RETROSPECT AND PROSPECT 



questions, but, as speculation upon them is always fascinating, some pos- 

 sibilities will be briefly outlined. 



Plant and Animal Breeding. One of the major ways in which man has 

 influenced evolution is through plant and animal breeding for agricultural 

 and other purposes. The achievements in this field are great. There is 

 probably not a single plant which now grows in the farms and gardens of 

 the world which is the same as when man first cultivated it. Indeed, the 

 very survival of those plants which man has domesticated may be due to 

 the protection given them by man. For the plants which thrive best in the 

 wild are often the most difficult to grow under cultivation, while those 

 which thrive best under cultivation, such as corn, may quickly die out in 

 competition with wild species. Because of these facts, Mangelsdorf has 

 suggested that man has domesticated plants with character complexes 

 already unsuited for competition in the wild, so that it may be said that 

 man has rescued them from impending extinction, to the mutual advan- 

 tage of plant and man. By artificial selection, agriculturally desirable char- 

 acters, such as volume of seed production in grain plants, have been ac- 

 centuated, while other characters, perhaps more important in a wild state, 

 have dwindled. The bearing season of many plants has been much ex- 

 tended. Even the biochemical characters of plants have been altered by 

 artificial selection, for protein and vitamin content of many plants has 

 been significantly increased by selection of favorable breeding stocks. By 

 the same method, the range over which particular kinds of plants can be 

 successfully grown has been greatly extended. And the development of 

 new, resistant strains of plants is one of the chief weapons in combating 

 plant diseases, such as wheat rust. Although not generally so described, 

 many of the agricultural productions of man may properly be described 

 as good subspecies, not qualitatively difiFerent from naturally produced 

 subspecies. But the new wheats and other plants which have been pro- 

 duced by the induction of allopolyploidy are best regarded as artificially 

 produced species, or even genera, again not qualitatively different from 

 those which occur in nature. Indeed, in some cases, such as Galeopsis 

 tetrahit, the natural species itself has been resynthesized artificially. 



The achievements in animal breeding have been more modest but still 

 significant. From the wild horse, such divergent breeds as the Thorough- 

 bred race horse and the Percheron draft horse have been formed by se- 

 lection of breeding stock for the purposes desired. Different breeds of 

 cattle have been perfected for high milk production or for high beef pro- 

 duction. Each has been adapted to a wide variety of climates, from tropi- 

 cal to subarctic. Sheep have been specialized for production of wool or of 

 mutton. Chickens with much increased egg production have been devel- 

 oped. The immense variety of dogs, from Pekinese to St. Bernard, have 

 been produced by artificial selection under the hand of man. If these 

 extremes were found in nature, no one would hesitate to call them distinct 

 species. But because we know their history, we refer them all to a single 

 species, Canis familiaris. 



While the past achievements of plant and animal breeding are great, 

 there is every reason to believe that far greater achievements lie ahead, 



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