1908-9] HuMAN EvoLUTION AND HUMAN DISEASE. 547 
disease, has been a most influential factor in human evolution. The human 
race in the step which it took from the arboreal anthropoid to man, rose 
above many of the selective influences which up to that point had deter- 
mined the survival of the fittest, but with that step in evolution a new 
series of selective influences arose and by no means the least important 
was disease. With the growth of civilization, however, there grew the 
knowledge of prophylaxis and step by step we began to interfere again 
in natural selection and to prevert the selective action of human disease. 
There are those who say that this is a mistake, that we are thus tending 
to preserve the unfit. But a very little consideration must show us that 
this cannot be so, it only seems to be the case because as yet our efforts 
are not successful) but, with improved knowledge and better methods, 
we must necessarily again rise superior to the slower workings of natural 
selection and the ultimate result upon the race must be beneficial. It 
is possible even now to give examples of this successful interference, 
but perhaps the most striking example of the present day is the fight 
against malaria and yellow fever in the tropics. How far reaching for 
tropical civilization this fight will be no one can prophesy, but there can 
be no doubt that whereas at present there are many tropical regions into 
which the civilized white man dares not enter, in the years to come he will 
live in them almost as safely as in the more temperate zones. 
And in the temperate zones the fight against all our epidemics, such 
as tuberculosis, typhoid and other infections must result in a higher evolu- 
tion of man which will come the more quickly the results of the scientific 
study of Medicine are applied to disease prophylaxis. It is, and will be 
delayed by ignorance and prejudjce, but here again natural selection will 
assert itself aud ignorance and prejudice cannct survive. 
