694 THE DESCENT OF MAN. 



others, such as the mutual affinities of the members of the 

 same group, their geographical distribution in past and 

 present times, and their geological succession. It is incredi- 

 ble that all these f;icts should speak falsely. He who is not 

 content to look, like a savage, at the phenomena of nature 

 as disconnected, cannot any longer believe that man is the 

 work of a separate act of creation. He will be forced to 

 admit that the close resemblance of the embryo of man to 

 that, for instance, of a dog the construction of his skull, 

 limbs and whole frame on the same plan with that of other 

 mammals, independently of the uses to which the parts 

 may be put the occasional reappearance of various 

 structures, for instance of several muscles, which man 

 does not normally possess, but which are common to i;Le 

 Quadrumana and a crowd of analogous facts all point 

 in the plainest manner to the conclusion that man is 

 the co - descendant with other mammals of a common 

 progenitor. 



We have seen that man incessantly presents individual 

 differences in all parts of his body and in his mental 

 faculties. These differences or variations seem to be 

 induced by the same general causes, and to obey the same 

 laws as with the lower animals. In both cases similar laws 

 of inheritance prevail. Man tends to increase at a greater 

 rate than his means of subsistence; consequently he is occa- 

 sionally subjected to a severe struggle for existence, and 

 natural selection will have effected whatever lies within its 

 scope. A succession of strongly marked variations of a 

 similar nature is by no means requisite; slight fluctuating 

 differences in the individual suffice for the work of natural 

 selection; not that we have any reason to suppose that in 

 the same species all parts of the organization tend to vary 

 to the same degree. We may feel assured that the inherited 

 effects of the long-continued use or disuse of parts will 

 have done much in the same direction with natural selec- 

 tion. Modifications formerly of importance, though no 

 longer of any special use, are long-inherited. When one 

 part is modified other parts change through the principle 

 of correlation, of which we have instances in many curious 

 cases of correlated monstrosities. Something may be 

 attributed to the direct and definite action of the surround- 

 ing conditions of life, such as abundant food, heat or 

 moisture; and, lastly, many characters of slight physio- 



