TABLE 1.

Evolutionary scenarios for selection against reactive aggression (i.e., self-domestication) in human evolution, applied to Homo sapiens.

Scenario	Merits	Problems
1. Genetic group selection	Theoretically plausible if groups sufficiently stable	Behavioral similarities between humans and chimpanzees not explained
2. Group-structured culture selection (GSCS)	Likely influenced much H. sapiens behavior	Unlikely to have been important 300,000 years ago. Selection against aggression not explained
3. Social selection by female mate choice	Female choice currently important	Constraints on violent males not explained
4. Social selection by choice of cooperative task partners	Male teamwork likely important	Constraints on violent males not explained
5. Self-control	Stronger self-control in species with bigger brains	Constraints on violent males not explained
6. Cooperative breeding	Extensive cooperation in human reproduction, associated with low aggression	Cooperating breeding proposed to characterize other Homo species, not just H. sapiens. Selection against aggression not explained
7. Population density	High population density sometimes associated with reduced aggression	H. sapiens population density apparently low in much of the past. Selection against aggression not explained
8. Use of lethal weapons	Facilitated control of reactive aggressors by safe killing	Likely too early to apply specifically to H. sapiens
9. Language-based conspiracy	Facilitated control of reactive aggressors by safe killing	Timing of language skills is speculative; hard to test (relevant cultural practices extinct)

Merits and problems shown are not exhaustive. See text for citations and further discussion.