168 



INITIATIVE IN EVOLUTION 



In this example of ridges developed on an abnormal situation we 

 see what is, perhaps, an undesigned experiment as to the production 

 of ridges by a more frequent habit of walking in captivity than 

 would be found to occur in the wild state, for, as Lydekker says 

 in the Royal Natural History, Vol. I, p. 27, " When the chimpanzee 

 goes on all-fours, he generally supports himself on the backs of his 

 closed fingers rather than on the palm of the hand (see Fig. 6 of the 



illustration on p. 15) and 

 he goes sometimes on the 

 soles of his feet and some- 

 times on his closed toes." 



I have underlined 

 purposely this word "some- 

 times," for in the instance 

 I have described, not only 

 the presence of the ridges 

 and their direction on the 

 backs of the fingers but 

 their absence on the backs 

 of the toes is significant, 

 and I suggest that the 

 chimpanzees examined have 

 not sufficiently often ex- 

 posed the backs of their 

 toes to pressure and friction 

 for the production of ridges, 

 whereas those on the backs 

 of the fingers have done so. 

 Another point worth notice 

 is that in the oldest of the 

 three chimpanzees, "Mickie," 

 set six years, the greatest 

 number of ridges is present ; 

 in " Jimmie," set two-and- 

 a-half years, they were 

 " small and ill-defined as if in process of development," and in 

 " Jack," set twenty months they were absent. This would agree at 

 any rate with the hypothesis that the element of time and frequent 

 repetition of stimuli enter into the causation of aberrant ridges. 



A similar condition, with aberrant papillary ridges, has been 

 found on the digits of the hand of the orang. 



On the heel of adult man ridges are found surrounding it, of 

 the average depth of one inch from the plantar surface, and in one 



Fig. 70. — Left hand of chacma baboon. 



