Neanderthal brains were, on average, slightly larger than modern human brains in absolute volume. That fact surprises most people, and for good reason: it cuts against the assumption that our species won some evolutionary contest by having the biggest brain on the block. But raw volume turns out to be one of the least interesting ways to compare the two. Once you account for body size, internal proportions, and the shape of the braincase itself, the picture flips in ways that help explain why Homo sapiens and Neanderthals ended up on such different trajectories.
Bigger Skulls, Smaller Adjusted Brains
Neanderthal endocranial capacity, the internal volume of the braincase, averaged somewhere around 1,400 to 1,600 cubic centimeters. Modern humans typically fall between 1,200 and 1,500 cc. So in raw terms, Neanderthals often had us beat. A recent reassessment confirmed that Neanderthal endocrania are “different in shape, though slightly larger in size than modern humans on average.”1PubMed Central. Neanderthal brain and cognition reconsidered
That advantage shrinks and eventually reverses when you factor in body mass. Neanderthals were stocky, heavily muscled, and adapted to cold European climates. A larger body demands a larger brain just to handle basic sensory and motor functions, regardless of how much capacity is left over for higher cognition. When researchers scaled brain mass against body mass, Neanderthals came out slightly smaller than early anatomically modern humans in relative terms. The major leap in encephalization within the genus Homo had already happened during the Middle Pleistocene, long before either species reached its final form.2PubMed. Body mass and encephalization in Pleistocene Homo
There is another adjustment that matters even more. Neanderthals had significantly larger eye sockets than contemporary modern humans, which implies larger eyeballs and a correspondingly larger visual processing system in the brain. When researchers accounted for both greater body mass and the extra neural tissue devoted to vision, Neanderthals ended up with significantly smaller adjusted endocranial capacities than the modern humans living alongside them.3PubMed Central. New insights into differences in brain organization between Neanderthals and anatomically modern humans In other words, more of the Neanderthal brain was spoken for before you even got to the regions involved in planning, social reasoning, or language.
A Globe Versus a Football
Hold a modern human skull next to a Neanderthal skull and the shape difference is obvious even to a non-expert. Ours is round, almost spherical. Theirs is elongated front to back, lower in profile, and wider at the rear. This distinction, often called globularization, is not just an aesthetic difference. It reflects how the underlying brain tissue is packed and, by extension, which regions have expanded most.
By about 300,000 years ago, early Homo sapiens already had brains that fell within the modern size range. But those early skulls were still somewhat elongated. The characteristically globular shape we carry today did not fully appear until somewhere between 100,000 and 35,000 years ago, evolving gradually within our own lineage.4PubMed Central. The evolution of modern human brain shape That means the shape change happened independently of the size increase. Something was reorganizing internally, even though total volume was staying roughly the same.
Neanderthals never made that shift. Their braincases retained the elongated form throughout their existence. Because brain shape reflects the relative proportions of different lobes, this matters for understanding what each species’ brain was optimized to do.
Where the Space Went
The visual system story is worth unpacking a bit more. The idea that Neanderthals devoted extra brain real estate to processing visual information was originally proposed based on their large orbits. Some researchers interpreted this as an adaptation to low-light conditions at high latitudes, since modern humans living at similar latitudes today also tend to have slightly larger visual cortices. But fossil evidence from southern Neanderthals in Spain complicated that explanation. Specimens from the El Sidrón site showed similarly large primary visual cortex dimensions, even though these individuals lived at lower latitudes with more ambient light. That finding suggests the large visual system was a general Neanderthal trait rather than a cold-climate adaptation that only showed up in the north.5PubMed Central. Primary visual cortex in neandertals as revealed from the occipital remains from the El Sidrón site, with emphasis on the new SD‐2300 specimen
While the visual system was oversized relative to ours, the cerebellum told the opposite story. Computational reconstructions of Neanderthal brains showed that their cerebellum, particularly the posterior hemispheres, was significantly smaller in relative terms compared to both early and modern Homo sapiens.6Scientific Reports. Reconstructing the Neanderthal brain using computational anatomy The cerebellum has long been associated with motor coordination, but its role is far broader. In modern humans, cerebellar volume correlates with performance on tasks involving attention, cognitive flexibility, language comprehension, language production, working memory, and episodic memory. A smaller cerebellum in Neanderthals could have meant reduced capacity across several of those cognitive domains.
The parietal lobe, the upper-rear region of the brain involved in spatial reasoning, tool use, and integrating sensory information, also differed between the two species. Modern humans display taller and more anteroposteriorly extended parietal lobes, with slightly larger surface areas in regions that include the supramarginal gyrus and angular gyrus. Those areas are linked to language processing, number sense, and attention. Still, the ranges overlap between species, so the difference is one of degree rather than a hard boundary.7PubMed. A morphometric comparison of the parietal lobe in modern humans and Neanderthals
Same Starting Size, Different Growth Patterns
One of the more striking findings from the last two decades is that Neanderthal and modern human babies started life with nearly identical brain sizes. Estimates from Neanderthal neonates place brain volume around 400 to 430 cc at birth, right in line with modern human newborns.8Current Biology. Brain development after birth differs between Neanderthals and modern humans The braincase shape was also similar at birth, with Neanderthals only slightly more elongated. So whatever made the adult brains so different was happening during postnatal development, not in the womb.
The growth trajectories diverged in two ways. First, Neanderthal infants appear to have grown their brains faster in early infancy, which contributed to their larger adult brain size. But that faster growth did not mean they finished developing sooner. Researchers concluded that Neanderthal life history was similarly slow-paced, or possibly even slower, than in modern humans, because growing a large brain at high rates demands a large, late-maturing mother.9PubMed Central. Neanderthal brain size at birth provides insights into the evolution of human life history
Earlier work had suggested that Neanderthals followed a more primitive mode of brain development, closer to chimpanzees than to us. But a study using an expanded sample of Neanderthal infants found that their endocranial development during the first two years of life actually looked largely similar to modern humans, challenging the idea that our postnatal brain development is uniquely derived.10PubMed. Brain development is similar in Neanderthals and modern humans The overall picture is messier than early narratives suggested. Both species shared a broadly similar developmental playbook, but with differences in rate and final shape that added up to real consequences in adulthood.
Genetic Differences That Changed the Wiring
We cannot scan a living Neanderthal brain, but we can now do something almost as informative: grow miniature brain-like structures in the lab using Neanderthal gene variants. Two experiments in particular have drawn attention.
The first involves a gene called TKTL1. The modern human version of this gene differs from the Neanderthal version by a single amino acid substitution. When researchers tested both versions in developing mouse and ferret brain tissue, and in human brain organoids that had been genome-edited to carry one or the other, the modern human variant increased the abundance of a particular type of neural progenitor cell that generates more cortical neurons. The Neanderthal variant did not produce the same boost.11PubMed. Human TKTL1 implies greater neurogenesis in frontal neocortex of modern humans than Neanderthals The implication is that modern humans may produce more neurons in the frontal neocortex than Neanderthals did, even if total brain size was similar or smaller.
The second experiment focused on NOVA1, a gene involved in regulating how neurons develop and form connections. When researchers reintroduced the archaic (Neanderthal-like) version of NOVA1 into cortical organoids, those organoids developed more slowly, had different surface complexity, and showed altered electrical signaling patterns compared to organoids with the modern human version.12PubMed Central. Reintroduction of the archaic variant of NOVA1 in cortical organoids alters neurodevelopment These are tiny, simplified brain-like structures grown in a dish, so extrapolating to behavior is speculative. But the results do suggest that even small genetic changes between the two species could have produced meaningful differences in how neurons wired themselves together.
What Neanderthal Brains Could Actually Do
The temptation when comparing brain anatomy is to treat Neanderthals as cognitively inferior. The archaeological record makes that harder to sustain than it used to be. Between about 160,000 and 40,000 years ago, the number and diversity of complex Neanderthal behaviors increased steadily: intentional burials, use of pigments, modified raw materials, composite tool-making, and body modification all appear in the record with growing frequency.13Cambridge Archaeological Journal. Behavioural Complexity in Eurasian Neanderthal Populations: a Chronological Examination of the Archaeological Evidence
A persistent puzzle is why Neanderthal art and symbolic expression appear far less often than in contemporary modern human populations. One recent analysis argued that the explanation is not cognitive ability. Instead, the low frequency of Neanderthal art is better explained by differences in social connectivity and population density. Neanderthals lived in smaller, more scattered groups, which limited the cultural transmission needed for symbolic traditions to accumulate and persist.14PubMed Central. Art beyond cognition: reframing Neanderthal art through social connectivity and cultural transmission A brain capable of creating art does not guarantee a social network capable of sustaining artistic traditions.
Speech is another area where the gap looks narrower than once thought. Endocranial casts of Neanderthal skulls show development in brain areas associated with speech production that resembles the modern human pattern.15PubMed. The language capability of Neanderthal man More compellingly, detailed micro-biomechanical analysis of the Kebara 2 Neanderthal’s hyoid bone, a small bone in the throat critical to speech, found that its internal structure and mechanical properties were consistent with use in speech production. The bone did not just resemble a modern human hyoid on the outside; it had been subjected to similar physical stresses, suggesting similar functional use.16PubMed Central. Micro-Biomechanics of the Kebara 2 Hyoid and Its Implications for Speech in Neanderthals This does not prove that Neanderthals spoke the way we do, but it makes the case that they had both the neural and anatomical equipment for some form of spoken communication.
Fueling a Large Brain
A brain this large, whether Neanderthal or modern human, is metabolically expensive. The brain consumes a disproportionate share of the body’s energy even at rest. Neanderthals, with their large brains and physically demanding lifestyles, would have required substantial caloric intake to keep everything running. Recent work on Neanderthal dietary requirements has emphasized that they likely needed high amounts of carbohydrates to support both brain metabolism and their active hunting-and-foraging existence.17PubMed. Reconstructing Neanderthal diet: The case for carbohydrates This challenges the older image of Neanderthals as pure meat-eaters and aligns with dental calculus evidence showing they consumed starchy plants, sometimes cooked.
Brain Lateralization and the Senses
Modern human brains are strongly lateralized, meaning the left and right hemispheres are asymmetric in ways tied to handedness, language, and spatial processing. About nine out of ten people are right-handed, reflecting a degree of left-hemisphere dominance that appears to be a relatively recent evolutionary development. Neanderthals and their ancestors show signs of lateralization too, but to a lesser degree. Analysis of endocranial asymmetries and hand-preference markers in Middle Pleistocene specimens from the Sima de los Huesos site found that while similarities existed in the pattern of brain asymmetry, the proportion of right-handers was lower than in modern populations, suggesting a different or reduced degree of brain lateralization.18Quaternary International. Brain asymmetries and handedness in the specimens from the Sima de los Huesos site (Atapuerca, Spain)
Beyond vision, the sensory landscape of the Neanderthal brain differed in subtler ways. Modern humans carry about 850 olfactory receptor genes, but roughly 55 percent of them are nonfunctional. Comparative analysis of the Neanderthal and Denisovan genomes revealed additional olfactory receptor losses in both species that differ from the modern human pattern: ten in Neanderthals and eight in Denisovans. Combined with the cranial shape differences that altered nasal and orbital proportions, these findings point to meaningfully different sensory arrangements between the species.19PubMed Central. Loss of olfactory receptor function in hominin evolution Neanderthals were not simply seeing the same world with a bigger visual system; their entire sensory profile was tuned differently.
How Reliably Can We Read a Fossil Brain?
All of these comparisons rest on a method with inherent limitations. We do not have preserved Neanderthal brains. What we have are endocasts, impressions of the interior of the braincase, either natural (filled with sediment over millennia) or virtual (created from CT scans). From these, researchers try to identify the positions of sulci and gyri, the folds and ridges of the cortical surface. That process is harder than it sounds. One study examining how well experts could identify sulcal imprints on endocasts found that while researchers perceived the imprints with reasonably high accuracy, correctly labeling them remained a challenge, especially for extinct species where there is no living brain to verify against.20PubMed Central. What do brain endocasts tell us? A comparative analysis of the accuracy of sulcal identification by experts and perspectives in palaeoanthropology
Computational approaches have improved the situation. By mapping modern human brain anatomy onto Neanderthal endocasts using statistical models, researchers can estimate where specific brain regions would have fallen. This method is parsimonious in the sense that it uses the best available proxy, but it still assumes that the modern human brain map is a reasonable stand-in for the ancestral layout.6Scientific Reports. Reconstructing the Neanderthal brain using computational anatomy Any conclusion about Neanderthal regional brain proportions carries this built-in uncertainty. The broad strokes, like total volume, overall shape, and the relative size of major structures like the cerebellum, are more secure than fine-grained claims about specific cortical areas.
Before Either Species Existed
Placing the Neanderthal-modern human comparison in evolutionary context helps keep things in proportion. Homo erectus, the shared ancestor or close relative of both lineages, had an average brain size of about 950 cc. By the Middle Pleistocene, hominins from both Africa and Europe had reached an average of about 1,230 cc.21PubMed. Homo erectus and Middle Pleistocene hominins: brain size, skull form, and species recognition Both Neanderthals and modern humans then pushed past that figure independently, arriving at overlapping adult brain sizes through different developmental and structural strategies. The parallel expansion suggests that large brains were advantageous across a range of environments and lifestyles, but the way each species filled that volume with functional tissue ended up being quite different. That internal organization, not the number on the measuring tape, is where the real story of these two brains diverges.