The Descent of Man 



point in the plainest manner to the conclusion 

 that man is the co-descendant of other mam- 

 mals of a common progenitor. 



We have seen that man incessantly pres 

 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 anunals. In both eases similar 

 laws of inheritance prevail. Man tends to in- 

 crease at a greater rate than his means of sub- 

 sistence; conesquently he is occasionally sub- 

 jected 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 in the work of natural 

 selection. 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 selection. Modifications formerly 

 of importance, though no longer of any special 

 use, are long-inherited. When one part is modi- 

 fied 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 surrounding conditions 

 of life, such as abundant food, heat or moistuiv: 

 and, lastly, many characters of slight physio- 

 logical importance, some indeed of considerable 

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