GENERAL BIOLOGY. 



47 



now peopling the earth were entirely different from those that 

 flourished in the past, the objections to the doctrine of descent 

 would be greatly strengthened ; but when it is found that there 

 is in some cases a scarcely broken succession of forms, great 

 force is added to the arguments by which we are led to infer 

 the connection of all forms with one another. 



To illustrate by a single instance: the existing group of 

 horses, with a single toe to each foot, was preceded in geological 



Fig. 48— Bonea of the feet of the difEerent genera of Sjuidm (after Marsh), a, foot 

 of Orohimus {'Eocene); b^ foot oi Anchwierium (Lower 'Miocene); c^footoiMip- 

 parion (Pliocene); d, toot of the recent genus Sguus. 



time in America by forms with a greater number of toes, the 

 latter increasing according to the antiquity of the group. 

 These forms occur in succeeding geological formations. It is 

 impossible to resist the conclusion that they are related gene- 

 alogically (phylogenetically). 



8. Progression. — Inasmuch as any form of specialization that 

 would give an anunal or plant an advantage in the struggle for 

 existence would be preserved, and as in most cases when the 

 competing forms are numerous such would be the case, it is 

 passible to understand how the organisms that have appeared 

 have tended, on the whole, toward a most pronounced pro- 

 gression in the scale of existence. This is well illustrated in 

 the history of civilization. Barbarous tribes give way before 

 civilized man with the numberless subdivisions of labor he in- 

 stitutes in the social organism. It enables greater numbers to 

 flourish, as the competition is not so keen as if activities could 

 be exercised in a few directions only. 



9. Domesticated Animals. — ^Darwin studied our domestic ani- 

 mals long and carefully, and drew many important conclusions 



