1School of Human Evolution and Social Change, Arizona State University, 2Department of Anatomy, Midwestern University, 3School of Anthropology, University of Arizona
March 26, 2015 , Archview Ballroom
Life history traits vary noticeably across and within species and are influenced by a variety of ultimate and proximate factors. At the proximate level, a variety of hormones are known to play a critical role in influencing the behavior and life history of mammals, including humans. Hormones are produced from multiple glands in the body. The pituitary gland is directly responsible for producing several hormones, including those related to growth and reproduction. Although we have a basic understanding of how hormones affect life history characteristics, we still have little knowledge of this relationship in an evolutionary context. Here, we used data from 136 mammal species representing 14 orders to investigate relationships between pituitary gland size and life history variation. Because pituitary gland size should be related to hormone production and action, we predicted that species with relatively large pituitaries should be associated with increased fetal and postnatal growth rates, as well as reduced longevity. Phylogenetic comparative analyses controlling for brain and body mass revealed that total pituitary size, as well as the size of the anterior lobe of the pituitary, significantly predicted mammal fetal and postnatal growth rates, but not maximum longevity. This is some of the first evidence that the size of a brain structure, the pituitary, is linked to life history variation through mediating hormone levels. In addition, we demonstrate that data related to endocrine gland size may be critical for fully understanding life history evolution.