Table 2.

Comparison of the four processes that can cause intraspecific variation in social organization.

process	genetics	influence of environment on behaviourb	variability within individuals?	environment in which it evolved	physiological mechanisms
(i) genetic variation	—polymorphism —narrow reaction norm	no	no	predictable	organizational
(ii) developmental plasticity	—monomorphisma —broad reaction norm	non-reversible	no	short-term: predictable long-term: unpredictable	organizational
(iii) social flexibility	—monomorphisma —broad reaction norm	reversible	yes	unpredictable	activational
(iv) entirely extrinsic factors	—monomorphisma —narrow reaction norm	no	yes	predictable	none that leads to variation in social organization

^aThe term genetic monomorphism does not imply that genetic variation is absent, only that the major part of variation observed in social behaviour is not due to genetic but to environmental factors.

^bOther behaviours can be influenced during early environment, but this cannot explain the variation in social organization.