NATXmAL SELECTION 



687 



6. She remains with the eggs and young 

 and protects and continuously feeds the 

 latter with prepared food (progressive pro- 

 visioning). 



7. The progeny are not only protected 

 and fed by the mother, but eventually 

 cooperate with her in rearing additional 

 broods of young, so that parent and off- 

 spring live together in an annual or peren- 

 nial society. 



Wheeler designates the first five cate- 

 gories as infrasocial; those of the sixth as 

 subsocial; and only the seventh as social 

 {sensu stricto). Division of labor among 

 the adults is characteristic of the seventh 

 category. These stages are not necessarily 

 phylogenetic in their linear sequence, al- 

 though they may often indicate evolution- 

 ary order. 



As has already been seen in the grada- 

 tions of integration in various types of ag- 

 gregations (Chap. 23), principles of fam- 

 ily organization are not the only principles 

 of group coordination. Although insect so- 

 cieties are doubtless primarily develop- 

 ments of family systems, adaptive group 

 life may emerge from aggregations of adults 

 not necessarily associated with family and 

 sex relations. 



The term "social" may be used in a 

 general sense to include "all groupings of 

 individuals which are sufficiently integrated 

 so that natural selection can act on them 

 as units" (Allee, 1940). In this general 

 sense every individual organism belongs to 

 a society. Each species population is inte- 

 grated through the continuity of the germ 

 plasm. In addition, various degrees of elab- 

 oration of other mechanisms of social co- 

 ordination give rise to a multipUcity of 

 population types (Chaps. 18-24; pp. 605, 

 625,684). 



It is significant that the highest systems 

 of intraspecies organismic and population 

 cooperation, with the exception of some 

 sexual adjustments, are coordinated individ- 

 ual units produced by asexual reproduc- 

 tion, parthenogenesis, or intense inbreed- 

 ing. By this means, any genes promoting 

 cooperation are spread into a large organi- 

 zation. The cells of a multicellular organism 

 or the segments of a metameric organism 

 have the same genes. The generations of 

 cyclomorphic species, such as aphids and 

 cestodes, usually have the same genetic 

 constitution. Mating among social insects 



is commonly between brother and sister, 

 thus tending to establish single rare muta- 

 tions in large populations, which may then 

 be selected as integrated units. Castes of 

 social insects are not produced by genetic 

 differentiation of the individuals (p. 428). 



Snell (1932) accepts the point of view 

 that the mating fhght in the social Hymen- 

 optera selects fit males, which are haploid 

 and therefore without distinction between 

 the phenotypic and genotypic individuals. 

 The female progeny from a single mating 

 are identical in at least one-half of their 

 germ plasm, because only one kind of 

 spermatozoan is produced. Spermatozoa 

 from a single mating in ants fertilize the 

 eggs of the queen for a period as long as 

 fifteen years, with a total progeny that may 

 reach 1,800,000. Large numbers of these 

 oflEspring may be haploid males and repro- 

 ductive diploid females which, if mated 

 brother to sister, would agaiii be hkely to 

 spread a gene originally appearing in a 

 grandparent to an enormous population. 



Swarming, the result of an increase in 

 numbers and of the presence of a new, 

 young, fertile queen, divides colonies of 

 honeybees (see p. 423). This behavior 

 seems to have evolved long ago; the honey- 

 bee queen has lost the abiUty to found a 

 new colony without large numbers of work- 

 ers. Probably colony subdivision is the re- 

 sult of the joint action of several instincts 

 that benefit the species as a whole. Instincts 

 may become overt under certain stimuli 

 and do not necessarily indicate genetic dif- 

 ferences between swarming and nonswarm- 

 ing bees. 



Let us now consider genetically diflFeren- 

 tiated classes within an integrated popula- 

 tion. Selection may result in a permanent 

 genetically determined polymorphism with- 

 in a species. Timofeeff-Ressovsky (1940) 

 records the seasonal fluctuation of the rela- 

 tive numbers of black and red forms of the 

 ladybird beetle, Adalia hipunctata, in the 

 vicinity of Berhn (Fig. 248). Over a period 

 of three years, the black genotypes were 

 less numerous than the red genotypes in 

 April, and more numerous in October. 

 There are about three generations of the 

 beetle per year in this locality, and 

 TimofeeflF-Ressovsky explains the polymor- 

 phism on the basis of selection favoring one 

 genotype in the spring and the other geno- 

 type in the fall. The color differences, of 



