CHAPTER XV 
HOMES AND DOMESTIC HABITS 
142. Importance of care of the young.—The nest-building 
and domestic habits of animals are adaptations, but adapta- 
tions of behavior or habit rather than of structure, and are 
based on instinct, intelligence, and reason. These instincts 
and habits are among the most important shown by animals, 
because on them depends largely the continuance of the 
species. Of primary importance in the perpetuation of the 
species is the possession by animals of adaptations of struc- 
ture and behavior, which help the individual live long enough 
to attain full development and to leave offspring. But in 
the case of many animals a successful start in life on the 
part of the offspring depends on the existence in the par- 
ents of certain domestic habits concerned with the care and 
protection of their young. The young of many animals de- 
pend absolutely, for a part of their lifetime, on this parental 
care. In these cases it is quite as necessary for the continued 
existence of the species that the habits that afford this care 
be successful as that the parent should come successfully to 
mature development and to the production of offspring. 
143. Care of the young, and communal life.—The nest- 
building or home-making habits and the continued per- 
sonal care of the young for a part of their lifetime are most 
highly developed and widespread among the birds, mam- 
mals, and insects; and it is both among the insects and 
the higher vertebrates that we find most developed those 
social and communal habits discussed in Chapter IX. The 
principal activities of an animal community have to do 
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