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Concept
Capacité crânienne
Résumé
The 'size of the brain' is a frequent topic of study within the fields of anatomy, biological anthropology, animal science 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 volumetric measurements of the brain. Regarding "intelligence testing", a question that has been frequently investigated is the relation of brain size to intelligence. This question is controversial and will be addressed further in the section on intelligence. The measure of brain size and cranial capacity is not just important to humans, but to all mammals.
In humans, 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 . 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. Yet another study argued that adult human brain weight is 1,300-1,400g for adult humans and 350-400g for newborn humans. There is a range of volume and weights, and not just one number that one can definitively rely on, as with body mass. It is also important to note that variation between individuals is not as important as variation within species, as overall the differences are much smaller. The mechanisms of interspecific and intraspecific variation also differ.
Evolution of the brain
From early primates to hominids and finally to Homo sapiens, the brain is progressively larger, with exception of extinct Neanderthals whose brain size exceeded modern Homo sapiens. The volume of the human brain has increased as humans have evolved (see Homininae), starting from about 600 cm3 in Homo habilis up to 1680 cm3 in Homo neanderthalensis, which was the hominid with the biggest brain size. Some data suggest that the average brain size has decreased since then, including a study concluding the decrease "was surprisingly recent, occurring in the last 3,000 years".
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