Comparative analysis of encephalization in mammals reveals relaxed constraints on anthropoid primate and cetacean brain scaling

Authors

  • A. M. BODDY,

    1. Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI, USA
    Search for more papers by this author
  • M. R. McGOWEN,

    1. Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI, USA
    Search for more papers by this author
  • C. C. SHERWOOD,

    1. Department of Anthropology, The George Washington University, Washington, DC, USA
    Search for more papers by this author
  • L. I. GROSSMAN,

    1. Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI, USA
    Search for more papers by this author
  • M. GOODMAN,

    1. Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI, USA
    2. Department of Anatomy & Cell Biology, Wayne State University School of Medicine, Detroit, MI, USA
    Search for more papers by this author
    • Deceased.

  • D. E. WILDMAN

    1. Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI, USA
    2. Department of Obstetrics and Gynecology, Wayne State University School of Medicine and Hutzel Women’s Hospital, Detroit, MI, USA
    Search for more papers by this author

Derek E. Wildman, Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, 540 E. Canfield, Detroit, MI 48201, USA.
Tel.: 313 577 1253; fax: 313 577 5218; e-mail: dwildman@wayne.edu

Abstract

There is a well-established allometric relationship between brain and body mass in mammals. Deviation of relatively increased brain size from this pattern appears to coincide with enhanced cognitive abilities. To examine whether there is a phylogenetic structure to such episodes of changes in encephalization across mammals, we used phylogenetic techniques to analyse brain mass, body mass and encephalization quotient (EQ) among 630 extant mammalian species. Among all mammals, anthropoid primates and odontocete cetaceans have significantly greater variance in EQ, suggesting that evolutionary constraints that result in a strict correlation between brain and body mass have independently become relaxed. Moreover, ancestral state reconstructions of absolute brain mass, body mass and EQ revealed patterns of increase and decrease in EQ within anthropoid primates and cetaceans. We propose both neutral drift and selective factors may have played a role in the evolution of brain–body allometry.

Ancillary