214 FROM THE GREEKS TO DARWIN 



mentions the suggestion of Linngeus: "From 

 hence [single hving filament], as Linnseus has 

 conjectured in respect to the vegetable world, it is 

 not impossible, but the great variety of species of 

 animals, which now tenant the earth, may have 

 had their origin from the mixture of a few natural 

 orders." Elsewhere he speaks of plants as having 

 arisen in the contest for light and air. He carries 

 the idea of sensibility and irritability into plant 

 life, and his theory of plant evolution is similar to 

 that of animal evolution. 



Erasmus Darwin was, however, fully con- 

 scious of the limitations of his theory of the origin 

 of adaptations, for in speaking of protective col- 

 oring he says:^ "The final cause of these colours 

 is easily understood, as they serve some purposes 

 of the animal, but the efficient cause would seem 

 almost beyond conjecture." The same problem of 

 adaptation we have seen propounded by Kant at 

 about the same period: "How can purposeful 

 forms of organization arise without a purposeful 

 working cause? How can a work full of design 

 build itself up without a design and without a 

 builder?" Of course we do not know whether 

 Darwin had this suggested to him by Kant, but 

 it is exceedingly interesting to see him so clearly 

 state the two-thousand-year-old problem of 'fit- 

 ness' which his grandson later largely solved. 



^Zoonomia, vol. 1, xxxix. 



