LECTURES IN BIOLOGICAL SCIENCES 



(2) Productivity— the ability to produce an understandable 

 utterance that is new to the speaker and hearer and to 

 the species. 



(3) Traditional transmission— the ability to transmit a com- 

 munication system by learning. (This ability is a part 

 of other chimpanzee behavior but seemingly is not ex- 

 tended to their call system.) 



(4) Duality ot patterning— the ability to combine a relatively 

 small number of meaningless but differentiating vocal 

 elements (phonemes) into an unlimited number of mean- 

 ingful elements (morphemes). 



We do not know the neurological basis foT these four abili- 

 ties. We have strong reason to believe that the expansion of 

 the temporal and parietal lobes of the cerebral cortex may be 

 both a cause and an effect of these four abilities. This brings 

 me to the last biological condition preadaptive to human be- 

 havior which I will discuss here. 



7. Expansion of the Cerebral Cortex 



The opening sentence in a definition of Homo sapiens by 

 Le Gros Clark (1955) is "A species of Homo characterized by a 

 mean cranial capacity of about 1,350 cc. . . ." A brain large 

 in both relative and absolute terms is one of the diagnostic 

 features of modern man. Among living animals, for example, a 

 150-pound sheep has a one-quarter pound brain, a 1500-pound 

 cow has a one-pound brain, while a 150-pound man has a three- 

 pound brain (Brody, 1945). Living primates in general have 

 large brains relative to body weight. Big brains were not typi- 

 cal of the earliest primates, but an evolutionary trend toward 

 increase in brain size is characteristic of most primate phyla 

 (Simpson, 1949; Clark, 1959). 



When the log of brain weight among mammals in general 

 is plotted against the log of body weight, we find that brain 

 weight increases by the 0.06th power of body weight. The slope 

 of the regression line is steeper in primates in general where 

 brain weight increases as the 0.79th power of body weight (von 

 Bonin, 1955). If we use this general primate equation and man's 

 body weight to predict his brain weight, we obtain a figure only 



86 



