358 "The Theory of ISIatural Selection 



there appear correlated divergences in the reproductive 

 mechanism. 



This raises the question whether selection itself brings 

 about changes in the constitution, something that Darwin 

 himself was inclined to doubt. 



The Origin of Fitness 



We note that there are many varieties of seed structures 

 and that the shape of some seeds fits them to be scattered 

 by the wind. We assume, therefore, that the advantage 

 which comes to the species from having its seeds widely 

 scattered is in some way a cause of the seeds having the shape 

 in question. It would be just as logical, however, to say that 

 many seeds having shapes or appendages of certain kinds 

 are scattered by the wind. If these plants had seeds of a 

 different shape they would be scattered by moving animals 

 or by migratory birds — as is indeed the case with some 

 species. 



Darwin pointed out that in the domestic duck the 

 bones of the wing weigh less, and the bones of the leg more, 

 in proportion to the body skeleton, than do the corresponding 

 bones in the wild duck. This change from the ancestral 

 condition may be safely attributed, he thought, to the fact 

 that the domestic duck flies much less and walks more than 

 did the wild ancestors. Accepting the facts as stated, how- 

 ever, would it not be as logical to say that the domestic 

 ducks with reduced wings fly less because their wings are 

 inadequate, as to say that they have reduced their wings be- 

 cause of their flightless mode of life? 



Neither Darwin nor Lamarck nor any other naturalist 

 pretends to know how a particular variation arose in the first 

 instance. It is a matter of common observation that homol- 

 ogous organs in a series of animals are actually adapted to 

 the varying conditions under which the several species live. 

 To say, however, that such organs are modified to suit the 

 conditions of life is to imply that the conditions were effective 



