322 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
Beagle. His caution is also indicated by the fact that his observa- 
tions were under consideration for some 20 years before his con- 
clusions were published. 
This second period in the history of evolution, which we may 
call the medieval period, is marked by the appearance of several ex- 
planations. I shall mention only the three most conspicuous ones, 
and there is no need to define these in detail. 
The explanation which ushered in the period was proposed simul- 
taneously and independently in 1790 by Goethe, of Germany, St. 
Hilaire, of France, and Erasmus Darwin, of England. Observa- 
tions of responses to changed environment led them to the con- 
clusion that environment is the direct cause of change, actually 
molding forms. This evolutionary factor, therefore, is entirely 
external to animal or plant. It was a natural first explanation, 
but of course it was too superficial, and environment as a direct 
cause of evolution soon passed into the historical background. It 
deserves mention only because it was the first attempt at an ex- 
planation. In 1801 Lamarck, in a series of lectures, announced 
his explanation, calling it the theory of “appetency.” This was 
really the first explanation with a body of doctrine, and hence,. 
Lamarck has often been called the “ founder of organic evolution.” 
The term “ appetency,” however, has been abandoned, and its real 
meaning expressed by the phrase “the effect of use and disuse.” 
With Lamarck, environment is not the direct cause of the change, 
according to the earlier explanations, but the occasion for the change. 
The cause is the striving, the effort to do something that had be- 
come necessary. Thus organs would become developed as a con- 
sequence of some change in environment calling them into use; and, 
conversely, organs would gradually become aborted as a consequence 
of some change in environment that eliminated their use. This 
explanation rests absolutely upon the inheritance of acquired char- 
acters, meaning characters not inherited by the possessor, but ac- 
quired during the life of the individual. 
In 1858 the epoch-making explanation of Darwin was announced, 
an explanation which was dominant for about 50 years. It is too 
familiar to need explanation. In brief, it claims that nature selects 
among variations, that the method of selection is competition, that 
the result is the destruction of the relatively unfit, or as Spencer 
puts it, “the survival of the fittest.” In brief, the theory is really 
an explanation of what is called adaptation. 
As facts multiplied, the current explanations of evolution were 
found to be inadequate to explain some of them. ‘This led to a 
general misunderstanding of the situation by the uninformed public. 
For example, more intensive study developed the fact that Darwin’s 
explanation does not always explain. His name is so identified 
