Mother–Infant Cosleeping, Breastfeeding and Sudden Infant Death Syndrome: What Biological Anthropology Has Discovered About Normal Infant Sleep and Pediatric Sleep Medicine James J. McKenna, 1 * Helen L. Ball, 2 and Lee T. Gettler 1,3 1 Department of Anthropology and Mother-Baby Behavioral Sleep Laboratory, University of Notre Dame, Notre Dame, IN 46556 2 Department of Anthropology, Medical Anthropology Research Group and Parent-Infant Sleep Laboratory, Durham University, Durham, DH1 3HN, UK 3 Department of Anthropology, Northwestern University, Evanston, IL 60208-1330 KEY WORDS mother–infant cosleeping; bed-sharing; SIDS; breastfeeding; infant sleep; evolutionary medicine ABSTRACT Twenty years ago a new area of inquiry was launched when anthropologists proposed that an ev- olutionary perspective on infancy could contribute to our understanding of unexplained infant deaths. Here we review two decades of research examining parent–infant sleep practices and the variability of maternal and infant sleep physiology and behavior in social and solitary sleeping environments. The results challenge clinical wisdom regarding ‘‘normal’’ infant sleep, and over the past two decades the perspective of evolutionary pedia- trics has challenged the supremacy of pediatric sleep medicine in defining what are appropriate sleep environ- ments and behaviors for healthy human infants. In this review, we employ a biocultural approach that integrates diverse lines of evidence in order to illustrate the limita- tions of pediatric sleep medicine in adopting a view of infants that prioritizes recent western social values over the human infant’s biological heritage. We review what is known regarding infant sleeping arrangements among nonhuman primates and briefly explore the possible paleoecological context within which early human sleep patterns and parent–infant sleeping arrangements might have evolved. The first challenges made by anthropolo- gists to the pediatric and SIDS research communities are traced, and two decades of studies into the behavior and physiology of mothers and infants sleeping together are presented up to the present. Laboratory, hospital and home studies are used to assess the biological func- tions of shared mother–infant sleep, especially with regard to breastfeeding promotion and SIDS reduction. Finally, we encourage other anthropologists to partici- pate in pediatric sleep research using the unique skills and insights anthropological data provide. By employing comparative, evolutionary and cross-cultural perspec- tives an anthropological approach stimulates new research insights that influence the traditional medical paradigm and help to make it more inclusive. That this review will potentially stimulate similar research by other anthropologists is one obvious goal. That this arti- cle might do so makes it ever more possible that anthro- pologically inspired work on infant sleep will ultimately lead to infant sleep scientists, pediatricians, and parents becoming more informed about the consequences of car- ing for human infants in ways that are not congruent with their evolutionary biology. Yrbk Phys Anthropol 50:133–161, 2007. V V C 2007 Wiley-Liss, Inc. ‘‘Telling mothers and fathers how to bring up their children in books is arguably as silly as sending false teeth through the post and hoping they fit’’ (Hardyment, 1983, p. 15). One aspect of evolutionary medicine with which most biological anthropologists are familiar (and in which some of us are actively engaged) examines the potential incompatibilities between the lifestyles and environ- ments in which humans currently live and the condi- tions under which human biology evolved (Nesse and Williams, 1994; Trevathan et al., 1999, in press). Researchers that explore the health implications of ‘‘western lifestyle’’ on conditions such as diabetes, obe- sity, ovarian function, reproductive cancers and degener- ative chronic disease (to name a few) have tested hypotheses derived from an evolutionary paradigm and advanced our understanding of the mechanisms by which a mismatch between current behavior (e.g., diet, activity, and timing of reproduction) and physiological mechanisms that evolved under very different living conditions (e.g., patterns of fat storage and attrition of ova) have come into conflict (Pollard, in press; Treva- than et al., in press). Encompassed by this umbrella, evolutionary pediatrics considers the consequences to Grant sponsors: NICHD RO1, Shannon Award Grant, Foundation for Study of Infant Deaths, Scottish Cot Death Trust, Babes in Arms, Leverhulme Trust, Nuffield Foundation, Newcastle Hospitals Charities Trust (Tiny Lives Fund), UK National Institute for Health Research (NIHR), Durham University. *Correspondence to: James J. McKenna, Department of Anthro- pology and Mother–Baby Behavioral Sleep Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA. E-mail: jmckenn1@nd.edu DOI 10.1002/ajpa.20736 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2007 WILEY-LISS, INC. YEARBOOK OF PHYSICAL ANTHROPOLOGY 50:133–161 (2007)