|
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. This means that larger brains tend to be more intelligent.
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.
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.
Here is a list of some species, along with their rough average brain sizes:
Reference
| 
