Adaptive Value:

-Adaptive value is the extent to which a trait, behavior, or characteristic positively influences the evolutionary fitness of an individual

There is adaptive value in living as a colony if the benefits of doing so outweigh the costs (see Phylogeny page for details)

-the allele for the altruistic behavior displayed by the sterile or “eusocial” workers can spread even in competition with a gene that promotes only personal reproduction. This is due to indirect fitness.

-The indirect Fitness theory on the adaptive value of social behavior: indirect fitness is fitness achieved by helping non-descendent kin survive. This involves altruistic behavior towards relatives: siblings, cousins, etc. While altruistic behavior may reduce the fitness of the altruistic individual, these fitness costs are outweighed by the indirect fitness gains of insuring the survival of non-descendent kin, i.e. the offspring of relative. Even though queen ants live longer than workers, the indirect benefits of ensuring the fitness of the queens offspring (who are genetically related to the workers) outweigh the costs of trying to break away from the colony and founding a new one, i.e. trying to ensure their own individual reproductive fitness. Self-sacrificing individuals almost always are assisting close relatives

Mutualism theory on the adaptive value of social behavior: The other theory of social behavior relevant for ant colonies is mutualism, in which members of a species help each other for each of their own mutual benefit. This latter theory can explain cooperation among castes, but cooperation between castes, specifically altruistic behavior of the sterile workers towards the queen ant can be explained by the theory of indirect fitness.

History:
Initially, biologists generally assumed that animals of the same species would help one another for the benefit of the species as a whole, known as “group selection.” In the mid 1960’s, however, George C. Williams pointed out in his seminal book: Adaptation and Natural Selection, that if some members of a population had an allele that fostered self-sacrifice for the betterment of the group, then that allele would be selected away as time progressed because more selfish non-sacrificing members will live longer and reproduce more. There are now several dominant theories: mutualism, in which members of a species help each other for each of their own mutual benefit, indirect fitness, which is fitness achieved b helping non-descendent kind survive. The latter is generally understood as the reason why there are eusocial sterile workers in ant colonies.


Indirect fitness makes it adaptive for these small sterile worker ants with shorter lives to cater to the every whim of their gigantic fertile queen that lives longer.

-Nearby colonies are less aggressive towards each other than colonies that live far away from each other. This suggests there is adaptive value to having new queens moving only a short distance away from their colonies to establish new ones, that being friendly, low fitness cost relationships with their neighbors as opposed to high aggressive territorial relationships which incur fitness costs.

-Transaction theory: organized social groups are arenas in which dominants and subordinates “negotiatie” their reproductive rights within the group. An example of this is the “concessions model” in which the dominant group member concedes some amount of reproduction rights to lower-ranking individuals in order to maintain a certain degree of advantage for the subordinates to stay within the colony.