THE LOPSIDED APE by Michael C. Corballis

Oxford University Press 1991. ISBN 0-19-508352-0

It's a fact that humans have a lesser degree of laterality than other animals. People are mostly right handed, right footed and right eyed whereas other animals are indifferent between the two.

Micheal Corballis, professor of psychology at the University of Auckland looks at this difference in laterality, sifting through the evidence to find any connections that this may have with the unique phenomenon of human cultural evolution. The book covers all the related areas, including the fossil record, DNA analysis, phases of reaching maturity, anatomy, experimental evidence and the greater or lesser role that genes play with respect to culture and learning.

Three chapters in this excellent book are dedicated to language since 1) it shows the strongest bias (almost purely left hemisphere) of mental activities and 2) it is intimately connected with the start of culture and the take off in human evolutionary success that started some 35000 years ago.

There are more references than I have ever seen in a book of this kind (hundreds of them) but Corballis succeeds in synthesising the material to give a balanced picture of the "state of the art" while at the same time advancing his own hypothesis of brain function/learning in the chapter entitled "The Generative Mind". His argument for human uniqueness builds on a theory of vision by David Marr in which a stored representation of an object is built up layer by layer, each giving a higher level of detail culminating in a 3D image . Corballis extends the idea to his Generative Assembling Device showing how language is generative, being built up of a series of simple elements (phonemes) that are combined to make language that can then be described by grammar.

The grammar aspect is a whole story in itself and he evaluates the "universal grammar" of Chomsky, rejecting it in favour of a buildup of (top)
 meaning in speech. There is no "universal grammar" but rather an evolution of speech from the simplest type- verb eg "Look!" through a more complicated type- verb+noun eg "George runs" to a final type- verb+noun+adjective eg "George runs to the old house". As he says about the first level, " such utterances do not really represent thoughts (his emphasis) but are immediate reactions to events. One cannot think that "Look!" but one can think that "George runs."

His search for evidence is fascinating. Endocasts (latex interior molds) of Homo Habilis skulls ( 1.7-2.2 million years old ) already show a prominent Broca's area - the specific part of the left frontal lobe concerned with human speech together with other speech related changes in brain shape. This begs the question of how they were communicating and it does look as if they had already gone beyond the simple vocal communication of animals to some kind of proto-speech.

On the question of genetic vs cultural influences in child development/ human affairs, the book should be read by the growing numbers of sociobiology fundamentalists ( see the good article by Tom Wolfe in Forbes Magazine The Big Issue, "Sorry-But Your Soul Just Died"). Corballis goes into the interesting gene saving aspect of human growth whereby the human world is so complex that a better environment fit is ensured for the child by a long plastic period prior to adulthood. As a related point he refers to the 20 or so ways, listed in 1926 by the Dutch anatomist Louis Bolk, that child-like characteristics are retained for life by humans in contrast to other animals.

The consequences of not getting the required cultural input at the right age can be seen in the discussion of "Genie", a girl who was deprived of almost all human contact before the age of 13.

This is a superb book even if you don't agree with his GAD hypothesis.

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