the brain, but at the age of one year as 1.3 times as great (Blinkov and 

 Glezer 1968). Siwe (1931), however, reports that the change is less marked. 

 The figures cited in Table 1 show that, by twenty years of age, no more than 

 80 per cent of the endocranial cavity is occupied by brain. These figures 

 have, of course, been determined on modern man. Even if we could accept 

 them as adequate and consistent results for modern Homo sapiens, we could 

 not lightly assume that the same percentages would apply to earlier hominids 

 at the same ages. The rate of growth of brain may have been different— and 

 we shall return to this theme when we discuss the work of Krantz (1961) in 

 Chapter 1 1. Moreover, the rate of growth of the non-neural contents of the 

 cranial cavity, as well as the rate of growth of the braincase itself, may have 

 differed. With all these possible variables entering into the picture, we 

 certainly would be unwise to take for granted that the percentage differences 

 reflected in the figures taken from Tabulae Biologicae would have applied, 

 age for age, to Australopithecus or any other early hominid. 



Our ignorance goes still deeper. Brandes showed that modern man's 

 brain contains as much as 50 gms. of cerebrospinal fluid before draining, 

 while the dura mater weighs on the average 50 to 60 gms. (Brandes 1927) 

 and has a volume of about 50 to 60 c.c. (Rudolph 1914). We shall never 

 know if similar values applied to Australopithecus and other extinct 

 hominids; and so we shall never be able to determine the brain size of fossil 

 man with precision. 



We shall have to rest content with the cranial capacity, recognizing 

 that this is only an approximation of the brain size. Through most of this 

 book I shall be dealing with this inexact parameter, cranial capacity, but I 

 hope to show that the changes that have occurred in cranial capacity have 

 been of such a magnitude as to point to an undoubted dramatic increase in 

 true brain size during hominid evolution. 



TWO 



$ THE CRANIAL CAPACITY OF 



Q THE AUSTRALOPITHECINES 



Of all the fossil crania assigned to the South and East African fossil 

 ape-man genus, Australopithecus sensu lato, only 8 specimens are sufficiently 

 complete and undistorted to permit a reasonable assessment of their endo- 

 cranial capacity. These 8 specimens exclude those Olduvai crania that have 



