Social and socio-
Ontogeny and symbolism
Evolution of the Human Brain
Abstract In the last 3-4 million years brain volume within the hominid lineage has increased from less than 400 ml to roughly 1400 ml. The first clear increase in hominid brain size is seen in early Homo at c.2 m.y.a. in East Africa (most reliably in cranial specimen KNM-ER 1470). This is an evolutionarily significant change that cannot be simply accounted for in terms of increased body size alone. From the appearance of H. erectus at c.1.7 m.y.a. to the present, the brain increases nearly twofold: from c.800 ml to 1500 ml in Late Pleistocene H. sapiens, without any apparent change in body size.
With regard to brain reorganization, left-right cerebral hemispheric asymmetries exist in extant pongids and the australopithecines, but neither the pattern nor direction is as strongly developed as in modern or fossil Homo. KNM-ER 1470 shows a strong pattern that may be related to handedness and tool-use/manufacture. The degree of asymmetry appears to increase in later hominids.
The appearance of a more human-like third inferior frontal
convolution provides another line of evidence about
evolutionary reorganization of the brain. None of the
australopithecine endocasts show this region preserved
satisfactorily. There is a consensus among palaeoneurologists
that the endocast of the specimen KNM-ER 1470 does show,
however, a somewhat more complex and modern-human-like third
inferior frontal convolution compared with those of pongids.
This region contains Broca's area, which in humans is related
to the motor control of speech. Unfortunately, later hominid
endocasts, including H. habilis and H. erectus
through archaic H. sapiens to the present, seldom show
the sulcal and gyral patterns faithfully. Thus nothing
palaeoneurological can be said with confidence about possible
changes with the emergence of anatomically modern H. sapiens.
On the other hand, there is nothing striking about Neanderthal
brain casts in comparison to more recent H. sapiens, except
their slightly larger size, suggesting no significant
evolutionary change thereon [Eds].
LinksFor further details, use this image as a link to Trevor Henderson's materials on the Evolution of the Human Brain at the Department of Anthropology, University of Toronto.
See also materials on brain evolution at the National Museum of Health and Medicine, University of Wisconsin