Characters as Adaptive and Specific. 179 



number of genera in the way above indicated. But 

 although the question of fact is thus really closed, 

 there remains a more ultimate question as to its 

 theoretical interpretation. For, as already pointed 

 out, no matter how great an accumulation of such 

 facts may be collected, our opponents are always able 

 to brush them aside by their a priori appeal to the 

 argument from ignorance. In effect they say We 

 do not care for any number of thousands of such 

 facts ; it makes no difference to us what " proportional 

 number" of specific characters fail to show evidence 

 of utility ; you are merely beating the air by adducing 

 them, for we are already persuaded, on antecedent 

 grounds, that all specific characters must be either 

 themselves useful, or correlated with others that are, 

 whether or not we can perceive the utility, or suggest 

 the correlation. 



To this question of theoretical interpretation, there- 

 fore, we must next address ourselves. And here, 

 first of all, I should like to point out how sturdy must 

 be the antecedent conviction of our opponents, if 

 they are to maintain it in the face of such facts as 

 have just been adduced. It must be remembered 

 that this antecedent conviction is of a most uncom- 

 promising kind. By its own premisses it is committed 

 to the doctrine that all specific characters, without 

 a single exception, must be either useful, vestigial, or 

 correlated. Well, if such be the case, is it not some- 

 what astonishing that out of 474 differences of colour 

 which are distinctive of the 23 species of the genus 

 Macropus, no single one appears capable of having any 

 utility demonstrated, or indeed so much as suggested ? 

 For even the recent theory that slight differences of 



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