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ESS 363: Demography and Life History Theory

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Life history theory is the branch of evolutionary biology that attempts to understand patterns of investment in growth, reproduction, and survival across the life cycle. It is the theory that explains the major transitions that mark individual organisms' life cycles from conception to death. The diversity of life reflects a tremendous diversity in life histories. Some organisms live very short lives and reproduce in large numbers. Others spread a modest amount of reproduction out over a long lifespan. Still others live an extraordinarily long time and still manage to reproduce in massive numbers. Why do organisms differ so much in traits such as age at maturity, age-specific fertility, life expectancy, or clutch size? Why would a biological entity ever voluntarily reduce its reproductive output and, presumably, its fitness? How do humans fit into this diversity?

Of central importance, from the perspective of Earth System Science, life history theory --- and its attendant tools of formal demography and decision theory --- provides a framework for understanding both the ecological context and the evolutionary underpinnings of human decision-making in the realms of subsistence, reproduction, and the many domains with which these intersect. Key problems such as population growth, ecological rationality, time preferences, and resilience have their foundations in the evolution of human life histories.

Life history theory lies at the very heart of evolutionary explanation because it deals with the mechanics of natural selection. If you want to argue that a trait -- any trait -- evolved via natural selection, you need to have at least a rudimentary understanding of life history theory.

In this class, we will focus on the central themes of life history theory and how they relate to specific problems of the human life cycle. Our class reading will focus on classic works that should be in the bibliography of any evolutionarily-informed student of human behavior. The approaches that we discuss will not be exhaustive, but instead will focus on the more explicitly demographic models of life history evolution. In addition to the classic questions of life history theory (e.g., evolution of reproductive effort, size vs. quality, etc.), we will discuss some peculiar issues that relate specifically to humans. In particular, we will explore the intersection of life history theory and more classical economic approaches to decision theory and rational choice. This will include an exploration of the evolution of economic transfers and their implications for demographic transitions, ecological resilience, and the consumption of natural resources. This discussion will explore how an understanding of life history theory might help in promoting investments in future welfare or developing policies that promote sustainability.

Previous Years' Syllabi

Course Description

Problems in life history theory and evolutionary demography applied to the human life cycle. The class will emphasize developing an understanding the classical models of life history theory and their relevance for understanding human evolution. Special emphasis will be placed on assumptions of the classical models are violated by empirical patterns of the human life cycle. In particular, we will focus on complications with classical theory introduced by age-structure. Topics include continuous and discrete time population models for age-structured populations, scaling and allometry, the evolution of reproductive effort in constant and variable environments, the evolution of clutch size and quality/quantity trade-offs more generally, state-dependent life history tactics, models of somatic growth, senescence, the evolution of childhood, and post-reproductive survival. Prerequisites: HUMBIO 137 or consent of instructor. (HEF III, V) (DA-C).