128 George A. Sacher 



inference will not be discussed, because in qualitative terms it 

 is readily evident, and a quantitative mathematical statement 

 is not testable at present owing to lack of appropriate data 

 on precision of physiological regulations in different species. 



In the absence of data that would permit a direct compari- 

 son of theory with experiment it was finally resolved to 

 approach the problem indirectly, by introducing the mediating 

 assumption that the precision of physiological regulation is 

 directly related to the degree of encephalization. Several 

 lines of published evidence suggested that such an approach 

 might be fruitful. First, there was the great discrepancy 

 between the human lifespan and that of other species, and also 

 Rubner's statement about the discrepancy between man and 

 other mammals in lifetime energy expenditure (see above). 

 Second, Flower's tabulation of lifespans of mammals brought 

 out the important point that man's long lifespan relative to 

 that of other mammals is not unique, for primate species in 

 general live longer than non-primates (Flower, 1931). Finally, 

 there was the massive literature on the index of cephalization 

 which indicated that this varies over wide limits (von Bonin, 

 1937), thus making possible an evaluation of the contribution 

 of brain weight independent of body weight. 



The statistical analysis presented above strongly supports 

 the hypothesis that lifespan is specifically related to brain 

 development. To establish my thesis completely I should 

 next justify the mediating assumption that the overall pre- 

 cision of physiological regulations is governed by the central 

 nervous system. To do so would take me far beyond the 

 bounds of this paper, for it would entail a review of the vast 

 and rapidly increasing literature on the control of vital physio- 

 logical functions by the central nervous system, and by the 

 cerebral cortex in particular {Ciba Found. Symp. Neurological 

 Basis of Behaviour, 1958). The developments of the last few 

 years have done much to dispel the dichotomy between 

 "higher" and "lower" forms of behaviour in so far as their 

 representation in the nervous system is concerned, and we 



