58 READINGS IN BIOLOGICAL SCIENCE 



of activity associated with, and subsidiary to, the function of reproduction. 

 This is the evolution of parental care. Maternal affection does not enter 

 upon the scene until comparatively late in the evolution of animal life. 

 The whole vast groups of worms, molluscs, echinoderms and Crustacea 

 do not manifest the least solicitude for the welfare of their offspring. 

 The same statement is true for the great majority of insects, spiders, fishes 

 and amphibians. Among the lower invertebrate animals the discharge of 

 the sex cells into the water fulfills all responsibility for the perpetuation 

 of the species. In the higher invertebrates the simple physiological func- 

 tions of producing and discharging sex cells are accompanied by accessory 

 activities of various kinds. Aiany species of insects devote much care to 

 laying eggs in situations that provide food for the future larvae. One might 

 write a whole treatise on the varied and highly specialized modifications 

 of egg laying. The cabbage butterfly is careful to deposit her eggs upon 

 cabbages, mustard or some other member of the natural order of Cruciferae. 

 The mother blowfly chooses meat, if tainted so much the better. The 

 solitary wasp, according to its kind, hunts out a narrowly restricted group 

 of beetles, grasshoppers or insect larvae, stings her victim so as to paralyze 

 but not to kill it, lays an egg upon it, buries it in a hole, carefully fills the 

 hole with dirt, then leaves her progeny to its fate. No maternal affection 

 here. In fact, the mothers do not recognize their offspring as any kin of 

 theirs, if they see them. The whole elaborate and highly specialized per- 

 formance is gone through blindly and instinctively. There are many 

 kinds of insects which spends much effort in making receptacles for eggs 

 and in storing food for their progeny. Numerous species of solitary bees 

 provision their nests with pollen and honey which the larva feeds upon. 

 Only in a few species do the mother bees remain with the nest and supply- 

 food directly to the larvae after they have hatched from the eggs. Care 

 for eggs long antedates care for what comes out of the eggs. But when the 

 association between the parents and their living offspring was once estab- 

 lished, a hne of evolution was started which has led to the most momentous 

 consequences for the further development of animal life. 



I shall pass over the manifestations of care for offspring as it has devel- 

 oped in ants, bees and termites among social insects, and its temporary 

 appearance in a few groups of fishes in which the parents may accompany 

 the young for a short time until the school becomes scattered. In birds 

 one may find various stages from types in which the parents foster and 

 protect the young for a short time and then leave them to shift for them- 

 selves, to the domestic behavior of the higher song birds which raise their 

 broods in carefully constructed nests and spend much of their time in keep- 

 ing the nests clean, brooding their offspring and finding food to fill their 

 hungry mouths. The more care is expended on offspring the more help- 

 less they become, and the more dependent they are upon the ministrations 

 of their parents. Successive generations become more closely tied together. 



