The psychiatrist diagnosed “delusional parasitosis”, the false belief that parasites have infested the body. The roughly 1-in-100,000 people who suffer from this condition imagine that ants, worms, ticks, mites or other bugs are moving around under their skin. It is, as the label suggests, a delusion, often brought on by schizophrenia or dementia. When the insects strike, nothing can persuade patients that the critters aren’t real.

Delusional parasitosis is a relatively rare condition, but it is indicative of a phenomenon that is surprisingly widespread: the presence of animals in psychological disorders. The medical literature contains tens of thousands of cases in which animals or thoughts of animals played a significant role in the expression of mental distress.

For the examples above, we could substitute the childhood victim of sexual assault who grew up obsessed with rats; the pet-loving psychotic whose facial tics made him look like a snarling dog; the mother in West Africa who woke from a dream convinced she had been impregnated by a baboon; the young woman who believed she was being controlled by her cat; or, closer to home, the child of a friend who took to howling like a wolf during the Covid lockdown.

Or we could consider the long history of sociogenic illness or “conversion disorder”, in which seemingly benign behaviors, often in imitation of animals, spread rapidly and without apparent cause within schools, religious orders and other close-knit institutions. Medieval records from France and Spain describe groups of nuns barking like dogs while running through the fields, or mewing like cats for hours each day, or bleating like sheep, tearing off their veils and convulsing in church.

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Of course, wild animals have been almost completely absent from most people’s lives for centuries. We have long considered them inferior: less conscious, less intelligent, less self-aware, less rational. An animal is everything humans are not, the quintessential “other”. Yet they feature in our psycho-pathologies, hallucinations and dreams, in art and story-telling, and in the mental lives of children. They creep into our psyche in spectacular and sometimes alarming ways. 

That’s especially true of people who suffer from medical disorders: whether blindness, or dementia, or schizophrenia. Their visions can be exceptionally strange. In 2019, a group of psychosis patients taking part in a medical study reported seeing snakes crawling out of their arms, a rhino crossing the street, a cow in the corridor of a school.

Fantastical creatures of this ilk can just as easily be summoned by swallowing psychedelic drugs like LSD or psilocybin — the chemical that gives certain mushrooms their magic. On trips of this kind, animals are almost always part of the landscape. During my first and probably last experience with psilocybin, I found myself in a world of reptilian and parasitic freakery, in which snakes, lizards, worms and other legless lifeforms crawled and slithered about a garden trellis, taunting me with grotesque faces that resembled the carved gargoyles on Gothic cathedrals. It sounds terrifying, though my feeling was more of benign interest. 

Nor am I alone: the psychologist Benny Shanon, who drank ayahuasca several hundred times while researching a book about its effects, encountered animals in his visions more frequently than anything else, mingling with lizards and crocodiles, fish and bees, butterflies and jaguars. All the while, many of us cross paths with animals, both magical and mundane, in our sleep. And if it’s tempting to seek meaning in such visions, they may tell us more about the animals than about ourselves. 

Alison Hawthorne Deming, a poet frequently visited by dream animals, describes them as barging into her brain, self-willed and unconstrained. After dreaming of a horse that had turned up for treatment at Sigmund Freud’s consulting rooms, she concluded that it was “a messenger from the animals’ homeland telling me that we’re driving them crazy and they have no science with which to treat themselves”.

The truth is that what causes highly realistic animistic images to surface in the non-conscious mind remains a mystery. Yet one compelling possibility is that the brain, when deprived of its usual stimuli, tries to make sense of the information it receives by providing a hypothesis or story of its own, or by over-activating the default mode network, a set of brain regions that supports daydreaming and introspection. Its tendency to conjure up an abundance of animals, rather than, say, inanimate objects, may relate to the fact that the human visual system evolved to be acutely sensitive to living things.

Over the hundreds of thousands of years that Homo sapiens and our antecedents lived as hunter-gatherers, individuals with the ability to detect animals quickly in the landscape were more likely to survive and reproduce, and this trait was gradually selected for until it became a universal inherited characteristic of the human brain. To coin a phrase, we became “animal-minded”, preoccupied with the circumstances of our fellow creatures and highly attuned to their anatomical forms and ways of moving.

Derek Hodgson, an archaeologist whose expertise also includes neuroscience and psychology, suggests this mechanism likely evolved in our ancestors over successive generations in response to both the persistent threat they faced from carnivores and the intense competition for food. An intuitive emotional reaction to the slightest possibility of an animal would have considerably increased their chances of survival. “They were competing with predators who were predating both on them and on the animals they were hunting for food,” Hodgson explains. “If they made a mistake and they didn’t react, they were in trouble. They had to be keenly aware of animals that used camouflage to remain concealed, otherwise they would have lost out in the long game of hide and seek.”

Modern brains still possess this attribute. Neuroscientists have discovered a dedicated neural pathway linking the visual part of the brain (the visual cortex) to the emotion-processing part (the amygdala). Known as the ventral stream, this pathway generates a fast visceral response at the sight of an animal, alerting us to its possible presence before we are consciously aware of it. We remain hypersensitive to living things, just like our Ice Age ancestors.

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While we rarely get a chance to test our animal-mindedness in everyday life, it becomes fully activated when our psyche is disrupted: in conditions of psychosis, neurosis, delusional thinking, phobia and obsession, or when we’re dreaming or hallucinating. The creatures that visit us during such times are, perhaps, indicative of the conflicted ways we think about animals, and our fraught deliberations over whether we are, in fact, one of them.

The mid-20th century American anthropologist Ernest Becker believed that our attitudes towards animals — indeed much of our behavior and thinking — are driven by the realization that we will one day die. The terror of ending up as compost drives us to raise families, cultivate values, subscribe to religions, and generally build things that will outlast us. Animals, which we are used to seeing as roadkill or meat on a plate, remind us of our own flesh-and-blood reality. Distinguishing ourselves from them is a step towards the symbolic immortality we crave.

Becker’s ideas help explain why we so resolutely cling to the notion of humans as a species apart, despite growing evidence that we have seriously underestimated the worlds and abilities of our fellow creatures. Most biologists now agree that all vertebrates and many non-vertebrates have some form of consciousness, and that animal emotions can be as complex as human ones. Our deliberate separation — the belief, which dates back to ancient Greece, that we are a superior species — has been a disaster for animals themselves. It has allowed us to kill them with impunity, and to keep their suffering at arm’s length. And it has enabled us to avoid the cognitive dissonance of having to face up to the truth that we are what we eat: meat on the bone.

The conceit that humans are exceptional is easy enough to maintain with full awareness. But when we are asleep, cognitively compromised, high on stimulants or otherwise distracted, our fellow other animals become our equals. What are they doing there? It is hard to know for sure. At the very least, they should remind us that our relationship has been longer, and more intimate, than most of us are prepared to acknowledge.

***

Animate: How Animals Shape the Human Mind is published by Picador on 19 March.

Now, in Rationality: What It Is, Why It Seems Scarce, Why It Matters, Pinker synthesises both aspects of his oeuvre. On the one hand, Rationality briskly introduces you to essential concepts like Bayesian reasoning and technical terms like modus ponens. But the technical, learned aspects of the book are accompanied by a polemical drive. Rationality matters — every day, everywhere. Especially at present, in a world that many think has gone mad, whipsawed irrationally by social media mobs and online conspiracy theories. Pinker argues that methods of rationality represent not an esoteric corner of cognitive science or philosophy, but an essential set of tools for individual human flourishing, maintaining our sanity and perpetuating civilisation as a collective whole. To reason and think clearly is to be modern, and even requisite in order to be moral.

In the wake of the financial crisis of 2008, the rational actor and “homo economicus” seemed to have failed us. Nature abhors a vacuum, so there was a vogue for the field of behavioural economics, a discipline that operates in the gray zone of economic frictions and psychological irrationalities powered by faulty intuition. A crop of authors harvested these ideas: Dan Ariely, Rom Brafman, Ori Brafman, Cass Sunstein, and Richard Thaler among them. More broadly, Daniel Kahneman and Amos Tversky’s heuristics and biases research program, to which all these authors owe a debt, entered the mainstream — Kahneman also contributed a bestseller, Thinking, Fast and Slow in 2011. Barack Obama’s administration tried to ‘nudge’ America through policy. David Cameron’s government, and the British civil service, embraced nudging too.

Rationality is part of a tacit backlash against these authors, their books, and the atmosphere they generated in public policy circles in the 2010s.

Today, Dan Ariely faces accusations of fraud at worst and scientific malpractice at best. More broadly, behavioural economics has been hit by the replication crisis. Humans respond to incentives, and for scientists, sexy and vivid results are rewarded, while negative findings can stall a career. The scientific culture of the aughts was defined at its peril by “publish or perish,” as well as sloppy experimental practices, a mechanically unthinking application of statistics, and cognitive biases in the very fields dedicated to understanding how rationality fails us. Kahneman himself began having doubts in 2012, justifiably, about some of the results reported in his 2011 book.

Pinker’s good news in Rationality is that with deliberate effort, humans can think clearly and move beyond their biases. Where much of cognitive psychology focuses on illusions and mental misfires, Rationality instead argues that our faculties are up to the task, and that this is all a natural consequence of our evolution. Evolutionary psychology leans heavily on the idea that humans are only equipped with “stone-age minds” in a technologically advanced present. Pinker seems a bit chagrined at this angle being so overplayed, and in Rationality he attempts to redress the balance, making the case that humans are naturally equipped to reason and that reason is not a dark art or the province of philosophers and mathematicians alone.

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If you are a consumer of anthropology and ethnography or even have simply watched The Gods Must Be Crazy, you are aware of the preternatural skills of the San hunters of the Kalahari desert. Pinker shows this is not due to inborn traits, but the ability of the San to take in the information around them, the time of the year, the season, the species of antelope, and make inferences in alignment with their overall goals. The San, like all humans, engage in a rough and ready form of syllogistic reasoning. They start with axioms, premises informed by their experiences, and deduce logical consequences from their assumptions. Things don’t just “happen” in the Kalahari, there is a rhythm and rhyme the hunters exploit, a pattern and sense of the world that allows them to survive and flourish. Steenbok antelope are hunted during the rainy season while eland are stalked during the dry season. You might think this is due to custom and tradition, but the San are aware that steenbok has stiff joints during the rainy season while eland hooves are ill-equipped to navigate sandy soil. They hunt animals in the season that loads the dice for a success hunt. The alternative, simply, is a higher risk of starvation. The San have goals, and they naturally use the tools of rationality to achieve them.

But what if the San did not rationally know the reasons for their actions?

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One of the essential points in Rationality is that reasoning and understanding the world are collective enterprises. We know that socially-generated knowledge and rationality can be embedded enduringly through rules and taboos. Yes, those executing a cultural script may not be aware of the ultimate reasons, but a deeper investigation by anthropologists can reveal that mindless traditions actually serve functional purposes.

Joe Henrich in 2015’s The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter reports how traditional societies across the world have a system of preparing cassava that prevents them from getting cyanide poisoning. Those following the methods do not know what cyanide is, nor do they even know that consuming unprepared cassava will lead to death, but their culture comes preloaded with the fruits of adaptive learning that are highly rational.

The deepest insight then is that our ability to reason through complex problems depends on our willingness to stand on the shoulders of giants. Though we can all reason, Pinker does not shy away from conventional pitfalls of human analysis such as the Monty Hall problem, the gambler’s fallacy and the base rate fallacy. He recounts that Paul Erdos, author of 1,500 mathematical papers, was as mystified by the Monty Hall problem as most people who encounter it. He refused to believe he was wrong, relying on his native intuitions, despite his prodigious ability to work through formal mathematics.

The point is that the most brilliant individual mind can fail at reasoning unless it approaches the enterprise with humility and the willingness to update beliefs and understanding. The scholarship reviewed in Rationality, from Aristotle to machine learning, is not just the product of singularly brilliant minds, but the collective efforts of whole scientific traditions. The replication crisis shows that groups of scholars can blunder into traps and dead ends en masse. But advances in fields like statistical decision theory would be impossible without the collective efforts of disparate research groups across numerous domains. Pinker’s treatment of deep learning neural networks also makes it clear that some of these tools for rationality are approaching the dark edge of Arthur C. Clarke’s formulation that “any sufficiently advanced technology is indistinguishable from magic.” And, like magic, they often fail without the guiding hand of human reasoning faculties.

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Rationality, Pinker says, was partly in response to students at Harvard finding the world puzzling, especially with much of psychology focused on how human rationality fails. If Pinker makes the case for thinking clearly, with the most powerful tools we have, whether it be 21st-century computational methods in machine learning or sharper formal analysis that draws upon mid-20th-century economic game theory, he still remains fully aware that he lives in an empirical world of irrationality.

Pinker was not one of the ‘Four Horsemen’ of New Atheism: Christopher Hitchens, Richard Dawkins, Daniel Dennett and Sam Harris. But he is, and long has been, a fellow traveller of the group (he is also personally close to Dawkins). In the early 2000’s he took equal-opportunity aim at the Right’s attachment to traditional religion in The Blank Slate while taking the Left to task for its denial of human nature. Twenty years later, he made an extended call for a revival of the cult of rationality in Enlightenment Now. Pinker’s enthusiasm for applying rationality and empiricism to the world reflects the intellectual culture of the mid-2000’s when Dawkins was riding high with his critiques of evangelical Christianity and public intellectuals were gathering to celebrate the Enlightenment in conferences like Beyond Belief. The familiar flame of this hopeful past burns bright throughout Rationality.

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But ours today is a world of cancel culture and QAnon. Ideological polarisation that has turned the pandemic into the object of a culture war in the United States. Pinker does address the reality that the world today is not the world he might have imagined it would be a generation ago, as irrationalities and superstitions spread like ideological pandemics on social media.

The vision of the aughts was one of a reason-ruled future, but Rationality was written in the wake of Donald Trump, whose rise and popularity as an emotive demagogue triggered a reactionary flare-up of identity politics on the cultural Left. This is the world where David Hume observed that “Reason is, and ought only to be the slave of the passions”. To a great extent, the project of making Bayesian reasoning, game theory and machine learning accessible and palatable to the public seems born of the disappointments of the past generation. If you are a deep reader of Scott Alexander’s Slate Star Codex, Rationality may not offer you much new food for thought. But if you are terrified by the insanities of the present, and wish to replenish your intellectual armoury in the fight for progress and reason in the 21st century, then Rationality is what you will want to bring to the battlefield.