ANT208H1 Lecture Notes - Weaning, Menopause

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Published on 22 Apr 2013
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Evolutionary Ecology of Human Life History
Main Concepts:
-Life-History Theory = Understand ways in which the stages of life and the associated behaviors are organized. Look
at ultimate causes for developing these traits.
-Focus on ultimate causes (non-biomedicine). Why and how did we develop a trait? What is the
advantage of having this trait?
-What are the social and behavioral effects of the trait on evolution of life-history?
-First need to determine ecology of typical ancestral population. Then decide if changing environment
was responsible for evolution of a particular trait.
-There was no clear-cut ancestral ecology so used African Village (1950-1975). Emphasis was placed on
picking population with strong social dynamic. Culture is just as important as ecology. Blah blah blah...
-Look at stages of human life history through ecology perspective.
-Evolutionary ecologists predict that human life history is unique because of our large brain. Other
primates have much smaller brains relative to body size.
-Selection pressures influencing mortality and fertility favor particular life-history strategies.
Evolution of Menopause:
Argument 1
- Grandmother hypothesis: women stop reproducing to help their own kids reproduce.
-Parents can start weaning (stop breastfeeding) sooner and grandmother can take care of kid so mom
can get kid 2 going.
-Grandmother being present lowers average child bearing age of mother by 1.
-Reduce competition amongst grandchildren. Survival of children that had living grandparents increased
significantly after ~18 months. No proof that increased no. of grandchildren outweighs cost of early
reprod. termination.
Argument 2
-Even if menopause did not exist, women giving birth at higher ages would die from complications
associated with birthing at older ages.
-Maternal medical complications like hemorrhage become more common when birthing. Plancenta mal-
alignment % also increases.
-Women have lower % healthy children as they age. Chance of child having down syndrome increases
exponentially every year after ~35.
Argument 3
-It costs a shit ton to raise kids nowadays. If women kept pumping out babies, they would need a lot of
resources. Some of this can be offset by older siblings helping out but article assumes that most help
comes from father with limited funds.
Demographic Transition (lower reprod. rate correlated with lower death rate):
-This is an evolutionary paradox. Why would you want less kids if death rate drops? There are more
family members to take care of new offspring / support mother.
-Cost of raising multiple children is huge.
-Fitness reward is greater if parents focus on fewer no. of quality offspring in contemporary civilization.
Political and economic situation is very stable. Ultra-competitive environment for offspring.
-Having more kids is only beneficial if there is both political and economic expansion. If there was no
significant increase in cost for increasing family size, then human life-history outcome would be
different.
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Document Summary

Life-history theory = understand ways in which the stages of life and the associated behaviors are organized. Look at ultimate causes for developing these traits. First need to determine ecology of typical ancestral population. Then decide if changing environment was responsible for evolution of a particular trait. There was no clear-cut ancestral ecology so used african village (1950-1975). Emphasis was placed on picking population with strong social dynamic. Look at stages of human life history through ecology perspective. Evolutionary ecologists predict that human life history is unique because of our large brain. Other primates have much smaller brains relative to body size. Selection pressures influencing mortality and fertility favor particular life-history strategies. Grandmother hypothesis: women stop reproducing to help their own kids reproduce. Parents can start weaning (stop breastfeeding) sooner and grandmother can take care of kid so mom can get kid 2 going. Grandmother being present lowers average child bearing age of mother by 1.

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