THE GROUPS AND ANCESTRY OF ORGANISMS 



113 



TABLE 7.1 GEOLOGICAL CALENDAR (conlinued) 



CRYPTOZOIC EON 



first work to establish definitely a prehistoric record of 

 life. Malthus, primarily a mathematician and econo- 

 mist, wrote An Essay on the Principle of Population. This 

 essay suggested that (1) the breeding potential (Mal- 

 thus referred to man) is much greater than environ- 

 mental resources; (2) this leads to competition for 

 available materials; therefore, (3) there is a struggle 

 for existence. Malthus pointed out that all this occurs 

 because population increase is geometric, whereas the 

 potential increase in environmental materials is, at 

 best, arithmetic. To summarize, these two men pro- 

 posed a prehistoric fossil record, portraying gradual 

 change in life; the means of population increase; the 

 presence of competition; and a struggle for existence. 

 These principles of evolution directly lead to five gen- 

 eral conclusions that usually are credited to Darwin 

 alone: (1) members of the same species display indi- 

 vidual differences, (2) more offspring are produced 

 than can survive, (3) overpopulation leads to competi- 

 tion, (4) competition ends in the survival of individu- 

 als that are best suited to their environment (survival 

 of the fittest), and (5) new species arise from survival 

 of the fittest. 



In 1858, while Charles Darwin (1809-1882) was 

 gathering evidence to verify these ideas, another 

 naturalist, Alfred R. Wallace (1823-1913), wrote 

 Darwin. In this letter Wallace showed that his years 



of study of East Indian plants and animals brought 

 him to the same ideas about evolution. Although 

 Wallace's ideas were independently derived, there is 

 little doubt that the ideas were stimulated by his cor- 

 respondence with Darwin. Wallace "s letter led to 

 the now famous Darwin-Wallace essay of July, 1858, 

 which presented their conclusions about evolution be- 

 fore the Linnean Society of London. However, Dar- 

 win now is credited as the father of evolution because 

 of his 1859 publication. On the Origin of Species by 

 Means of Natural Selection. 



Darwinism was a tremendous contribution to mod- 

 ern evolutionary thought. However, certain of his 

 hypotheses were invalid. Competition and struggle 

 for existence do exist, but these factors are not neces- 

 sarily most intense among individuals of the same 

 species. Of equal and sometimes greater significance 

 are relationships between individuals and their phys- 

 ical environment or their predators, prey, parasites, 

 and/or diseases. Darwinism was right in the con- 

 cepts of potential increase, competition, and struggle, 

 but did now allow for the importance of multiple en- 

 vironmental factors or even chance alone eliminating 

 members of a single species. Also, there was no men- 

 tion that population sizes could and do vary tremen- 

 dously from season to season and year to year. Dar- 

 win assumed population sizes to be essentially fixed. 



