582 



CONTINUITY OF LIFE 



Fig. 24-1. Gregor Mendel (1822-1884), working with 

 plants, laid the foundation for modern genetics, al- 

 though his great work was not recognized by the 

 scientific world until 1900. 



tifully adapted by size, aggressiveness, and 

 behavior to all of the whims of primitive 

 man, to say nothing of the idealistic require- 

 ments of man today. The greatest changes 

 were acquired through selection long be- 

 fore anything was known about the science 

 of genetics. Selection is still going on today 

 but witli the aid of some understanding as 

 to how it should be done. 



Other animals, such as horses, cattle, and 

 sheep, as well as many plants, were domes- 

 ticated later, and in all of them intentional 

 selection for improvement was practiced. 

 This was done simply by applying the rule 

 that "like begets like." Even though we 

 know now that this "principle" does not al- 

 . ways follow, the fact remains that after 

 thousands of years of selection animals and 

 plants were gradually changed toward the 

 kind that could best be utilized by man. 

 Therefore, the principles of genetics were 

 beneficially employed by man for centuries 

 without any knowledge whatever of how 

 they operated. 



Although information concerning selec- 



tive breeding of domestic plants and ani- 

 mals was accumulating through the eight- 

 eenth century and the first half of the 

 nineteenth, no one had been successful in 

 formulating any definite theory or law as 

 to how this all came about. Inspired by 

 Darwin's Origin of Species, Sir Francis Gal- 

 ton began a series of studies on inheritance 

 in about 1857 which resulted in significant 

 conclusions concerning variation within a 

 species. In regard to inheritance he, like 

 many others, had studied certain complex 

 characters such as height and intelligence 

 and tried to follow them in succeeding gen- 

 erations. This resulted in an impossible situ- 

 ation because the problem became too 

 complicated and no generalizations could 

 be made from such a study. 



It was left for Gregor Mendel, an obscure 

 Austrian monk, to solve the problem (Fig. 

 24-1). In 1864, he presented his efforts in 

 the form of a short paper read before a 

 scientific society of his day. Mendel's paper 

 could hardly be heard above the heated 

 arguments that had been stimulated by 

 Darwin's forceful presentation of evolution 

 published seven years previously, yet in it 

 one of the principal keys to evolution was 

 handsomely portrayed by this modest 

 clergyman. One can easily imagine the cha- 

 grin that swept over this truly great man 

 when he realized that his findings, which to 

 him must have seemed fundamental, were 

 passed over by the scientific world. The 

 significance of his monumental work was 

 not appreciated for 36 years, 16 years after 

 Mendel had died. About 1900, three scien- 

 tists working in different parts of the world 

 came upon essentially the same thing that 

 Mendel had discovered many years before. 

 They were: DeVries in Holland, Correns in 

 Germany, and Tschermak in Austria. Men- 

 del's paper, which had gathered dust 

 through the years, was republished and only 

 then did this humble man receive the 

 credit due him. With this rediscovery of 

 Mendel's Laws the science of genetics was 

 born. 



