regard to the immense variety of locomotion patterns that exist in modern primates. (Fleagle, 1999)

Crook and Gartlan (1966) as well as Eisenberg et al (1972) believed the solitary pattern of social organisation to be present in most nocturnal prosimians and considered it to be the most primitive system. Therefore the solitary pattern was believed to be the ancestral condition. Despite the fact that primates with this kind of social organisation are solitary foragers, they are still social animals because they often have very complex systems of communication e.g. by vocalisations, scent marking etc. Further, it has been found that these solitary species exhibit social networks which differ among species and thus this system is not actually as primitive as it was regarded to be originally. In an attempt to trace the ancestral pattern of social organisation, Müller and Thalmann (2000) looked at the patterns of the Malagasy mouse and dwarf lemurs and the Afrc-Asian bushbabies and lorises as they were thought to approach the ancestral condition most closely. (All are small, nocturnal and forage solitarily.) These species had generally been believed to exhibit a dispersed harem system as their pattern of social organisation – ‘dispersed’ meaning that individuals forage solitarily, but exhibit a social network. Therefore, the ancestral pattern of primate social organisation was inferred to be a dispersed harem. Müller and Thalmann showed that new field data on cherogaleids combined with a review of patterns of social organisation in strepsirhines (lemurs, bushbabies and lorises) has revealed that they exhibit either dispersed multi-male systems or dispersed monogamy. Thus, the concept of a dispersed harem system as the ancestral condition of primate social organisation could no longer be supported. After reviewing the social organisation of placentals and marsupials that are believed to be close to the initial ancestral stock, Müller and Thalmann proposed that promiscuity was the ancestral mammalian pattern of social organisation from which a dispersed multi-male system evolved as the ancestral pattern of primate social organisation. This evolved to a dispersed monogamous system whenever required by ecological circumstances and with the shift to a diurnal lifestyle, a gregarious multi-male system evolved. This could then evolve to produce either a gregarious harem or a monogamous system. Further, Müller and Thalmann proposed that the aptterns of social organisation of owl monkeys, woolly lemurs and tarsiers (gregarious

2

monogamy) evolved from gregarious patterns of social organisation of diurnal primates rather than from the dispersed nocturnal type. (Müller and Thalmann, 2000)

There are three main theories of primate origins: the arboreal theory, the visualpredation hypothesis and the angiosperm exploitation hypothesis. Traditionally, the morphological traits of primates were assumed to be adaptations to an arboreal way of life. The founding fathers of the arboreal theory were G.E. Smith (1912) and W. Jones (1916). Stereoscopic vision, reduced olfaction, grasping hands and feet and large brains were seen as specific adaptations to the demands of locomotion and information processing in a complex, 3-D arboreal habitat. Thus it was concluded that the decisive moment in primate evolution was the move from the ground up into the trees. Nevertheless, Szalay (1973) argued that the arboreal habits of primates represent a primitive archontan feature (Archonta is a superorder of mammals which includes primates, tree shrews, flying lemurs and bats.) and the specific behaviours that distinguished the primate order from other archontans was a shift to a more herbivorous diet and a more acrobatic grasp-leaping type of locomotion. (Sussman, 1991; Rasmussen, 1990; Fleagle, 1999)

Cartmill (1972/1974) noted several problems with the arboreal hypothesis, most importantly the fact that many other mammalian orders contain arboreal species which have not evolved primate-like vision or grasping abilities, proving that arboreality itself does not necessarily lead to primate structure. He noted that stereoscopic vision is particularly characteristic of predators such as cats and owls, which rely on vision to detect their prey. Similarly, he noted that the hands of most arboreal mammals are equipped with claws rather than nails, and that the nailed, grasping hands of primates are probably and adaptation for grasping prey rather than arboreal supports. Thus, he concluded that the ancestral primate was specifically designed to be a visual predator that stalked and grasped its prey in either the canopy or the forest undergrowth. Nevertheless, it has been shown that most nocturnal primates feed mainly on crawling insects, many of which are captured on the ground. Further, very few primates are known to have a diet including a greater proportion of insects than plant material and there is evidence that the primitive primate condition is omnivory. Also, many primates do not detect their prey by vision but rather by smell (e.g. lorises) and sound (e.g. tarsiers). Especially nocturnal

3