HUMAN ORGANIC EVOLUTION: FACT OR FANCY? 



may be perpetuated, even though harmful and may in an 

 altered environment be responsible for the very perpetuation 

 of the species, though the species will now be slightly altered. 

 This effect has been noted repeatedly as for instance in the 

 bacterial resistance to streptomycine, the resistance of the fly 

 to DDT, and possibly the resistance of man possessing the 

 sickle-cell blood trait to malaria. Thus, mutations play an 

 important role in the adaptation to the environment, even 

 though they may appear at first as "useless" mutations. The 

 advantage then lies in the fact that the small changes help the 

 organisms to adapt at some critical time when the environment 

 changes. In the long run, it may be said that mutability is a 

 useful trait. 1^ This knowledge the early evolutionists did not 

 have. Instead they struggled with the problem in terms of 

 inherited acquired traits. 



However, it must be pointed out that in a stable environ- 

 ment, the rate of mutation for each gene may be so slow that 

 it cannot be observed in any easy manner. Very little is known 

 about the process in man. For instance Haldane (1935) 

 estimated that the allele of the hemophylic gene mutates about 

 once in every 50,000 individuals per generation. But this is a 

 high rate, and since the action of selection is to eliminate this 

 trait it would have disappeared long ago if it did not mutate 

 again and again. Thus a kind of equilibrium has been 

 established between the two opposing forces of ^harmful 

 mutations and natural selection and the trait remains in a 

 population at about this rate. 



Selection as a mechanism was of course one of the earliest 

 and most important mechanisms to explain evolution, and the 

 subtitle of Darwin's Origin of Species makes this eminently 

 clear. But while in Darwin's explanation natural selection 

 meant more or less the survival of the fittest, genetics has 

 shown that this process is rather more complicated. Selection 

 then means "that organisms possessing certain characteristics 

 survive in relatively large numbers, and leave relatively more 

 offspring, than do other organisms of the same kind possessing 

 other characteristics. "19 Selection then favors the character- 

 istics best adapted to a certain environment, and can be inter- 



im Op. cit, p. 107. 



19 Op. cit, pp. 141-142. 



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