XVI] THE PROBLEM OF PHYLOGENY 1019 



where pressure falls there growth springs up in strength to meet it. 

 And, pursuing the same train of thought, we see that all this is true 

 not of the skeleton alone but of the whole fabric of the body. Muscle 

 and bone, for instance, are inseparably associated and connected; 

 they are moulded one with another ; they come into being together, 

 and act and react together*. We may study them apart, but it 

 is as a concession to our weakness and to the narrow outlook of 

 our minds. We see, dimly perhaps but yet with all the assurance 

 of conviction, that between muscle and bone there can be no change 

 in the one but it is correlated with changes in the other; that 

 through and through they are linked in indissoluble association; 

 that they are only separate entities m this limited and suboi'dinate 

 sense, that they are parts of a whole which, when it loses its com- 

 posite integrity, ceases to exist. 



The biologist, as well as the philosopher, learns to recognise that 

 the whole is not merely the sum of its parts. It is this, and much 

 more than this. For it is not a bundle of parts but an organisation 

 of parts, of parts in their mutual arrangement, fitting one with 

 another, in what Aristotle calls "a single and indivisible principle 

 of unity " ; and this is no merely metaphysical conception, but is in 

 biology t])e fundamental truth which lies at the basis of Geoffroy's 

 (or Goethe's) law of "compensation," or "balancement of growth," 



Nevertheless Darwin found no difficulty in believing that "natural 

 selection will tend in the long run to reduce any part of the organisa- 

 tion, as soon as, through changed habits, it becomes superfluous: 

 without by any means causing some oth^r part to be largely developed 

 in a corresponding degree. And conversely, that natural selection 

 may perfectly well succeed in largely developing an organ without 

 requiring as a necessary compensation the reduction of some ad- 

 joining partf " This view has been developed into a doctrine of 

 the "independence of single characters" (not to be confused with 

 the germinal "unit characters" of Mendelism), especially by the 

 palaeontologists. Thus Osborn asserts a "principle of hereditary 

 correlation," combined with a "principle of hereditary separability ^ 



* John Hunter was seldom wrong; but I cannot believe that he was right when 

 he said {Scientific Works, ed. Owen, i, p. 371), "The bones, in a mechanical view, 

 appear to be the first that are to be considered. We can study their shape, 

 connections, number, uses, etc., without considering any other part of the body.'' 



t Origin of Species, 6th ed. p. 118. 



