360 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1958 
of life. Organic evolution consists of a succession of threatened losses 
and recapturings of the adaptedness of living matter to its environ- 
ment. But the environment does not change the genotype of a living 
species directly, as some evolutionists of the past have wrongly as- 
sumed. The role of the environment consists rather in that it con- 
stantly presents challenges to the species; to these challenges the 
species may respond either by adaptive modification or by extinction. 
Tt would be an exaggeration to say that the above view of the evolu- 
tionary process is universally accepted. Few biological theories really 
are. However, the importance of natural selection, at least as an 
agent which guards against degenerative changes in populations, is 
denied by scarcely anyone. We need not labor the point that the 
evolution of the ancestors of the human species was brought about 
by the operation of the same fundamental biological processes which 
act elsewhere in the living world. A new situation has arisen with 
the advent of the human phase. Species other than man become 
adapted to their environment by changing their genes. In man, the 
adaptation to the environment occurs in part through development 
and modification of his learned tradition and culture. Man is able 
to adapt by changing either his genes or hisculture, or both. 
Another innovation has also occurred in the evolutionary pattern 
of the human species. Owing to the protection conferred upon cer- 
tain weaker genotypes by civilization, natural selection against these 
genotypes has become weakened or removed. Individuals and popu- 
lations which would die out under allegedly “natural” conditions 
survive and procreate in civilized societies. A large share of the 
blame for this interference with “normal” evolutionary processes is 
laid at the door of modern medicine. Although man possesses meth- 
ods of adaptation which are peculiar to his species, he is still subject 
to general biological laws. Biological evolutionary processes operate 
in the human species within the unique evolutionary pattern condi- 
tioned by human intellectual powers; yet it would certainly be a 
dangerous matter to abolish the controlling influence of the processes 
of selection. 
STRUGGLE FOR EXISTENCE AND SURVIVAL OF THE FITTEST 
According to Darwin’s own testimony, the theory of natural selec- 
tion was suggested to him in 1838, when he “happened to read for 
amusement” Malthus’s “Essay on the Principles of Population.” Any 
living species is able to multiply in geometric progression, and hence 
to increase in numbers until it outgrows its food supply. In reality 
this happens quite rarely, and populations of most species are stable 
within relatively narrow limits. The causes which bring about the 
relative constancy of numbers are by no means well known even at 
