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Human Females (human + female)
Selected AbstractsThe strategic use of sex in wild female western gorillasAMERICAN JOURNAL OF PRIMATOLOGY, Issue 12 2009Diane M. Doran-Sheehy Abstract Human females, unlike most mammals, are sexually active outside of fertile periods. This decoupling of sexual behavior from its conceptive function has had an enormous impact on human social relationships, and yet we know little about why there was selection for nonconceptive mating. Here we examine one form of nonconceptive mating, the mating that occurs during pregnancy or post-conceptive (PC) mating, in wild western gorillas (Gorilla gorilla). Using a near complete mating record for five females during gestation, we show that pregnant females varied in the timing and frequency of mating, and used PC mating conditionally, synchronizing copulations to occur on days when other females mated, and refraining from mating for lengthy periods when no other females mated. As pregnant females mated exclusively with the same male before and after conception, and mated in response to group female (and not male) behavior, we conclude that western gorillas used PC mating as a form of female competition, and not to confuse paternity or to obtain immediate benefits from the male, as suggested earlier. The male initiated copulations preferentially with females of high rank, rather than distinguishing between pregnant and cycling females. Therefore, PC mating appears to be a strategy by which high-ranking pregnant females attempt to minimize male interest in other females, while reinforcing their own status and potentially delaying conception in others. These findings indicate that female-mating competition is more important than considered earlier, and may be a factor in the evolution of nonconceptive mating in humans. Am. J. Primatol. 71:1011,1020, 2009. © 2009 Wiley-Liss, Inc. [source] The ecology and evolutionary endocrinology of reproduction in the human femaleAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue S49 2009Virginia J. Vitzthum Abstract Human reproductive ecology (HRE) is the study of the mechanisms that link variation in reproductive traits with variation in local habitats. Empirical and theoretical contributions from biological anthropology, physiology, and demography have established the foundation necessary for developing a comprehensive understanding, grounded in life history theory (LHT), of temporal, individual, and populational variation in women's reproductive functioning. LHT posits that natural selection leads to the evolution of mechanisms that tend to allocate resources to the competing demands of growth, reproduction, and survival such that fitness is locally maximized. (That is, among alternative allocation patterns exhibited in a population, those having the highest inclusive fitness will become more common over generational time.) Hence, strategic modulation of reproductive effort is potentially adaptive because investment in a new conception may risk one's own survival, future reproductive opportunities, and/or current offspring survival. The hypothalamic-pituitary-ovarian (HPO) axis is the principal neuroendocrine pathway by which the human female modulates reproductive functioning according to the changing conditions in her habitat. Adjustments of reproductive investment in a potential conception are manifested in temporal and individual variation in ovarian cycle length, ovulation, hormone levels, and the probability of conception. Understanding the extent and causes of adaptive and non-adaptive variation in ovarian functioning is fundamental to ascertaining the proximate and remote determinants of human reproductive patterns. In this review I consider what is known and what still needs to be learned of the ecology of women's reproductive biology, beginning with a discussion of the principal explanatory frameworks in HRE and the biometry of ovarian functioning. Turning next to empirical studies, it is evident that marked variation between cycles, women, and populations is the norm rather than an aberration. Other than woman's age, the determinants of these differences are not well characterized, although developmental conditions, dietary practices, genetic variation, and epigenetic mechanisms have all been hypothesized to play some role. It is also evident that the reproductive functioning of women born and living in arduous conditions is not analogous to that of athletes, dieters, or even the lower end of the "normal range" of HPO functioning in wealthier populations. Contrary to the presumption that humans have low fecundity and an inefficient reproductive system, both theory and present evidence suggest that we may actually have very high fecundity and a reproductive system that has evolved to be flexible, ruthlessly efficient and, most importantly, strategic. Yrbk Phys Anthropol 52:95,136, 2009. © 2009 Wiley-Liss, Inc. [source] Eastern bluebirds Sialia sialis do not avoid nest boxes with chemical cues from two common nest predatorsJOURNAL OF AVIAN BIOLOGY, Issue 1 2007Renee D. Godard Chemodetection of common nest predators may be advantageous for nesting birds; however, few studies have examined the ability of songbirds to detect chemical odors from predators. Thus, in 2002, we presented eastern bluebirds Sialia sialis with pairs of nest boxes; one box in the pair was regularly scented with chemical cues from a common nest predator, the black rat snake Elaphe obsoleta, and the other with a neutral cue. In 2004, we again presented bluebirds with pairs of boxes, one scented with chemical cues from a different nest predator, the deer mouse Peromyscus maniculatus, and the other with a neutral scent. Although human females were able to correctly distinguish paper laced with predator cues from paper with neutral cues, bluebirds were as likely to lay eggs in boxes with predator cues as in boxes with neutral cues. While it remains possible that bluebirds may detect scent from potential nest predators, it appears that the presence of these chemical cues does not ultimately influence selection of nest sites. [source] A reassessment of sexual dimorphism in human senescence: Theory, evidence, and causationAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2006Brent M. Graves Age-specific mortality rates of men are higher than those of women, and men have shorter average life spans than women. This has been interpreted as evidence of sexual dimorphism in rates of senescence. However, because mortality can be caused by numerous factors in addition to senescence, higher mortality rates do not necessarily indicate more rapid senescence. In this paper, we (1) emphasize the necessity of decoupling mortality and senescence when considering sexual dimorphism in senescence, (2) present a theoretical framework for the hypothesis that selection affects senescence in human males and females differently due to different life history characteristics, (3) consider phenotypic evidence from the literature that human males show a later onset of senescence than human females, despite exhibiting higher mortality rates, and (4) discuss the potential roles of mutation accumulation and antagonistic pleiotropy in the evolution of sexual dimorphism in senescence. Am. J. Hum. Biol. 18:161,168, 2006. © 2006 Wiley-Liss, Inc. [source] Comparative and evolutionary dimensions of the energetics of human pregnancy and lactationAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2002D.L. Dufour The purpose of this article is to compare the energetics of reproduction for human and other primates in order to evaluate the extent to which human reproductive energetics are distinct from other primates and other large-bodied placental mammals. The article also evaluates the energetics of human and primate gestation and lactation using data from a variety of different populations living under different environmental circumstances. Energetics refers to energy intake and expenditure, and changes in body fat stores. Human and nonhuman primates have longer periods of gestation and lactation and slower prenatal and postnatal growth than other mammals of similar size. This reduces daily maternal energy costs. The development of sizable fat stores is not unique to humans, but fat stores are typically greater in human females and may play a greater role in reproduction. The strategies used to meet the energy costs of pregnancy vary among populations of humans and nonhuman primates and among humans interindividual variability is high. In pregnancy, some increase energy intake but others apparently do not. Increases in metabolic efficiency are evident in some human populations, whereas decreases in physical activity occur, but are not seen in all human or primate populations. Lactation is more energetically costly on a daily basis among humans and nonhuman primates, but has not been as well studied. It appears that both nonhuman and human primates tend to increase energy intake to meet in part the cost of lactation. They also use other strategies such as relying on body tissue stores, reductions in physical activity, and/or increases in metabolic efficiency to meet the remainder of the cost. It is also clear that human females in different populations and different women in the same population use a different combination of strategies to meet the cost of lactation. Am. J. Hum. Biol. 14:584,602, 2002. © 2002 Wiley-Liss, Inc. [source] A critique of the grandmother hypotheses: Old and newAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2001Jocelyn Scott Peccei The singularity of reproductive senescence in human females has led many investigators to consider menopause an adaptation permitting increased maternal investment in existing progeny. Much of the focus has been on the grandmother hypothesis,the notion that aging women gain an inclusive fitness advantage from investing in their grandchildren. This hypothesis has evolved from an explanation for menopause into an explanation for the exceptionally long postreproductive lifespan in human females. In the old grandmother hypothesis, menopause is an adaptation facilitating grandmothering; it is about stopping early in order to create a postreproductive lifespan. In the new grandmother hypothesis, grandmothering is an adaptation facilitating increased longevity, and menopause is a byproduct. This paper reviews and critically evaluates the evidence for and against both hypotheses, focusing on key predictions of each. If menopause is the result of selection for increased maternal investment, this involved mainly mothers, not grandmothers. Am. J. Hum. Biol. 13:434,452, 2001. © 2001 Wiley-Liss, Inc. [source] Synchrony between growth and reproductive patterns in human females: Early investment in growth among Pumé foragersAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010Karen L. Kramer Abstract Life history is an important framework for understanding many aspects of ontogeny and reproduction relative to fitness outcomes. Because growth is a key influence on the timing of reproductive maturity and age at first birth is a critical demographic variable predicting lifetime fertility, it raises questions about the synchrony of growth and reproductive strategies. Among the Pumé, a group of South American foragers, young women give birth to their first child on average at age 15.5. Previous research showed that this early age at first birth maximizes surviving fertility under conditions of high infant mortality. In this study we evaluate Pumé growth data to test the expectation that if early reproduction is advantageous, then girls should have a developmental trajectory that best prepares them for young childbearing. Analyses show that comparatively Pumé girls invest in skeletal growth early, enter puberty having achieved a greater proportion of adult body size and grow at low velocities during adolescence. For early reproducers growing up in a food-limited environment, a precocious investment in growth is advantageous because juveniles have no chance of pregnancy and it occurs before the onset of the competing metabolic demands of final reproductive maturation and childbearing. Documenting growth patterns under preindustrial energetic and demographic conditions expands the range of developmental variation not otherwise captured by normative growth standards and contributes to research on human phenotypic plasticity in diverse environments. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Kinship and social bonds in female chimpanzees (Pan troglodytes)AMERICAN JOURNAL OF PRIMATOLOGY, Issue 10 2009Kevin Langergraber A large body of theoretical and empirical research suggests that kinship influences the development and maintenance of social bonds among group-living female mammals, and that human females may be unusual in the extent to which individuals form differentiated social relationships with nonrelatives. Here we combine behavioral observations of party association, spatial proximity, grooming, and space use with extensive molecular genetic analyses to determine whether female chimpanzees form strong social bonds with unrelated individuals of the same sex. We compare our results with those obtained from male chimpanzees who live in the same community and have been shown to form strong social bonds with each other. We demonstrate that party association is as good a predictor of spatial proximity and grooming in females as it is in males, that the highest party association indices are consistently found between female dyads, that the sexes do not differ in the long-term stability of their party association patterns, and that these results cannot be explained as a by-product of the tendency of females to selectively range in particular areas of the territory. We also show that close kin (i.e. mother,daughter and sibling dyads) are very rare, indicating that the vast majority of female dyads that form strong social bonds are not closely related. Additional analyses reveal that "subgroups" of females, consisting of individuals who frequently associate with one another in similar areas of the territory, do not consist of relatives. This suggests that a passive form of kin-biased dispersal, involving the differential migration of females from neighboring communities into subgroups, was also unlikely to be occurring. These results show that, as in males, kinship plays a limited role in structuring the intrasexual social relationships of female chimpanzees. Am. J. Primatol. 71:840,851, 2009. © 2009 Wiley-Liss, Inc. [source] Female post-reproductive lifespan: a general mammalian traitBIOLOGICAL REVIEWS, Issue 4 2004Alan A. Cohen ABSTRACT Traditional explanations for the evolution of menopause and post-reproductive lifespan in human females have been based on the benefits of maternal or grand-maternal care outweighing the cost of lost reproduction. These explanations assume an evolutionary origin of menopause since human divergence with the most recent common ancestor. In this study, I conduct a literature survey of studies of 42 mammal species from eight orders, showing that post-reproductive lifespan appears to be widespread among mammals. I then propose an alternative to traditional hypotheses: following accepted theories of trade-offs and senescence, I suggest that the cost of extending reproductive lifespan might be relatively high in female mammals. Somatic and reproductive senescence appear to follow separate trajectories, so it is not surprising that the two processes should occur on different schedules. The timing of each process is probably determined by maximization of reproductive performance and survival early in adulthood, with consequent trajectories resulting in a post-reproductive lifespan. The early end of reproduction relative to lifespan may be due to the cost of production and/or maintenance of oocytes, which decline exponentially over time. Oocyte number below a threshold may trigger an end to normal hormonal cycling. 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