THE WEAK SIDES OF NATURAL SELECTION. to 



being devoured by wolves, and in another through being deprived 

 of pasture by the competition of goats, the difference would be 

 important from a naturalist's point of view. 



When the Darwinian (I say this without being myself a 

 Darwinian) is assailed with a volley of questions, "Can your theory 

 account for this, or for that ? " it is generally wisest to reply " No, 

 we are human, and do not profess to account for everything." 

 When Mr. Slater asks " why do we never see in any vertebrate 

 animal more than two pairs of limbs, or their rudiments ? Why 

 fire p:u*ts that have lost their function, such as the external ear in 

 mankind, or the vermiform appendage to the cascum, still produced 

 in generation after generation?" it is a sufficient answer to 

 say that we have no means of measuring the force of heredity, 

 which tends to the preservation of such organs, against the forces 

 which tend to their disappearance; but the Darwinian, or any 

 other, theory of evolution must take account of the existence of 

 both. And when he goes on to ask " why is the secretion of silk 

 confined to invertelmite animals, and the production of physio- 

 logical venoms to cold-blooded ones? "he is propounding questions 

 far more difficult than if he were to ask why certain crystalline 

 forms are correlated with certain chemical properties ; yet, so far 

 as I am aware, the first step has not yet been taken in the 

 explanation of such correlations in the inorganic world. The same 

 applies to his concluding difficulty. " Natural selection may tell 

 us that the colours of an animal approximate to the colours of the 

 objects by which it is surrounded. This is very well as far as it 

 can be demonstrated, but we rather seek to know how, when, 

 where, anclfrom what materials thecolouring matters are produced." 

 This is as reasonable as if he were to see a shipyard with machines 

 of magnificent power and precision for forging steel, and then 

 complain because he was informed by his guide that the chemistry 

 of stael is very imperfectly understood. 



I will conclude my reply to Mr. Slater with the consideration of 

 what appears to me a purely imaginary difficulty, though 1 am 

 aware that it has been strongly insisted on. I mean the position 

 of the mouth in the shark, which is on the under side of the fish, 

 some way back from the snout, instead of at the snout, as in some 

 allied fishes. Mr. Slater says, " This peculiarity of the mouth 

 must be a constant disadvantage to the shark. By it he often loses 

 an expected prey, as many a diver and many a sailor who has 

 fallen overboard can testify." This has been constantly repeated, 

 and yet a little reflection will show its untenability. If a diver 

 or a half-drowned sailor seriously asserts that he was saved from 

 being devoured by a shark because the shark lost the imperceptible 

 fraction of a second which he required to swim through the 

 distance between his snout and his mouth, I cannot credit it.* 



* The position of the mouth may be fitted for his usual prey, but the 

 shark having to turn to seize a man, gives the latter an advantage. — Ed. 



