250 



GROWTH 



PRINCIPLES AND THEORY 



corresponds to conclusions arrived at otherwise, is that Neanderthal man is not in the 

 evolutionary series leading to modern man. According to Kummer, the concept of 

 "fetalization" is to be refused with respect to the ontogeny and evolution of the human 

 skull; for this is not the result of an arrest of growth at an early phase but of a differentiation 

 in changed direction, manifest in the propulsive growth of the neurocranium owing to 

 the enlargement of the forebrain, the change of the viscerocranium, the skoliosis of the 

 skull base, etc. Hence we may correctly speak of "retardation" but not of "fetalization" 

 in human development. 



TABLE 17 



BRAIN WEIGHT IN MAMMALS 



After Portmann, 1944 



The table shows that, in nidicolous as compared to nidifugous species, the brain is much 

 more immature at birth and hence shows larger increase postembryonically. Man's 

 position as a "secondary nidicolous" is apparent. 



{f) The evolution of the brain 



A third problem pertaining to growth is the probably most important of all 

 orthogenetic series: The increase in brain size eventually cn'Tiinating in man 

 {cf. Table 17). 



In the way of a first crude approximation, the interspecific increase of brain size 

 in mammals in relation to body size follov/s the allometric equation, with an 

 allometry constant a = 2/3 {i.e. surface-proportionality) and a high correlation 

 coefficient (p = o.g) (Snell, 1891; Bonin, 1937; Jerison, 1955). The more exact 

 form of the evolutionary allometry of the brain is disputed. 



According to E. Dubois (1930), brain size in the series of mammals is controlled 

 by two independent factors: i. The relation between the size of the brain and 

 the body, a value a = 5/9 [i.e. slightly less than surface-proportionality) being 

 assumed in interspecific comparison of related species; 2. Cephalization, i.e. a 

 different degree of development of the brain in ratio to body size which is assumed 



