Adaptation: Levels of selection and "altruistic" features
I. Strength of selection is predicted to decrease with increasing taxonomic hierarchy
A. Selection requires (results from) heredity, variation, and multiplication (i.e., selection works with entities that demonstrate genealogical relationships and have heritable variations affecting that entity's ability to survive to reproduce)
B. With increasing levels of groupings (e.g., from species to genera to families...), there are fewer units (and thus less variation among units) and slower rates of multiplication, thus reducing the strength of selection (i.e., the response to selection)
C. Thus, attempts to explain features of organisms that appear to benefit a group rather than an individual (i.e., "altruistic" traits) should first consider whether or not selection mechanisms at lower hierarchical levels (e.g., at the level of individuals) can provide an explanation.
D. That is, the decreasing strength of selection with higher taxonomic level is the main argument against "group selection" mechanisms:
1. Under group selection, a trait might be expected to increase in the species as a whole if the rate of extinction of a group is lowered by a high frequency of the trait. (An example of such a trait might be recombination and mutation.)
2. Alternatively, under group selection, the frequency might increase of a trait that somehow enhances the proliferation of new populations carrying the trait. (An example of such a trait might be cooperative behavior.)
II. Explanations for evolution of "altruistic" features that provide an alternative to "group selection"
A. "Altruism" may be an illusion based on our anthropocentric viewpoint
B. Some features purportedly advantageous to a population may actually be favorable to individuals
C. Kin selection can provide an explanation for some features that increase the fitness of an individual's relatives, even if the trait is disadvantageous to the individual
1. According to Hamilton's "rule", the frequency of the trait depends on both the direct influence of the trait on an individual and on its indirect effect, and can increase as long as it confers sufficient advantage on the bearer's relatives: