As a life history characteristic of human females, menopause is universal, it occurs halfway through the maximum lifespan of the species, and it consistently occurs a t approximately age 50 in different populations. Menopause is fundamentally distinct from the reproductive senescence that has been described for a very small number of very old individual alloprimates. Menopause is not a recent historical artifact. As a species universal showing little variation in occurrence across contemporary populations, it must be understood in evolutionary terms. Supporters of the "grandmother hypothesis" explain menopause as an adaptive feature in itself. Others see menopause as a byproduct of the increased lifespan of Homo sapiens. Plieotropy theory may help to explain menopause in broader mammalian terms.In recent years menopause has been increasingly examined from clinical, social, and scientific perspectives. Physical anthropologists have a n approach to menopause that is at once unique and diverse, as it incorporates primatological, historical, cross-cultural, and evolutionary views. While many of us are interested in the menopause, it is clear that physical anthropologists do not share a n interpretation with which all agree. It is common to find confident yet contradictory statements in the literature. For example, menopause is described as being a n illness, and a developmental process; as a uniquely human characteristic, and one shared by the alloprimates; as being a recent historical phenomenon, and a distant evolutionary one; as a primary adaptation, and as a secondary or tertiary by-product.In this paper we provide a n overview of menopause and of controversies in the menopause literature in the hope of giving physical anthropologists the common base of knowledge that is essential to informed theory development. Our general approach throughout the paper is structured by a life history perspective. As DeRousseau recently noted (1990:1), "Life history is a n exciting new direction in evolutionary studies. It focuses attention on the processes and events that occur in the lives of individual organisms, and questions their evolutionary significance." In the case of menopause, we will be stressing three characteristics that make it a significant phenomenon in life history studies of the human female: its universality (virtually every woman who survives into her sixth decade will experience menopause); its relative timing in the overall life course (approximately half-way through the maximum life span of the species); and its age-specificity (an approximate age of 50 years has been widely reported for different populations). Four major questions are addressed.First, what is menopause? To answer this question we begin by defining a variety of relevant terms, including premenopause, perimenopause, postmenopause, climacteric, lifespan, and life expectancy, and we address the sex differences in 0 1991 Wiley-Liss, Inc. [Vol. 34, 1991 reproductive senescence in humans and the misnomer of male menopause. Basic fe...

High cortisol levels are known to cause low fecundity and increased mortality; thus, the prospect of using cortisol as a measure of population health is an exciting one. However, because so many factors can interact to influence cortisol release, it can be difficult to interpret what exactly is creating changes to cortisol levels. This study investigates variation in fecal cortisol levels in a population of black howlers (Alouatta pigra) from 350 fecal samples collected from 33 individuals in more than 4 years. A general linear mixed model revealed that cortisol varied significantly with fruit availability and contact with tourists. When fruit availability was low, cortisol increased, likely because when fruit availability is low monkeys eat less fruit, thus obtaining less sugar. This result may simply reflect cortisol's metabolic function of mobilizing glucose. It also indicates that these monkeys may be experiencing periods of food stress throughout the year, which was earlier thought to be minimal for a primarily folivorous species. Presence of tourists was the only other factor found to lead to high cortisol; with exposure to tourists increasing stress levels. These results highlight the importance of understanding how physiological factors can influence cortisol, making it easier to interpret results and determine the external social or ecological stressors that may increase cortisol.

Patterns of melanin pigmentation in birds are extremely varied. Nevertheless it is easy to think of many patterns that are never observed, and others that frequently recur in diverse and distantly related species. Using as our model the avian genus Phyl/oscopus we ask how the restricted range of observed patterns might be attributable to a restricted range of variants produced by developmental perturbations. The patterns we consider consist of unmelanized patches on the wings, crown and rump on otherwise pigmented upperparts. We use reaction-diffusion models to show that gross features of the pattern can be simply predicted from considerations of embryo shape. We suggest that birds are expected to have more patterned heads, because the head region is relatively larger than other regions in the developing embryo. A comparative analysis across many species of birds and a phylogenetic analysis within the genus Phylloscopus show that the component elements of the pattern have repeatedly been lost and gained during evolution. A shift in a threshold reading could explain the appearance and disappearance of the unmelanized patches, perhaps through changes in the sensitivity of melanocytes to epidermal signals. Such threshold shifts would make the transition between patterned and unpatterned forms particularly easy once the patterns have been exposed to selection in some distant ancestor. This partitioning of the roles of selection and development implies that many features of the patterns reflect developmental mechanisms in both immediate and more distant ancestors.

The ecological-constraints model assumes that food items occur in depletable patches and proposes that an increase in group size leads to increased day range due to more rapid patch depletion. Smaller groups become advantageous when an increase in travel costs is not repaid by an increase in energy gained or some other fitness advantage. On the other hand, we also know that group size can be influenced by social factors. Here we contrast the diet and group size of red colobus (Procolobus badius) and black-and-white colobus (Colobus guereza) in Kibale National Park, Uganda to consider how ecological and social factors are affecting their group sizes. Subsequently, we examine whether the insights gained from this detailed comparison can provide an understanding of why the social organization and group size of mantled howlers (Alouatta palliata) and black howlers (A. pigra) differ. Two groups of red colobus and two groups of black-and-white colobus were studied over 10 months. Red colobus groups were larger (48 and 24) than black-and-white colobus groups (9 and 6). The two groups of red colobus overlap home ranges with the two groups of black-and-white colobus; 75% and 95% of their home ranges were within red colobus's home range. There was a great deal of similarity in the plant parts eaten by the two species and both species fed primarily on young leaves (red colobus 70%, black-and-white colobus 76%). In terms of the actual species consumed, again there was a great deal of similarity between species. The average dietary overlap among months for the two neighboring groups of red colobus was 37.3%, while the dietary overlap between the red colobus and the black-and-white colobus group that had its home range almost entirely within the home range of the red colobus groups averaged 43.2% among months. If ecological conditions were responsible for the difference in group size between the two colobine species, one would expect the density of food trees to be lower in the home ranges of the black-and-white colobus monkeys, since they have the smaller group size. We found the opposite to be true. Both black-and-white colobus groups had more food trees and the cumulative size of those trees was greater than those in the red colobus's home ranges. We quantify how these differences parallel differences in mantled and black howlers. The average group size for mantled howlers was 12.9 individuals, and for black howlers it was 5.3 individuals. We explore possible social constraints, such as infanticide, that prevent black-and-white colobus and black howlers from living in large groups.

This study reports on the diet and activity budgets of Central American black howling monkeys ( Alouatta pigra) at Monkey River, Belize. This is a previously unstudied population, close to the southern boundary of the species range, and it provides comparative data on A. pigra from a new study site. Both diet and activity are within the ranges reported for other A.pigra sites and for mantled howlers ( A. palliata). No age-sex differences could be discerned in either diet or activity, though monthly variation was apparent. The monkeys switch from consuming leaves 86% of the time in January to March to consuming 67% fruit in April to July. This difference was statistically significant, and provided the opportunity to compare activity levels of the monkeys over two dietary periods, one characterized primarily by folivory, the other by frugivory. Howlers are often seen as a relatively inactive species, something that is associated with a low quality, folivorous diet. However, A. pigra have been described as being as frugivorous as possible and as folivorous as necessary. Yet, despite the opportunistic consumption of large quantities of high-energy foods, A. pigra has been observed as conforming to the howler lifestyle, resting as much as 80% of the day. The data in this paper support both of these reports. Black howlers at Monkey River Belize are typically inactive, maintaining high levels of inactivity even during months characterized by frugivory, suggesting that diet is more flexible and varied than is behavior and calling into question the assumption that howler inactivity is due to the digestion of large quantities of leaves.