The Descent of Mau 27 



preibrnied (with a view to man) in a condition of perfection 

 beyond their needs, he says : — 



' On the contrary, I see no reason to doubt that a more perfectly 

 constructed hand would have been an advantage to them, provided, 

 and it is important to note this, that their hands had not thus been 

 rendered less well adapted for climbing trees. We may suspect that 

 a perfect hand would have been disadvantageous for climbing ; as the 

 most arboreal monkeys in the world, namely Ateles in America and 

 Hylobates in Asia, either have their thumbs much reduced in size 

 and even rudimentary, or their fingers partially coherent, so that their 

 hands are converted into grasping-hooks.' — Vol. i. p. 140. 



In a note, Mr. Darwin refers to the Syndactyle Gibbon 

 as having two of the digits coherent. But these digits are 

 not, as he supposes, digits of the hand but toes. Moreover, 

 though doubtless the Gibbons and spider-monkeys are ad- 

 mirably organised for their needs, yet it is plain that a well 

 developed thumb is no impediment to climbing, for the 

 strictly arboreal Lemurs are exceedingly well furnished in 

 this respect. Again he says (vol. i. p. 143) of the Gibbons, 

 that they, 'without having been taught, can walk or run 

 upright with tolerable quickness, though they move awk- 

 wardly, and much less securely than man.' This is a little 

 misleading, inasmuch as it is not stated that this upright 

 progression is effected by placing the enormously long arms 

 behind the head or holding them out backwards as a balance 

 in progression. 



We have already seen that Mr. Darwin tries to account 

 for man's hairlessness by the help of ' sexual selection.' He 

 also, however, speculates as to the possibility of his having 

 lost it through heat of climate, saying : — ' Elephants and 

 rhinoceroses are almost hairless ; and as certain extinct 

 species which formerly lived under an arctic climate were 

 covered with long wool or hair, it would almost appear as if 

 the existing species of both genera have lost their hairy 

 covering from exposure to heat ' (vol. i. p. 148). 



