xv GENERAL ADAPTATIONS 317 



scientific, so utterly contemptible as it has hitherto been 

 declared to be by many of our great authorities, it is 

 certainly advisable to show how various facts in nature 

 bear upon it and are explained by it. I will therefore 

 now add a few more considerations to those I have hitherto 

 set forth. 



On the question of the colour-sense I have already 

 argued that though it may exist in birds and insects, it is 

 hardly likely that it produces any such high aesthetic 

 pleasure as it does in pur own case. All that the evidence 

 shows is, that they do perceive what are to us broad 

 differences of colour, but we have no means whatever of 

 knowing what they really perceive. It is a suggestive 

 fact that colour-blind persons, though they do not see 

 red and green as strongly contrasted as do those with 

 normal vision, yet do perceive a difference between them. 

 It is therefore quite possible that birds may see differences 

 between one strongly marked colour and another without 

 any sense of what we should term colour, and at all events 

 without seeing " colours " exactly as we see them. It is 

 now generally admitted that birds arose out of primitive 

 reptiles, and from their very origin have been quite distinct 

 from mammals, which latter probably diverged a little later 

 from a different stock and in a somewhat different direction. 

 The eyes of both were developed from the already existing 

 reptilian eye, and their type of binocular vision may be 

 very similar. But at that early period there were, it is 

 believed, no coloured flowers or edible coloured fruits, and 

 it is probable that the perception of colour arose at a 

 much later period. It is therefore unlikely that a faculty 

 separately developed in two such fundamentally different 

 groups of organisms should be identical in degree or even 

 in nature unless its use and purpose were identical. But 

 birds are much more extensive fruit- eaters than are 

 mammals, the latter, as we have seen, being feeders on 

 nuts which are protectively tinted rather than on fruits, 

 while their largely developed sense of smell would render 

 very accurate perception of colour needless. It is sugges- 

 tive that the orang-utan of Borneo feeds on the large, green, 

 spiny Durian fruit ; and I have also seen them feeding 



