There's more than one path to evolving intelligence
For decades, scientists believed that large brains were nature's answer to the demands of social life — that managing alliances, hierarchies, and relationships was what drove intelligence to flourish. Now, a study of 79 cephalopod species published in iScience quietly dismantles that assumption: octopuses, squid, and cuttlefish have evolved remarkably large brains while living almost entirely alone, suggesting that a complex environment, not a complex society, may be equally capable of growing a mind. The finding does not erase what came before, but it opens the door to a more plural understanding of how intelligence finds its way into the world.
- The social brain hypothesis — the long-held idea that bigger brains evolved to manage bigger social groups — has guided neuroscience for decades, but octopuses have always been an uncomfortable exception it couldn't explain.
- Cephalopods are solitary, sometimes cannibalistic, die before they can parent their young, and yet possess brains that rival those of far more social creatures — a contradiction urgent enough to demand a new theory.
- Researchers from the London School of Economics and the University of Lethbridge analyzed 79 cephalopod species and found that habitat complexity — rich seafloors, diverse prey, intricate terrain — predicted brain size far better than any measure of social behavior.
- They propose the cultural brain hypothesis: brains may be selected not for sociality specifically, but for the capacity to learn and adapt, whether the teacher is a social group or a demanding, solitary environment.
- The science still rests on correlation rather than proven causation, but the pattern is strong enough to suggest that intelligence did not evolve along a single road — and that scientific consensus, as one researcher put it, always needs to be questioned.
For decades, neuroscientists operated from a tidy assumption: bigger brains belong to social animals. Managing group hierarchies, tracking alliances, remembering faces — these demands, the thinking went, were what drove intelligence to evolve. Wolves, dolphins, primates, and sheep all seemed to confirm it. The social brain hypothesis became orthodoxy.
Then there are the cephalopods. Octopuses, squid, and cuttlefish have brains that are large relative to their body size, and they solve puzzles, use tools, and adapt with startling creativity. Yet they are almost entirely solitary — many are hostile to their own kind, some are cannibalistic, and all die shortly after reproducing, never raising young or building the social structures the hypothesis depends on.
A research team led by anthropologist Kiran Basava and economist-psychologist Michael Muthukrishna of the London School of Economics decided to take the contradiction seriously. Analyzing data on 79 cephalopod species, they found that habitat complexity — rich seafloors, diverse prey, intricate terrain — predicted brain size far more reliably than sociality did. An octopus hunting alone on the ocean floor, squeezing through crevasses, learning which tools work for which prey, faces a relentless cognitive challenge that may be just as evolutionarily demanding as managing a social group.
The team calls their alternative the cultural brain hypothesis: brains may be selected for their capacity to store and process information, regardless of whether that information comes from social learning or solitary problem-solving. Co-lead Jennifer Mather, an octopus psychologist from the University of Lethbridge, put it plainly — scientific dogma needs questioning, and cephalopods have never followed predictable evolutionary paths.
The research still relies on correlation rather than direct proof of causation, but the pattern is compelling. Intelligence, it seems, did not evolve along a single road. Some minds grew large to navigate social worlds; others grew large to master complex environments. The octopus, learning alone in the dark, may be telling us something fundamental about the many ways a mind can come to be.
For decades, neuroscientists have operated from a tidy assumption: animals with bigger brains relative to their body size tend to be social creatures. The logic seemed sound. Managing a complex group—remembering faces, tracking hierarchies, navigating alliances—demands cognitive horsepower. Wolves, dolphins, primates, sheep: the pattern held. Larger social networks correlated with larger brains, particularly in the mammalian neocortex. This became known as the social brain hypothesis, and it explained a lot about how intelligence evolved across the animal kingdom.
Then there are the cephalopods. Octopuses, squid, and cuttlefish possess brains that are remarkably large for their body size. They solve puzzles, use tools, change color and texture in milliseconds, and demonstrate problem-solving abilities that astonish anyone who watches them work. Yet they are almost entirely solitary. Many are actively hostile to their own kind. Some are cannibalistic. A few species gather in groups, but even then the gatherings are often violent. And here's the kicker: cephalopods die shortly after reproducing, which means they never parent their young, never build the social structures that supposedly drive brain evolution in the first place.
This contradiction prompted a team of researchers to ask a different question. If cephalopods have large brains but no social life to speak of, what actually drove their intelligence? The answer, published in iScience, points not to sociality but to habitat. The researchers, led by anthropologist Kiran Basava and including economist-psychologist Michael Muthukrishna from the London School of Economics, compiled data on 79 cephalopod species. They measured brain size against ecological factors, behavior, and social structure. What emerged was striking: cephalopods living on the sea floor and in shallow waters—environments rich with food, complex terrain, and diverse prey—had significantly larger brains. Sociality played almost no role in predicting brain size.
The team proposes an alternative framework called the cultural brain hypothesis. Rather than social complexity driving brain evolution, the hypothesis suggests that brains are selected for their capacity to store and process information—whether that information comes from social learning or from navigating a complex, solitary environment. A benthic octopus, for instance, spends its life alone on the ocean floor, encountering countless different prey species, fitting its boneless body into crevasses of varying shapes, and learning which tools work for which tasks. That constant problem-solving, that endless need to adapt and learn, may be just as powerful an evolutionary pressure as managing a wolf pack.
The findings challenge what has become scientific orthodoxy. "For decades the main story of why brains got big has been a social one," Muthukrishna notes, "where bigger brains evolve to manage bigger, more complex groups. Cephalopods reveal that there's another path to bigger brains. They're often solitary, short-lived, sometimes even cannibalistic, and yet have large brains and intelligent behavior." Jennifer Mather, an octopus psychologist from the University of Lethbridge who co-led the study, frames it more bluntly: "Scientific dogma always needs to be questioned, and that once again it shows that cephalopods don't follow the predictable evolutionary paths."
It's worth noting that this research, like the social brain hypothesis before it, still relies on correlation rather than direct proof of causation. But the pattern is compelling enough to suggest that intelligence did not evolve along a single path. Some animals grew smart because they had to manage complex social worlds. Others grew smart because they had to master complex environments. The octopus, hunting alone in the dark, learning by trial and error, building its intelligence one problem at a time, may be telling us something fundamental: that there is more than one way to evolve a mind.
Notable Quotes
Cephalopods reveal that there's another path to bigger brains. They're often solitary, short-lived, sometimes even cannibalistic, and yet have large brains and intelligent behavior.— Michael Muthukrishna, London School of Economics
Scientific dogma always needs to be questioned, and that once again it shows that cephalopods don't follow the predictable evolutionary paths.— Jennifer Mather, octopus psychologist, University of Lethbridge
The Hearth Conversation Another angle on the story
So the social brain hypothesis worked fine for mammals and primates. Why didn't anyone notice cephalopods breaking the pattern earlier?
They did notice—cephalopods have always been known for their intelligence. But the social brain hypothesis was so elegant, so well-supported by data from our own branch of the tree, that it became the default explanation. It's easier to assume a pattern holds universally than to ask why one group of animals is an exception.
But octopuses are solitary. They don't even raise their young. How does that not immediately disqualify them from the social brain hypothesis?
It should have. That's the whole point of this paper. The hypothesis was treated as universal law when it was really just a strong correlation within one group. No one was systematically asking: what if there's another path?
And the answer is habitat complexity? That seems almost too simple.
It's not simple at all. An octopus on the sea floor has to learn hundreds of different prey behaviors, figure out how to manipulate tools, navigate three-dimensional space, solve novel problems constantly. That's not simple—it's just a different kind of complexity than managing a social hierarchy.
So intelligence isn't about other minds. It's about the world itself.
For cephalopods, yes. For us, it was about both. The research suggests evolution had multiple levers to pull. Some animals got smart by reading each other. Others got smart by reading their environment.
Does this change how we should think about intelligence in other animals?
It should make us more humble. We've been looking for intelligence through a social lens for so long that we might have missed it elsewhere. What other solitary animals might be smarter than we give them credit for?
And what about the cephalopods that are social—the squid? Did they have bigger brains?
No. That's the really telling part. The social squid didn't have proportionally larger brains than the solitary octopuses. It suggests that even within cephalopods, sociality isn't the driver.