Abstract: Abstract
The evolution and origin of primate social organisation has attracted the attention of many researchers, and a solitary pattern, believed to be present in most nocturnal prosimians, has been generally considered as the most primitive system. Nocturnal prosimians are in fact mostly seen alone during their nightly activities and therefore termed “solitary foragers”, but that does not mean that they are not social. Moreover, designating their social organisation as “solitary”, implies that their way of life is uniform in all species. It has, however, emerged over the last decades that all of them exhibit not only some kind of social network but also that those networks differ among species. There is a need to classify these social networks in the same manner as with group-living (gregarious) animals if we wish to link up the different forms of primate social organisation with ecological, morphological or phylogenetic variables. In this review, we establish a basic classification based on spatial relations and sociality in order to describe and cope properly with the social organisation patterns of the different species of nocturnal prosimians and other mammals that do not forage in cohesive groups. In attempting to trace the ancestral pattern of primate social organisation, the Malagasy mouse and dwarf lemurs and the Afro-Asian bushbabies and lorises are of special interest because they are thought to approach the ancestral conditions most closely. These species have generally been believed to exhibit a dispersed harem system as their pattern of social organisation (“dispersed” means that individuals forage solitarily but exhibit a social network). Therefore, the ancestral pattern of primate social organisation was inferred to be a dispersed harem. In fact, new field data on cheirogaleids combined with a review of patterns of social organisation in strepsirhines (lemurs, bushbabies and lorises) revealed that they exhibit either dispersed multi-male systems or dispersed monogamy rather than a dispersed harem system. Therefore, the concept of a dispersed harem system as the ancestral condition of primate social organisation can no longer be supported. In combination with data on social organisation patterns in “primitive” placentals and marsupials, and in monotremes, it is in fact most probable that promiscuity is the ancestral pattern for mammalian social organisation. Subsequently, a dispersed multi-male system derived from promiscuity should be regarded as the ancestral condition for primates. We further suggest that the gregarious patterns of social organisation in Aotus and Avahi, and the dispersed form in Tarsius evolved from the gregarious patterns of diurnal primates rather than from the dispersed nocturnal type. It is consequently proposed that, in addition to Aotus and Tarsius, Avahi is also secondarily nocturnal.

Abstract: The claim that differences in brain size across primate species has mainly been driven by the demands of sociality (the “social brain” hypothesis) is now widely accepted. Some of the evidence to support this comes from the fact that species that live in large social groups have larger brains, and in particular larger neocortices. Lindenfors and colleagues (BMC Biology 5:20) add significantly to our appreciation of this process by showing that there are striking differences between the two sexes in the social mechanisms and brain units involved. Female sociality (which is more affiliative) is related most closely to neocortex volume, but male sociality (which is more competitive and combative) is more closely related to subcortical units (notably those associated with emotional responses). Thus different brain units have responded to different selection pressures.

Abstract: We report morphological data on brains of four African, Loxodonta africana, and three Asian elephants, Elephas maximus, and compare findings to literature. Brains exhibit a gyral pattern more complex and with more numerous gyri than in primates, humans included, and in carnivores, but less complex than in cetaceans. Cerebral frontal, parietal, temporal, limbic, and insular lobes are well developed, whereas the occipital lobe is relatively small. The insula is not as opercularized as in man. The temporal lobe is disproportionately large and expands laterally. Humans and elephants have three parallel temporal gyri: superior, middle, and inferior. Hippocampal sizes in elephants and humans are comparable, but proportionally smaller in elephant. A possible carotid rete was observed at the base of the brain. Brain size appears to be related to body size, ecology, sociality, and longevity. Elephant adult brain averages 4783 g, the largest among living and extinct terrestrial mammals; elephant neonate brain averages 50% of its adult brain weight (25% in humans). Cerebellar weight averages 18.6% of brain (1.8 times larger than in humans). During evolution, encephalization quotient has increased by 10-fold (0.2 for extinct Moeritherium, approximately 2.0 for extant elephants). We present 20 figures of the elephant brain, 16 of which contain new material. Similarities between human and elephant brains could be due to convergent evolution; both display mosaic characters and are highly derived mammals. Humans and elephants use and make tools and show a range of complex learning skills and behaviors. In elephants, the large amount of cerebral cortex, especially in the temporal lobe, and the well-developed olfactory system, structures associated with complex learning and behavioral functions in humans, may provide the substrate for such complex skills and behavior.

Abstract: The size of the hippocampus has been previously shown to reflect species differences and sex differences in reliance on spatial memory to locate ecologically important resources, such as food and mates. Black-capped chickadees (Parus atricapillus) cached more food than did either Mexican chickadees (P. sclateri) or bridled titmice (P. wollweberi) in two tests of food storing, one conducted in an aviary and another in smaller home cages. Black-capped chickadees were also found to have a larger hippocampus, relative to the size of the telencephalon, than the other two species. Differences in the frequency of food storing behavior among the three species have probably produced differences in the use of hippocampus-dependent memory and spatial information processing to recover stored food, resulting in graded selection for size of the hippocampus.

Abstract: Abstract
Several comparative research programs have focusedon the cognitive, life history and ecological traits thataccount for variation in brain size. We review one ofthese programs, a program that uses the reported frequencyof behavioral innovation as an operational measureof cognition. In both birds and primates, innovationrate is positively correlated with the relative size of associationareas in the brain, the hyperstriatum ventrale andneostriatum in birds and the isocortex and striatum inprimates. Innovation rate is also positively correlatedwith the taxonomic distribution of tool use, as well asinterspecific differences in learning. Some features ofcognition have thus evolved in a remarkably similar wayin primates and at least six phyletically-independent avianlineages. In birds, innovation rate is associated withthe ability of species to deal with seasonal changes in theenvironment and to establish themselves in new regions,and it also appears to be related to the rate atwhich lineages diversify. Innovation rate provides a usefultool to quantify inter-taxon differences in cognitionand to test classic hypotheses regarding the evolution ofthe brain.