How Humans Grew Acorn Brains

If we are going to tackle humanity's biggest long-term challenges, we will need to use our unrivaled ability to think long-term. Understanding how we developed this ability can help us use it to its full potential.

Human beings are quite capable of dealing with immediate crises. A devastating flood takes place and we send in the emergency relief. A pandemic occurs and we shut the borders and develop the vaccines. A war erupts and the refugees are found homes. More or less.

But when it comes to long-term crises, humanity’s record is less exemplary. Our response to the climate emergency – which is already here but whose greatest impacts are yet to come – has been painstakingly slow. We freely create technologies, from AI to bioweapons, that could pose devastating risks for our descendants. We fail to tackle deep problems like wealth inequality and racial injustice, which get passed on from generation to generation.

This temporal imbalance raises a question: is it even in the nature of our species to take the long view? Looking at the record so far, you would be right to be skeptical.

But there’s some unexpectedly good news: we are wired for long-term thinking like almost no other animals on the planet. As I argue in my recent book The Good Ancestor, grasping this scientific truth requires understanding the crucial difference between what I call the Marshmallow Brain and the Acorn Brain.

The Marshmallow Brain is an ancient part of our neuroanatomy, around 80 million years old, that focuses our minds on instant rewards and immediate gratification. This is the part exploited by social media platforms that give us dopamine hits by getting us to constantly click, scroll and swipe, as so brilliantly depicted in the film The Social Dilemma. It is named after the famous Marshmallow Test psychology experiment of the 01960s, where children who resisted eating a marshmallow for 15 minutes were rewarded with a second one: the majority failed.

There are well-known critiques of the test, for instance the fact that the ability to delay gratification is highly dependent on socioeconomic position: those from wealthier backgrounds find it easier to resist the treat, while a lack of trust and fear of scarcity can push kids towards gobbling it up.

A more fundamental critique, however, is that we are not simply driven by immediate rewards. Alongside the Marshmallow Brain we also possess a long-term Acorn Brain located in the frontal lobe just above our eyes, especially in an area known as the dorsolateral prefrontal cortex. This is a relatively new part of our neuroanatomy – a mere two million years old – giving us a rare ability to think, plan and strategize over long timeframes.

But don’t other creatures think and plan ahead? Sure, animals such as chimpanzees make plans, like when they strip leaves off a branch to make a tool to poke in a termite hole. But they will never make a dozen of these tools and set them aside for next week.

Yet this is precisely what a human being will do. We are long-term planners extraordinaire. The Acorn Brain enables us to save for our pensions and write song lists for our own funerals. It’s how we built the Great Wall of China and voyaged into space. It’s why we’ll plant an acorn in the ground as a gift for posterity, like in the beautiful story The Man Who Planted Trees.

If we are going to tackle long-term challenges like the ecological crisis, we will need to use this unrivaled ability to become part-time residents of the future. Let’s recognize that we are not just short-term marshmallow snatchers, but long-term acorn planters.

The human capacity to think long term “is one of the brain’s most stunning innovations,” writes the psychologist Dan Gilbert, one of the founders of a newly emerging field called “prospective psychology.”. But as he also points out, in evolutionary terms it’s a recent skill and we’re not very good at putting it into practice: we’re much better at ducking out of the way of a baseball thrown at our heads than at dealing with a danger whose biggest impacts are coming several years or decades down the line, like climate change.

Still, if we want to bring out the full potential of the Acorn Brain, we need to understand it better. Where did it come from and how does it work?

Evolutionary psychologists and archaeologists offer four main explanations for how our brains evolved this remarkable cognitive ability to think and plan over long timespans.

First is a survival skill known as “wayfinding.” Over a period of two million years our protohuman ancestors developed a capacity to orient themselves in physical space and navigate from place to place when they went on hunting or foraging expeditions, or roamed in search of shelter. In doing so they evolved an ability to create “cognitive maps” in their minds. But as University of Michigan ecologist Thomas Princen argues, this mental cartography required not just mapping place but also mapping time. Hunters could save precious energy – and even lives – if they not only planned the route but forward planned the time, identifying how long it might take to get from the stream to the forest and then back home again.

A second enabler of long-term brains, sometimes known as the “grandmother effect,” relates to the growing evidence that the presence of grandparents – especially maternal grandmothers – is important for reducing infant and child mortality. Recent research from anthropologists and evolutionary biologists reveals that older post-reproductive females provide vital childcare, knowledge and other forms of support that increase the survival chances of the young. Through this grandmother effect our ancestors became embedded in multigenerational kinship groups that helped them develop time horizons – and an ethic of care and responsibility – encompassing some five generations, stretching at least forwards by two and backwards by two from their own.

This was reinforced by the deep human instinct for social cooperation, which requires an imaginative capacity to see into the future. Relationships of trust and reciprocity work best when people know that the help they give to someone in the present will likely be returned at a future date, when they are in need themselves: time is woven into the fabric of mutual aid. Similarly, empathy is based on an ability to anticipate the needs, feelings and goals of others. When a friend loses her job, we may try to imagine what her emotional state might be and the best support we could give. In doing so we are prospecting the future by simulating an array of possibilities. Even the simple act of gauging someone’s intentions requires identifying different possible futures. As psychologist Martin Seligman points out, “How would we coordinate and cooperate if we could not form reliable expectations of what others would do in a range of situations?” The conclusion is clear: our social nature evolved in tandem with a talent for mental time travel.

A final explanation concerns the human genius for toolmaking. Over two million years, our capacity to make stone tools became increasingly sophisticated. The earliest tools simply had natural points and edges. But then our Paleolithic ancestors learned to flake off part of the stone by hitting it against a surface, and eventually made three-dimensional tools where multiple planes met at a single point. Creating these wasn’t just a matter of randomly bashing off bits of stone: it required forward planning and envisioning future goals. According to historian of technology Sander Van der Leeuw, as our brains grew and we developed the ability to make complex tools, we also developed “the capacity to plan and execute complex sequences of actions.” The ability to plan making a stone tool enabled us to plan other forward-looking actions with long time horizons such as crop rotation or building a pyramid. All those stone tools gathering dust in museums reveal the greatest of all human achievements: the emergence of civilization itself.

The human brain is designed for so much more than constantly checking our phones. With an understanding of these four origins of our long brains, we have the beginnings of a new story about human nature. We are not merely prisoners of our Marshmallow Brains but have Acorn Brains wired into us. We have evolved with a unique ability to plan over long time periods. That’s what enabled medieval cathedral builders to embark on projects they knew might never be completed within their own lifetimes. Such “cathedral thinking” is precisely what we urgently need today to tackle the long-term ecological, political and technological challenges of our time.

Narratives about human nature matter. Studies of economics students have shown that those who are taught that human beings are essentially rational, self-interested creatures are more likely to act selfishly after completing their courses than their freshman counterparts. It’s time to get the narrative about our temporal selves right. Let us embrace the Acorn Brain as part of who we are and recognize it as a vital foundation for creating a long-now civilization, where we take responsibility for the impacts of our actions on the citizens of tomorrow.

Roman Krznaric is a public philosopher. His latest book is The Good Ancestor: A Radical Prescription for Long-Term Thinking.

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