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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]
Brain volume is prominent in the scientific literature for discussing taxonomic identification, behavioral complexity, intelligence, and dissimilar rates of evolution. In modern humans, cranial capacity can vary by as much as 1000 cc, without any correlation to behavior.
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.
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]
Larger average cranial capacity is correlated with living in cold regions. Inuit adaptation to high-fat diet and cold climate has been traced to a mutation dated the Last Glacial Maximum (20,000 years ago). [66] Average cranial capacity among modern male human populations varies in the range of 1,200 to 1,450 cm 3.