PSYCH
Lecture 3 - life history theory overview 2017.pdf

16 20 1 2 3 4 5 surviving offspring litter size

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0.0 0.4 0.8 1.2 1.6 2.0 1 2 3 4 5 # surviving offspring Litter size Example of predicted optimization “Fitness”
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Life history trade off #3: Age vs. size at maturity
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Why is there a trade-off between the age vs. size at maturity Benefits of being a large adult? Larger adult body Lower risk of predation Slower metabolism (allows lower quality diet) Larger offspring Æ higher offspring survival Costs of delaying maturity to grow larger? “Compounding” fitness – early offspring start reproducing earlier, spreading genes There is always a chance of mortality: delaying maturity thus increases the chances of dying before reproducing
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2 principles that shape life histories: I. Organisms have finite energy and time to invest in different functions, leading unavoidably to trade-offs: Current vs. future reproduction Offspring size/quality vs. number of offspring Size at maturity vs. age at maturity II. Extrinsic (unavoidable) mortality: helps determine whether a species can afford to be “slow” or whether they must be “fast”
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How extrinsic mortality drives species differences in life history strategy…
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Elephants can take their time and are “slow” because they are optimistic about their futures. Mice are “fast” because they are pessimistic about surviving into the future. “fast” vs. “slow” life history species
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What are the characteristics of the human life history?
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Features of human life history? Early weaning & complementary feeding Reduced IBI and increased fertility Very slow growth rate Delayed age at maturity “Stacked” dependent offspring Long post-reproductive life Leads to grandparental allocare Somatic durability (slow aging) & long lifespan
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Features of human life history? Early weaning & complementary feeding Reduced IBI and increased fertility Very slow growth rate Delayed age at maturity “Stacked” dependent offspring Long post-reproductive life Leads to grandparental allocare Somatic durability (slow aging) & long lifespan These differentiate our species from others, however… “fast” “slow”
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There is extensive variation in life history strategy within our species Much of this variation traces to behavioral and developmental plasticity. Our bodies & brains have the capacity to modify aspects of our life history strategy in response to cues of nutrition and mortality risk in our environments. This shapes aspects of our individual life history strategies. This has important implications for understanding many social, public health, and policy issues.
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Improved nutrition has broad impacts on plasticity in life history variation: Earlier maturation at larger adult size Larger offspring size Longer lifespan Improved maintenance/immunity Faster growth rate
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The secular trend (menarche) Improved nutrition
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Mortality cues also drive individual plasticity in life history variation: Leads to pessimism about future prospects:
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Mortality cues predict life history traits Nettle D, Phil Trans Roy Soc B, 2010 116 country means UK: neighborhoods
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Male life expectancy predicts homicide rate in chicago neighborhoods Wilson and Daly, BMJ, 1997
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  • Winter '08
  • McCaslin
  • Evolution, IBI, Life history theory

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