372 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1958 
Selection for many traits at once always makes slower progress 
than selection for one or a few traits. Insofar as natural selection 
formerly maintained genetic traits that have now become useless, 
civilization has eliminated a probable source of interference that 
impeded selection for cultural adaptability. Whether selection in the 
latter respect is in an absolute sense stronger or weaker than formerly, 
it is probably operating more efficiently. 
Whatever emphasis is placed here on the positive aspects of natural 
selection under civilization is not intended as a denial of all negative 
aspects. Man’s increasing physical dependence on his cultural her- 
itage, beginning with clothing and cooked food, can be taken as a 
historical fact, and accelerated specialization in this direction is to 
some extent inevitable. Conflicts in our present culture between re- 
production and higher education, or between reproduction and self- 
control, are almost completely new selective forces in human evolution. 
It is not at all apparent how these conflicts would be resolved in the 
natural course of cultural progress. On the other hand, artificial 
attempts to counter such selection by “eugenic” support of culturally 
desirable types would inevitably lead to another type of dangerous 
specialization; the very need of these types for such support, insofar 
as the need exists, proves their failure to adapt biologically to civil- 
ization. Dependence of society upon complex reproductive controls 
seems to be a higher order of specialization, whether better or worse, 
than dependence of the individual on medical and technical aids. 
From a long-term point of view, another effect of civilization may 
be more important than changes in selection pressures per se. Indi- 
vidual genetic variation is the basis for selection, and this has been 
accentuated in modern man for several reasons. First, relaxation 
of selection in any respect immediately increases the proportion of 
minor and extreme abnormalities in the surviving population. 
Second, new environments, as well as the increasing proportion of 
deviant individuals, permit fuller expression of genetic differences 
formerly masked in uniform phenotypes. An example of this is 
perhaps to be seen in some childhood reading disorders, which would 
make little or no difference in an illiterate population. Third, migra- 
tion and intermarriage of formerly separate races or groups produce 
a great new diversity of genotypes. Fourth, increased survival of 
mutations results, to a small extent, in greater prevalence of genes 
that raise the mutation rate. 
Even if selection should be reversed for a brief period of time the 
above sources of increased genetic variation will, in Schmalhausen’s 
words, mobilize the variability of the species. Thus, civilization is 
now preparing man for rapid evolution in whatever direction long- 
term selection may determine. As Jong as populations remain large, 
and as long as competition exists in any form, degenerative evolution- 
