The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


Are human infants altricial?

KAREN R. ROSENBERG1 and WENDA R. TREVATHAN2.

1Department of Anthropology, University of Delaware, 2Department of Anthropology, New Mexico State University

March 26, 2015 1:15, Grand Ballroom D Add to calendar

Human babies are born in an unusually helpless condition that Portmann called “secondary altriciality.” Ashley Montagu characterized them as “exterogestate fetuses”. These scholars and others have emphasized the helplessness of our newborns and the resulting needs that they have for intensive care by parents and alloparents. In many ways, however, human infants are completely unlike the infants of other animals who are also born helpless. The terms precocial and altricial describe a continuum of developmental states in birds and mammals, but it is difficult to place humans on this continuum. Humans have relatively long gestation lengths similar to the precocial great apes (e.g., averaging 268 days for Homo, 232 days for Pan, 257 days for Gorilla), but our babies are relatively larger than theirs (6.1% of maternal weight compared to about 3% in African apes) with relatively small brains (29% of adult brain size compared to 40-45% in African apes). This combination of large bodies, small relative brain size, and extreme motor immaturity makes human infants costly creatures to carry around and to parent. The use of the term “secondarily altricial” to describe their helpless condition fails to capture the unusual nature of the human newborn developmental status and the opportunities for learning that our infants may experience in their early entrance into the cultural and social world. The human pattern accommodates the obstetrical, locomotor and energetic constraints imposed by encephalization, with the recognition of a headstart in infant learning afforded by birth of an immature infant.