This essay is adapted from an article entitled “On the Origin and Progressive Evolution of the Triune Brain” in Primate Brain Evolution: Methods and Concepts, E. Armonstrong and D. Falk, eds., Advances in Primatology series (New York: Plenum Press, 1982). A shorter version of these ideas was presented at a symposium on “Humanity's Place in Nature” in honor of Ralph Wendell Burhoe, sponsored by the Institute on Religion in an Age of Science at the annual meeting of the American Association for the Advancement of Science in Toronto, Canada, January 4, 1981.
EVOLUTION OF THE PSYCHENCEPHALON
Version of Record online: 15 DEC 2005
Volume 17, Issue 2, pages 187–211, June 1982
How to Cite
MacLean, P. D. (1982), EVOLUTION OF THE PSYCHENCEPHALON. Zygon, 17: 187–211. doi: 10.1111/j.1467-9744.1982.tb00478.x
- Issue online: 15 DEC 2005
- Version of Record online: 15 DEC 2005
In evolving to its great size the human brain has retained the distinctive features and chemistry of three kinds of brains that reflect an ancestral relationship to reptiles, early mammals, and late mammals. It constitutes, so to speak, a psychencephalon comprised of three-brains-in-one, a triune brain. In the evolution from reptiles to mammals two key changes were the development of nursing and maternal care. Through the agency of “newer” parts of the brain a parental concern for family eventually generalizes not only to other members of the species but to the entire biosphere, a psychological development that amounts to the evolution of responsibility and what we call conscience. Given our freedom to decide “yes” or “no” on various issues, we need not look beyond the evolving family to find a reason for being, an ethic to live by.