THE HISTORY OF BIOLOGY 385 



by studying the time it took to make present changes in the earth's sur- 

 face, estimate the length of time and the age of the various strata of the 

 earth. 



With the intellectual soil prepared in this way Charles Darwin (1809- 

 1882), published his epoch-making book, The Origin of Species by Nat- 

 ural Selection, in 1859. Darwin accepted, without explaining, the fact 

 that variations do occur. He assumed that the origin of existing species 

 could be explained by accepting the fact that variations did occur, and 

 that nature then selected which organisms should continue to exist by 

 killing off those which did not inherit as many variations of a survival 

 value. He assumed that acquired characteristics were inheritable, and 

 that the struggle for existence eliminated the unfit. Darwin had spent 

 twenty years in gathering the facts on which he based his theory, but 

 Alfred Russel Wallace (1822-1913) had reasoned out a similar theory 

 without having the facts that Darwin had, and it is an interesting coinci- 

 dence that both men were working on the same thought at the same time, 

 though independently. Darwin was willing to surrender all his work to 

 the younger man, but Wallace insisted that Darwin was to have the 

 credit as the latter had done such an immense amount of work on the 

 matter. 



Evolution now serves the biological world as a sort of general plan 

 of the results of heredity, while genetics deals with the factors which 

 produce these results. 



Thomas Huxley (1825-1895), though not a believer in the Darwinian 

 theory of Natural Selection, sprang to the defense of Darwin, primarily, 

 as Professor Poulton says, because Darwin was so constantly and per- 

 sistently treated unjustly. And it was Huxley who made Darwinism 

 popular. Hooker (1817-1911) in England, Haeckel (1834-1919) and 

 Weismann in Germany, and the Botanist Gray (1810-1888) in America, 

 were early converts. Haeckel, however, was too much of the showman, 

 and was always willing to sacrifice truth and accuracy to win his point. 



Summing up what has been said, we may say that the basis of great- 

 ness in science is not the brilliancy of an individual discovery, but the 

 finding and enunciating of a principle which can find many applications 

 by those who follow. 



The great findings, considered from this point of view of obtaining 

 principles and wide influence in biology, may be said to be the discovery 

 of protoplasm ; the establishment of the cell-theory ; the theory of organic 

 evolution ; the demonstration that germs are a tremendous factor in dis- 

 ease; and the experimental study of inheritance as suggested by the work 

 of Mendel and Weismann. 



And the most important writings of the most important men may 

 be summarized here by following Professor Wm. Locy's account, which 

 we have modified slightly. 



