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In 1987, the University of Chicago Press published Primate Societies, the standard reference in the field of primate behavior for an entire generation of students and scientists. But in the twenty-five years since its publication, new theories and research techniques for studying the Primate order have been developed, debated, and tested, forcing scientists to revise their understanding of our closest living relatives. Intended as a sequel to Primate Societies, The Evolution of Primate Societies compiles thirty-one chapters that review the current state of knowledge regarding the behavior of nonhuman primates. Chapters are written by the leading authorities in the field and organized around four major adaptive problems primates face as they strive to grow, maintain themselves, and reproduce in the wild. The inclusion of chapters on the behavior of humans at the end of each major section represents one particularly novel aspect of the book, and it will remind readers what we can learn about ourselves through research on nonhuman primates. The final section highlights some of the innovative and cutting-edge research designed to reveal the similarities and differences between nonhuman and human primate cognition. The Evolution of Primate Societies will be every bit the landmark publication its predecessor has been.

It has been widely recognized that mammal brain size predominantly increases over evolutionary time. Safi et al. [Biol Lett 2005;1:283-286] questioned the generality of this trend, arguing that brain size evolution among bats involved reduction in multiple lineages as well as enlargement in others. Our study explored the direction of change in the evolution of bat brain size by estimating brain volume in fossil bats, using synchrotron radiation X-ray tomographic microscopy. Virtual endocasts were generated from 2 Hipposideros species: 3 specimens of Oligocene Hipposideros schlosseri (∼35 Ma) and 3 of Miocene Hipposideros bouziguensis (∼20 Ma). Upper molar tooth dimensions (M(2) length × width) collected for 43 extant insectivorous bat species were used to derive empirical formulae to estimate body mass in the fossil bats. Brain size was found to be relatively smaller in the fossil bats than in the average extant bat both with raw data and after allowing for phylogenetic inertia. Phylogenetic modeling of ancestral relative brain size with and without fossil bats confirmed a general trend towards evolutionary increase in this bat lineage.

Bivariate scaling analyses can reveal interesting correlations between individual biological variables, but inference of actual causal links in complex networks requires multiple tests to satisfy the criterion of isolation. Mammalian brain tissue has high energy demands, so energy supply is inevitably a key issue in evolution of the primate brain, especially for large-brained hominids. Various hypotheses have proposed a direct link between brain size and metabolic turnover in adults, but the author’s Maternal Energy Hypothesis (MEH) instead focuses on energy supplied by the mother during brain development up to weaning. This hypothesis is supported by various empirical findings, but it has also been challenged, particularly on the basis that these findings do not survive tests conducted to eliminate effects of phylogenetic inertia. New comparative analyses of brain size in mammals with improved datasets have, however, confirmed links to both basal metabolic rate and gestation period, complying with core predictions of MEH. The evidence now available in support of MEH is reviewed and some implications for brain evolution are explored. A widely recognized general trend towards increase in average relative brain size during mammalian evolution has recently been challenged by a study of brain size in bats that inferred, exclusively through analysis of data from extant species, that brain size has actually undergone reduction in numerous lineages. It is shown that the statistical test used to test for directionality of evolution was inappropriate. A review of fossil evidence for brain evolution in primates, cetaceans and carnivores confirms the generally accepted trend towards increased average brain size through the Tertiary. Progressive increase in mammalian relative brain size over time is at least partially attributable to increases in the level and efficiency of maternal investment. Energetic aspects, including those invoked in the MEH, are of special importance for

Menschen unterscheiden sich grundlegend von den anderen Menschenaffen. In diesem Beitrag betrachten wir insbesondere die Unterschiede in der Hirngröße und im Verlauf der Lebensabschnitte (life history). Wir werden erklären, wie sie entstanden sind und warum sie zusammenhängen, indem wir die neuesten Studien zu Rate ziehen, in denen die allgemeinen Beziehungen zwischen Hirngröße und Lebensverlauf bei Vögeln und Säugetieren theoretisch und empirisch untersucht worden sind.

We assessed water-body use by elephants through monitoring elephant signs around them. Elephant footprints and dung piles were recorded at 25 water bodies fortnightly for one year. Elephants preferred perennial water bodies and avoided those with temporary human dwellings. Human activities did not significantly affect elephant use of water bodies, suggesting low incidence of activities and behavioral adaptation to them by elephants. Elephant signs at perennial water bodies increased in the dry season. The monitoring technique was able to detect differences in elephant densities in two areas and establish the presence of herds even at low densities. We conclude that outside protected areas, large perennial water bodies represent a preferred resource for elephants, and that assessing elephant signs around water bodies is a useful technique for monitoring elephant presence for management and research purposes.

The processes that underlie the formation of the dominance hierarchy in a group are since long under debate. Models of self-organisation suggest that dominance hierarchies develop by the self-reinforcing effects of winning and losing fights (the so-called winner-loser effect), but according to ‘the prior attribute hypothesis’, dominance hierarchies develop from pre-existing individual differences, such as in body mass. In the present paper, we investigate the relevance of each of these two theories for the degree of female dominance over males. We investigate this in a correlative study in which we compare female dominance between groups of 22 species throughout the primate order. In our study female dominance may range from 0 (no female dominance) to 1 (complete female dominance). As regards ‘the prior attribute hypothesis’, we expected a negative correlation between female dominance over males and species-specific sexual dimorphism in body mass. However, to our surprise we found none (we use the method of independent contrasts). Instead, we confirm the self- organisation hypothesis: our model based on the winner-loser effect predicts that female dominance over males increases with the percentage of males in the group. We confirm this pattern at several levels in empirical data (among groups of a single species and between species of the same genus and of different ones). Since the winner-loser effect has been shown to work in many taxa including humans, these results may have broad implications.

Comparative neurobiologists have provided ample evidence that in vertebrates small animals have proportionally larger brains: in a double-logarithmic plot of brain weight versus body weight all data points conform quite closely to a straight line with a slope of less than one. Hence vertebrate brains scale allometrically, rather than isometrically, with body size. Here we extend the phylogenetic scope of such studies and the size range of the brains under investigation to the insects, especially ants. We show that the principle of (negative) allometry applies as well, but that ants have considerably smaller brains than any ant-sized vertebrate would have, and that this result holds even if the relatively higher exoskeleton weights of ants (as compared to endoskeleton weights of mammals) are taken into account. Finally, interspecific comparisons within one genus of ants, Cataglyphis, show that species exhibiting small colony sizes (of a few hundred individuals) have significantly smaller brains than species in which colonies are composed of several thousand individuals.