Jamie Jones - Stanford

The Evolutionary Demography of the Human Life Cycle

    Date:  11/08/2018 (Thu)

    Time:  3:30pm- 5:00pm

    Location:  Seminar will be held on-site: Gross Hall 270

    Organizer:  Jenny Tung

Meeting Schedule: Login or email the organizer to schedule a meeting.

    All meetings will be held in the same location as the seminar unless otherwise noted.

    8:30am - Breakfast at 21C Hotel with graduate students (Claire LeBarbenchon, Allison Stolte, DNAC students)

    9:00am - Breakfast at 21C Hotel with graduate students

    9:30am - Breakfast at 21C Hotel with graduate students

   10:00am - Anne Pusey

   10:30am - Charlie Nunn

   11:00am - Giovanna Merli

   11:30am - Dana Pasquale

   12:00pm - Lunch- Brian Hare

   12:30pm - Lunch- Brian Hare

    1:00pm - Lunch- Brian Hare

    1:30pm - Jenny Tung

    2:00pm - Herman Pontzer

    2:30pm - Jim Moody

    3:00pm - Seminar Prep

    3:30pm - Seminar Presentation (3:30pm to 5:00pm)

    6:00pm - Dinner w/ Giovanna Merli, Jim Moody, Jenny Tung

    Additional Comments:  Human life histories combine late age at first reproduction, long reproductive span, relatively high fertility, extensive allomaternal economic transfers, and substantial post-reproductive survival. This unusual constellation of life-history elements suggests that human reproductive strategies are characterized by substantial bet-hedging. This observation is consistent with the fact that the genus Homo is a product of the Pleistocene, a geological epoch characterized by substantial environmental volatility at various temporal scales. In this talk, I will lay out the key features of the human life cycle and their relationship with a bet-hedging reproductive strategy. I describe demographic methods we have developed to measure life-history trade-offs and discuss the possibilities of extending these to understanding the selective consequences of economic decisions more generally. Typically, evolutionary analyses of human reproductive decision-making measure fitness using lifetime reproductive success. This fitness measure implicitly assumes that women are risk neutral in their decisions since all births contribute equally to fitness. However, ample demographic evidence demonstrates that the decision to have another child is fraught with risk and that such risks are magnified during periods of economic crisis. I employ an alternative measure of fitness, the individual rate of increase, which predicts that mothers should be risk averse in their reproductive decisions. Using the theory of decision-making under risk, I predict that risk-averse women should reduce fertility during economic shocks, but that this reduction should be modified by age. Specifically, older women should be less risk averse than younger women because diminishing marginal fitness gains mean that older women pay less cost in the case of an adverse outcome. I provide a test of the risk-sensitive-fertility hypothesis in an analysis of demographic change on the American Frontier. Fertility reduction is an adaptive response to changing economic conditions and the changing costs of child-rearing. Using a genealogical database of over 800,000 births from Utah, 1859-1949, I show the complex ways that fertility has declined from a total fertility rate (TFR) of over 10 to a TFR of about 4 by the mid-twentieth century. Fertility decline was nonlinear in age, period, and parity and there were substantial interactions between these factors. This hypothesis of risk-sensitive fertility is supported: while younger women dramatically reduced fertility during the Depression, older, high-parity women actually increased their fertility moderately. This finding has powerful implications for understanding fertility transitions and suggests avenues for the further synthesis of economics and evolutionary biology.