HUMAN ORGANIC EVOLUTION: FACT OR FANCY? 



mathematically, unfortunately for man very few predictions 

 can be made because we do not know the genetic composition 

 and the numbers involved in matings. 



The next mechanism to be considered is mutation. There 

 are many kinds of mutations, involving changes in whole sets 

 of chromosomes, in single chromosomes, in amounts of portions 

 of chromosomes, in relations of parts of chromosomes and 

 finally, the one definitely known to be operative in man, 

 changes in the composition of the individual gene. (The other 

 gene changes may eventually also be shown to play a role 

 in human genetics). 



It has been objected that mutations produce deleterious 

 efects and hence bring forth degeneration rather than evolu- 

 tion. But it must be understood, that most mutations which 

 occur are of a rather minor moment, and, as Dobzhanskyi^ 

 points out, contribute to what has become to be known as 

 micro-evolution. That is to say, certain minor changes, which 

 may not even be visible, may, if the environment changes, 

 become important and help the organism in adapting to the 

 changed environment provided that mutant has been per- 

 petuated in the offspring. There are on record observed 

 mutations which have had more dramatic efects, such as the 

 shortening of legs on sheep both in New England and 

 independently again in Norway. But generally, as will be 

 seen presently, they are not that far-reaching. 



Genes generally mutate, but do not have to, in one general 

 direction. In fact, reversal or a return to the original structure 

 has also been observed. What is more important is the fact 

 that a mutation does not change the species or race. Rather, 

 it is the summation of many mutations which bring about 

 lasting and fundamental changes. This seems to be contra- 

 dicted by the fact that mutations have been observed to be 

 harmful or even lethal to the organism. But it is here that the 

 idea of selection plays an important role. Those individuals 

 which have harmful mutants tend to be eliminated, while 

 those which do not possess these will perpetuate themselves. 

 Furthermore, genes always act in combination, and often the 

 deleterious effects do not become obvious. On the other hand, 

 some mutations, which, if not too frequent in one environment, 



1^ Op. cit, pp. 91^108. 

 44 



