Relative Brain Size, Gut Size, and Evolution in New World Monkeys


  • Walter Hartwig,

    Corresponding author
    1. Department of Clinical Education, Touro University College of Osteopathic Medicine, Vallejo, California
    • Department of Clinical Education, Touro University College of Osteopathic Medicine, 1310 Club Drive, Vallejo, CA, 94592.
    Search for more papers by this author
  • Alfred L. Rosenberger,

    1. Department of Anthropology and Archaeology, Brooklyn College, CUNY, Brooklyn, New York
    2. Department of Anthropology, City University of New York Graduate Center, New York
    3. Consortium in Evolutionary Primatology (NYCEP), New York, New York
    4. Mammalogy, American Museum of Natural History, New York, New York
    Search for more papers by this author
  • Marilyn A. Norconk,

    1. Department of Anthropology, Kent State University, Kent, Ohio
    Search for more papers by this author
  • Marcus Young Owl

    1. Department of Anthropology, California State University, Long Beach, California 90840
    Search for more papers by this author


The dynamics of brain evolution in New World monkeys are poorly understood. New data on brain weight and body weight from 162 necropsied adult individuals, and a second series on body weight and gut size from 59 individuals, are compared with previously published reports based on smaller samples as well as large databases derived from museum records. We confirm elevated brain sizes for Cebus and Saimiri and also report that Cacajao and Chiropotes have relatively large brains. From more limited data we show that gut size and brain mass have a strongly inverse relationship at the low end of the relative brain size scale but a more diffuse interaction at the upper end, where platyrrhines with relatively high encephalization quotients may have either relatively undifferentiated guts or similar within-gut proportions to low-EQ species. Three of the four main platyrrhine clades exhibit a wide range of relative brain sizes, suggesting each may have differentiated while brains were relatively small and a multiplicity of forces acting to maintain or drive encephalization. Alouatta is a likely candidate for de-encephalization, although its “starting point” is difficult to establish. Factors that may have compelled parallel evolution of relatively large brains in cebids, atelids and pitheciids may involve large social group sizes as well as complex foraging strategies, with both aspects exaggerated in the hyper-encephalized Cebus. With diet playing an important role selecting for digestive strategies among the seed-eating pitheciins, comparable in ways to folivores, Chiropotes evolved a relatively larger brain in conjunction with a moderately large and differentiated gut. Anat Rec, 2011. © 2011 Wiley Periodicals, Inc.