Jane B. Lancaster

A theory of human life history evolution: Diet, intelligence, and longevity

Human life histories, as compared to those of other primates and mammals, have at least four distinctive characteristics: an exceptionally long lifespan, an extended period of juvenile dependence, support of reproduction by older post‐reproductive individuals, and male support of reproduction through the provisioning of females and their offspring. Another distinctive feature of our species is a large brain, with its associated psychological attributes: increased capacities for learning, cognition, and insight. In this paper, we propose a theory that unites and organizes these observations and generates many theoretical and empirical predictions. We present some tests of those predictions and outline new predictions that can be tested in future research by comparative biologists, archeologists, paleontologists, biological anthropologists, demographers, geneticists, and cultural anthropologists.

Origins and Evolution of Language and Speech

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Paternal Care by Genetic Fathers and Stepfathers I: Reports from Albuquerque Men

Abstract We present a biosocial model of human male parental care that allows male parental allocations to be influenced not only by changes in the fitness (welfare) of the recipient offspring, but also by their effects on the mans relationship with the childs mother. The model recognizes four classes of relationships between males and the children they parent: genetic offspring of current mates (combined relationship and parental effort), genetic offspring of previous mates (parental effort solely), step offspring of current mates (relationship effort solely), and stepchildren of previous mates (essentially no expected investment). We test the model using data on parental investments collected from adult males living in Albuquerque, New Mexico, U.S.A. Four measures of paternal investment are examined: the probability that a child attends college (2,191 offspring), the probability that a child who attends college receives money for it ( N = 1,212), current financial expenditures on children ( N = 635), and the amount of time per week that men spend with children ages 5 to 12 years ( N = 2,589). The tests are consistent with a role for relationship effort in parental care: men invest more in the children of their current mates, even when coresidence with offspring is not a confounder.

Paternal Care by Genetic Fathers and Stepfathers II: Reports by Xhosa High School Students

Abstract In this article we present a biosocial model of human male parental care that allows relationship (mating) effort to influence male parental allocations. The model recognizes four classes of relationships between men and the children they parent: genetic offspring of current mates (combined relationship and parental effort), genetic offspring of previous mates (parental effort solely), step offspring of current mates (relationship effort solely), and stepchildren of previous mates (essentially no expected investment). We test the model using data on parental investment collected from 340 Xhosa high school students in Cape Town, South Africa. Six measures of paternal investment are examined: the amount of money men spent on students for school, clothing, and miscellaneous expenditures, respectively, and how often men spent time with children, helped them with their homework, or spoke English with them. The tests provide support for the roles of both parental and relationship effort in influencing parental care: men invest significantly more in their genetic offspring and in the children of their current mates. We also examine several proximate influences on parental care, specifically the age and sex of the child, and the percentage of the childs life the father figure coresided with him or her.

Does observed fertility maximize fitness among New Mexican men

Our objective is to test an optimality model of human fertility that specifies the behavioral requirements for fitness maximization in order (a) to determine whether current behavior does maximize fitness and, if not, (b) to use the specific nature of the behavioral deviations from fitness maximization towards the development of models of evolved proximate mechanisms that may have maximized fitness in the past but lead to deviations under present conditions. To test the model we use data from a representative sample of 7,107 men living in Albuquerque, New Mexico, between 1990 and 1993. The model we test proposes that low fertility in modern settings maximizes number of grandchildren as a result of a trade-off between parental fertility and next generation fertility. Results do not show the optimization, although the data do reveal a trade-off between parental fertility and offspring education and income.We propose that two characteristics of modern economies have led to a period of sustained fertility reduction and to a corresponding lack of association between income and fertility. The first is the direct link between costs of investment and wage rates due to the forces of supply and demand for labor in competitive economies. The second is the increasing emphasis on cumulative knowledge, skills, and technologies in the production of resources. Together they produce historically novel conditions. These two features of modern economies may interact with evolved psychological and physiological mechanisms governing fertility and parental investment to produce behavior that maximizes the economic productivity of lineages at the expense of fitness. If cognitive processes evolved to track diminishing returns to parental investment and if physiological processes evolved to regulate fertility in response to nutritional state and patterns of breast feeding, we might expect non-adaptive responses when returns from parental investment do not diminish until extremely high levels are reached. With high economic payoffs from parental investment, people have begun to exercise cognitive regulation of fertility through contraception and family planning practices. Those cognitive processes maynot have evolved to handle fitness trade-offs between fertility and parental investment.

Teen motherhood in cross-cultural perspective

Abstract Teen motherhood is the prevalent childbearing pattern in most traditional populations. Yet early motherhood is associated with negative biological and social outcomes in the developed world. We review the teen pregnancy literature in light of this discrepancy, emphasizing two core debates. The first debate centers on whether teens have poor pregnancy outcomes compared to older women, and whether negative outcomes are biologically based. Second, we consider the debate over the confounding effects of socio-economic conditions associated with being young. When teens are considered as a group, results are inconsistent across studies. When teens are disaggregated by age, the strongest finding across studies is that biological risk is concentrated in only the youngest of mothers. Negative consequences are associated with teen motherhood not because of chronological age per se, but because of relative developmental maturity and the availability of non-maternal support. In most traditional societies as well as in some sectors of developed societies, teen motherhood occurs within the context of extended kin networks and is subsidized through reliable economic and childcare assistance. Child-rearing practices, rather than pregnancy per se, may explain much of the discrepancy in the prevalence, success and attitudes toward teen motherhood in traditional and developed societies.

Fertility and Fitness Among Albuquerque Men: A Competitive Labour Market Theory

The reduction in fertility accompanying modernisation poses a scientific puzzle that has yet to be solved. Despite the fact the problem has received a great deal of attention from economists, sociologists, demographers, anthropologists and biologists, no discipline in the social or biological sciences has offered a fully developed and coherent theory of fertility reduction that explains the timing and pattern of fertility reduction in the developed or developing world. The inability to offer an adequate theory raises fundamental questions about the theoretical foundations of those disciplines. For example, although economics has made great strides in explaining consumer behaviour, time allocation and labour force participation through the recognition that the household is a fundamental organisational unit of human action, there is no adequate explanation of why households are mostly composed of men and women who marry and have children. There is no economic theory of why reproductive partnerships form such a fundamental organisational principle in human societies nor of why people have and want children in the first place. The very modest progress of economists in explaining long-, medium- and short-term trends in fertility highlights this weakness.

Primate Social Behavior and Ostracism

Abstract Ostracism, and its attendant processes, emigration and immigration, are now recognized as basic mechanisms intrinsic to the long-term adaptation of primate society. Ostracism, defined as socially determined exclusion from the resources and opportunities necessary to successful reproduction, is a basic mechanism by which individuals strive to maximize their own reproductive success at the expense of others. Among males this process most often involves exclusion from opportunities to fertilize females (zygote formation) whereas among females it leads to competition for the resources necessary to raise these zygotes to adulthood. Ostracism from intrasexual competition may be so intense that it leads to the migration of less successful individuals into social groups offering greater opportunity. The “passports” most often used in primate immigration are sexual affinity and kinship alliance. Migration carries high risk and is associated with increased mortality and morbidity. Nevertheless, ostracism, emigration, and immigration remain as the basic social processes by which the ratio of resources to individuals shifts and balances from one year to the next. Such adjustments are made through the process of individual “decisions” and “strategies” to optimize personal reproductive success, but their net effect is to constantly redistribute individuals in relation to resources vital to reproduction.

The Evolutionary History of Human Parental Investment in Relation to Population Growth and Social Stratification

A valve for controlling the level of water in a toilet flush tank includes a body and cover having interfacing surfaces defining a valve chamber and a diaphragm chamber. A valve seat in the valve chamber communicates with a water inlet by way of a projection integral with the body adapted to extend through the flush tank water inlet opening to mount the housing in a normally submerged position. A diaphragm is held in the diaphragm chamber between the cover and body, and a flexible valve member is held in the valve chamber between the cover and body. An air passage defined in part by the projection vents the diaphragm chamber to atmosphere through the flush tank floor, and liquid pressure is communicated through the cover to the opposite side of the diaphragm. The water inlet passage extends to the center of the valve seat, which is surrounded by a valving surface having a number of segment shaped outlet ports communicating with water outlet passages in the valve body. Movement of the diaphragm in response to changes in water level results in opening and closing of the valve member to maintain the desired water level.

The Evolution of Life History, Intelligence and Diet Among Chimpanzees and Human Foragers

Compared to those of other primates and mammals, human life histories exhibit at least four distinctive characteristics: (a) an exceptionally long lifespan, (b) an extended period of juvenile dependence, (c) support of reproduction by older, post-reproductive males and females, and (d) male support of reproduction through the provisioning of females and their off-spring. Another distinctive feature of our species is a large brain size and its associated psychological attributes: increased capacities for learning, cognition and insight. Humans and chimpanzees, compared to other primates, lie closely on a dietary continuum that emphasizes difficult-to-acquire foods. However, the extreme commitment of humans to such a diet has led to distinctive life history traits and age profiles of food production. What underlies these features is a qualitative difference in the role of males through their provisioning of meat to females and young. Meat is a preeminently provisionable resource of great value to growth and reproduction, but its acquisition comes at the cost of both skill and risk. The commitment of human males to specialize in this enterprise is the foundation of the four distinctive characteristics of human life histories. In this chapter, we propose a theory that unites and organizes these observations through comparisons of the behavior, biology, and life histories of chimpanzees and humans.