Mary Ellen Morbeck

The Evolving Female: A Life History Perspective

A human female is born, lives her life, and dies within the space of a few decades, but the shape of her life has been strongly influenced by 50 million years of primate evolution and more than 100 million years of mammalian evolution. How the individual female plays out the stages of her life--from infancy, through the reproductive period, to old age-- and how these stages have been formed by a long evolutionary process, is the theme of this collection. Written by leading scholars in fields ranging from evolutionary biology to cultural anthropology, these essays together examine what it means to be female, integrating the life histories of marine mammals, monkeys, apes, and humans. The result is a fascinating inquiry into the similarities among the ways females of different species balance the need for survival with their role in reproduction and mothering. The Evolving Female offers an outlook integrating life history with an intimate examination of female life paths. Behavior, anatomy and physiology, growth and development, cultural identity of women, the individual, and the society are among the topics investigated. In addition to the editors, the contributors are Linda Fedigan, Kathryn Ono, Joanne Reiter, Barbara Smuts, Mariko Hiraiwa-Hasegawa, Mary McDonald Pavelka, Caroline Pond, Robin McFarland, Silvana Borgognini Tarli and Elena Repetto, Gilda Morelli, Patricia Draper, Catherine Panter- Brick, Virginia J. Vitzthum, Alison Jolly, and Beverly McLeod.

Body size and proportions in chimpanzees, with special reference toPan troglodytes schweinfurthii from Gombe National Park, Tanzania

Body weight, cranial capacity, linear and joint area data from ten free-ranging adult chimpanzees from Gombe National Park, Tanzania with known life histories allow study of variation in a local population and comparison to other populations ofPan troglodytes and toPan paniscus. Because individuals in the Gombe population are small compared to other common chimpanzees, they provide a useful comparison toPan paniscus. Body weight and some linear dimensions overlap withPan paniscus. However, cranial capacity, tooth size, and body proportions of Gombe individuals lie within the range of otherPan troglodytes and are distinct fromPan paniscus.

Poliomyelitis and skeletal asymmetry in Gombe chimpanzees

Skeletons of free-ranging chimpanzees from Gombe National Park, Tanzania allow assessment of the effects of long-term, unilateral upper limb paralysis due to the infectious viral disease, poliomyelitis. Comparison of left and right upper limb bone weights, lengths, joint areas, and diaphysial diameters between two adult females with long-term, partial paralysis and a group of unaffected adult Gombe chimpanzees show that the disease caused considerable asymmetries in the skeleton. Detailed analyses of mineral content and diaphysial cross-sectional geometry of the humerus in the affected females show individual differences. The analysis extends to consideration of bone-muscle relationships and peripheral and central nervous system involvement. For each individual, sex, estimated age at death, and behavioral information during life are known from field studies. The impact of the disease on survival and reproductive outcome of the affected individuals is discussed.

Role of nonbehavioral factors in adjusting long bone diaphyseal structure in free-ranging Pan troglodytes

Limb bones deform during locomotion and can resist the deformations by adjusting their shapes. For example, a tubular-shaped diaphysis best resists variably-oriented deformations. As behavioral profiles change during adulthood, patterns of bone deformation may exhibit age trends. Habitat characteristics, e.g., annual rainfall, tree density, and elevation changes, may influence bone deformations by eliciting individual components of behavioral repertoires and suppressing others, or by influencing movements during particular components. Habituated chimpanzee communities provide a unique opportunity to examine these factors because of the availability of morphological data and behavioral observations from known-age individuals inhabiting natural habitats. We evaluated adult femora and humeri of 18 female and 10 male free-ranging chimpanzees (Pan troglodytes) from communities in Gombe (Tanzania), Mahale Mountains (Tanzania), and Taï Forest (Côte d’Ivoire) National Parks. We compare cross sections at several locations (35%, 50%, 65% diaphyseal lengths). Community comparisons highlight different diaphyseal shapes of Taï females relative to Mahale and Gombe females, particularly in humeral diaphyses. Age trends in diaphyseal shapes are consistent with reduced activity levels in general, not only reduced arboreal activity. Age-related bone loss is apparent among community females, but is less striking among males. Community trends in diaphyseal shape are qualitatively consistent with ranked annual rainfall at localities, tree density, and elevation change or ruggedness of terrain. Habitat characteristics may contribute to variation in diaphyseal shape among chimpanzee communities, much like among modern human groups, but verification awaits further rigorous experimental and comparative analyses.

Skeletal asymmetry and hand preference during termite fishing by gombe chimpanzees

Skeletons of chimpanzees with recorded life stories allow assessment of the potential relationships among hard tissue features and expressed behaviors. We analyze bone size, weight, and mineralization to assess osteological characters for identification of laterality of expressed behaviors involving the upper body. Results show that associations are not yet clearly defined.

Future Adults or Old Children? Integrating Life History Frameworks for Understanding Primate Positional Patterns

Positional behavior is a measurable and observable link between the functional morphology/physiology and behavior of an animal in its environment. Locomotion, posture, and the morphology that allows movement abilities and expressed behaviors throughout the life stages interact with every aspect of an individual primate’s life and are important life history characteristics. Locomotion and posture in adults relate to survival and maintenance, thus allowing for reproduction, whereas in infants and juveniles, positional behavior is essential to survival and growth to reproductive maturity. The timing of life stages and biobehavioral strategies for survival and reproduction in different species are the products of natural selection. A life history perspective integrates knowledge of evolutionary processes with understanding the multifaceted roles of positional behavior in primates.

Comparisons of Limb Structural Properties in Free-ranging Chimpanzees from Kibale, Gombe, Mahale, and Taï Communities

Structural characteristics of limb bones provide insight into how an animal dynamically loads its limbs during life. Cause-and-effect relationships between loading and the osteogenic response it elicits are complex. In spite of such complexities, cross-sectional geometric properties can be useful indicators of locomotor repertoires. Typical comparisons use primates that are distinguished by broad habitual locomotor differences, usually with samples garnered from several museum collections. Intraspecific variability is difficult to investigate in such samples because knowledge of their behavior or life histories, which are tools for interpreting intraspecific variability, is limited. Clearly, intraspecific variation both in morphology and behavior/life history exists. Here we expand an ongoing effort toward understanding intraspecific variation in limb structural properties by comparing free-ranging chimpanzees that have associated behavioral and life history data. Humeral and femoral data from 11 adult chimpanzees (Pan troglodytes) of Kibale National Park (Uganda) are compared to 29 adult chimpanzees from Gombe (Tanzania), Mahale Mountains (Tanzania), and Tai Forest (Cote d’Ivoire) National Park communities. Overall, limb structural morphology of Kibale chimpanzees most resembles limb structural morphology of Mahale chimpanzees. Shape ratios and percentage cortical areas of Kibale chimpanzees are most similar to non-Gombe chimpanzees, while Kibale structural properties, e.g., maximum rigidity, are most similar to non-Tai structural properties. Even after adding Kibale females, Tai females continue to stand out from females in other communities.

Sex differences in the vertebral column of gombe chimpanzees

Male and female chimpanzees from Gombe National Park, Tanzania (Pan troglodytes schweinfurthii) differ in live body weights but not in cranial capacity or fore-and hindlimb long bone lengths. Skeletal dimensions of the limbs and vertebral column indicate a mosaic of sex differences. Vertebral column measurements generally are greater in males. While linear measurements identify differences in the breadth and depth of the lower cervical and upper thoracic vertebrae, areal assessments show significant differences in weight-bearing surfaces throughout the thoracic and lumbar segments. These can be interpreted in terms of distribution of weight and body composition (i.e. amount of musculature).

Gombe chimpanzee sex differences in the pelvis and observations of pubic and preauricular areas

The skeletons of Gombe chimpanzees provide an opportunity for analysis of bony tissue with reference to known sex and parity in combination with observations on other life history variables and behavior. Measurements of the pelvic bones show a mosaic of sex differences. Well-defined resorption areas on the dorsomedial aspect of the pubis and the preauricular area of the ilium have been associated with sex and parity in humans and other species. However, these are not present in either females or males in this chimpanzee skeletal series.