Primates are noted f o r their mental abilities but the selective basis f o r such traits has Aleles, Alouatta] MOST PRIMATES SHOW A REMARKABLE CAPACITY for learning and retention. As noted by Eisenberg (1973), what appear to set primate societies apart from those of other relatively long-lived and large-brained animals are particular sets of attributes related to the storage and retrieval of a great deal of independently acquired information about the environment. The complex brain of higher primates forms the basis for a plasticity of behavior that permits a wide variety of responses to a given situation (Napier 1970). Hominids are at the zenith of this trend and many hypotheses have been advanced as to why increasing mental complexity might have been favored in their evolution. Hunting is frequently singled out as a critical factor (Waahburn and Lancaster 1968). According to this hypothesis, proto-humans living in savanna-mosaic areas during the Pliocene may FOODS A N D M E N T A L DEVELOPMENT 535have become increasingly dependent on animal protein in the diet. This dependency, in time, could have resulted in strong selective pressure toward increased hunting efficiency through cooperative hunting, food sharing, manufacture of tools and a symbolic system of communication (Hockett and Ascher 1964; Holloway 1967). It is indeed possible that selective pressures related to increased hunting efficiency may have served as an important stimulus in the evolution of the hominid brain. What is omitted from this and similar explanations, however, is why increasing mental complexity might have been favored in hominid evolution in the first place. The key to understanding any adaptive trait comes not only from a knowledge of current selective pressures but also from the past evolutionary history of the species in question. New adaptations are not creations sui generis but rather are modifications of past adaptations. Some critical pressures in the evolutionary history of certain higher primates resulted in an increasing dependence on memory and learning-the hominid line represents an intensification of what must have been a preexisting trend in primate evolution.Early primate field studies were largely concerned with the behavior of savanna-living primates since these were thought to offer possible analogues for hominid evolution (Washburn and DeVore 1961). It must be remembered, however, that proto-humans did not evolve in the savannas, but rather came gradually to them from tropical forest>. bringing with them many millions of years of adaptations to forest conditions. To u n d w stand the origins of mental complexity in hominids, we must look not only at life in the savannas but also at life in tropical forests, for it is here that the first steps toward an increasing dependence on mental abilities must have been taken. What pressures on forestliving primates might have stimulated evolution along these lines?Larger, forest-living primates today are all either partially or entirely primary consumers-that is to say, ...

In lorisines (Loris, Nycticebus, Perodicticus, Arctocebus), the tip of the ulna is reduced to the dimensions of a styloid process, a new and more proximal ulnar head is developed, and the pisiform is displaced distally away from its primitive contact with the ulna. In some Nycticebus, intra-articular tissues separate the ulna from the triquetrum. These traits are not seen in other quadrupedal primates, but they are characteristic of extant hominoids. Among hominoids, these features have been interpreted as adaptations to arm-swinging locomotion. Since hominoid-like features of the wrist joint are found in lorisines, but not in New World monkeys that practice arm-swinging locomotion, these features may have been evolved in both lorisines and large hominoids to enhance wrist mobility for cautious arboreal locomotion involving little or no leaping. Most of the other morphological traits characteristic of modern hominoids can be explained as adaptations to cautious quadrupedalism as well as to brachiation, and may have developed for different reasons in different lineages descended from an unspecialized cautious quadruped resembling Alouatta.

Primates show a strong positive relationship between body weight and home range area. Dietary habits also influence home range area. Folivorous primates occupy smaller home range areas for their body weight than do frugivores and omnivores. Primates generally require smaller home range area per individual than solitary terrestrial mammals, but primates living in social groups have much larger total home range than individual solitary mammals. This trend may necessitate higher expenditures of energy in food-gathering or modifications in movement patterns.

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Wild primates take most of the daily diet from plant sources, eating moderate to small amounts of animal source foods (ASF). Plant materials make up from 87% to >99% of the annual diet of great apes, the closest living relatives of modern humans (Homo sapiens sapiens). Reflecting their close genetic relationship, gut form and nutrient requirements of apes and humans (Hominoidea) are very similar, as is their pattern of digestive kinetics-one predicated on a relatively slow turnover of ingesta. In plant-eating mammals, in contrast to carnivorous mammals, greater body size is associated with lower dietary quality. Turning to ASF as a routine rather than occasional dietary component would have permitted the evolving human lineage to evade the nutritional constraints placed on body size increases in apes. Without routine access to ASF, it is highly unlikely that evolving humans could have achieved their unusually large and complex brain while simultaneously continuing their evolutionary trajectory as large, active and highly social primates. As human evolution progressed, young children in particular, with their rapidly expanding large brain and high metabolic and nutritional demands relative to adults would have benefited from volumetrically concentrated, high quality foods such as meat. Today, many humans, particularly those in high income nations, have a variety of high quality, non-ASF dietary alternatives, but such foods were not generally available to paleolithic human ancestors nor to many people today in low income nations.

With 1 plate and 7 figures in the text)To evaluate effects of persistent bot fly (Alouattamyia baevi) parasitism on a host population of Panamanian howler monkeys (Alouatta palliata), a 68-month study was carried out which included: (i) examination of the parasite's life cycle; (ii) monthly estimates of prevalence and mean intensity; (iii) monitoring of howler mortality; (iv) censuses of howler monkey troops; and (v) analysis of blood samples from infected and uninfected monkeys. A complete life cycle of A . baeri takes approximately 13 weeks; larvae remain in howlers for approximately six weeks, passing through three instars. Overall prevalence of infection was 60%, overall mean intensity 2.8 f 0.04. No difference in prevalence or mean intensity was found between adult males and females. As a class, juveniles had a significantly higher prevalence and a significantly lower mean intensity than adults; the adult and juvenile classes both showed a significantly higher prevalence and mean intensity than the infant class. Such differences may relate to characteristics of younger age classes rather than host selectivity on the part of the parasite. Although larvae were observed in the howler population throughout the year, relative density fluctuated from month to month, showing from one to three significant peaks per year. Larvae were most abundant during the mid-to-late rainy season (Aug.-Nov.). Relative density was strongly correlated with howler mortality. Several hematological parameters including serum albumin levels and albumin/ globulin ratio were significantly lower in individuals with heavy larval burdens. No endoparasites or diseases were found in blood samples. I conclude that the annual pattern of howler mortality results from a synergistic effect between the age, physical condition, and fat reserves of parasitized individuals, the size of the larval burden, and increasing dietary stress as the rainy season progresses. The lack of growth in this closed primate population over >20 years apparently results, in large part, from primary and secondary effects of bot fly parasitism. Parasite and hostCuterebrid bot flies comprise a specialized line of myiasis-producing primitive calypterates confined to the New World (Catts. 1982). Little is known about their biology and life history, particularly in tropical regions (Vieira. 1993). To date. the best studied cuterebrid is Dermurohia horninis. sometimes, though incorrectly, referred to as the human bot fly. This monospecific genus lays its eggs primarily on mosquitoes and muscoids (Zeledon, 1957: Catts. 1982. When the carrier insect visits a vertebrate host to feed, larvae emerge from eggs and penetrate the host's skin where they pass through 3 instars as subcutaneous parasites. The wide range of hosts tolerated by D. horiziriis strongly contrasts with the behaviour of other cuterebrid species which typically are obligate larval parasites of specific host species and whose larvae enter and pass much of EFFECTS OF BOT FLY PARASITISM O N HOWLER MONKEYS 400. 41

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