NATURAL SELECTION—DOBZHANSKY AND ALLEN 373 
ary trends are likely to be outweighed by adaptive changes, but the 
direction of these changes is uncertain. 
CONCLUSIONS AND SUMMARY 
The idea explicit or implicit in many writings, that all would be 
well with the human species if obstructions to natural selection were 
removed, does not stand critical examination. Man, like any other 
biological species, is constantly subject to natural selection. The 
genotypes which possess the highest Darwinian fitness in the environ- 
ments created by man’s inventive genius are, however, not the ones 
which were most favored by selection in the past. Natural selection 
cannot maintain the adaptedness of modern human populations to 
environments which no longer exist, nor can it preadapt them to 
environments of the future. 
Natural selection is opportunistic; it does not always lead to im- 
proved adaptedness. After all, extinction has been the fate of count- 
less biological species which lived in the state of nature and which 
were at all times subject to natural selection. It would be folly for 
our species to risk the same fate for the juggernaut of blind biological 
force. One of the causes of extinction is too narrow an adaptedness 
to a circumscribed biological opportunity which proves only tempo- 
rary. Man has reached a solitary pinnacle of evolutionary success 
by having evolved a novel method of adapting to the environment, 
that by means of culture. Having ventured on this biological experi- 
ment, our species cannot any longer rely entirely on forces of natural 
selection as they operate on the biological level. Man must carefully 
survey the course that lies ahead and constantly study his genetic 
progress. He can then prepare to take over the controls from nature 
if it should become necessary to correct the deficiencies of natural 
selection. Only thus can he insure for himself continued evolutionary 
advance. 
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