HUMAN ORGANIC EVOLUTION: FACT OR FANCY? 



preted only if the environment is known. This cannot be 

 overstressed, because as was pointed out above, it is not 

 possible to predict the direction of future developments even 

 if mutations are known and their rates are known unless also 

 the environment is known. And the variables that compose 

 an environment are so numerous, so uncontrollable that it is 

 impossible to predict forward. But for purposes of interpreting 

 the fossil record, knowledge of this mechanism is extremely 

 useful in understanding evolution. 



Genetic selection can be calculated mathematically, and 

 has been verified experimentally. The most sophisticated 

 mathematical treatment of selection is important here because 

 it gives an idea of the number of generations it takes for 

 changes to take place in the racial history of man. Thus a 

 dominant gene, having a selective advantage of one per cent 

 (relatively high) to reach a frequency of 100% in a population 

 takes 900,230 generations. This suggests then that selection 

 works very slowly. The slow change represented by the fossil 

 record seems to verify this. There are changes that do occur 

 more rapidly, but then the action of mutation (which may be 

 advantageous or disadvantageous) must be brought into the 

 picture. Also changes come about more rapidly by the action 

 of mixtures of several populations, when it is possible, by the 

 introduction of new genes to increase the selective advantage. 



Although people once doubted the effectivenes of selection, 

 today there is considerable evidence especially from lower 

 organisms that selection is very effective, and this can explain 

 the sweeping changes that are represented in the fossil record. 

 To observe selection was of course denied to Darwin. A good 

 example of selection is the increase of the incidence of dark 

 coloring (melanism) in certain moths. Melanism has been 

 observed to have increased in the last century, and this 

 change has been associated with progressive industrialization 

 of the areas where these dark colored moths are found. In 

 some cases the entire population of moths has become 

 melanotic. Now it is worth noting that melanism in moths is 

 generally to be inherited as dominant. From Haldane's formula 

 it can be calculated that selection is very rapid by increasing 

 the frequency of the dominant gene which had an appreciable 

 advantage in natural selection. 



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