500 LIFE : OUTLINES OF GENERAL BIOLOGY 



and a light-o'-love lizard may linger beside his mate after the 

 physiological storm has passed. Very gradually there is an ascent to 

 cases where the marriage, if we dare use the word, lasts for a season 

 or for life. 



In many birds, where asthetic courtship reaches a very high level, 

 the sex-urge is sharply punctuated. It is intense while it lasts, but 

 it does not last long. The reproductive organs soon begin to dwindle, 

 and the bodily excitement wanes; the hormones or chemical mes- 

 sengers from the gonads cease to be made and distributed in any- 

 thing like the same degree; the whole life becomes quieter and more 

 commonplace. Thus even at a high level there may be seasonal 

 mating which is automatically dissolved when the sex-urge sinks 

 for the time being into quiescence. In some short-Uved animals 

 there is only one love season in the lifetime. 



What seems to man the highest level of sex-association is 

 permanent mating; and this may be evolved on polygamous or on 

 monogamous lines. Thus in the case of the South American Ostrich, 

 the Rhea or Nandu, the troop consists of a male with half a dozen 

 or so hens. It is a lasting a.ssociation, persisting even when troop 

 joins with troop outside the breeding season. The females of a troop 

 pool their eggs, or as many of them as possible, and the male-bird 

 broods. The young birds follow their father at first, but the mothers 

 gradually insinuate themselves. Among the guanacos and vicunas, 

 the wild ancestors of alpacas and llamas, there are permanent 

 troops, a male and a harem; and so it is with wild horses and zebras, 

 kangaroos and macaque monkeys. There may be a large herd of 

 wild horses or a large community of monkeys, within which there 

 arc permanent polygamous, or, better, polygynous, groups — each 

 consisting of one male and several females. 



Solitary monogamy is characteristic of many birds, such as eagles, 

 ravens, cranes, storks, and swans. It is of course difficult to be 

 always sure that the two birds are the same year after year, but in 

 some cases this has been securely proved. There is the same difficulty 

 with wild mammals who live in pairs; for marking is even more 

 difficult than with birds, but there are instances that seem reliable, 

 such as rhinoceros and orang. Monogamy within a herd or community 

 is illustrated by some gorillas and chimpanzees, just as by penguins 

 and parrots among birds. In some cases the monogamy is loosely 

 observed, especially on the male's part, as is well known for sparrows 

 and rabbits; in many cases, however, the lifelong monogamy is 

 strict and is loyally respected. It is an arrangement that works well 

 for the family, but a little con.sidcration shows that this is not its 

 chief significance in the animal world. For the welfare of the family 

 is satisfactorily secured by other arrangements besides those of 

 monogamy. The true inwardness of lifelong monogamy is deeper. 

 Mating for life means that psychical love has prevailed over physical 



