1352 



HORMONAL REGULATION OF BEHAVIOR 



ing results in the hands of observers who 

 did not have an accurate conception of the 

 organization of the animal's behavior pat- 

 terns. 



D. GENETIC AND EVOLUTIONARY ASPECTS OF 

 HORMONE-INDUCED PARENTAL BEHAVIOR 



1. Taxonomic Differences in Parental Be- 

 havior and in the Mechanisms Under- 

 lying It 



Taxonomic variation in parental behavior 

 patterns. Throughout our discussions of pa- 

 rental behavior, it has been clear that each 

 component of the over-all pattern of pa- 

 rental behavior can occur in a wide variety 

 of forms, and that these forms of behavior 

 are characteristic of the species of animals 

 in which they occur. Generally speaking, 

 patterns of behavior, including parental be- 

 havior, may be characteristic not only of 

 species, but also of the higher taxonomic 

 categories, such as genera, families, orders, 

 and even classes. Indeed, in spite of the 

 fact that scattered exceptions may be found, 

 the statements that mammals nurse their 

 young, and that birds incubate their eggs, 

 may be used to characterize membership in 

 these two classes with almost as much pre- 

 cision as any single statement about struc- 

 ture. 



Characteristic differences can be found 

 between different orders of mammals with 

 respect to their parental behavior and the 

 structure of parent-young relationships. For 

 example, the herd-living ungulates are usu- 

 ally characterized by a high degree of in- 

 dividual recognition of the young, by a long 

 period of association between mother and 

 young, and by the continuation of occa- 

 sional nursing behavior long after the young 

 have become capable of grazing for them- 

 selves (Altmann, 1952). In most rodents, 

 on the other hand, relations between mother 

 and young are not so long-lasting, "adop- 

 tion" of young by strange mothers, even 

 of other species, occurs very easily, and the 

 transition between suckling and the eating 

 of solid food is fairly abrupt (Eibl-Eibes- 

 feldt, 1958). Relations between the male 

 and the young, too, are different in different 

 families of mammals. For example, among 

 bears, the male is likelv to attack and even 



to eat its own young when association be- 

 tween them is forced, as in a zoo cage, al- 

 though in the various species of wolves, the 

 males often take an active role in the care 

 of the young. Different groups of mammals 

 also have characteristic ways of carrying 

 their young when retrieving them, some 

 carrying the young by the scruff of the neck, 

 some by the belly, and some holding the 

 young in the hands (Curio, 1955; Hediger, 

 1959). 



The type of nest built by birds, the 

 methods and patterns of incubating, and 

 the pattern of parental care of the young 

 may all be characteristic of particular fami- 

 lies or genera. For example, Mayr and Bond 

 (1943) noted that different genera of swal- 

 lows reliably use different methods of nest- 

 building, some laying eggs in natural hol- 

 lows, some excavating burrows in sand- or 

 mud-banks, others constructing nests of 

 mud. All swifts use their saliva for sticking 

 nesting materials together (Lack, 1956a), 

 and their salivary glands develop and re- 

 gress seasonally (Johnston, 1958). It is 

 possible to trace, within one family, evolu- 

 tionary changes in the patterns of parental 

 behavior, as in the ease we have already 

 discussed (see above, p. 1277), of the New 

 World cuckoos in which some species are 

 parasitic, others communal nesters, and still 

 others nest in colonies of individual nests 

 (Davis, 1942b). 



Although patterns of parental behavior 

 may characterize entire families, we can 

 also find many ways in which closely re- 

 lated animals have differing patterns. For 

 example, the male Galapagos sea lion takes 

 part in the care of the young, unlike other 

 species of seal (Eibl-Eibesfeldt, 1955c). 

 Hohn (1957) reports that female Pacific 

 eiders always fly from the nest when an 

 observer approaches within a few feet, 

 whereas incubating king eiders sit so tight 

 on the eggs that some allow themselves to 

 be picked off the eggs by the observer. 

 Watson (1908) observed that male and fe- 

 male noddy terns change places on the eggs 

 about every two hours, although the closely 

 related sooty terns change places only once 

 a day. Van Oordt (1934) found that com- 

 mon terns began incubating after the laying 

 of the first egg, whereas arctic terns did 



