GENETIC ADAPTATIONS TO THE i 



tends to overemphasize the signifi- 

 cance of genetic adaptation for the 

 survival of populations. 



Adaptation and the Future 

 of Human Society 



Because fitness expresses the ability 

 of individuals to survive — as well as 

 to reproduce — fitness differences 

 among individuals or genotypic dif- 

 ferences among papulations are usu- 

 ally assumed to have considerable ef- 

 fect on the population's survival in the 

 course of evolution. However, geno- 

 typic evolution has minimal effect 

 on a population's ability to survive. 

 The huge variation in mortality and 

 fertility rates among human popula- 

 tion has practically no relationship to 

 genetic variation. Darwinism seems 

 to have given rise to such statements 

 as "the polar bear survives in the 

 arctic because it is adapted to that 

 environment"; but in terms of the 

 course of evolution, the opposite is 

 true — that is, the polar bear is 

 adapted to the arctic because it has 

 survived there. Again, Coon has 

 stated that Negroes survived in ma- 

 larial environments because they had 

 the sickle-cell gene. But why do 

 several African populations have high 

 frequencies of this gene? Because 

 they have survived for centuries in 

 a malarial environment. (See Figure 

 XI-3) If, with a simple model for 

 this sickle-cell locus, one compares 

 the average fitness of a population 

 with a high frequency of the sickle- 

 cell gene to that of one with no sickle- 

 cell genes, the difference is at most 

 5 percent per generation. In terms 

 of a difference in mortality rate, this 

 is about 2 per 1,000 per year — which 

 is insignificant when compared to the 

 vast differences in African mortality 

 rates that are due to cultural differ- 

 ences. 



Genotypic evolution is the result 

 of competition between individuals 

 within a population and has little 

 effect on population competition. 

 Similarly, genes have little effect on 

 other aspects of culture. Cultures 

 can make any kind of martyr, from 

 kamikaze pilot to celibate, any time 



one is needed; genetic differences in 

 behavior traits are thus not the major, 

 or even a minor, cause of cultural 

 evolution. Even within a population 

 it is usually considered that such 

 traits as dominance are genetically 

 determined; but recent research is 

 pointing to the opposite view: that 

 the greater size, intelligence, aggres- 

 sion, etc., of dominants is the result 

 of being dominant and not vice versa. 

 This is only more evidence that 

 "adaptations" that are almost auto- 

 matically assumed to be genetic may 

 actually be environmental. 



In summary, there have been 

 siderable advances in our knowlec 

 of genetic adaptation where the ac- 

 tual genes are known, although its 

 effect vis-a-vis the other determinants 

 of genetic change is being debated. 

 On the other hand, the extension of 

 the concept of genetic adaptation to 

 other human characteristics is still 

 much in limbo. This review has been 

 mostly critical of such work — not 

 because it is valueless but because 

 of its very significance for our knowl- 

 edge of human society. Already, 

 some are saying that genetic in- 



Figure XI-3 — FREQUENCY OF SICKLE-CELL GENE IN LIBERIA 



>.ioo 



.075-.100 



§ .050-.075 



Kff^j .025-.050 



I 1 .005-.025 



The map shows the percentage frequency of occurrence of the sickle-cell gene in 

 the Liberian population. The malaria parasite has been endemic throughout most 

 of Liberia, but the sickle-cell gene varies greatly among tribal populations. The 

 latter variation may be due to the length of time that different Liberian populations 

 have been exposed to malaria. P. falciparum, the malaria parasite is spread by 

 the mosquito Anopheles gambiae, which cannot breed in heavily shaded rain 

 forests. Thus, it— and malaria — were able to advance where rain forest was 

 destoyed to provide land for agriculture. Slash-and-burn practices began in 

 northern Liberia and gradually spread southward. Today, the gradation of the 

 sickle-cell gene follows this same pattern, thus illustrating on a microscale how 

 the evolutionary process operates. The highest frequency of the sickle-cell gene 

 exists where the rain forest has been opened up for the longest time. 



377 



