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872 OUTLINES OF EVOLUTIONAKY BIOLOGY 



that the difference of their forms and qualities has arisen only 

 from the different irritabilities and sensibilities, or voluntaries, 

 or associabilities, of this original living filament ; and perhaps in 

 some degree from the different forms of the particles of the fluids, 

 by which it has been at first stimulated into activity." 



" From their first rudiment, or primordium, to the termina- 

 tion of their lives, all animals undergo perpetual transformations; 

 which are in part produced by their own exertions inconsequence 

 of their desires and aversions, of their pleasures and their pains, 

 or of irritations, or of associations ; and many of these acquired 

 forms or propensities are transmitted to th9ir posterity." 



Dr. Darwin thus passes from the discussion of what is now 

 termed the qrUogenv or development of the individual to that of 

 the phylogeny or development of the race. From consideration 

 of the former he endeavoured to gain some insight into the latter, 

 and it may be fairly claimed that he thus anticipated what is 

 known in modern biology as the Eecapitulation Hypothesis : 



"From thus meditating on the great similarity of the struc- 

 ture of the warm-blooded animals, and at the same time of the 

 great changes they undergo both before and after their nativity ; 

 and by considering in how minute a portion of time many of 

 he changes of animals above described have been produced ; 



ould it be too bold to imagine, that in the great length of time, 

 since the earth began to exist, perhaps millions of ages before 

 the commencement of the history of mankind, would it be too 

 bold to imagine, that all warm-blooded animals have arisen from 

 one living filament, which the great First Cause endued with ani- 

 mality, with the power of acquiring new parts, attended with 

 new propensities, directed by irritations, sensations, volitions 

 and associations ; and thus possessing the faculty of continuing 

 to improve by its own inherent activity, and of delivering down 

 those improvements by generation to its posterity, world without 

 end ! " 



Erasmus Darwin was perfectly familiar with the idea f 

 adaptation, as manifested, for example, in the colours f 

 animals : 



" The colours of many animals seem adapted to their purposes 

 of concealing themselves either to avoid danger, or to spring upfn 

 their prey. Thus the snake and wild cat, and leopard, are s* 

 coloured as to resemble dark leaves and their lighter interstices* ; 

 birds resemble the colour of the brown ground, or the green 



