Non-senescence in
Neoclassical Growth
Theory
Personal Background
Livelihood
Decision
consulting
Research
• Energy economics &
climate change
• Legal theory
(Law of Evidence)
• Evolutionary Biology
• Research objective:
• Provide academic practitioners
with practical tools that meet
exacting theoretical standards
• Motivation:
• Curiosity
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AGENDA
 The Model
 Reznick Results
 Non-senescence
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The model:
 Assumes populations consist of distinct genotypes
with different traits that affect intrinsic lifespan.
 Assumes heritability of these traits is imperfect.
 Adheres to the formalities of Dynamic Systems
Theory.
 Operates in two dynamic modes:
 Mode 1: mutation accumulation (purely deleterious
mutations)
 Mode 2: genotypes select different
fecundity/lifespan tradeoffs under a metabolic
budget constraint
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The dynamic modes:
Genotype choice of
“Maintenance Investment Program”
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The model delivers results consistent
with standard theory.
 Population fecundity and mortality trends with age
 Williams’ Hypothesis
 The evolution of semelparity and iteroparity
 A natural extension of the Euler-Lotka equation
 Differential survival of individuals removed from
extrinsic death hazards
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AGENDA
 The Model
 Reznick Results
 Non-senescence
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The model also helps explain the
Reznick results.
 Guppies from high predation environments show longer
lifespan than low predation guppies (in apparent
violation of Williams’ Hypothesis:
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The model also helps explain the
Reznick results (continued).
 Guppies from high predation environments also exhibit
higher fecundity than low predation guppies:
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The model can explain the increased
lifespan.
 The “predator pruning hypothesis” of Abrams-WilliamsDay:
 Different genotypes have different intrinsic lifespan
 Predators select individuals nearing the end of their
intrinsic lifespan
 These individuals show deteriorating escape performance
 Genotypes with longer intrinsic lifespan therefore have a
selective advantage
 Under predation, the intrinsic lifespan of the population
increases
 But this is not essentially inconsistent with Williams’
Hypothesis
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However, it may not explain the increased
fecundity rate.
 The model takes the different fecundity rates for the
High-predation vs. Low-predation populations as a
given input.
 Current analysis is attempting to see if the model can
be predictive of fecundity rates.
 Reznick claims that the High-predation populations are
“better at everything”—higher fecundity, longer intrinsic
lifespan, and better predator avoidance. It is as if they
have an inherently greater metabolic budget to work
with.
 This is a great puzzle.
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AGENDA
 The Model
 Reznick Results
 Non-senescence
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Under certain conditions, standard theory predicts nonsenescent genotypes will dominate senescent ones.
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