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The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution.Measuring brain size and cranial capacity is relevant both to humans and other animals, and can be done by weight or volume via MRI scans, by skull volume, or by neuroimaging intelligence testing.
A "cerebral rubicon" in paleontology is the minimum cranial capacity required for a specimen to be classified as a certain paleospecies or genus. The term is mostly used in reference to human evolution. [1] The Scottish anthropologist Sir Arthur Keith set the limit at 750 cc for the genus Homo. [1]
A human skull and measurement device from 1902. Craniometry is measurement of the cranium (the main part of the skull), usually the human cranium.It is a subset of cephalometry, measurement of the head, which in humans is a subset of anthropometry, measurement of the human body.
Homo neaderthalensis, living 400,000 to 40,000 years ago, had a cranial capacity comparable to that of modern humans at around 1500–1600 cm 3 on average, with some specimens of Neanderthal having even greater cranial capacity. [58] [59] Neanderthals are estimated to have had around 85 billion neurons. [50]
For example, the average cranial capacity for Australopithecines is 440 cc, and the post-orbital constriction index is 0.66. [1] [5] However, with the evolutionary change in brain size in Australopithecines to the Homo genus, the average cranial capacity for Homo Habilis is 640 cc, and the post-orbital constriction index is 0.72.
Paleoneurobiology is the study of brain evolution by analysis of brain endocasts to determine endocranial traits and volumes. Considered a subdivision of neuroscience, paleoneurobiology combines techniques from other fields of study including paleontology and archaeology. It reveals specific insight concerning human evolution.
The concept of encephalization has been a key evolutionary trend throughout human evolution, and consequently an important area of study. Over the course of hominin evolution, brain size has seen an overall increase from 400 cm 3 to 1400 cm 3. [42] Furthermore, the genus Homo is specifically defined by a significant increase in brain size. [43]
Along with similarities to contemporary Homo, they share several characteristics with the ancestral Australopithecus as well as early Homo (mosaic evolution), most notably a small cranial capacity of 465–610 cm 3 (28.4–37.2 cu in), compared with 1,270–1,330 cm 3 (78–81 cu in) in modern humans.