This brief discusses factors associated with group formation, group
maintenance, group population structure, and other events and processes
(e.g., physiology, behavior) related to mammalian social evolution.
Within- and between-lineages, features of prehistoric and extant social
mammals, patterns and linkages are discussed as components of a possible
social "tool-kit". "Top-down" (predators to nutrients), as well as
"bottom-up" (nutrients to predators) effects are assessed. The present
synthesis also emphasizes outcomes of Hebbian (synaptic) decisions on
Malthusian parameters (growth rates of populations) and their
consequences for (shifting) mean fitnesses of populations. Ecology and
evolution (EcoEvo) are connected via the organism's "norms of
reaction" (genotype x environment interactions; life-history tradeoffs
of reproduction, survival, and growth) exposed to selection, with the
success of genotypes influenced by intensities of selection as well as
neutral (e.g. mutation rates) and stochastic effects. At every turn,
life history trajectories are assumed to arise from "decisions" made by
types responding to competition for limiting resources constrained by
Hamilton's rule (inclusive fitness operations).