If primordial Man had a cranial capacity of only 450 cc, a third of the modern average, this appears to exclude a human level of intelligence for this creature.
It has been calculated, however, that the volume of the cerebral cortex for Australopithecus could have been 242 ml, for Homo habilis 366 ml and for early Homo erectus 540 ml (Blumenberg 1983, Table 3, page 591). The modern range for the volume of the cerebral cortex varies from 230 to 561 ml or cc (Blinkov 1968, page 172). This means that all species in the human line fall within the range of modern man. The reason for this is that the volume of the cerebral cortex depends on how much an individual uses their brain, though all people, whether high usage or low usage are human.
The crucial faculty of humans is the ability to use language.
What is the evidence for use of language in early species of mankind?
The parts of the brain involved in language are Broca’s Area and Wernicke’s Area. These areas are dominant on the left side of the brain.
Features of the endocasts of Taung and Hadar 162-28, fossil skulls of Homo primocreatus / Australopithecus have markings showing that the language areas had increased in size.
Symbolic language is associated with handedness. Right-handed people have greater development of the lobes on the left side of the brain. Asymmetry of the cortex in Homo primocreatus / Australopithecus such as in the fossil MLD 1 indicates that they were using their right hands for intricate tasks. These tasks are later associated with tool-making.
It is really use of language that would secure a place for Australopithecus in the Homo genus among anthropologists. This genus has human adaptation rather than animal adaptation.
Homo habilis fossils come from Olduvai Gorge, East Rudolf and Omo in East Africa dating from 2 million to 1.3 million years ago. Cranial capacity has increased to 700 cc although this species is very similar to previous australopithecines / Homo primocreatus. The Homo habilis fossils KNM-ER 1470, 1805 and 1813 show clear asymmetries of the cortex relating to right-handedness. The specimen ER-1470 endocast has a more complex pattern of the third inferior convolution which includes Broca’s Area. Broca’s Area controls the motor aspects of speech.
This leaves me in no doubt that these early species of mankind were right-handed, using their hands to make things, and used speech to communicate to each other.
Small brain size does not preclude the ability to use language, and this has been observed in living people. There have been examples of people born with genetic problems causing them to be microcephalic and have dwarfism. There have been known people with cranial capacities of 500 to 700 cc who nevertheless used articulate language.
The chatter started a long time ago with people only a metre high living a primitive, but a human life.