Faecal parasites increase with age but not reproductive effort in wild female chimpanzees.

Energy investment in reproduction is predicted to trade off against other necessary physiological functions like immunity, but it is unclear to what extent this impacts fitness in long-lived species. Among mammals, female primates, and especially apes, exhibit extensive periods of investment in each offspring. During this time, energy diverted to gestation and lactation is hypothesized to incur short and long-term deficits in maternal immunity and lead to accelerated ageing. We examined the relationship between reproduction and immunity, as measured by faecal parasite counts, in wild female chimpanzees (Pan troglodytes schweinfurthii) of Kibale National Park, Uganda. While we observed higher parasite shedding (counts of eggs, cysts and larvae) in pregnant chimpanzees relative to cycling females, parasites rapidly decreased during early lactation, the most energetically taxing phase of the reproductive cycle. Additionally, while our results indicate that parasite shedding increases with age, females with higher fertility for their age had lower faecal parasite counts. Such findings support the hypothesis that the relatively conservative rate of female reproduction in chimpanzees may be protective against the negative effects of reproductive effort on health. This article is part of the theme issue 'Evolution of the primate ageing process'.

Cooking and the human commitment to a high-quality diet.

For our body size, humans exhibit higher energy use yet reduced structures for mastication and digestion of food compared to chimpanzees, our closest living relatives. This suite of features suggests that humans are adapted to a high-quality diet. Although increased consumption of meat during human evolution certainly contributed to dietary quality, meat-eating alone appears to be insufficient to support the evolution of these traits, because modern humans fare poorly on raw diets that include meat. Here, we suggest that cooking confers physical and chemical benefits to food that are consistent with observed human dietary adaptations. We review evidence showing that cooking facilitates mastication, increases digestibility, and otherwise improves the net energy value of plant and animal foods regularly consumed by humans. We also address the likelihood that cooking was adopted more than 250,000 years ago (kya), a period that we believe is sufficient in length for the proposed adaptations to have occurred. Additional experimental work is needed to help discriminate the relative contributions of cooking, meat eating, and other innovations such as nonthermal food processing in supporting the human transition toward dietary quality.

Relationship between chimpanzee (Pan troglodytes) density and large, fleshy-fruit tree density: conservation implications.

Conservation efforts to protect chimpanzees in their natural habitat are of the highest priority. Unfortunately, chimpanzee density is notoriously difficult to determine, making it difficult to assess potential chimpanzee conservation areas. The objective of this study was to determine whether chimpanzee density could be predicted from the density of trees that produce large, fleshy fruits. Using chimpanzee nest counts from six sites within Kibale National Park, Uganda, collected during a year-long study, a predictive trend was found between chimpanzee nest density and large, fleshy-fruit tree density. This relationship may offer a quick, reasonably reliable method of estimating potential chimpanzee densities in previously unsurveyed habitats and may be used to evaluate the suitability of possible re-introduction sites. Thus, in conjunction with other survey techniques, such as forest reconnaissance, it may provide an effective and efficient means of determining appropriate chimpanzee habitat in which to allocate conservation efforts.

Intestinal parasites of the chimpanzee Pan troglodytes in Kibale Forest, Uganda.

One-hundred-and-twenty-three stool samples were examined from 45 chimpanzees in a natural population in western Uganda. Comparison with previous studies is complicated by the diversity of techniques used and interpretations. The Ugandan population had relatively many intestinal protozoa, including the probably beneficial entodiniomorph ciliates. Strongyloid nematodes are universal among chimpanzees, but were surprisingly absent from those on Mount Assirik in Senegal. Railletina tapeworms are sporadic in their occurrence. The absence of spiruroid nematodes in the Ugandan population reflects the absence of insectivory in this population. There was little evidence of seasonal difference in prevalences.

A view on the science: physical anthropology at the millennium.

EDITOR's NOTE The year 2000 marks the onset of the 21st century. Physical anthropologists will provide brief reflections on our discipline, including what attracted them to it, and their views on the directions our discipline may pursue as we enter, in January 2001, the third millennium.

Evolution of coalitionary killing.

Warfare has traditionally been considered unique to humans. It has, therefore, often been explained as deriving from features that are unique to humans, such as the possession of weapons or the adoption of a patriarchal ideology. Mounting evidence suggests, however, that coalitional killing of adults in neighboring groups also occurs regularly in other species, including wolves and chimpanzees. This implies that selection can favor components of intergroup aggression important to human warfare, including lethal raiding. Here I present the principal adaptive hypothesis for explaining the species distribution of intergroup coalitional killing. This is the "imbalance-of-power hypothesis," which suggests that coalitional killing is the expression of a drive for dominance over neighbors. Two conditions are proposed to be both necessary and sufficient to account for coalitional killing of neighbors: (1) a state of intergroup hostility; (2) sufficient imbalances of power between parties that one party can attack the other with impunity. Under these conditions, it is suggested, selection favors the tendency to hunt and kill rivals when the costs are sufficiently low. The imbalance-of-power hypothesis has been criticized on a variety of empirical and theoretical grounds which are discussed. To be further tested, studies of the proximate determinants of aggression are needed. However, current evidence supports the hypothesis that selection has favored a hunt-and-kill propensity in chimpanzees and humans, and that coalitional killing has a long history in the evolution of both species.

Cultures in chimpanzees.

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation. Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumulated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans. We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds. The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinctive, a phenomenon characteristic of human cultures but previously unrecognised in non-human species.

Manual laterality in anvil use: wild chimpanzees cracking Strychnos fruits.

Wild chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania, smash open the hard-shelled fruits of Strychnos spp. on anvils of stone or woody vegetation. In this food-processing task, most of the apes show exclusive use of one hand or the other, that is, strong individual hand preferences. Such extreme laterality of manual functioning corresponds to Level 3 on a five-level descriptive model of lateralisation that appears to reflect the increasingly skillful demands of object manipulation. There is precise congruence in laterality between anvil use and another subsistence task involving elementary technology-termite fishing-in almost all cases.

The evolution of sexuality in chimpanzees and bonobos.

The evolution of nonconceptive sexuality in bonobos and chimpanzees is discussed from a functional perspective. Bonobos and chimpanzees have three functions of sexual activity in common (paternity confusion, practice sex, and exchange for favors), but only bonobos use sex purely for communication about social relationships. Bonobo hypersexuality appears closely linked to the evolution of female-female alliances. I suggest that these alliances were made possible by relaxed feeding competition, that they were favored through their effect on reducing sexual coercion, and that they are ultimately responsible for the relaxed social conditions that allowed the evolution of "communication sex."

The significance of fibrous foods for Kibale Forest chimpanzees.

Four categories of plant food dominated the diet of chimpanzees in Kibale Forest, Uganda: non-fig tree fruits, fig tree fruits, herbaceous piths and terrestrial leaves. Fruit abundance varied unpredictably, more among non-figs than figs. Pith intake was correlated negatively with fruit abundance and positively with rainfall, whereas leaf intake was not influenced by fruit abundance. Piths typically have low sugar and protein levels. Compared with fruits and leaves they are consistently high in hemicellulose and cellulose, which are insoluble fibres partly digestible by chimpanzees. Herbaceous piths appear to be a vital resource for African forest apes, offering an alternative energy supply when fruits are scarce.

The significance of fibrous foods for Kibale forest Chimpanzees

Four categories of plant dominated the diet of chimpanzees in Kibale forest; Uganda: non-fig tree fruits; fig tree fruits; herbaceous piths and terrestrial leaves. Fruit abundance varied unpredictably; more among non-figs than figs. Pith intake was correlated negatively with fruit abundance and low sugar and protein levels. Compared with fruits and leaves they are consistently high in hemicellulose and cellulose; which are insoluble fibres partly digestible by chimpanzees. Herbaceous paths appear to be a vital resource for African forest apes; offering an alternative energy supply when fruits are ecarse

The significance of fibrous foods for Kibale Forest chimpanzees

Four categories of plant food dominated the diet of chimpanzees in Kibale Forest; Uganda: non-fig tree fruits; fig tree fruits; herbaceous piths and terrestrial leaves. Fruit abundance varied unpredictably; more among non-figs than figs. Pith intake was correlated negatively with fruit abundance and positively with rainfall; whereas leaf intake was not influenced by fruit abundance. Piths typically have low sugar and protein levels. Compared with fruits and leaves they are consistently high in hemicellulose and cellulose; which are insoluble fibres partly digestible by chimpanzees. Herbaceous piths appear to be a vital resource for African forest apes; offering an alternative energy supply when fruits are scarce

Sex differences in the behavioural ecology of chimpanzees in the Gombe National Park, Tanzania.

All-day observations of focal individuals were analysed to compare grouping and ranging patterns and the proportion of time spent feeding by females and males; sexually receptive females were not included. Females spent most of their time alone, whereas males spent most of their time in parties with other males. Females travelled shorter distances than males, and spent their time in smaller core areas: when they joined parties, however, they often travelled outside their normal core areas. Grouping and ranging patterns appear to be related to foraging strategies in different ways in each sex. Females often joined parties for a short time only (< 1 1/2 h), apparently at rich food sources. Males tended to stay for longer, even though they then spent less time feeding than when alone. Spending all day in a party was associated with reduced feeding time for both sexes, but on these days ranging patterns differed between the sexes because males, but not females, travelled further when in parties. The results support the idea that the form of the chimpanzee social system is determined by the interaction of two different strategies: females attempt to forage so as to maximize net energy intake, while males sacrifice an optimal foraging strategy for the sake of reproductive competition.