The adaptive nature of most of the normal relationships between members of one species is usually apparent. Active participants seem to derive benefits from these relationships. Several individuals working cooperatively, for instance, might accomplish what would be impossible for the same individuals working independently. Pack-forming behavior of wolves may be an example. Presumably it was developed because of increased reproductive success of individuals that had greater than average inclinations to form cooperative groups. The development of a placental attachment by a foetus, a very different sort of "social" phenomenon, also has patent survival value to the foetus. Sometimes, however, active participation in a social activity places an individual at a personal disadvantage, for instance, the mother in the foetal-maternal relationship. At best, the mother must sacrifice some food energy, and there may be other disadvantages, such as increased predator liability. The sacrifices made by the mother may sometimes result in her death, but they cannot be regarded as deleterious in an evolutionary sense, because they play an essential part in reproduction. The immediate sacrifices involved in any type of parental care may be regarded as a price paid for attendant reproductive advantages, and no special explanation is required. Parental care probably accounts for most of the examples of social activities in which one individual sacrifices or endangers its own well-being for the benefit
[1]
E. Wilson,et al.
The Origin and Evolution of Polymorphism in Ants
,
1953,
The Quarterly Review of Biology.
[2]
G. C. L. Bertram,et al.
Principles of animal ecology
,
1951
.
[3]
Karl P. Schmidt,et al.
Principles of Animal Ecology
,
1950
.
[4]
S. Wright.
Tempo and Mode in Evolution: A Critical Review
,
1945
.
[5]
S. F. Light.
The Determination of the Castes of Social Insects
,
1942,
The Quarterly Review of Biology.
[6]
A. Sturtevant.
Essays on Evolution. II. On the Effects of Selection on Social Insects
,
1938,
The Quarterly Review of Biology.
[7]
M. Talbot.
Colony‐Founding Among Ants
,
1933
.
[8]
W. E. Ritter.
AS TO THE CAUSES OF EVOLUTION.
,
1923,
Science.