behaviour is “embedded in the pure cause and effect of the animal world,” and she rejects the notion that there is a “metaphysical loophole where freedom might be hiding” in the “differences between identical twins, or the limits of statistical prediction.”

Having rejected this view, one might have expected Harden to bite the bullet and either accept that responsibility is compatible with causation or accept that responsibility cannot exist. But instead of confronting the determinist’s dilemma, she introduces yet another anachronistic theological idea into the secular free-will debate. Enlisting the 5th-century theologian Augustine, she argues that we’re responsible for our actions even though the prior causes of our behaviour mean we have no choice but to act as we do. According to Harden, we remain morally responsible despite being victims of circumstance because holding each other accountable with praise and blame is just an inescapable part of how human beings relate to each other.