HUMAN ORGANIC EVOLUTION: FACT OR FANCY? 



although certain phenotypical characteristics seem to be repro- 

 duced more or less in the offspring, the real unit of heredity 

 is not blood, but a unit of molecular dimensions, called the 

 gene. The genetic inheritance represents the conservative force 

 in reproduction which assures the offspring of becoming a 

 copy of the parent. But, of course, the copy is never perfect, 

 and in Darwin's day, this was assumed to be the result of the 

 mixing of two strains from unlike parents. It was not until 

 Mendel's law of segregation and independent assortment was 

 rediscovered at the turn of the century that an understanding 

 of biological changes was greatly advanced. The new genetics 

 also demonstrated that the organic forms observed represent 

 the end products of the interaction of the genetic units with 

 each other and with the environment. This led to the recog^ 

 nition that the units of heredity are rarely lost, but may 

 reappear, depending on combinations of recessive and dominant 

 alleles in heterozygous populations according to Mendel's 

 laws. This is very important to an understanding of the variety 

 of forms that we find in the fossil record, and the recurring 

 similarities of morphological types, throughout the human 

 fossil record. In other words, modern man has to a large 

 extent the same genes as the fossilized ancestors did. This, 

 however, represents an oversimplication, because there are 

 losses, there are changes in genes themselves and there are 

 changes in the frequency of different kinds of genes in popu- 

 lations, all conspiring to produce different kinds of genotypes 

 under the influence of selection which are responsible for the 

 variety of morphological types both in the fossil record, and 

 in modern man. 



It may be valuable, therefore, to review briefly the genetic 

 mechanisms which seem to be responsible for changes in 

 organic forms. ^^ Xhe knowledge at hand is mostly derived 

 from work done on non-human organisms. This seems justified 

 because, as Father Cooper^^ observed, man's body must obey 

 many biological rules which seem to be essentially similar to 

 those of non-human organisms, and if the principles apply 



^^ Most of the description of genetic mechanisms is derived from William 

 C. Boyd, Genetics and the Races o[ Man. Boston, 1955, ch. V, pp. 

 131 — 161, and Dobzhansky, op. cit., chaps. 2 — 8, pp. 23 — 191. 



^« Op. cit., pp. 15^16. 



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