GENERAL ZOOLOGY 



EVIDENCE FROM DOMESTICATION AND SELECTIVE BREEDING 



We need discuss only briefly another line of evidence bearing on the reality 

 ot organic evolution and on mechanisms which may have operated to bring 

 it about. It is common knowledge that mankind began, long before the dawn 

 of recorded history, to bring wild species of animals and plants under 

 domestication, for his own convenience and welfare. The establishment of 

 practices of agriculture and animal husbandry undoubtedlv marked a most 

 significant epoch in the cultural evolution of man, leading to the rise of 

 settled population groups with a relatively dependable supplv of foods and 

 other necessities yielded by domesticated plants and animals. In the 

 thousands of years during which these practices have developed, distinctive 

 types of organisms have been produced, differing markedly from their wild 

 forebears. In some cases it is possible to identify with reasonable certainty 

 the original wild species from which all the domestic breeds appear to have 

 descended; for example, the multitudinous breeds of domestic poultrv are 

 believed to have descended, by different genetic paths, from wild Asiatic 

 jungle fowl. The differences among modern breeds, and between these and 

 the ancestral types, could hardly be greater, considering that the process 

 of domestication has been in progress during only a few thousand years. 



Man has, in a very real sense, brought about evolution in the lines of 

 animals and plants he has domesticated. He has done this bv a constant 

 process of artificial selection, choosing for breeding those types which from 

 his own standpoint possessed desirable characteristics. By thus selecting 

 some forms for survival and reproduction and rejecting others with less 

 desirable traits, man has arranged for "the survival of the fittest" — the 

 fittest in this case being the types that best suited man's needs of the moment. 



Charles Darwin, in his famous works on evolution, argued very forcefully 

 that evolution by this artificial selection appears completely analogous to 

 evolution by natural selection in wild populations under conditions in nature, 

 without man's intervention. If we substitute for man's standards of selection 

 the many environmental factors which presumably operate in nature to select 

 some types for survival while eliminating others, the comparison seems apt 

 indeed. One fact has been raised in exception to this line of reasoning: 

 whereas among natural populations different species can seldom be succes- 

 fully interbred, the "species" man has developed through artificial selection 

 are usually interfertile. That is, no matter how vast the apparent differences 

 may be between two kinds of dogs, or two kinds of poultry or cattle, these 

 animals can usually be crossed to produce fertile offspring. This is one 

 reason for referring to varieties or breeds of domestic animals, rather than 

 calling them different species, even though their differences may be so extreme 

 that if these types were discovered in nature they would probably be identified 

 as different species. Undoubtedly, however, one of man's criteria for the 

 preservation of types has been fertility, and continued interfertility may, 



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