Human behavior. Sex equality can explain the unique social structure of hunter-gatherer bands.

The social organization of mobile hunter-gatherers has several derived features, including low within-camp relatedness and fluid meta-groups. Although these features have been proposed to have provided the selective context for the evolution of human hypercooperation and cumulative culture, how such a distinctive social system may have emerged remains unclear. We present an agent-based model suggesting that, even if all individuals in a community seek to live with as many kin as possible, within-camp relatedness is reduced if men and women have equal influence in selecting camp members. Our model closely approximates observed patterns of co-residence among Agta and Mbendjele BaYaka hunter-gatherers. Our results suggest that pair-bonding and increased sex egalitarianism in human evolutionary history may have had a transformative effect on human social organization.

A dynamic framework for the study of optimal birth intervals reveals the importance of sibling competition and mortality risks.

Human reproductive patterns have been well studied, but the mechanisms by which physiology, ecology and existing kin interact to affect the life history need quantification. Here, we create a model to investigate how age-specific interbirth intervals adapt to environmental and intrinsic mortality, and how birth patterns can be shaped by competition and help between siblings. The model provides a flexible framework for studying the processes underlying human reproductive scheduling. We developed a state-based optimality model to determine age-dependent and family-dependent sets of reproductive strategies, including the state of the mother and her offspring. We parameterized the model with realistic mortality curves derived from five human populations. Overall, optimal birth intervals increase until the age of 30 after which they remain relatively constant until the end of the reproductive lifespan. Offspring helping each other does not have much effect on birth intervals. Increasing infant and senescent mortality in different populations decreases interbirth intervals. We show that sibling competition and infant mortality interact to lengthen interbirth intervals. In lower-mortality populations, intense sibling competition pushes births further apart. Varying the adult risk of mortality alone has no effect on birth intervals between populations; competition between offspring drives the differences in birth intervals only when infant mortality is low. These results are relevant to understanding the demographic transition, because our model predicts that sibling competition becomes an important determinant of optimal interbirth intervals only when mortality is low, as in post-transition societies. We do not predict that these effects alone can select for menopause.

Contrasting approaches to end of life and palliative care in end stage kidney disease.

With increased numbers of the elderly, including nursing home patients, being accepted for end-stage kidney disease (ESKD) management, there is heightened interest and focus on end of life decisions, advanced care planning and directives, withdrawal from dialysis and palliative care in this setting. Despite this, care at the individual patient level can vary greatly. Here, we present two contrasting cases to highlight the importance of early and ongoing involvement of palliative care in patients with ESKD. In the first case, a high quality of life was preserved before the patient died with dignity, with early interdisciplinary palliative care involvement. In the second case there was a long protracted period of poor quality of life prior to death. This was associated with resistance to the involvement of palliative care, mainly from the family. Addressing end of life care issues early in the chronic kidney disease (CKD) trajectory and ensuring patients, their families and health care providers are well informed, may contribute to a better outcome for the patient and their family.

Magnetic moment nonconservation in magnetohydrodynamic turbulence models.

The fundamental assumptions of the adiabatic theory do not apply in the presence of sharp field gradients or in the presence of well-developed magnetohydrodynamic turbulence. For this reason, in such conditions the magnetic moment µ is no longer expected to be constant. This can influence particle acceleration and have considerable implications in many astrophysical problems. Starting with the resonant interaction between ions and a single parallel propagating electromagnetic wave, we derive expressions for the magnetic moment trapping width Δµ (defined as the half peak-to-peak difference in the particle magnetic moments) and the bounce frequency ω(b). We perform test-particle simulations to investigate magnetic moment behavior when resonance overlapping occurs and during the interaction of a ring-beam particle distribution with a broadband slab spectrum. We find that the changes of magnetic moment and changes of pitch angle are related when the level of magnetic fluctuations is low, δB/B(0) = (10(-3),10(-2)), where B(0) is the constant and uniform background magnetic field. Stochasticity arises for intermediate fluctuation values and its effect on pitch angle is the isotropization of the distribution function f(α). This is a transient regime during which magnetic moment distribution f(µ) exhibits a characteristic one-sided long tail and starts to be influenced by the onset of spatial parallel diffusion, i.e., the variance <(Δz)(2)> grows linearly in time as in normal diffusion. With strong fluctuations f(α) becomes completely isotropic, spatial diffusion sets in, and the f(µ) behavior is closely related to the sampling of the varying magnetic field associated with that spatial diffusion.

Why replication is important in landscape genetics: American black bear in the Rocky Mountains.

We investigated how landscape features influence gene flow of black bears by testing the relative support for 36 alternative landscape resistance hypotheses, including isolation by distance (IBD) in each of 12 study areas in the north central U.S. Rocky Mountains. The study areas all contained the same basic elements, but differed in extent of forest fragmentation, altitude, variation in elevation and road coverage. In all but one of the study areas, isolation by landscape resistance was more supported than IBD suggesting gene flow is likely influenced by elevation, forest cover, and roads. However, the landscape features influencing gene flow varied among study areas. Using subsets of loci usually gave models with the very similar landscape features influencing gene flow as with all loci, suggesting the landscape features influencing gene flow were correctly identified. To test if the cause of the variability of supported landscape features in study areas resulted from landscape differences among study areas, we conducted a limiting factor analysis. We found that features were supported in landscape models only when the features were highly variable. This is perhaps not surprising but suggests an important cautionary note - that if landscape features are not found to influence gene flow, researchers should not automatically conclude that the features are unimportant to the species' movement and gene flow. Failure to investigate multiple study areas that have a range of variability in landscape features could cause misleading inferences about which landscape features generally limit gene flow. This could lead to potentially erroneous identification of corridors and barriers if models are transferred between areas with different landscape characteristics.

An evolutionary model of stature, age at first birth and reproductive success in Gambian women.

We have built a model to predict optimal age at first birth for women in a natural fertility population. The only existing fully evolutionary model, based on Ache hunter-gatherers, argues that as women gain weight, their fertility (rate of giving birth) increases-thus age at first birth represents a trade-off between time allocated to weight gain and greater fertility when mature. We identify the life-history implications of female age at first birth in a Gambian population, using uniquely detailed longitudinal data collected from 1950 to date. We use height rather than weight as an indicator of growth as it is more strongly correlated with age at first birth. Stature does not greatly influence fertility in this population but has a significant effect on offspring mortality. We model age at first reproduction as a trade-off between the time spent growing and reduced infant mortality after maturation. Parameters derived from this population are fitted to show that the predicted optimal mean age of first birth, which maximizes reproductive success, is 18 years, very close to that observed. The reaction norm associated with variation in growth rate during childhood also satisfactorily predicts the variation in age at first birth.

Relationship between emotional state and performance during international field hockey matches.

The present study examined the relationship between the emotions experienced by 15 international hockey players, both immediately before and during competition, and their performance levels. Data were collected on the players' emotional states using a revised version of the Feelings Scale of Butler, which was completed retrospectively after the match was played. Players reported more annoyance and less tension during the match than before. A logistic regression correctly classified 70.2% of players from the emotional ratings immediately before the match and 85.1% of the players from the ratings during the match as either a good or poor performer. Those individuals who performed well retrospectively reported feeling Nervous and 'Quick/Alert/Active' before the game and Confident and Relaxed during the game. The results indicate that emotions fluctuate over the competition period, and in long duration sports assessment of emotion during competition predicts variation in performance better than assessment prior to competition.

Evolutionary ecology of human life history.

The human life history is characterized by several unusual features, including large babies, late puberty and menopause, and the fact that there is a strong cultural influence on reproductive decisions throughout life. In this review I examine human life history from an evolutionary ecological perspective. I first review the evidence for life history trade-offs between fertility and mortality in humans. Patterns of growth, fertility and mortality across the life span are then discussed and illustrated with data from a traditional Gambian population. After outlining the stages of the human life course, I discuss two phenomena of particular interest in evolutionary anthropology, both of which are apparently unique to humans and neither yet fully understood. First, I discuss the evolution of menopause, the curtailing of female reproduction long before death. The evidence that this evolved because investment in existing children's future reproductive success is more important than continuing child bearing into old age is reviewed, along with data relating to the biological constraints that may be operating. Second, I discuss the demographic transition. Declining fertility at a time of increasingly abundant resources represents a serious challenge to an evolutionary view of human life history and behaviour, and is thus examined in detail. Parental investment in children in competition with each other may be key to understanding both of these unusual human phenomena. Copyright 2000 The Association for the Study of Animal Behaviour.

Maternal grandmothers improve nutritional status and survival of children in rural Gambia.

Hypotheses for the evolution of human female life-history characteristics have often focused on the social nature of human societies, which allows women to share the burden of childcare and provisioning amongst other members of their kin group. We test the hypothesis that child health and survival probabilities will be improved by the presence of kin using a longitudinal database from rural Gambia. We find that the only kin to improve the nutritional status of children significantly (apart from mothers) are maternal grandmothers, and that this is reflected in higher survival probabilities for children with living maternal grandmothers. There is also evidence that the reproductive status of the maternal grandmother influences child nutrition, with young children being taller in the presence of non-reproductive grandmothers than grandmothers who are still reproductively active. Paternal grandmothers and male kin, including fathers, have negligible impacts on the nutritional status and survival of children.

Sexual dimorphism in stature and women's work: a phylogenetic cross-cultural analysis.

The following cultural variables were tested for their association with sexual dimorphism: sexual division of labor, type of subsistence (hunting and agriculture), and polygyny. The transmission of these traits among populations was investigated. All the traits were found to be associated with phylogeny, indicating that they are inherited from mother to daughter populations. A cross-cultural comparative method was used which controls for the statistical effects of similarity due to common ancestry (Galton's problem). Cross-cultural variation in sexual dimorphism in stature is negatively associated with women's contribution to subsistence. Women are taller, relative to men, in societies where women contribute more to food production. This may be because female nutritional status is better in these societies. No relationship was found between sexual dimorphism and other aspects of subsistence or polygyny. These results are discussed in relation to other studies of sexual dimorphism in modern and archaeological populations, and in relation to cross-cultural variation in sex-biased parental investment.

A phylogenetic analysis of the relationship between sub-adult mortality and mode of subsistence.

The hypothesis that measures of sub-adult mortality rates in natural fertility populations are associated with subsistence practices in a selected cross-cultural sample (n = 39) was tested. After controlling for both distance from the equator and the general likelihood of cultural similarities between genetically closely related cultures using phylogenetic comparative methods, it was found that dependence on extractive modes of subsistence (hunting, gathering and fishing) was a significant positive correlated of total child mortality (15q0). Both increases in dependence on foraging and permanent settlement were associated with increases in child mortality between pairs of historically related cultures. The results indicated little association between infant mortality (1q0) and either dependence on foraging or settlement.

PIP: Studies have suggested that among traditional, pre-industrial human populations, some demographic parameters are or were associated with the mode of subsistence. Based upon the analysis of data on a cross-cultural sample of 39 cultures, findings are reported from a test of the hypothesis that measures of sub-adult mortality rates in natural fertility populations are associated with subsistence practices. After controlling for distance from the equator and the general likelihood of cultural similarities between genetically closely related cultures using phylogenetic methods, it was found that dependence upon extractive modes of subsistence such as hunting, fishing, and gathering, was a significant positive correlate of total child mortality. Increases in dependence upon foraging and permanent settlement were associated with increases in child mortality between pairs of historically related cultures. Little association, however, was found between infant mortality and dependence upon foraging or settlement.

The coevolution of human fertility and wealth inheritance strategies.

Life history theory concerns the scheduling of births and the level of parental investment in each offspring. In most human societies the inheritance of wealth is an important part of parental investment. Patterns of wealth inheritance and other reproductive decisions, such as family size, would be expected to influence each other. Here I present an adaptive model of human reproductive decision-making, using a state-dependent dynamic model. Two decisions made by parents are considered: when to have another baby, and thus the pattern of reproduction through life; and how to allocate resources between children at the end of the parents' life. Optimal decision rules are those that maximize the number of grandchildren. Decisions are assumed to depend on the state of the parent, which is described at any time by two variables: number of living sons, and wealth. The dynamics of the model are based on a traditional African pastoralist system, but it is general enough to approximate to any means of subsistence where an increase in the amount of wealth owned increases the capacity for future production of resources. The model is used to show that, in the unpredictable environment of a traditional pastoralist society, high fertility and a biasing of wealth inheritance to a small number of children are frequently optimal. Most such societies are now undergoing a transition to lower fertility, known as the demographic transition. The effects on fertility and wealth inheritance strategies of reducing mortality risks, reducing the unpredictability of the environment and increasing the costs of raising children are explored. Reducing mortality has little effect on completed family sizes of living children or on the wealth they inherit. Increasing the costs of raising children decreases optimal fertility and increases the inheritance left to each child at each level of wealth, and has the potential to reduce fertility to very low levels. The results offer an explanation for why wealthy families are frequently also those with the smallest number of children in heterogeneous, post-transition societies.

PIP: An adaptive model of human reproductive decision-making is presented, using a state-dependent dynamic model. The author considers the following decisions parents make: when to have another child and how to allocate resources between children at the end of the parents' life. Optimal decision rules are those which maximize the number of grandchildren, with decisions assumed to depend upon the state of the parent described at any time by the number of living sons and degree of wealth. The model dynamics are based upon a traditional African pastoralist system. The model is used to show that in a traditional pastoralist society, high fertility and a biasing of wealth inheritance to a small number of children are often optimal. Most of those societies are undergoing a transition to lower fertility. The effects upon fertility and wealth inheritance strategies of reducing mortality risks, reducing the unpredictability of the environment, and increasing the costs of raising children are explored. Reducing mortality has little effect upon the completed family sizes of living children or upon the wealth they inherit. Increasing the costs of raising children decreases optimal fertility and increases the inheritance left to each child at each level of wealth, and has the potential to reduce fertility to very low levels.

Universal design in housing.

Universal design in housing is a growing and beneficial concept. It is subtle in its differences from barrier-free, accessible, and industry standard housing. Accessibility standards and codes have not mandated universal design and do not apply to most housing. Universal design exceeds their minimum specifications for accessible design and results in homes that are usable by and marketable to almost everyone. Universal homes avoid use of special assistive technology devices and, instead, incorporate consumer products and design features that are easily usable and commonly available.

Phylogenetic analysis of the evolution of lactose digestion in adults.

In most of the world's population the ability to digest lactose declines sharply after infancy. High lactose digestion capacity in adults is common only in populations of European and circum-Mediterranean origin and is thought to be an evolutionary adaptation to millennia of drinking milk from domestic livestock. Milk can also be consumed in a processed form, such as cheese or soured milk, which has a reduced lactose content. Two other selective pressures for drinking fresh milk with a high lactose content have been proposed: promotion of calcium uptake in high-latitude populations prone to vitamin-D deficiency and maintainance of water and electrolytes in the body in highly and environments. These three hypotheses are all supported by the geographic distribution of high lactose digestion capacity in adults. However, the relationships between environmental variables and adult lactose digestion capacity are highly confounded by the shared ancestry of many populations whose lactose digestion capacity has been tested. The three hypotheses for the evolution of high adult lactose digestion capacity are tested here using a comparative method of analysis that takes the problem of phylogenetic confounding into account. This analysis supports the hypothesis that high adult lactose digestion capacity is an adaptation to dairying but does not support the hypotheses that lactose digestion capacity is additionally selected for either at high latitudes or in highly arid environments. Furthermore, methods using maximum likelihood are used to show that the evolution of milking preceded the evolution of high lactose digestion.

Birth interval and the sex of children in a traditional African population: an evolutionary analysis.

Birth interval is a major determinant of rates of fertility, and is also a measure of parental investment in a child. In this paper the length of the birth interval in a traditional African population is analysed by sex of children. Birth intervals after the birth of a boy were significantly longer than after the birth of a girl, indicating higher parental investment in boys. However, in women of high parity, this differential disappeared. Birth intervals for women with no son were shorter than for those with at least one son. All these results are compatible with an evolutionary analysis of reproductive decision-making. First born sons have particularly high reproductive success, daughters have average reproductive success and late born sons have low reproductive success. The birth interval follows a similar trend, suggesting that longer birth intervals represent higher maternal investment in children of high reproductive potential.

PIP: This study examines variation in birth intervals among a nomadic population from northern Kenya. Data are obtained from a survey conducted in 1993 of about 850 Gabbra pastoralist families. The total fertility rate was 5.63 children per woman in this largely non-polygynous society. The mean length of birth interval of ever married Gabbra women of all ages ranged from about 2.9 years to 3.2 years. The analysis excluded all intervals over 5 years and included all women who had at least 2 births. The mean length of the birth interval of 3170 birth intervals was shorter for female followed by male births and two female births. The statistically significant difference was about 2 months. The birth intervals after boys were longer, but the sex of the child closing the birth interval had no significant effect. Hazard model analysis of only married women under 49 years old indicates that a male child was followed by a longer birth interval for all of the first five birth intervals, but it was significant only for the second birth interval. A Kaplan-Meier plot of all birth intervals after the first one for women with children of both sexes, daughters only, and sons only reveals that women with children of both sexes had the longest birth intervals. Women with only daughters had the shortest intervals. Women with only sons had shorter birth intervals than women with at least 1 son and 1 daughter. All differences were significant. A hazards analysis that included age of the mother finds that the total number of sons, but not parity, had a highly significant effect on the birth interval length. Findings suggest that the determination of birth interval is not simply the effect of maternal age; that parents make an active decision about the length of the birth interval; and that maternal investment in male infants, except at higher parities, was greater than in female infants as an investment strategy favoring children with the highest reproductive potential.

Role of postreplicative DNA mismatch repair in the cytotoxic action of thioguanine.

It is proposed here that the delayed cytotoxicity of thioguanine involves the postreplicative DNA mismatch repair system. After incorporation into DNA, the thioguanine is chemically methylated by S-adenosylmethionine to form S6-methylthioguanine. During DNA replication, the S6-methylthioguanine directs incorporation of either thymine or cytosine into the growing DNA strand, and the resultant S6-methylthioguanine-thymine pairs are recognized by the postreplicative mismatch repair system. Azathioprine, an immunosuppressant used in organ transplantation, is partly converted to thioguanine. Because the carcinogenicity of N-nitrosamines depends on formation of O6-alkylguanine in DNA, the formation of the analog S6-methylthioguanine during azathioprine treatment may partly explain the high incidence of cancer after transplantation.

Maternal mortality in a Kenyan pastoralist population.

OBJECTIVE: To measure maternal mortality among the Gabbra, a group of nomadic pastoralists living in a remote area of Kenya. METHOD: As part of a survey of 851 households, information on the number of sisters of respondents who died of pregnancy-related causes was collected and the data were used to calculate maternal mortality statistics using the sisterhood (an indirect) method. RESULTS: The maternal mortality ratio for this population was 599 deaths per 100,000 births (95% C.I. 424-775). The lifetime risk of dying around childbirth is 1 in 30, and the proportion of ever-married sisters that died under 50 years of age who died from maternal causes is 0.48 (95% C.I. 0.38-0.58). CONCLUSION: The risk of dying of maternal causes is high in this population.

Biased parental investment and reproductive success in Gabbra pastoralists.

PIP: This study of wealth and reproductive success is based on interviews obtained from 848 rural nomadic Gabbra families from northern Kenya. The Gabbra are nomadic pastoralists who herd camels, goats, and sometimes sheep. Household is defined as a unit that owns a camel herd. Findings indicate that size of the camel herd (wealth) is positively related to the reproductive success of both men and women and is independent of age. The effect is greatest for men. Poverty effects vary between men and women. Very poor men are at a greater disadvantage than very poor women. Poor men and women tend to marry at a later age. It is posited that the beneficial effects of wealth on reproductive success may be underestimated. Both richer and poorer families showed a slightly male-biased sex ratio. There was no evidence that poorer Gabbra households might favor daughters, as suggested in the literature on sex-biased parental investment. There was no evidence that the Gabbra practiced infanticide. The average dowry size was 16.5 sheep units, where one camel is valued at about 10 sheep or goats. The traditional brideprice is 3 camels. Each son takes about 10 camels for his marriage, when brideprice is accounted for. Heads of household reported that their initial herd size was about 6.75 camels. If there is bias in parental investment, it probably occurs in the number of animals passed on to a child at marriage. Boys are disadvantaged by elder brothers, while girls are not disadvantaged by elder sisters. Lower birth order sons are prone to migrate into another ethnic group. It is likely that fathers maximize their wealth by making certain that a small number are well provided for rather than equally dividing investments. The number of elder sisters has a small effect on dowry size. Competition for parental investment appears to occur only among siblings of the same sex, particularly brothers.^ieng