ance of existing functions within the organ- 

 ism. Thus natural selection is restricted 

 mainly to small changes and must, therefore, 

 work very slowly. Moreover, since heredity 

 is particulate in nature, each new gene must 

 be selected or discarded as a whole. This 

 means that disadvantageous phenotypic 

 effects may be carried along with advanta- 

 geous ones, if the former are less important 

 in survival. The survival of a particular indi- 

 vidual or race is determined, not by the per- 

 fection of any one characteristic, but by the 

 aggregate fitness of all its characteristics. The 

 survivors in the struggle for existence need 

 not be perfectly adapted, but merely suffi- 

 ciently adapted to "get by" until they pro- 

 duce an adequate number of offspring. Each 

 organism is "made over" and "patched up" 

 to meet its new environment each time there 

 is a swing in the mighty pendulum of geo- 

 logic time. Consequently, each plant and 

 animal may possess a number of useless or 

 even definitely harmful characteristics, re- 

 sulting from the sorting out of innumerable 

 chance variations. Survival does not require 

 perfect adaptation. It merely demands that 

 the individual be as well adapted as its com- 

 petitors — all of which have also been pro- 

 duced by the same method. 



LAMARCKISM: AN EARLY THEORY OF 

 EVOLUTION 



Prior to Darwin, evolution had many pro- 

 ponents, and several theories were advanced 

 as to how evolution had wrought its slow 

 but tremendous changes in the species. These 

 theories rested mainly on the supposition 

 that all variations in the characteristics of the 

 organism are transmitted to the offspring — 

 a weakness that is well exemplified by the 

 theory of Lamarck. This work on evolution 

 was published in 1809; and Lamarck's con- 

 tribution was important, despite the fact that 

 the central theme — as to the mechanism of 

 evolutionary change — is not tenable in the 

 light of modern genetics. 



According to the Lamarckian view, each 



Natural Selection; Origin of Species - 549 



organism is molded by its contacts with the 

 environment, and these acquired character- 

 istics are subsequently transmitted to the off- 

 spring. In other words, Lamarck held that 

 the environment produces heritable varia- 

 tions that fit each organism to cope with the 

 particular conditions of its habitat; and that 

 the perpetuation of these acquired charac- 

 ters produced changes in the species in ac- 

 cordance with the geological changes of the 

 environment. 



Lamarck's ideas had great appeal in the 

 early part of the nineteenth century, and the 

 theory was not abandoned until it was 

 proved beyond reasonable doubt that ac- 

 quired characteristics are not inherited. The 

 environment, to be sure, is very effective in 

 determining the qualities of every individual, 

 but these modifications are localized in the 

 somatic tissues of the body, and the germ 

 cells remain unchanged. 



To exemplify the noninheritance of ac- 

 quired characters, we will consider a homo- 

 zygous stock of garden peas. When grown in 

 well-watered soil these plants develop a 

 moderately extensive root system. But if the 

 same plants are grown in unusually dry soil, 

 the roots become distinctly deeper and 

 broader up to a limit that is determined 

 by the genetic potentiality of the stock. In 

 fact, so long as the same relatively dry envi- 

 ronment is maintained, the well-developed 

 root system will continue to appear, genera- 

 tion after generation; but no progressive im- 

 provement is likely to occur within any 

 reasonable span of time. Moreover, when the 

 seedlings of this stock are finally restored to 

 normal conditions, no permanent change in 

 the root system can be observed. The dry 

 environment has brought out the utmost of 

 root development in the given stock, but the 

 environment has not been effective in mold- 

 ing the genetic constitution of the stock in 

 the direction of greater fitness to cope with 

 the dry condition. Aside from the remote pos- 

 sibility that a favorable mutation might 

 occur during the period of the study, the 

 plant experimentalist has no hope of im- 



