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 connectedvia the organisms 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 Hamiltons rule (inclusive fitness operations).

Clara B. Jones received her Ph.D. in Biopsychology from Cornell University. Since then she has served as Harvard University Postdoctoral Fellow in Population Genetics and as visiting faculty at Rutgers University in New Jersey as well as a visiting researcher at the Max Planck Institute for Behavioral Physiology in Bavaria. Dr. Jones has conducted fieldwork in Central and South America and has published over 100 articles and book chapters as well as four books.

1.Introduction: Definitions, Background.- 2. Competition For Limiting Resources, Hamiltons Rule And ChessonsR*.- 3. Flexible And Derived Varieties of Mammalian Social Organization: Promiscuity In Aggregations May Have Served As A Recent Toolkit Giving Rise To Sexual Segregation, Polygynous Social Structures, Monogamy, Polyandry And Leks Abstract.- 4. Multimale-Multifemale Groups And Nested Architectures: Collaboration Among Mammalian Males.- 5. Higher Grades Of Sociality In Class Mammalia: Primitive Eusociality.- 6. Ecological Models As Working Paradigms For Unpacking Positive And Negative Interactions Among Social Mammals.- 7. Mechanisms Underlying The Behavioral Ecology Of Group Formation.- 8. The Evolution Of Mammalian Sociality By Sexual Selection.- 9. Proximate Causation: Functional Traits And The Ubiquity Of Signaler To Receiver Interactions: From Biochemical To Whole Organism Levels Of Mammalian Social Organization.- 10. Synopsis.