title: Multivariate Meta-Analysis of Brain-Mass Correlations in Eutherian Mammals.
abstract: The general assumption that brain size differences are an adequate proxy for subtler differences in brain organization turned neurobiologists toward the question why some groups of mammals such as primates, elephants, and whales have such remarkably large brains. In this meta-analysis, an extensive sample of eutherian mammals (115 species distributed in 14 orders) provided data about several different biological traits and measures of brain size such as absolute brain mass (AB), relative brain mass (RB; quotient from AB and body mass), and encephalization quotient (EQ). These data were analyzed by established multivariate statistics without taking specific phylogenetic information into account. Species with high AB tend to (1) feed on protein-rich nutrition, (2) have a long lifespan, (3) delayed sexual maturity, and (4) long and rare pregnancies with small litter sizes. Animals with high RB usually have (1) a short life span, (2) reach sexual maturity early, and (3) have short and frequent gestations. Moreover, males of species with high RB also have few potential sexual partners. In contrast, animals with high EQs have (1) a high number of potential sexual partners, (2) delayed sexual maturity, and (3) rare gestations with small litter sizes. Based on these correlations, we conclude that Eutheria with either high AB or high EQ occupy positions at the top of the network of food chains (high trophic levels). Eutheria of low trophic levels can develop a high RB only if they have small body masses.
authors.affiliation: Department II of Anatomy, University of CologneCologne, Germany; Biocenter, University of CologneCologne, Germany.
authors.forename: Charlene
authors.initials: C
authors.lastname: Steinhausen
authors.affiliation: Biocenter, University of CologneCologne, Germany; Jülich Research Centre, Institute of Neuroscience and Medicine (INM-6) and Institute for Advanced Simulation (IAS-6) and JARA BRAIN Institute IJülich, Germany.
authors.forename: Lyuba
authors.initials: L
authors.lastname: Zehl
authors.affiliation: Department of Anatomy III (Dr. Senckenbergische Anatomie), Goethe University of Frankfurt am Main Frankfurt am Main, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Haas-Rioth
authors.affiliation: Department II of Anatomy, University of Cologne Cologne, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Morcinek
authors.affiliation: Biocenter, University of Cologne Cologne, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Walkowiak
authors.affiliation: Department II of Anatomy, University of CologneCologne, Germany; Biocenter, University of CologneCologne, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Huggenberger
keywords: EQ; brain mass; brain size; cluster analysis; eutheria; mammals; trophic level