362 The Theory of Natural Selection 



selves in successive generations and the effect of a virtual 

 isolation. There is no doubt that a social or religious process 

 which virtually confines a group of people to restricted 

 mating or inbreeding will tend to preserve hereditary traits 

 that would otherwise become diffused in the larger popula- 

 tion, and to intensify recessive traits that would otherwise 

 be masked by their dominant alternatives. Beyond that, 

 however, it has been difficult, in considering the evolu- 

 tion of human qualities, to separate with certainty organic 

 traits that are truly inherited from the effects of social 

 processes. 



Proving Too Much 



One of the standard illustrations of a highly specialized 

 adaptation used to show how natural selection could bring 

 about a distinct type is that of the kallima butterfly (see 

 Fig- 95)' According to the theory of natural selection, the 

 resemblance of this insect to a dead leaf is of protective 

 value. This pattern is the result, according to the theory, 

 of accumulation through many generations of progressively 

 closer resemblances to the dry leaf. It is assumed that some 

 remote ancestors of this species included among their num- 

 ber some that resemble a dry leaf only slightly and that these 

 survived in competition with their fellows who looked less 

 like a dry leaf. It is assumed further that in succeeding 

 generations the progeny contained a larger proportion of 

 individuals resembling the dry leaf and that this resemblance 

 increased from generation to generation. Suppose we grant, 

 for the sake of the argument, that this process of natural 

 selection and transmission of favorable variations continues. 

 We may then conceive that a point is reached at which the 

 resemblances of the ordinary individual of the species to a 

 dead leaf is sufficient to secure complete protection. An 

 examination of the existing kallima, however, shows us an 

 over-refinement of the resemblance for which the theory 

 of natural selection offers no explanation. 



