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Based on this, neonatal brain size was estimated to have been 165.5–190 cc (10.10–11.59 cu in) using trends seen in adult and neonate brain size in modern primates. If correct, this would indicate that A. africanus was born with about 38% of its total brain size, which is more similar to non-human great apes at 40% than humans at 30%. [26]
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.
The brains of most species of Australopithecus were roughly 35% of the size of a modern human brain [40] with an endocranial volume average of 466 cc (28.4 cu in). [13]
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. [52] Furthermore, the genus Homo is specifically defined by a significant increase in brain size. [53]
It has generally been thought that brain size increased along the human line especially rapidly at the transition between species, with H. habilis brain size smaller than that of H. ergaster / H. erectus, jumping from about 600–650 cc (37–40 cu in) in H. habilis to about 900–1,000 cc (55–61 cu in) in H. ergaster and H. erectus.
There were several reasons that it took decades for the field to accept Dart's claim that Australopithecus africanus was in the human line of descent. First and foremost was the fact that the British scientific establishment had been fooled by the hoax of the Piltdown Man, which had a large brain and ape-like teeth. [15]
Homo rudolfensis is an extinct species of archaic human from the Early Pleistocene of East Africa about 2 million years ago (mya). Because H. rudolfensis coexisted with several other hominins, it is debated what specimens can be confidently assigned to this species beyond the lectotype skull KNM-ER 1470 and other partial skull aspects.
[142] [143] [144] [53] Fossilized skulls shows the brain size in early humans fell within the range of modern humans 300,000 years ago, but only got its present-day brain shape between 100,000 and 35,000 years ago. [145] The size and shape of the skull changed over time. The leftmost, and largest, is a replica of a modern human skull.