Tag: neocortex

  • Comparative Cortices: Why a Crow’s Walnut-Sized Brain Outperforms an Elephant’s

    A New Caledonian crow weighs roughly 300 grams. Its brain weighs about 7.5 grams — less than two teaspoons of water. An African elephant weighs 6,000 kilograms. Its brain weighs roughly 4,800 grams — six hundred times heavier than the crow’s. The crow makes tools from sticks and leaves, solves multi-step puzzles it has never encountered before, plans for future needs, recognizes itself in a mirror, and remembers the faces of individual humans who threatened it years earlier. The elephant does extraordinary things too — navigates to water sources visited decades ago, communicates across kilometers through infrasound, maintains social relationships across a 50-year lifespan, and grieves its dead. But if you put both animals in a novel problem-solving paradigm — the kind of controlled laboratory task that comparative psychologists use to measure flexible cognition — the crow consistently outperforms the elephant. It outperforms most primates. It outperforms every mammal except the great apes and, depending on the task, humans. A brain the size of a walnut is beating a brain the size of a bowling ball. Something other than size is doing the work.

    What’s doing the work is architecture.

    Two ways to build a thinking machine

    The mammalian neocortex is a six-layered sheet of neurons draped over the surface of the brain like a crumpled tablecloth stuffed inside a skull. The crumpling is the point — gyrification, the folding of the cortical surface into ridges and grooves, is how mammals fit more cortical surface area into a fixed cranial volume. Cetaceans are the most gyrified mammals on Earth: a bottlenose dolphin’s cortex is more folded than a human’s, regardless of brain mass. The six layers are arranged vertically, with each layer containing different neuron types performing different computational roles — sensory input arrives in layer IV, output to motor systems leaves from layer V, inter-cortical communication runs through layers II and III, and feedback projections from higher areas target layer I. The architecture is modular: the same six-layer circuit repeats across the entire cortical surface, with regional specializations for vision, hearing, touch, motor control, and association — the “higher” cognitive functions that neuroscientists have historically credited with intelligence.

    Birds do not have a neocortex. They do not have six layers. They do not have a cortical sheet. What they have is the pallium — a collection of neuronal cell-body clusters organized into nuclei rather than layers, occupying the dorsal telencephalon in the same developmental position that the mammalian neocortex occupies, derived from the same embryonic tissue, expressing many of the same genes, and performing — according to a landmark 2025 cluster of papers in Science — computations that are functionally equivalent to neocortical processing despite being architecturally unrecognizable.

    The 2025 Science papers, published simultaneously by multiple groups, used single-cell transcriptomics to compare cell types in the bird pallium and the mammalian neocortex at the molecular level. The finding: birds and mammals share a conserved set of neuronal cell types — glutamatergic projection neurons, GABAergic interneurons with matching subtypes, and shared gene-expression profiles — that trace back to the last common ancestor of mammals and reptiles, approximately 320 million years ago. The cell types are conserved. The way they’re arranged is not. Mammals stack them into layers. Birds cluster them into nuclei. The evolutionary divergence is structural, not cellular. Two blueprints, same parts, different assembly.

    The neuron density revolution

    In 2016, Seweryn Olkowicz and colleagues at Charles University in Prague published a study in PNAS that recounted the neurons in the brains of 28 bird species using the isotropic fractionator method — a technique that dissolves brain tissue into a suspension of individual nuclei and counts them, producing neuron totals that are far more accurate than the density estimates derived from histological sampling. The finding upended a century of assumptions about brain size and cognitive capacity.

    Songbird and parrot forebrains contain neuron densities that match or exceed those of primates — and in some cases dramatically exceed them. A macaw’s forebrain contains roughly 1.8 billion neurons packed into a brain that weighs 20 grams. A macaque monkey’s forebrain — seven times heavier at 140 grams — contains approximately 1.7 billion neurons. The macaw has more forebrain neurons in a smaller brain. A corvid’s pallial neuron density is approximately twice that of a primate of equivalent brain mass. The neurons are smaller, packed tighter, with shorter interneuronal distances — which means faster signal propagation and potentially faster processing.

    The elephant’s brain is the counterpoint. At 4,800 grams, the African elephant brain has approximately 5.6 billion cortical neurons — more than three times the human cortex’s roughly 16 billion? No. Herculano-Houzel’s 2014 counting study found that 97.5% of the elephant’s neurons — approximately 257 billion of its 257.5 billion total — are in the cerebellum, not the cortex. The elephant’s neocortex contains only 5.6 billion neurons. The human neocortex contains 16 billion. The elephant’s brain is massive, but most of its computational investment is in the cerebellar circuitry required to control that 40,000-muscle trunk and coordinate a 6,000-kilogram body through complex terrain. The elephant’s brain is not a general-purpose cognitive engine that happens to be large. It is a specialized motor-control and sensory-integration machine whose cortical allocation reflects the demands of operating, as the brain-body co-evolution post documented, the most complex appendage in the vertebrate kingdom.

    The dolphin problem

    Dolphins are the taxon that most aggressively resists clean categorization. Bottlenose dolphin brains weigh approximately 1,500-1,800 grams — comparable to or slightly larger than the human brain. Their cortical surface area is greater than the human’s. Their gyrification index is higher. They have von Economo neurons — large, spindle-shaped cells found otherwise only in great apes, elephants, and humans, associated with rapid social and emotional processing. They pass the mirror self-recognition test. They use tools (sponges on their rostra to protect against abrasion while foraging). They have individually distinctive signature whistles that function as names. They engage in coalition politics that would make a Shadowcraft case study look straightforward.

    But their cortical neuron count, estimated by Herculano-Houzel at approximately 5.8 billion, is roughly one-third of the human total. Their cortex is thin — approximately 1.5 millimeters versus the human’s 2.5 millimeters — and their cortical neuron density is lower than that of primates. The massive surface area, the dramatic gyrification, the impressive gross anatomy — all of it contains fewer cortical neurons than a human brain that weighs the same or less. What dolphins have, volumetrically, is more glial cells (the non-neuronal cells that support, insulate, and modulate neural activity) and more white matter (the myelinated axon bundles that connect distant cortical areas). Whether the glia are doing computational work, whether the white matter connectivity compensates for lower neuron counts, and whether cetacean intelligence operates on a fundamentally different computational substrate than primate intelligence are open questions that the field has not resolved.

    The dolphin’s cortex also has a peculiar developmental history: cetaceans returned to the ocean roughly 50 million years ago, and their cortical architecture shows features — like the relative expansion of paralimbic and insular cortex over associative cortex — that may reflect the sensory demands of an aquatic environment rather than the general-purpose cognitive expansion that characterizes primate brain evolution. The dolphin’s Umwelt is acoustic, three-dimensional, and social in ways the primate Umwelt is not. The cortex that serves that Umwelt may be optimized for different problems than the cortex that serves ours.

    The insect counterargument

    The comparison becomes more destabilizing when you include insects. A honeybee has approximately 960,000 neurons — total, not just cortex — in a brain that weighs less than a milligram. As the swarm intelligence post documented, a colony of bees running parallel search algorithms selects optimal nest sites 90% of the time. Individual bees navigate using path integration, sun compass, landmarks, and lateralized olfactory learning. They communicate through the waggle dance — a symbolic representation of distance and direction that constitutes, by some definitions, the only non-human referential communication system outside of primate gesture.

    A fruit fly — Drosophila melanogaster — has approximately 100,000 neurons. The FlyWire consortium published the complete connectome of the adult Drosophila brain in 2024: 139,255 neurons and approximately 50 million synaptic connections, mapped in their entirety. The fly can learn odor-reward associations, perform courtship rituals with multiple decision points, navigate complex three-dimensional environments, and — in certain conditioning paradigms — exhibit behavior that meets operational definitions of attention. A hundred thousand neurons, fully mapped, performing computations that have occupied neuroscience laboratories for decades.

    The insect brain has no cortex, no pallium, no layered structure in any mammalian sense. Its computational architecture — the mushroom bodies for learning and memory, the central complex for navigation and spatial orientation, the lateral horn for innate behavioral responses — is organized on principles that have no structural homologue in vertebrates. Yet it produces flexible behavior, learning, memory, spatial navigation, and social communication. Whatever “cognition” is, it doesn’t require a cortex.

    Why it matters for the course

    Comparative cortices is the Neurozoology lecture that demolishes the two most persistent misconceptions in popular neuroscience: that bigger brains are smarter brains, and that the neocortex is the seat of intelligence. Bigger brains are not smarter brains — the elephant proves it, and the crow proves it from the other direction. The neocortex is not the seat of intelligence — birds don’t have one, and they rival primates in flexible cognition. What matters is neuron count in the right circuits, neuron density in the computational regions, and the match between the brain’s architecture and the ecological demands the organism faces.

    The 2016 Olkowicz counting data and the 2025 Science cell-type studies together provide the framework: birds and mammals inherited the same neuronal cell types from a common ancestor 320 million years ago, arranged them differently — layers versus nuclei — and converged on similar cognitive capabilities through independent architectural strategies. The convergence is what makes the comparison scientifically valuable. Two independent experiments in how to build a thinking machine, running for 320 million years, arriving at overlapping cognitive outputs from non-overlapping structural blueprints. The conclusion is not that brains don’t matter. The conclusion is that what matters about brains — neuron count, packing density, circuit organization, and sensory-motor match — is invisible to the naked eye and has almost nothing to do with how much the organ weighs.

    This is the kind of question our Neurozoology course was built to explore — where a crow with 1.5 billion forebrain neurons packed into 7.5 grams outperforms an elephant with 5.6 billion cortical neurons spread across 4,800 grams, a dolphin’s spectacularly folded cortex contains fewer neurons than a human brain half its weight, a fruit fly with 100,000 neurons has been fully connectome-mapped and still surprises researchers with what it can do, and the two most important numbers in comparative neuroscience turn out to be neuron count and packing density — not brain size, not cortical surface area, and definitely not the metaphor about how much of our brains we supposedly use.

  • Baboon Politics: Social Hierarchies, Alliances, and Machiavellian Intelligence in Primates

    A baboon can do something that most humans find cognitively demanding and many find socially impossible: induce a more powerful individual to attack a third party on its behalf, without the powerful individual realizing it’s being used as a weapon. The maneuver is called a “protected threat.” The baboon appeases the dominant member of its group, positions itself to make a subordinate appear threatening, and maneuvers to prevent the target from doing the same thing in reverse. It’s social tool use—using another organism as an instrument to achieve a goal—and baboons master it at puberty. Chimpanzees, by comparison, don’t learn to use a stone to crack nuts until adulthood. Primates appear to manipulate social objects with more sophistication and at earlier developmental stages than physical tools, which raises an uncomfortable question about what primate brains actually evolved to do.

    The answer, according to a hypothesis that has shaped comparative cognition for nearly four decades, is politics.

    The Machiavellian intelligence hypothesis

    In the 1960s, lemur researcher Alison Jolly noticed something counterintuitive. Lemurs were terrible at manipulating objects—far worse than monkeys at the mechanical problem-solving tasks that laboratories used to measure intelligence. But their social skills were just as sophisticated as monkeys’. Jolly proposed reversing the common assumption: instead of social complexity being a product of intelligence, intelligence might be a product of social complexity. The technical challenges of foraging—finding food, processing it, remembering where it grows—might matter less than the social challenges of living in permanent groups with dozens of individuals who are simultaneously your allies, rivals, mates, competitors, and kin.

    Psychologist Nicholas Humphrey extended this in 1976. He’d watched captive monkeys handle laboratory puzzles with impressive skill, but he couldn’t find anything comparably challenging in their natural foraging environment. The hardest problem these animals faced, he argued, wasn’t physical. It was social—navigating a group where every interaction involved weighing cooperation against competition, tracking who owes what to whom, remembering past conflicts and predicting future alliances, and doing all of this with individuals who are simultaneously doing the same calculations about you.

    Frans de Waal’s 1982 book Chimpanzee Politics documented the social maneuvering of chimpanzees in terms that read like a dispatch from the Florentine court—coalition formation, strategic alliance shifts, betrayals, reconciliations, and the systematic deployment of social favors as a form of political currency. Andrew Whiten and Richard Byrne formalized the concept in 1988 as the Machiavellian intelligence hypothesis: the pressure to outmaneuver other members of your social group is a primary driver of the evolution of primate intelligence. The brain got bigger not because the environment got harder but because the social group got more complicated.

    Robin Dunbar demonstrated a correlation between primate group size and neocortex size—the most recently evolved part of the brain, and the part that expanded most dramatically in the primate lineage compared to other mammals. Larger groups require tracking more relationships, remembering more histories, predicting more behaviors. The cognitive load scales with the number of social connections, not with the complexity of the physical environment. Primates have brains roughly twice as large as expected for mammals of equivalent body size, and the Machiavellian intelligence hypothesis argues that social computation—not tool use, not foraging, not predator avoidance—is the primary reason.

    What baboons actually do

    Baboon troops are not democracies. They’re hierarchies maintained through a combination of aggression, alliance formation, grooming, and the careful management of social relationships that function as a currency more stable than any physical resource. Male baboons compete for rank through direct confrontation, but rank alone doesn’t determine reproductive success. Males who form alliances—particularly with unrelated males—can collectively outcompete higher-ranking individuals. The alpha male is not always the most reproductively successful male. The most politically connected male sometimes is.

    Female baboons form their own hierarchies, typically more stable than male hierarchies and based heavily on kinship. A female’s rank often follows her mother’s, creating lineages of dominant and subordinate families that persist across generations. High-ranking females get better access to food and water, experience lower stress hormone levels, and have offspring with higher survival rates. The fitness consequences of social rank are measurable, heritable, and real.

    Grooming is the central social technology. Baboons groom each other for hours daily, and the distribution of grooming is not random. It correlates with alliance patterns, kinship, and—critically—with what the grooming partner can offer in the immediate social marketplace. Research on wild chacma baboons found that female coalitions were not long-term strategic alliances built through reciprocal grooming over months. They were opportunistic, short-term transactions where both parties benefited immediately. Baboons don’t trade favors across time the way the Machiavellian framework originally suggested. They trade in real time, in a social marketplace where the value of a grooming partner fluctuates based on current social conditions.

    This finding—published by Silk, Cheney, Seyfarth, and others—complicated the original hypothesis significantly. The Machiavellian framework emphasized long-term strategic planning, deception, and reciprocal exchange. The field data suggested something more like a spot market: baboons assessing the current value of social partners and adjusting their behavior accordingly, not executing multi-step schemes that require remembering who did what three weeks ago.

    Tactical deception

    Byrne and Whiten documented tactical deception in baboons—behaviors designed to create false impressions in the minds of other individuals. A subordinate baboon feeding on a preferred food item while a dominant individual approaches will sometimes casually move away from the food and adopt a relaxed posture, as if it had finished eating or hadn’t been eating at all. Once the dominant passes, the subordinate returns to the food. The behavior requires, at minimum, an understanding that the dominant’s behavior is influenced by what it believes about the subordinate’s behavior—a rudimentary form of the social cognition that in humans we’d call theory of mind.

    Mountain gorillas suppress their copulation vocalizations during secretive matings with subordinate males, conducted out of sight of the dominant silverback. Both the female and the junior male remain silent—a coordinated deception that requires both parties to understand that the dominant male’s response depends on what he perceives. When these matings are discovered, the dominant male invariably attacks the female, adding a punitive dimension to the social calculation: the cost of being caught is asymmetric, falling more heavily on the female, which means the decision to mate secretly involves weighing the reproductive benefit against a gendered risk of punishment.

    Dario Maestripieri at the University of Chicago, studying rhesus macaques, found that these monkeys share with humans “strong tendencies for nepotism and political maneuvering.” His conclusion: “Our Machiavellian intelligence is not something we can be proud of, but it may be the secret of our success.” The cognitive machinery that enables a baboon to manipulate a dominant individual into attacking a rival may be the same machinery that, scaled up and elaborated over millions of years, enables a human to navigate corporate politics, negotiate a trade deal, or run for office.

    What the critics found

    The Machiavellian intelligence hypothesis has generated productive pushback. Barrett and Henzi, studying baboons and other primates in the field, argued that the hypothesis overemphasizes exploitation and deception at the expense of tolerance, coordination, and cooperation. Primate social life, they contended, is not primarily a chess game of strategic manipulation. It’s “an intricate tapestry of competition and cooperation, of aggression and reconciliation, of nonaggressive social alternatives, and of behaviors and relationships that cannot be easily categorized into simple opposites.”

    The orangutan problem is frequently cited: orangutans are largely solitary but outperform the highly social baboon on cognitive tests. If social complexity drives intelligence, the most social species should be the smartest. They’re often not. The relationship between sociality and cognition is real but messier than the original hypothesis suggested—group size correlates with neocortex size across the primate order, but individual species frequently violate the pattern.

    The current consensus treats the Machiavellian intelligence hypothesis as an important partial explanation rather than a complete theory. Social complexity is a major driver of primate brain evolution, but it’s not the only driver, and the specific form that social cognition takes—long-term strategic planning versus real-time marketplace trading, deceptive manipulation versus cooperative coordination—varies between species in ways the original framework didn’t predict.

    Why it matters beyond primatology

    The baboon troop is a small-scale version of the problem every human organization faces: how do you maintain a stable group when every member has individual interests that partially conflict with the group’s interests? The baboon’s solution set—hierarchy, coalition, grooming, deception, reconciliation, punishment, nepotism—is recognizable to anyone who has spent time in a corporate office, a political party, or a homeowners association. The specifics differ. The architecture doesn’t.

    The deeper implication is about what brains are for. If the Machiavellian intelligence hypothesis is even partially correct, the enormous human neocortex didn’t evolve primarily to solve physics problems or build tools or develop language. It evolved to navigate other humans—to predict what they’ll do, influence what they think, form alliances that advance your interests, and detect when someone is doing the same to you. The math, the engineering, the art, the philosophy—all of it may be a secondary application of cognitive hardware that was built, under evolutionary pressure, for politics.

    We cover baboon social intelligence alongside chimpanzee tool traditions, dolphin communication, and the full landscape of animal cognition across our Animal Culture & Knowledge course—including why the most revealing thing about human intelligence might be how much of it we share with a monkey that learned to weaponize its friends.