140 THE DESCENT OF MAN. Part I. 



branches until the rind is cracked, and then tear it off 

 with the fingers of the two hands. Other monkeys open 

 mussel-shells with the two thumbs. With their fingers 

 they pull out thorns and burs, and hunt for each other's 

 parasites. In a state of nature they break open hard 

 fruits with the aid of stones. They roll down stones 

 or throw them at their enemies ; nevertheless, they 

 perform these various actions clumsily, and they are 

 quite unable, as I have myself seen, to throw a stone 

 with precision. 



It seems to me far from true that because " objects 

 " are grasped clumsily " by monkeys, " a much less 

 " specialised organ of prehension " would have served 

 them 62 as well as their present hands. On the con- 

 trary, 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 con- 

 verted into mere grasping-hooks. 63 



As soon as some ancient member in the great series 

 of the Primates came, owing to a change in its manner 

 of procuring subsistence, or to a change in the con- 



62 'Quarterly Review,' April, 1869, p. 392. 



63 In Hylobates syndactylus, as the name expresses, two of the digits 

 regularly cohere ; and this, as Mr. Blyth informs me, is occasiorjally 

 the case with the digits of H. agilis, lar, and leuciscm. In Colobus the 

 thumb is likewise deficient ; these monkeys are strictly arboreal and 

 extraordinarily active (Brehni, ' Thierleben,' B. i. s. 50), but whether 

 they are better climbers or graspers than the species of the allied 

 genera, I do not know. 



