Humans have brain sizes ranging up to 2000cm³, with the average being about 1400cm³.

Larger brains do not necessarily imply higher intelligence. This means that someone with a larger brain may be less intelligent than someone with a smaller brain. However, larger brains do correlate with higher intelligence, particularly between different species. This means that larger brains tend to be more intelligent. The sheer size of the brain is relevant for two reasons. Most obviously, a small brain simply cannot hold as many brain cells as a large one. Less obvious, but more important, is that the true quality of a brain must be measured by the complexity of linkages between cells. (Note: The term correlation is sometimes used to specify the cross-correlation of two functions, and sometimes to specify the correlation coefficient between two random variables. ... In biology, a species is a kind of organism. ...

Modern studies using magnetic resonance imaging show that brain size correlates with IQ by a factor of roughly .35 to .40. In 1991, Willerman et al used data from 40 white American unversity students and reported a correlation coefficient of .35.[1] (http://lib.stat.cmu.edu/DASL/Datafiles/Brainsize.html) Other studies done on samples of Caucasians show similar results, with Andreasen et al (1993) determining a correlation of .38 [2] (http://ajp.psychiatryonline.org/cgi/content/abstract/150/1/130), while Raz et al (1993) obtained a figure of .43 and Wickett et al (1994) obtained a figure of .40. Recently, an MRI study on twins (Thompson et al., 2001) showed that frontal gray matter volume was highly significantly correlated with g and was highly heritable. A related study has reported that the correlation between brain size (reported to have a heritability of 0.85) and g is 0.4, and that correlation is mediated entirely by genetic factors (Posthuma et al 2002). Magnetic Resonance Image Magnetic resonance imaging (MRI) - also called magnetic resonance tomography (MRT) - is a method of creating images of the inside of opaque organs in living organisms as well as detecting the amount of bound water in geological structures. ... In probability theory and statistics, correlation, also called correlation coefficient, is a numeric measure of the strength of linear relationship between two random variables. ... Caucasian is originally a geographical term, meaning relative or pertaining to the Caucasus region of Eastern Europe and West Asia. ... The title given to this article is incorrect due to technical limitations. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ...

The brain is a metabolically expensive organ, and consumes about 25% of the body's metabolic energy. Because of this fact, although larger brains are associated with higher intelligence, smaller brains might be advantageous from an evolutionary point of view if they are equal in intelligence to larger brains.

Brain size is a rudimentary indicator of the intelligence of a brain, and many other factors affect the intelligence of a brain. Higher ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Brain to body mass ratio (also known as the Encephalisation Quotient) is a method to quickly get a rough estimate of the possible intelligence of an organism. ...

Here is a list of some species, along with their rough average brain sizes:

Binomial name Homo erectus Dubois, 1894 Homo erectus (upright man) is a hominid species that is believed to be an ancestor of modern humans. ... Binomial name Homo habilis Leakey et al. ... Binomial name Homo floresiensis P. Brown , 2004 Homo floresiensis (Man of Flores) is a newly described species in the genus Homo, remarkable for its small body, small brain, and recent survival. ...

See also:

• Race and intelligence
• Sex and intelligence

Race and intelligence refers to the controversy surrounding the findings of many studies of cognitive ability that some racial groups differ in average IQ scores. ... It has been proposed at numerous times throughout history that the human sexes display differences in mental abilities on different tasks. ...

Reference

• Washington State University (http://www.wsu.edu:8001/vwsu/gened/learn-modules/top_longfor/phychar/culture-humans-2two.html)
• Neuroscience for Kids (http://faculty.washington.edu/chudler/brainsize.html)