SELECTION ON MAN. 307 
seems that the best of the argument is on the side of 
- those who maintain the primitive diversity of man. 
Their opponents have not been able to refute the per- 
manence of existing races as far back as we can trace 
them, and have failed to show, in a single case, that 
at any former epoch the well marked varieties of man- 
kind approximated more closely than they do at the 
present day. At the same time this is but negative 
evidence. A condition of immobility for four or five 
thousand’ years, does not preclude an advance at an 
earlier epoch, and—if we can show that there are 
causes in nature which would check any further phy- 
sical change when certain conditions were fulfilled— 
does not even render such an advance improbable, if 
‘there are any general arguments to be adduced in its 
favour. Such a cause, I believe, does exist; and I 
shall now endeavour to point out its nature and its 
mode of operation. ‘ 
Outline of the Theory of Natural Selection. 
In order to make my argument intelligible, it is 
necessary for me to explain very briefly the theory of 
‘“‘ Natural Selection” promulgated by Mr. Darwin, 
and the power which it possesses of modifying the 
forms of animals and plants. The grand feature in 
the multiplication of organic life is, that close general 
resemblance is combined with more or less individual 
variation. The child resembles its parents or ancestors 
more or less closely in all its peculiarities, deformities, 
or beauties ; it resembles them in general more than it 
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