RETROSPECT AND PROSPECT 



for the greatest past achievements, such as the development of hybrid 

 corn, have been accomphshed during the past fifty, or even thirty, years, 

 using the tools of genetics which were previously not available. It is reason- 

 able to believe that the continued application of these principles will lead 

 to even better agricultural products, both plant and animal. Thus man is 

 truly achieving dominion over the world of life. 



Distribution and Evolution of Wild Species. Man has also had a 

 great influence on the distribution and evolution of wild species, and that 

 influence may be expected to continue and to increase. So far as his effects 

 on other organisms were concerned, primitive man probably was not 

 much more important than were many of the larger wild animals. But, as 

 his proficiency in the use of tools and the tilling of the soil increased, so 

 also did his influence on other organisms. Soon the presence of man be- 

 came a major selective force to which wild species, both plant and animal, 

 had to adapt themselves in order to survive. With the development of the 

 Industrial Age and the tilling of a very large portion of the arable soil in 

 all civilized countries, man's selective influence on other organisms has 

 reached a peak. In order to survive now, all living things must either 

 become adapted to the presence and activities of man, or else they must 

 be restricted to those dwindling refuges in which man's influence is least 

 prominent. 



Thus man has caused the extinction of many species and the extreme 

 reduction of others within recent times. The case of the passenger pigeon, 

 Ectopisies migratorius, is a well known example. Within the memory of 

 some persons still living, the passenger pigeons were so numerous that 

 flocks of them literally blackened the sky for hours at a time. The supply 

 of pigeons was regarded as inexhaustible, and they were very intensively 

 hunted and trapped for the market. But by 1880, passenger pigeons were 

 noticeably less numerous. By 1890, their numbers were seriously depleted. 

 By 1900, they were a rare bird, and movements were afoot to save the 

 pigeons. But all efforts to save them failed, and the last one died in the 

 Cincinnati Zoo in 1914. Extinction of the passenger pigeons is commonly 

 attributed to intensive hunting, but the equally intensive destruction of 

 the forests in which they found cover may have been quite as important 

 a factor. 



The buffalo were also prodigiously numerous when the white man in- 

 vaded North America. They are now reduced to a few isolated and pro- 

 tected herds, and to exhibition specimens. Again, intensive hunting may 

 have been an important factor in the decimation of the buffalo, but the 

 fencing of the range was equally important. Comparable stories could be 

 recited for many other species which inhabited North America before the 

 white man came. But they all simplv emphasize the statement with which 

 this discussion began, that if organisms are to survive, they must either 

 become adapted to the presence and activities of man, or they must be 

 restricted to those dwindling refuges in which his influence is not great. 



But man's influence is not always negative. Some organisms have profited 

 greatly by the activities of man. This is obvious in the case of domesticated 

 plants and animals, but it is also true of many wild species. Rats and mice, 



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