Males and females of the South European green lizard, for example, defend their territories against members of the same sex only. The male takes no action against an encroaching female, indeed he cannot because he is prevented by the inhibition described on page 105 from attacking a female. Night herons behave very similarly to storks, but there are several other species of herons in which, as Otto Koenig has shown, the mates certainly recognize each other individually and associate up to a certain extent even away from the nest. The young of a brood know each other even as tiny nestlings and attack any strange night heron baby, even of their own age, if it is introduced into the nest. Selective habituation to all stimuli emanating from individually known members of the species is probably the prerequisite for the origin of every personal bond and it is probably its precursor in the phylogenetic evolution of social behaviour.