INTKODUCTORY 17 



endless diversity of actual plant forms. But at first he certainly 

 thought of this transformation only in the ideal sense, and not as 

 a factual evolutionary process. 



The first who definitely maintained the latter view was, remark- 

 ably enough, the gx'and father of the man who, in our own day, made 

 the theory of descent finally triumphant, the English physician 

 Erasmus Darwin, born 1731. This quiet thinker published, in 1794, 

 a book entitled Zoonomia, and in it he takes the important step of 

 substituting for Goethe's ' secret law ' a real relationship of species. He 

 proclaims the gradual establishment and ennobling of the animal 

 world, and bases his view mainly on the numerous obvious adapta- 

 tions of the structure of an organ to its use. I have not been able 

 to find any passage in the book in which he has expressly indicated 

 that, because many of the conditions of life could not have existed 

 from the beginning, these adaptations are therefore, as such, an 

 argument for the gradual transformation of species. But he assumed 

 that such exact adaptations to the functions of an organ could only 

 arise through the exercise of that function, and in this he saw a proof 

 of transformation. Goethe had expressed the same idea when he 

 said, ' Thus the eagle has conformed itself through the air to the air, 

 the mole through the earth to the earth, and the seal through the 

 water to the water,' and this shows that he too at one time thought 

 of an actual transformation. But neither he nor Erasmus Darwin 

 were at all clear as to hoiu the use of an organ could bring about its 

 variation and transformation. The latter only says that, for instance, 

 the snout of the pig has become hard through its constant grubbing in 

 the ground ; the trunk of the elephant has acquired its great mobility 

 through the perpetual use of it for all sorts of purposes ; the tongue 

 of the herbivore owes its hard, grater-like condition to the rubbing to 

 and fro of the hard grass in the mouth, and so on. How acute and 

 thoughtful an observer Erasmus Darwin was, is shown by the fact 

 that he had correctly appreciated the biological significance of many 

 of the colour-adaptations of animals to their surroundings, though it 

 was reserved for his grandson to make this fully clear at a much 

 later date. Thus he regarded the varied colouring of the python, 

 of the leopard, and of the wild cat as the best adapted for concealing 

 them from their prey amid the play of light and shadow in a leafy 

 thicket. The black spot in front of the eye of the swan he con- 

 sidered an arrangement to prevent the bird from being dazzled, 

 as would happen if. that spot were as snow-white as the rest of the 

 plumage. 



At the end of the book he sums up his views in the following 

 I. c 



