Contents
Section 1
Palaeoanthropology
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Photogallery Outline of Human Phylogeny Evolutionary Trees and DNA Brain Evolution Hand and Bipedality |
Section 2
Social and socio-
cultural systems
Section 3
Ontogeny and symbolism
Section 4
Language systems
Links
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Links Policy Relevant Links |
Evolution of the Human Brain
Ralph Holloway
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].
Links
For 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