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After all of the data, all observations concluded that the main development that occurred during evolution was the increase of brain size. [52] However, recent research has called into question the hypothesis of a threefold increase in brain size when comparing Homo sapiens with Australopithecus and chimpanzees. For example, in an article ...
Australopithecus fossils become more widely dispersed throughout eastern and southern Africa (the Chadian A. bahrelghazali indicates that the genus was much more widespread than the fossil record suggests), before eventually becoming pseudo-extinct 1.9 million years ago (or 1.2 to 0.6 million years ago if Paranthropus is included).
A. ramidus had a small brain, measuring between 300 and 350 cm 3. This is about the same size as the modern bonobo and female chimpanzee brain; it is somewhat smaller than the brain of australopithecines like Lucy (400 to 550 cm 3) and slightly over a fifth the size of the modern Homo sapiens brain.
[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.
It is thought that they averaged heights of 1.2–1.5 metres (3.9–4.9 ft) and weighed between 30 and 55 kilograms (66 and 121 lb). The brain size may have been 350 cc to 600 cc. The postcanines (the teeth behind the canines) were relatively large, and had more enamel compared to contemporary apes and humans, whereas the incisors and canines ...
In a sample of 10 P. boisei specimens, brain size varied from 444–545 cc (27.1–33.3 cu in) with an average of 487.5 cc (29.75 cu in). [36] However, the lower-end specimen, Omo L338‐y6, is a juvenile, and many skull specimens have a highly damaged or missing frontal bone which can alter brain volume estimates. [ 37 ]
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]
A. sediba, much like earlier and contemporary hominins, appears to have had an ape-like growth rate based on dental development rate, so MH1 may have reached about 85% of its adult size assuming a chimpanzeelike growth trajectory, or 80% assuming a humanlike trajectory. This would equate to roughly 150 or 156 cm (4 ft 11 in or 5 ft 1 in).