This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)(Learn how and when to remove this template message)
The size of the brain is a frequent topic of study within the fields of anatomy and evolution. Brain size is sometimes measured by weight and sometimes by volume (via MRI scans or by skull volume). Neuroimaging intelligence testing can be used to study the size of the brain in males and females. One question that has been frequently investigated is the relation of brain size to intelligence.
The balance of findings for human-brain size, largely based on participants of European ancestry, indicates an average adult brain volume of 1260 cubic centimeters (cm3) for men and 1130 cm3 for women. There is, however, substantial variation; a study of 46 adults aged 22–49 years and of mainly European descent found an average brain volume of 1273.6 cm3 for men, ranging from 1052.9 to 1498.5 cm3, and 1131.1 cm3 for women, ranging from 974.9 to 1398.1 cm3.
The right cerebral hemisphere is typically larger than the left, whereas the cerebellar hemispheres are typically closer in size. The adult human brain weighs on average about 1.5 kg (3.3 lb). In men the average weight is about 1370 g and in women about 1200 g. The volume is around 1260 cm3 in men and 1130 cm3 in women, although there is substantial individual variation.
From early primates to hominids and finally to Homo sapiens, the human brain has continued to grow. The increase in brain size stopped with neanderthals. Since then, the average brain size has been shrinking over the past 28,000 years. The cranial capacity has decreased from around 1,550 cm3 to around 1,440 cm3 in males while the female cranial capacity has shrunk from around 1,500 cm3 to around 1,240 cm3. Other sources with bigger sample sizes of modern Homo sapiens find approximately the same cranial capacity for males but a higher cranial capacity of around 1330 cm3 in females.
In recent years, experiments have been conducted drawing conclusions to brain size in association to the gene mutation that causes MCPH, a neural developmental disorder that affects cerebral cortical volume.
Subsequently, there has been a shrinking over the past 28,000 years. The male brain has decreased from 1,500 cm3 to 1,350 cm3 while the female brain has shrunk by about the same relative proportion. For comparison, Homo erectus, a relative of humans, had a brain size of 1,100 cm3. However, the smaller Homo floresiensis, with a brain size of 380 cm3, a third of that of their proposed ancestor Homo erectus, used fire, hunted, and made stone tools at least as sophisticated as those of Homo erectus. The Neanderthals had a slightly larger brain in comparison to modern humans, perhaps due to larger visual systems. The notion "As large as you need and as small as you can" has been used to summarize the opposite evolutionary constraints on human-brain size. But it is also argued that, with the advance of human technology and agriculture, the evolutionary pressure on intelligence (i.e. the ability to comprehend and manipulate the environment through the development of primitive technology) was partially relieved for coming generations. Following the initial major advances in tool crafting, weaponry, building construction and agriculture, humanity experienced a population boom as the circumstances that they were forced to survive under had been tremendously relieved by past generations. War, pathogens, and other threats overcame individual survival, whereupon evolutionary demand on intelligence was diminished and a subsequent decline was recordable. Changes in the size of the human brain during evolution have been reflected in changes in the ASPM and microcephalin genes.
A number of studies have found correlation between variation in brain size in cranial capacity and geographic ancestry in humans. This variation in cranial capacity is believed to be primarily caused by climatic adaptation that favor large round heads in colder climates because they conserve heat and slender heads in warm climates closer to the equator (See Bergmann's rule and Allen's rule).
The largest study done on the subject of geographic variation in brain size is the 1984 study Brain Size, Cranial Morphology, Climate, and Time Machines. The study found that human brain size varied with latitude of biogeographic ancestry. The relationship between latitude and cranial size is described in the study as an example of Bergmann’s principle that crania are more spherical in cold climates because mass increases relative to surface area to conserve core temperatures and behaves independently of "race".
Overall, adult brain volumes have remained consistent according to age and sex. Nevertheless[contradictory], underlying structural asymmetries do exist. A baby's brain at birth averages 369 cm3 and increases, during the first year of life, to about 961 cm3, after which the growth rate declines. As children develop, brain size varies between sexes and among individuals. Brain volume peaks at the 40 years, after which it begins to decline by 5% per decade, speeding up at around 70 years. The average brain weight in adult males is 1,345 grams; in adult females, 1,222 grams. Males have been found to have, on average, greater cerebral, cerebellar, and cerebral cortical lobar volumes, except possibly left parietal. The sex differences in size are found in specific brain regions. Studies generally indicate that, in men, the amygdala and hypothalamus are larger, while, in women, the caudate nucleus and the hippocampus are larger. When covaried for intracranial volume, height, and weight, the balance of Kelly (2007) indicates that women have a higher percentage of gray matter, whereas men have a higher percentage of white matter and cerebrospinal fluid. There is high variability among individuals in these studies, however.
However, Yaki (2011) found no statistically significant gender differences in the gray matter ratio for most ages (grouped by decade), except in the 3rd and 6th decades of life in the sample of 758 women and 702 men aged 20–69. The average male in their third decade (ages 20–29) had a significantly higher gray matter ratio than the average female of the same age group. In contrast, among subjects in their sixth decade, the average woman had a significantly larger gray matter ratio, though no meaningful difference was found among those in their 7th decade of life.
Total cerebral and gray matter volumes peak between 10 and 20 years (earlier in girls than in boys), whereas white matter and ventricular volumes increase. There is a general pattern in which neural development peaks in childhood and declines in adolescence, a process known as synaptic pruning. Consistent with findings in adults, average cerebral volume is approximately 10% larger in boys than in girls. However, such differences should not be construed as imparting any sort of functional advantage or disadvantage; gross structural measures may not reflect functionally relevant factors such as neuronal connectivity and receptor density. Moreover, brain volumes, even in narrowly defined groups (e.g. children of the same age), may vary by as much as 50%. Young girls have, on average, larger hippocampi, whereas young boys have larger amygdalas.
Significant dynamic changes in brain structure take place throughout adulthood, with substantial variation between individuals. In later decades, men show greater volume loss in whole brain volume and in the frontal lobes, and temporal lobes, whereas in women there is increased volume loss in the hippocampi and parietal lobes. Men show a steeper decline in global gray matter volume, although in both sexes it varies by region with some areas exhibiting little or no age effect. Overall white matter volume does not appear to decline with age, although there is variation among brain regions.
J. Philippe Rushton published multiple studies claiming that average brain size was lowest in blacks ("Negroids") and highest in Asians ("Mongoloids"), with whites ("Caucasoids") in between the two. His work in this area has been criticized for relying on flawed studies, for failing to consider explanations other than genetics for the observed differences, and for ignoring other studies with contradictory conclusions. Nathan Brody has also argued that the evidence regarding racial differences in brain size is not conclusive, and that even if one accepts it, this difference does not support a genetic hypothesis regarding racial differences in intelligence.
According to a study published by Smith and Beals im 1990, based on measurements of approximately 20,000 crania from 87 populations worldwide, arctic indigenous peoples and East Asians have the biggest brains in the world, with an average volume of 1,443 cm3 and 1,416 cm3 respectively, followed by Europeans with an average volume of 1,369 cm3. Among the Europeans, Italians have the biggest brains (1,411 cm3).
Adult twin studies have indicated high heritability estimates for overall brain size in adulthood (between 66% and 97%). The effect varies regionally within the brain, however, with high heritabilities of frontal lobe volumes (90-95%), moderate estimates in the hippocampi (40-69%), and environmental factors influencing several medial brain areas. In addition, lateral ventricle volume appears to be mainly explained by environmental factors, suggesting such factors also play a role in the surrounding brain tissue. Genes may cause the association between brain structure and cognitive functions, or the latter may influence the former during life. A number of candidate genes have been identified or suggested, but they await replication.
Studies demonstrate a correlation between brain size and intelligence, with larger brains predicting higher intelligence. It is however not clear if the correlation is causal. The majority of MRI studies report moderate correlations around 0.3 to 0.4 between brain volume and intelligence. The most consistent associations are observed within the frontal, temporal, and parietal lobes, the hippocampus, and the cerebellum, but only account for a relatively small amount of variance in IQ, which suggests that while brain size may be related to human intelligence, other factors also play a role. In addition, brain volumes do not correlate strongly with other and more specific cognitive measures. In men, IQ correlates more with gray matter volume in the frontal lobe and parietal lobe, which is roughly involved in sensory integration and attention, whereas in women it correlates with gray matter volume in the frontal lobe and Broca's area, which is involved in language.
Research measuring brain volume, P300 auditory evoked potentials, and intelligence shows a dissociation, such that both brain volume and speed of P300 correlate with measured aspects of intelligence, but not with each other. Evidence conflicts on the question of whether brain size variation also predicts intelligence between siblings, with some studies finding moderate correlations and others finding none. A recent review by Nesbitt, Flynn et al. (2012) point out that crude brain size is unlikely to be a good measure of IQ, for example brain size also differs between men and women, but without well documented differences in IQ.
A discovery in recent years is that the structure of the adult human brain changes when a new cognitive or motor skill, including vocabulary, is learned. Structural neuroplasticity (increased gray matter volume) has been demonstrated in adults after three months of training in a visual-motor skill, with the qualitative change (i.e. learning of a new task) appearing more critical for the brain to change its structure than continued training of an already-learned task. Such changes (e.g. revising for medical exams) have been shown to last for at least 3 months without further practicing; other examples include learning novel speech sounds, musical ability, navigation skills and learning to read mirror-reflected words.
The largest brains are those of sperm whales, weighing about 8 kg (18 lb), and killer whales, weighing about 12–15 lb (5.4–6.8 kg). An elephant's brain weighs just over 5 kg (11 lb) and a bottlenose dolphin's 1.5 to 1.7 kg (3.3 to 3.7 lb), whereas a human brain is around 1.3 to 1.5 kg (2.9 to 3.3 lb). Brain size tends to vary according to body size. The relationship is not proportional, however; the brain-to-body mass ratio varies. The largest ratio found is in the shrew. Averaging brain weight across all orders of mammals, it follows a power law, with an exponent of about 0.75. There are good reasons to expect a power law: for example, the body-size to body-length relationship follows a power law with an exponent of 0.33, and the body-size to surface-area relationship follows a power law with an exponent of 0.67. The explanation for an exponent of 0.75 is not obvious; however, it is worth noting that several physiological variables appear to be related to body size by approximately the same exponent—for example, the basal metabolic rate.
This power law formula applies to the "average" brain of mammals taken as a whole, but each family (cats, rodents, primates, etc.) departs from it to some degree, in a way that generally reflects the overall "sophistication" of behavior. Primates, for a given body size, have brains 5 to 10 times as large as the formula predicts. Predators tend to have relatively larger brains than the animals they prey on; placental mammals (the great majority) have relatively larger brains than marsupials such as the opossum. A standard formula for assessing an animal's brain size compared to what would be expected from its body size is known as the encephalization quotient. The encephalization quotient for humans is approximately 4.6.
When the mammalian brain increases in size, not all parts increase at the same rate. In particular, the larger the brain of a species, the greater the fraction taken up by the cortex. Thus, in the species with the largest brains, most of their volume is filled with cortex: this applies not only to humans, but also to animals such as dolphins, whales or elephants.The evolution of Homo sapiens over the past two million years has been marked by a steady increase in brain size, but much of it can be accounted for by corresponding increases in body size. There are, however, many departures from the trend that are difficult to explain in a systematic way: in particular, the appearance of modern man about 100,000 years ago was marked by a decrease in body size at the same time as an increase in brain size. Even so, it is noteworthy that Neanderthals, which became extinct about 40,000 years ago, had larger brains than modern Homo sapiens.
Not all investigators are happy with the amount of attention that has been paid to brain size. Roth and Dicke, for example, have argued that factors other than size are more highly correlated with intelligence, such as the number of cortical neurons and the speed of their connections. Moreover, they point out that intelligence depends not just on the amount of brain tissue, but on the details of how it is structured. It is also well known that crows, ravens, and African gray parrots are quite intelligent even though they have small brains.
While humans have the largest encephalization quotient of extant animals, it is not out of line for a primate. Gorillas are out of line, having a smaller brain to body ratio than would be expected. Some other anatomical trends are correlated in the human evolutionary path with brain size: the basicranium becomes more flexed with increasing brain size relative to basicranial length.
Cranial capacity is a measure of the volume of the interior of the cranium (also called the braincase or brainpan or skull) of those vertebrates who have both a cranium and a brain. The most commonly used unit of measure is the cubic centimetre or cm3. The volume of the cranium is used as a rough indicator of the size of the brain, although due to the thickness of the membranes that surround the brain, brain volume is less than cranial capacity. Cranial Capacity is often tested by filling the cranial cavity with particulate material (as mustard seed or small shot) and measuring the volume of the latter. However, this method of measuring cranial capacity must be validated in each species to know whether it is an accurate representation of the braincase. A more accurate way of measuring cranial capacity, is to make an endocranial cast and measure the amount of water the cast displaces. In the past there have been dozens of studies done to estimate cranial capacity on skulls, most of these studies have been done on dry skull using linear dimensions, packing methods or occasionally radiological methods.
Knowledge of the volume of the cranial cavity can be important information for the study of different populations with various differences like geographical, racial, or ethnic origin. Other things can also affect cranial capacity such as nutrition. It is also used to study correlating between cranial capacity with other cranial measurements and in comparing skulls from different beings. It is commonly used to study abnormalities of cranial size and shape or aspects of growth and development of the volume of the brain. Cranial capacity is an indirect approach to test the size of the brain. A few studies on cranial capacity have been done on living beings through linear dimensions.
However, larger cranial capacity is not always indicative of a more intelligent organism, since larger capacities are required for controlling a larger body, or in many cases are an adaptive feature for life in a colder environment. For instance, among modern Homo Sapiens, northern populations have a 20% larger visual cortex than those in the southern latitude populations, and this potentially explains the population differences in brain size (and roughly cranial capacity). Neurological functions are determined more by the organization of the brain rather than the volume. Individual variability is also important when considering cranial capacity, for example the average Neanderthal cranial capacity for females was 1300 cm3 and 1600 cm3 for males  The volume of the human braincase has increased as humans have evolved (see Homininae), starting from about 600 cm3 in Homo habilis up to 1600 cm3 in Homo neanderthalensis, which was the hominid with the biggest brain size.
In an attempt to use cranial capacity as an objective indicator of brain size, the encephalization quotient (EQ) was developed in 1973 by Harry Jerison. It compares the size of the brain of the specimen to the expected brain size of animals with roughly the same weight. This way a more objective judgement can be made on the cranial capacity of an individual animal. A large scientific collection of brain endocasts and measurements of cranial capacity has been compiled by Holloway.
Examples of cranial capacity
- Orangutans: 275–500 cm3 (16.8–30.5 cu in)
- Chimpanzees: 275–500 cm3 (16.8–30.5 cu in)
- Gorillas: 340–752 cm3 (20.7–45.9 cu in)
- Homo sapiens sapiens: 1,496.5 cm3 (91.32 cu in)
- Homo neanderthalensis: 1,427.2 cm3 (87.09 cu in)
- Homo heidelbergensis: 1,262.8 cm3 (77.06 cu in)
- Homo erectus soloensis: 1,155.8 cm3 (70.53 cu in)
- Homo erectus: 1,092.9 cm3 (66.69 cu in)
- Homo habilis: 610.3 cm3 (37.24 cu in)
- Australopithecus africanus: 491.2 cm3 (29.97 cu in)
- Australopithecus afarensis: 445.8 cm3 (27.20 cu in)
Human races, not corrected for body size
- Brain-to-body mass ratio
- Encephalization quotient
- Craniometry — includes historical discussion
- Neuroscience and intelligence
- Human brain
- Cosgrove et al., 2007
- Allen et al., 2002
- Parent, A; Carpenter MB (1995). "Ch. 1". Carpenter's Human Neuroanatomy. Williams & Wilkins. ISBN 978-0-683-06752-1.
- Harrison, Paul J.; Freemantle, Nick; Geddes, John R. (2003-11-01). "Meta-analysis of brain weight in schizophrenia". Schizophrenia Research. 64 (1): 25–34. ISSN 0920-9964. PMID 14511798. doi:10.1016/s0920-9964(02)00502-9.
- Cosgrove, KP; Mazure CM; Staley JK (2007). "Evolving knowledge of sex differences in brain structure, function, and chemistry". Biol Psychiat. 62 (8): 847–55. PMC . PMID 17544382. doi:10.1016/j.biopsych.2007.03.001.
- "If Modern Humans Are So Smart, Why Are Our Brains Shrinking?". DiscoverMagazine.com. 2011-01-20. Retrieved 2014-03-05.
- Henneberg, Maciej (1988). "Decrease of human skull size in the Holocene". Human Biology. 60: 395–405. JSTOR 41464021.
- Rushton, John Philippe (1992). "Cranial capacity related to sex, rank, and race in a stratified random sample of 6,325 U.S. military personnel". Intelligence. 16 (3–4): 401–413. doi:10.1016/0160-2896(92)90017-l.
- Kouprina, Natalay; Pavlicek, Adam; Mochida, Ganeshwaran H.; Solomon, Gregory; Gersch, William; Yoon, Young-Ho; Collura, Randall; Ruvolo, Maryellen; Barrett, J. Carl; Woods, C. Geoffrey; Walsh, Christopher A.; Jurka, Jerzy; Larionov, Vladimir (2004). "Accelerated Evolution of the ASPM Gene Controlling Brain Size Begins Prior to Human Brain Expansion". PLoS Biology. 2 (5): e126. PMC . PMID 15045028. doi:10.1371/journal.pbio.0020126. Retrieved 19 February 2015.
- Brown, P.; Sutikna, T.; Morwood, M. J.; Soejono, R. P.; Jatmiko; Saptomo, E. Wayhu; Due, Rokus Awe (October 2004). "A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia". Nature. 431 (7012): 1055–1061. PMID 15514638. doi:10.1038/nature02999.
- Pearce, Eiluned; Stringer, Chris; Dunbar, R. I. M. (2013-05-07). "New insights into differences in brain organization between Neanderthals and anatomically modern humans". Proceedings of the Royal Society of London B: Biological Sciences. 280 (1758): 20130168. ISSN 0962-8452. PMC . PMID 23486442. doi:10.1098/rspb.2013.0168.
- Davidson, Iain. "As large as you need and as small as you can'--implications of the brain size of Homo floresiensis, (Iain Davidson)". Une-au.academia.edu. Retrieved 2011-10-30.
- P. Thomas Schoenemann (2006). "Evolution of the Size and Functional Areas of the Human Brain". Annu. Rev. Anthropol. 35: 379–406. doi:10.1146/annurev.anthro.35.081705.123210.
- "Brain Size, Cranial Morphology, Climate, and Time Machines" (PDF). Kenneth L. Beals, Courtland L. Smith, and Stephen M. Dodd. 3 June 1984.
- "Morphological Adaptation to Climate in Modern Homo sapiens Crania: The Importance of Basicranial Breadth". Wioletta Nowaczewska, Pawe D browski1 and Lukasz KuŸmiñski.
- James Mielke, Lyle W. Konigsberg & John Relethford. 2006. Human biological variation". Oxford University Press 274-75
- Lange et al., 1997
- Peters, R. (2006). "Ageing and the brain". ncbi.nlm. 82: 84–8. PMC . PMID 16461469. doi:10.1136/pgmj.2005.036665.
- Kelley Hays; David S. Reader in Gender archaeology. Routlegde. Retrieved 2014-09-21.
- Carne et al., 2006
- Taki, Y.; Thyreau, B.; Kinomura, S.; Sato, K.; Goto, R.; Kawashima, R.; Fukuda, H. (2011). He, Yong, ed. "Correlations among Brain Gray Matter Volumes, Age, Gender, and Hemisphere in Healthy Individuals". PLoS ONE. 6 (7): e22734. PMC . PMID 21818377. doi:10.1371/journal.pone.0022734.
- Giedd, 2008
- Good et al., 2001
- Rushton, J.Philippe (January 1988). "Race differences in behaviour: A review and evolutionary analysis". Personality and Individual Differences. 9 (6): 1009–1024. doi:10.1016/0191-8869(88)90135-3.
- Rushton, J.Philippe; Rushton, Elizabeth W. (March 2003). "Brain size, IQ, and racial-group differences". Intelligence. 31 (2): 139–155. doi:10.1016/S0160-2896(02)00137-X.
- Rushton, J. Philippe; Ankney, C. Davison (March 1996). "Brain size and cognitive ability: Correlations with age, sex, social class, and race". Psychonomic Bulletin & Review. 3 (1): 21–36. doi:10.3758/BF03210739.
- Cain, Donald P.; Vanderwolf, C.H. (1990). "A critique of Rushton on race, brain size and intelligence". Personality and Individual Differences. 11 (8): 777–784. doi:10.1016/0191-8869(90)90185-T.
- Brody, Nathan (2003). https://books.google.com/books?hl=en&lr=&id=rPNFXBnwuNoC&oi=fnd&pg=PA397
|chapter-url=missing title (help). The Scientific Study of General Intelligence: Tribute to Arthur Jensen. Elsevier Science. pp. 397–410.
- Smith, C. L., Beals, K. L. (1990). "Cultural correlates with cranial capacity". American Anthropologist. 92: 193–200.
- Peper, 2007
- Zhang, 2003
- Nisbett et al. 2012b, p. 142.
- McDaniel, Michael (2005). "Big-brained people are smarter" (PDF). Intelligence. 33: 337–346. doi:10.1016/j.intell.2004.11.005.
- Luders et al., 2008
- Hoppe & Stojanovic, 2008
- Egan et al., 1993
- Egan et al, 1995
- Nisbett et al. 2012b.
- Lee et al., 2007
- Driemeyer et al., 2008
- Ilg et al., 2008
- Kevin Kelly. "The Technium: Brains of White Matter". kk.org.
- Armstrong, 1983
- Savage et al., 2004
- Jerison, Evolution of the Brain and Intelligence
- Aiello & Wheeler, 1995
- Finlay et al., 2001
- Kappelman, 1993
- Holloway, 1995
- Roth & Dicke, 2005
- "Size isn't everything: The big brain myth" by Alison Motluk, New Scientist, July 31, 2010, pp. 38-41.
- Azevedo, F. A. C.; Carvalho, L. R. B.; Grinberg, L. T.; Farfel, J. M.; Ferretti, R. E. L.; Leite, R. E. P.; Jacob Filho, W. J.; Lent, R.; Herculano-Houzel, S. (2009). "Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain". The Journal of Comparative Neurology. 513 (5): 532–541. PMID 19226510. doi:10.1002/cne.21974.
We find that the adult male human brain contains on average 86.1 ± 8.1 billion NeuN-positive cells (“neurons”) and 84.6 ± 9.8 billion NeuN-negative (“nonneuronal”) cells. [...] These findings challenge the common view that humans stand out from other primates in their brain composition and indicate that, with regard to numbers of neuronal and nonneuronal cells, the human brain is an isometrically scaled-up primate brain.
- Ross & Henneberg, 1995
- Logan & Clutton-Brock (2013). "Validating methods for estimating endocranial volume in individual red deer (Cervus elaphus)" (PDF). Behavioural Processes. 92: 143–146. doi:10.1016/j.beproc.2012.10.015.
- Logan & Palmstrom (2015). "Can endocranial volume be estimated accurately from external skull measurements in great-tailed grackles (Quiscalus mexicanus)?". PeerJ. 3: e1000. PMC . PMID 26082858. doi:10.7717/peerj.1000.
- Ezejindu D.N., 1Chinweife K. C., 2 Ihentuge C.J., 2Uloleme G. C (2013). "Studies of Cranial Capacity between the Ages of 14 – 20 Yrs of Ogidi People of Anambra State, Nigeria." (PDF). Journal of Dental and Medical Sciences.
- J. Philippe Rushton; Arthur R. Jensen. "THIRTY YEARS OF RESEARCH ON RACE DIFFERENCES IN COGNITIVE ABILITY" (PDF). American Psychological Association.
- Ezejindu D.N.; Chinweife K. C.; Ihentuge C.J.; Uloleme G. C. "Studies of Cranial Capacity between the Ages of 14 – 20 Yrs of Ogidi People of Anambra State, Nigeria." (PDF). Journal of Dental and Medical Sciences.
- Ezejindu D.N., Chinweife K. C., Ihentuge C.J., 2Uloleme G. C. "Studies of Cranial Capacity between the Ages of 14 – 20 Yrs of Ogidi People of Anambra State, Nigeria." (PDF). Journal of Dental and Medical Sciences.
- "BBC News - Dark winters 'led to bigger human brains and eyeballs'". BBC News.
- Alok Jha. "People at darker, higher latitudes evolved bigger eyes and brains". the Guardian.
- Stanford, C., Allen, J.S., Anton, S.C., Lovell, N.C. (2009). Biological Anthropology: the Natural History of Humankind. Toronto: Pearson Canada. p. 301
- "Neanderthal man". infoplease.
- Brown, Graham; Fairfax, Stephanie; Sarao, Nidhi. "Human Evolution". Tree of Life. Tree of Life Project. Retrieved 19 May 2016.
- Campbell, G.C., Loy, J.D., Cruz-Uribe, K. (2006). Humankind Emerging: Ninth Edition. Boston: Pearson. p346
- Holloway, Ralph L., Yuan, M. S., and Broadfield, D.C. (2004). The Human Fossil Record: Brain Endocasts: The Paleoneurological Evidence. New York. John Wiley & Sons Publishers (http://www.columbia.edu/~rlh2/PartII.pdf and http://www.columbia.edu/~rlh2/available_pdfs.html for further references).
- Aiello, L; Wheeler, P (1995). "The Expensive Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution" (PDF). Current Anthropology. 36 (2): 199–221. doi:10.1086/204350. Retrieved 15 April 2011.
- Allen, JS; Damasio H; Grabowski TJ (2002). "Normal neuroanatomical variation in the human brain: An MRI-volumetric study". Am J Phys Anthropol. 118 (4): 341–58. PMID 12124914. doi:10.1002/ajpa.10092.
- Armstrong, E (1983). "Relative brain size and metabolism in mammals". Science. 220 (4603): 1302–4. PMID 6407108. doi:10.1126/science.6407108.
- Carne, RP; Vogrin S; Litewka L; Cook MJ (2006). "Cerebral cortex: An MRI-based study of volume and variance with age and sex". J Clin Neurosci. 13 (1): 60–72. PMID 16410199. doi:10.1016/j.jocn.2005.02.013.
- Cosgrove, KP; Mazure CM; Staley JK (2007). "Evolving Knowledge of Sex Differences in Brain Structure, Function and Chemistry". Biol Psychiat. 62 (8): 847–55. PMC . PMID 17544382. doi:10.1016/j.biopsych.2007.03.001.
- Driemeyer, J; Boyke, J; Gaser, C; Buchel, C; May, A (2008). Eagleman, David M., ed. "Changes in Gray Matter Induced by Learning—Revisited". PLoS ONE. 3 (7): 7. PMC . PMID 18648501. doi:10.1371/journal.pone.0002669.
- Egan, V; Chiswick A; Santosh C; Naidu K; Rimmington JE; Best JJK (1993). "Size isn’t everything: A study of brain volume, intelligence and auditory evoked potentials". Pers Ind Diff. 17 (3): 357–367. doi:10.1016/0191-8869(94)90283-6.
- Egan, V; Wickett JC; Vernon PA (1995). "Brain size and intelligence: Erratum,addendum, and correction." (PDF). Personality and Individual Differences. 19 (1): 113–115. doi:10.1016/0191-8869(95)00043-6.
- Finlay, BL; Darlington RB; Nicastro N (2001). "Developmental structure in brain evolution" (PDF). Behav Brain Sci. 24 (2): 263–308. PMID 11530543. doi:10.1017/S0140525X01003958.
- Giedd, JN (2008). "The teen brain: insights from neuroimaging" (PDF). J Adolescent Health. 42 (4): 335–43. PMID 18346658. doi:10.1016/j.jadohealth.2008.01.007.
- Good CD, Johnsrude IS, Ashburner J, Henson RN, Friston KJ, Frackowiak RS (2001). "A voxel-based morphometric study of ageing in 465 normal adult human brains". NeuroImage. 14 (1 Pt 1): 21–36. PMID 11525331. doi:10.1006/nimg.2001.0786.
- Holloway, RL (1995). Changeaux JP, Chavillon J, ed. Origins of the Human Brain. Clarendon. pp. 42–54. ISBN 978-0-19-852307-9.
- Ilg, R; Wohlschläger AM; Gaser C; Liebau Y; Dauner R; Wöller A; Zimmer C; Zihl J; Mühlau M (2008). "Gray matter increase induced by practice correlates with task-specific activation: a combined functional and morphometric magnetic resonance imaging study". J Neurosci. 28 (16): 4210–5. PMID 18417700. doi:10.1523/JNEUROSCI.5722-07.2008.
- Jerison, HJ (1973). Evolution of the Brain and Intelligence. Academic Press. ISBN 978-0-12-385250-2.
- Kappelman, J (1993). "The evolution of body mass and relative brain size in fossil hominids". Journal of Human Evolution. 30 (3): 243–76. doi:10.1006/jhev.1996.0021.
- Lange, N; Giedd JN; Castellanos FX; Vaituzis AC; Rapoport JL (1997). "Variability of human brain structure size: ages 4–20 years". Psychiat Res: Neuroimaging. 74 (6): 1–12. PMID 10710158. doi:10.1016/S0925-4927(96)03054-5.
- Lee, H; Devlin JT; Shakeshaft C; Stewart LH; Brennan A; Glensman J; Pitcher K; Crinion J; Mechelli A; Frackowiak RS; Green DW; Price CJ (2007). "Anatomical traces of vocabulary acquisition in the adolescent brain". J Neurosci. 27 (5): 1184–9. PMID 17267574. doi:10.1523/JNEUROSCI.4442-06.2007.
- Hoppe, C; Stojanovic J (2008). "High-aptitude minds: the neurological roots of genius". Scientific American.
- Luders, E; Narr KL; Thompson PM; Toga AW (2008). "Neuroanatomical Correlates of Intelligence". Intelligence. 37 (2): 156–163. PMC . PMID 20160919. doi:10.1016/j.intell.2008.07.002.
- Peper, JS; Brouwer, RM; Boomsma, DI; Kahn, RS; Hulshoff Pol, HE (2007). "Genetic influences on human brain structure: A review of brain imaging studies in twins". Human Brain Mapping. 28 (6): 464–73. PMID 17415783. doi:10.1002/hbm.20398.
- Ross, C; Henneberg M (1995). "Basicranial flexion, relative brain size, and facial kyphosis in Homo sapiens and some fossil hominids" (PDF). Am J Phys Anthropol. 98 (4): 575–93. PMID 8599387. doi:10.1002/ajpa.1330980413.
- Roth, G; Dicke U (2005). "Evolution of the brain and intelligence" (PDF). Trends Cogn Sci. 9 (5): 250–7. PMID 15866152. doi:10.1016/j.tics.2005.03.005.
- Savage, MV; Gillooly JF; Woodruff WH; West GB; Allen AP; Enquist BJ; Brown JH (2004). "The predominance of quarter-power scaling in biology". Functional Ecol. 18 (2): 257–82. doi:10.1111/j.0269-8463.2004.00856.x.
- Zhang, J (2003). "Evolution of the human ASPM gene, a major determinant of brain size". Genetics. 165 (4): 2063–70. PMC . PMID 14704186.
- Jabr, Ferris (28 November 2015). "How Humans Ended Up With Freakishly Huge Brains". Wired. Retrieved 29 November 2015.