Recent research suggests that witnessing events of fission (e.g., the splitting of a solid object) impairs human infants', human adults', and non-human primates' object representations. The present studies investigated the reactions of gorillas and orangutans to cohesion violation across different types of fission events implementing a behavioral…

Contemporary evolution biology has recognized the role of development in evolution. Evolutionarily oriented psychologists have similarly recognized the role that behavioral plasticity, particularly early in development, may have had on the evolution of species, harking back to the ideas of Baldwin (the Baldwin effect). Epigenetic theories of…

The social development of a female rhesus monkey was followed from birth until death, age 32 months. The monkey had an extra autosome and was hydrocephalic. The monkey showed serious motor deficiencies, delayed social development, poorly established dominance relationships, and heavy dependence on mother and kin. The monkey was, however, well…

Four studies involving 40 pigtail monkeys are described in which relatively short separation experiences in infancy were associated with evidence of persistent changes in social behavioral function (less sociability, fewer close friends) and immunological function (suppression of lymphocyte proliferation) up to 6 years later. (Author/JDD)