CiiAi-. XXI. General Summary. 609 



to modifications acquired independently of selection, and due 

 to variations arising from the nature of the organism and the 

 action of the surrounding conditions, or from changed habits of 

 life, no single pair will have been modified much more than the 

 other pairs inhabiting the same country, for all will have been 

 continually blended through free intercrossing. 



By considering the embryological structure of man, — the 

 homologies which he presents with the lower animals, — the 

 rudiments which he retains,— and the reversions to which he is 

 liable, we can partly recall in imagination the former condition 

 of our early progenitors ; and can approximately place them in 

 their proper place in the zoological series. We thus learn that 

 man is descended from a hairy, tailed quadruped, probably 

 arboreal in its habits, and an inhabitant of the Old World. 

 This creature, if its whole structure had been examined by a 

 naturalist, would have been classed amongst the Quadrumana, 

 as surely as the still more ancient progenitor of the Old and 

 New World monkeys. The Quadrumana and all the higher 

 mammals are probably derived from an ancient marsupial 

 animal, and this through a long line of diversified forms, from 

 some amphibian-like creature, and this again from some fish-like 

 animal. In the dim obscurity of the past we can see that the 

 early progenitor of all the Vertebrata must have been an aquatic 

 animal, provided with branchiae, with the two sexes united in 

 the same individual, and with the most important organs of the 

 body (such as the brain and heart) imperfectly or not at all 

 developed. This animal seems to have been more like the larvae 

 of the existing marine Ascidians than any other known form. 



The high standard of our intellectual powers and moral dis- 

 position is the greatest difficulty which presents itself, after we 

 have been driven to this conclusion on the origin of man. But 

 every one who admits the principle of evolution, must see that 

 the mental powers of the higher animals, which are the same in 

 kind with those of man, though so different in degree, are 

 capable of advancement. Thus the interval between the mental 

 powers of one of the higher apes and of a fish, or between those 

 of an ant and scale-insect, is immense ; yef their development 

 does not offer any special difficulty ; for with our domesticated 

 animals, the mental faculties are certainly variable, and the 

 variations are inherited. No one doubts that they are of the 

 utmost importance to animals in a state of nature. Therefore 

 the conditions are favourable for their development through 

 natural selection. The same conclusion may be extended to man ; 

 the intellect must have been all-important to him, even at a very 



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