Smartest animals: neurons vs test scores in 222 species

01 Key findings

1. The top animal changes with the measure. Among 222 species, the African elephant has the heaviest brain (4.6 kg) and the most neurons (257 billion); the long-finned pilot whale has the most neurons in the cortex (37.2 billion, against 16.3 billion in humans); humans have the highest EQ (8.3).Neuron counts published 2007-2022 (Herculano-Houzel et al. 2014; Mortensen et al. 2014; Azevedo et al. 2009); n = 222 species
2. Ravens tie chimpanzees on self-control. On the cylinder task, ravens and chimpanzees both scored 100%, jackdaws 97% and New Caledonian crows 92%, level with gorillas (94%) and above dogs (79%).MacLean et al. 2014 (open data) and Kabadayi et al. 2016; 35 species, 464 animals
3. Bigger brains and more cortical neurons go with better self-control. In the 8 species with every measure, the rank correlation with the cylinder task is 0.80 for cortex or pallium neurons (95% CI 0.20 to 0.96), 0.74 for EQ and 0.73 for brain mass. The intervals overlap, so the data cannot yet single out one measure.IQ Metrics Research, October 2026; n = 8 species
4. Birds pack about 3.9 times as many neurons into the pallium as mammals put in the cortex at the same 10-gram brain (95% CI 2.9 to 5.4).IQ Metrics Research fit of 65 birds and 44 mammals (Olkowicz et al. 2016; Kverkova et al. 2022 and others)
5. Good at one test, good at another. Primate species that scored well on self-control also did well on the ManyPrimates short-term memory test (rank correlation 0.73, 95% CI 0.28 to 0.92).13 primate species in both studies (MacLean et al. 2014; ManyPrimates et al. 2022)

02 Statistics to quote

03 What is the smartest animal?

Every “smartest animal” list picks one yardstick and calls the result intelligence. We put the main yardsticks side by side for the same animals, using only numbers measured in primary studies: brain mass, brain size for body size, neuron counts and scores on a test given the same way to dozens of species. No yardstick gives an animal an IQ score: IQ tests are built and normed for people.

Brain mass

The weight of the whole brain in grams. Big bodies need big brains to run them, so on this measure the largest animals win: the elephant (4.6 kg) and the pilot whale (3.6 kg) beat humans (1.5 kg) ^{[11] [12] [4]}.

Brain size for body size (EQ)

The encephalization quotient: the brain mass divided by the mass expected for an animal of that body weight, here 0.12 x body mass^2/3 in grams ^[20]. 1 = as expected; humans score 8.3, the dog 0.99.

Neurons in the whole brain

The total count of nerve cells, measured by dissolving the brain into a soup of cell nuclei and counting the ones that carry a neuron marker (the isotropic fractionator). Most of them sit in the cerebellum, which controls movement.

Neurons in the cortex or pallium

The cells in the mammal cerebral cortex, or in the bird pallium, which does the same kind of work: memory, planning and problem solving. Some neuroscientists argue that this count explains differences in thinking ability better than brain size does ^[11].

Self-control score

How often an animal holds back from reaching straight at visible food and takes the detour that works ^[16]. It is one ability, measured the same way across dozens of species, not a measure of overall intelligence.

Figure 1

Who comes first depends on what you measure

Rank among 14 well-known animals on three measures of brain capacity (1 = highest). Blue: climbs 3 or more places from brain mass to cortex or pallium neurons; orange-red: drops 3 or more. Whole-brain neurons are in Figure 2 and Table 1.

Climbs on cortex neuronsDrops on cortex neuronsHumanOthers

Brain massBrainEQEQCortex neuronsCtx

Human 3Elephant 1Pilot whale 2Chimp 5Baboon 8Giraffe 4Brown bear 6Lion 7Dog 9Pig 10Cat 11Raven 13Macaw 12Rat 14

2 Human4 Elephant1 Pilot whale3 Chimp5 Baboon7 Giraffe12 Brown bear9 Lion10 Dog11 Pig13 Cat8 Raven6 Macaw14 Rat

EQ = brain size for body size. Cortex neurons = the cerebral cortex in mammals, the pallium in birds. Chimpanzee: one animal, one hemisphere counted and doubled.

Humans are near the top on every brain measure, but first on only one: EQ. The African elephant has the heaviest brain and 257 billion neurons, three times the human count, yet 251 billion of them (98%) sit in the cerebellum, which controls movement ^[11]. On neurons in the cortex, the long-finned pilot whale leads with 37.2 billion ^[12]. Birds climb the furthest: the blue-and-yellow macaw’s 21-gram brain ranks 12 of 14 by mass but 6 by cortex or pallium neurons (1.9 billion) ^[2].

04 Which animal has the most neurons?

The African elephant: 257 billion neurons in one adult male’s brain ^[11], against 86.1 billion in the adult human brain (four men counted) ^[3]. Counting only the cortex, the record holder is the long-finned pilot whale at 37.2 billion (neocortex, 10 whales) ^[12], then humans (16.3 billion) and the chimpanzee (about 7.4 billion, from one hemisphere) ^[5]. Our data set holds 222 species with a published count: 49 mammals, 65 birds and 108 reptiles, from 14 papers published 2007-2022.

Figure 2

Brain mass and neurons in 219 species

Each bubble is one species: brain mass across, neurons in the whole brain up. Both axes are logarithmic (each step is ten times the one before). Bubble area = body mass. At the same brain mass, birds sit above mammals and reptiles below.

PrimatesOther mammalsBirdsReptiles

Body mass1k100k1M

Neurons in the whole brain (log scale)

1M10M100M1B10B100B

African elephantGiraffeBrown bearCommon ostrichNile crocodileHumanDogCommon ravenBlue-and-yellow macawHouse mouseGoldcrest

0.010.11101001000

Brain mass (grams, log scale)

Body mass keys: 1k = 1 kg, 100k = 100 kg, 1M = 1 tonne (grams).

Table 1

The 20 animals with the most neurons in the cortex or pallium

Cortex in mammals, pallium in birds (the forebrain region that does the same work). Millions of neurons; select a column to sort.

Animal	Cortex or pallium, millions	Whole brain, millions	Brain, g	Group	Source
Long-finned pilot whale	37,200	–	3608.2	Mammal	[12]
Human	16,300	86,100	1508.0	Primate	[3]
Chimpanzee	7,400	–	344.0	Primate	[5]
African elephant	5,590	257,040	4618.6	Mammal	[11]
Yellow baboon	2,880	10,950	151.2	Primate	[7]
Blue-and-yellow macaw	1,918	3,136	20.7	Bird	[2]
Giraffe	1,670	11,210	528.0	Mammal	[10]
Bonnet macaque	1,660	3,780	61.5	Primate	[7]
Eurasian eagle-owl	1,328	1,898	15.8	Bird	[1]
Kea	1,282	2,149	13.6	Bird	[2]
Snowy owl	1,270	1,808	17.8	Bird	[1]
Common raven	1,204	2,171	14.1	Bird	[2]
Tawny owl	1,153	1,581	8.9	Bird	[1]
Sulphur-crested cockatoo	1,136	2,122	10.1	Bird	[2]
Capuchin monkey	1,100	3,691	52.2	Primate	[6]
Grey parrot	850	1,566	8.8	Bird	[2]
Rook	821	1,509	8.4	Bird	[2]
Long-tailed macaque	801	3,440	46.2	Primate	[7]
Greater kudu	793	6,090	308.5	Mammal	[10]
Long-eared owl	673	991	5.4	Bird	[1]

For scale: the whole nervous system of the worm C. elegans has 302 neurons ^[31] and the brain of a fruit fly 139,255 ^[32]. The 86 billion human figure replaced an older “100 billion” that nobody had counted: see our fact-check of viral brain numbers.

Table 2

From 302 neurons to 257 billion

Whole nervous systems and brains counted cell by cell or with the same isotropic-fractionator method as the rest of this study.

Animal	Neurons	What was counted
Nematode worm (C. elegans) [31]	302	whole nervous system, adult hermaphrodite
Fruit fly (Drosophila) [32]	139,255	whole brain, one adult female
House mouse [8]	67,870,000	whole brain
Common raven [2]	2,170,680,000	whole brain
Dog [9]	2,252,690,000	whole brain, mean of two dogs
Human [3]	86,100,000,000	whole brain, four men
African elephant [11]	257,040,000,000	whole brain, one male

05 Why do small bird brains hold so many neurons?

Bird neurons are smaller and packed more tightly. The median songbird brain holds 218,000 neurons per milligram and the median parrot 198,000, against 78,000 in primates and 63,000 in other mammals. In the pallium alone the gap is wider: about 143,000 neurons per milligram in songbirds and 157,000 in parrots, against 24,000 in the primate cortex.

Figure 3

How tightly brains are packed with neurons

Neurons per milligram of brain, in thousands, for every species with a whole-brain count. Box = the middle half of each group, line = the median species, whiskers = lowest to highest; each dot is one species.

Middle halfMedianLowest to highestOne species

Songbirds13 species218k

Parrots11 species198k

Other birds41 species110k

Primates10 species78k

Other mammals36 species63k

Reptiles108 species48k

0k100k200k300k400k500k

Thousand neurons per milligram of brain.

Fitted across all 65 birds and 44 mammals with both counts, a 10-gram bird brain has about 3.9 times as many pallial neurons as a 10-gram mammal brain has in its cortex (95% CI 2.9 to 5.4; at 1 gram, 3.1 times). That is how a raven, with a 14.1 g brain, has 1.2 billion pallial neurons, more than the 528 million in the cortex of a dog whose brain weighs 86.5 g ^{[2] [9]}. Reptile brains are the least dense of the three classes ^[1].

06 Which animals score highest on intelligence tests?

Few tests have been given the same way to many species. The largest is a 2014 study in which researchers at many labs tested 567 animals of 36 species on two self-control tasks ^[16]; its data are open ^[19]. In the cylinder task an animal learns to take food from an opaque tube, then faces a see-through one: reaching straight at the food hits the wall. In the A-not-B task food is hidden twice in one place, then moved to another while the animal watches.

Figure 4

Self-control test scores of 35 species

Cylinder task: food sits inside a see-through tube open at both ends. The animal has to go round to an open end instead of reaching straight at the food. Score = share of 10 test trials done right, averaged over each species' animals (464 animals in all). The three crows (orange) were tested later with the same method.

Chimpanzee100%

Common raven100%

Orangutan99%

Jackdaw97%

Capuchin monkey96%

Bonobo95%

Coyote95%

Gorilla94%

New Caledonian crow92%

Rhesus macaque80%

Dog79%

Gray wolf77%

Western scrub jay77%

Olive baboon76%

Ruffed lemur70%

Mongolian gerbil69%

Ring-tailed lemur68%

Hamadryas baboon68%

Fox squirrel67%

Red-bellied lemur64%

Golden-headed lion tamarin63%

Mongoose lemur59%

Eurasian jay58%

Zebra finch52%

Aye-aye51%

Black lemur51%

Orange-winged amazon51%

Brown lemur43%

Coquerel's sifaka36%

Golden snub-nosed monkey35%

Squirrel monkey34%

Pigeon (White Carneau)32%

Common marmoset32%

Song sparrow26%

Swamp sparrow26%

Great apes and crows lead; small songbirds trail. Chimpanzees scored 100%, orangutans 99%, bonobos 95%. Ravens, jackdaws and New Caledonian crows, tested in 2016 with the same method, scored 100%, 97% and 92% ^[17]. The A-not-B task ranks some species very differently: Asian elephants scored 0 of 7 ^[19], although elephants are among the few animals that have passed the mirror test.

Species that do well on one test tend to do well on another. Across the 13 primate species tested both on the cylinder task and in the ManyPrimates short-term memory study (421 animals, 41 species in all) ^[18], the rank correlation is 0.73 (95% CI 0.28 to 0.92).

07 Does a bigger brain make a smarter animal?

Only 10 species have both a neuron count and a cylinder-task score, and 8 of them also have a cortex or pallium count: Capuchin monkey, Chimpanzee, Dog, Zebra finch, Eurasian jay, Jackdaw, Common raven, Rock pigeon. On those 8, all three brain measures track self-control: neurons in the cortex or pallium (rank correlation 0.80, 95% CI 0.20 to 0.96), brain size for body size (0.74) and brain mass (0.73). Whole-brain neurons (0.43, 9 species) and neuron density (0.10) show weaker links.

Figure 5

Which brain measure tracks self-control best?

Rank correlation (Spearman) between each brain measure and the species' self-control score, with its 95% confidence interval. +1 = the bigger the measure, the better the score; 0 = no link. First view: the same 8 species for every measure (the fair comparison); the others use every species that has the measure, so the species differ from row to row.

One brain measure (size = species)95% confidence interval

Choose a viewCylinder task, the same 8 speciesCylinder task, every species with the measure (10 in all)A-not-B task, every species with the measure (8 in all)

Neurons in the cortex or pallium8 species0.800.20–0.96

Brain size for body size (EQ)8 species0.740.05–0.95

Brain mass8 species0.730.03–0.95

-1-0.500.51

Spearman rank correlation with the test score, -1 to +1; 0 = no link

Read the intervals before the ranking: with 8 species they overlap almost completely, so the data cannot say which measure matters most. Dropping any one species moves the cortex correlation between 0.71 and 0.92; over all 10 species, brain mass gives 0.49 and EQ 0.32. On the one-trial A-not-B task (8 species) brain mass comes first (0.81, 95% CI 0.22 to 0.97) and neuron density runs the other way (-0.89, 7 species): the dog, with the least tightly packed brain in that group, scored highest, and the Eurasian jay, with the most tightly packed, second lowest. MacLean and colleagues, with brain volumes for all 36 species and a method that allows for shared ancestry, found that absolute brain size predicted self-control better than brain size for body size ^[16].

Figure 6

How the measures move together

Spearman rank correlation for each pair, over every species with both values: 107 to 221 species for the brain measures, 8 to 10 for self-control. +1 = always rise together, 0 = no link, -1 = one rises as the other falls.

-1 (opposite)+1 (move together)

BodyBodyBrainBrainEQEQAll neuronsAll NCortexCtxDensityDens.Brain mass+0.78Brain size for body size (EQ)+0.10+0.68Neurons in the whole brain+0.64+0.97+0.78Neurons in the cortex or pallium+0.59+0.80+0.64+0.93Neurons per milligram of brain-0.46+0.07+0.62+0.24-0.13Self-control (cylinder task)+0.46+0.49+0.32+0.43+0.80+0.10

08 How does each animal's brain compare?

Pick an animal to see where it stands on five brain measures against 27 other well-known animals. The raven sits below the middle on brain mass but above it on cortex neurons and density; the brown bear is the reverse, a heavy brain with few cortical neurons.

Figure 7

Pick an animal: its brain on five measures

Each score is the share of the other 27 animals in this list that have a lower value on that measure (0 to 100). EQ = brain size for body size; cortex neurons = cortex in mammals, pallium in birds; density = neurons per milligram of brain. The dashed shape is the middle animal, 50 on every measure.

Common ravenMiddle animal

Choose an animalHumanAfrican elephantYellow baboonLong-tailed macaqueCapuchin monkeyDogCatLionBrown bearRaccoonPigGiraffeRabbitRatHouse mouseCommon ravenRookEurasian magpieJackdawGrey parrotBlue-and-yellow macawKeaRock pigeonRed junglefowl (wild chicken)Snowy owlBarn owlEmuCommon ostrich

Brain mass41Middle 50EQ59Middle 50All neurons59Middle 50Cortex neurons74Middle 50Density78Middle 50

09 Which animals pass the mirror test?

The mirror test asks whether an animal recognises its own reflection. Few species pass, and results within a species vary: one of three Asian elephants passed ^[26], and jackdaws, close relatives of the magpies that passed, did not ^{[27] [28]}. A fish, the cleaner wrasse, passed a modified version ^[30]. Of the animals in the table, only humans, chimpanzees, magpies, jackdaws and pigeons also have neuron counts in our data.

Table 3

The mirror test, in the original studies

An animal is marked where it can only see the mark in a mirror. Touching or rubbing the mark in front of the mirror counts as a pass.

Animal and study	Result in the study
Human children Amsterdam 1972 [24]	Pass, before age two
Chimpanzee Gallup 1970 [22]	Pass
Orangutan Suarez and Gallup 1981 [23]	Pass
Gorilla Suarez and Gallup 1981 [23]	No pass in that study
Monkeys Gallup 1970 [22]	No pass
Bottlenose dolphin Reiss and Marino 2001 [25]	Pass, 2 of 2
Asian elephant Plotnik et al. 2006 [26]	1 of 3 passed
Eurasian magpie Prior et al. 2008 [27]	2 of 5 touched the mark
Jackdaw Soler et al. 2014 [28]	0 of 9 passed
Rock pigeon Epstein et al. 1981 [29]	3 of 3, after training
Cleaner wrasse (a fish) Kohda et al. 2019 [30]	3 of 4 scraped the mark

10 How can teachers use this data?

The CSV and every figure may be reused with credit under CC BY 4.0, ready for a biology, psychology or neuroscience class. Four activities:

1. Rank it three ways. Sort the CSV by brain mass, then EQ, then cortex or pallium neurons, and track five animals. Which one moves the most, and why?
2. Work out an EQ. A dog has an 86.5 g brain and a 19.7 kg body. Compute 0.12 x 19,700^2/3 = 87.5 g, then 86.5 / 87.5 = 0.99. Try it for a raven.
3. Correlation is not cause. Take the 8 species named above Figure 5, rank them by brain mass and by test score, and compute a rank correlation by hand. Then ask what else, such as diet or family tree, could explain the link.
4. Design a fair test. A cylinder suits a crow and a chimpanzee, but what about an elephant or a fish? Compare the A-not-B result for elephants with their mirror-test result.

Our animal guides go deeper on single species: crows and ravens, parrots, chimpanzees, gorillas, dolphins, elephants, dogs, cats, pigs, horses, octopuses.

11 How we built the data set

1. 01

   Collect the counts

   Every neuron count in the data set comes from a primary paper that counted whole brains with the isotropic fractionator (or, for the pilot whale and the chimpanzee, stereology and flow fractionation), read from the paper’s own tables: 14 papers, 2007-2022. We did not copy any secondary list.

2. 02

   Make them comparable

   Whole brain without the olfactory bulbs; cortex with the hippocampus, as most of these papers count it. Bird pallium = telencephalon minus the subpallium share in Olkowicz et al. ^[2]. One-hemisphere counts are doubled (marked in the CSV).

3. 03

   Add body mass and EQ

   Body mass from the same paper where it gives one; otherwise (human, African elephant, pilot whale, squirrel monkey) the PanTHERIA species average ^[15]. EQ = brain / (0.12 x body^2/3) ^[20].

4. 04

   Add the tests

   Species means from MacLean et al.’s open data, one row per animal ^[19], computed as the paper defines them; they match the published means. Corvid scores from Kabadayi et al. ^[17]; short-term memory from the ManyPrimates trial data ^[18].

5. 05

   Join by species name

   Tests and counts are joined only when the scientific name matches. The one exception is the squirrel monkey, named only at genus level in the test file (flagged in the CSV).

6. 06

   Check every number

   A script confirms that each typed number appears verbatim in its paper’s table; birds and reptiles are read straight from the papers’ files. 95% intervals for rank correlations use Fisher’s z with the Fieller-Hartley-Pearson variance ^[21]; the bird and mammal gap uses 4,000 bootstrap resamples.