Transcript Chapter 10 Adaptation, Perfection, Function

Chapter 10
Adaptation, Perfection, Function
Nicolas Crossley K
Sex and Death
Summer ‘05
E. Oberheim
• Index
– 1. Definitions in Adaptionism: traits and
functions
– 2. Methodological Problems and redefining
adaptionist groups
– 3. The alternative theory
– 4. Looking for another methods for adaptionism
Definitions - Methodological Problems - Alternative Theory - New Methods
• 10.1 Definitions:
– adaptive trait: trait that increases the relative
fitness of their bearers
• how to choose them?
– adaptation: trait that has been selected by
natural selection.
– vestigial trait: relic of previous selection.
– exaptation: trait used for a different purpose
than the originally selected for.
Definitions
• 10.2 Functions
– etiological theory: asking for function is asking
for evolutionary origins.
– propensity theory: asking for functions is
looking at adaptive effects of traits.
• No need to do an evolutionary history.
– causal role functions: a functional analysis
refering to a particular capacity (might be
capacity to reproduce)
Definitions
• 10.3 The attack on Adaptationism (Gould
and Lewontin)
– every useful trait exists because it is useful
– every trait is explained by adaptation
• what features of an organism are its traits?
– unfalsifiability
Definitions - Methodological Problems
• 10.4 Defining adaptationism:
– Empirical adaptationism: natural selection is
the main factor in evolutionary history
– Explanatory adaptationism: natural selection
may not be the main factor, but it is the only
mechanism that produces complex adaptation.
– Methodological adaptationism: biological
systems should be studied looking for a good
design.
Definitions - Methodological Problems
• 10.5 The alternative: Structuralism and the
Bauplan
– Each organism is designed as a variation of a
basic plan.
– Explanation by classification.
– Darwin’s objection: earlier adaptation of
common ancestors.
• Being useless, shouldn’t they disappear?
Definitions - Methodological Problems - Alternative Theory
• Developmental constraints and canalization:
Process Structuralists
– certain traits are essential in the development of
the organisms, and therefore are not explained
by the environmental pressure.
– Highly conserved traits are strong attractors for
development
– Design space is smaller than adaptionists think.
Definitions - Methodological Problems - Alternative Theory
• The synthesis: generative entrenchment
– similarities are common due to incremental
design (probability of each stage vs the whole
design)
– the incremental design asks for the maintenance
of previous modifications
– Counter example: animals which modified their
developmental trajectories retaining their
similarities.
Definitions - Methodological Problems - Alternative Theory
• 10.6 How to test theories: Optimality and
Game models
– Optimality models
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Fitness measure (measure of success)
Heritability assumption
Phenotype set (alternatives)
State equations (interactions)
– Game theoretic models
• interaction with others is also considered
• game matrix / strategies / payoff
• Instead of optimal strategies, evolutionary stable
– can’t be invaded
– fixed if everyone uses the same phenotypes
Definitions - Methodological Problems - Alternative Theory - New Methods
• Modelling to save the unfalsifiable
– they are tested by their similarities with reality
– Problems:
• depends on being able to independently test
physiological and ecological assumptions
• mismatch is explained by problems in the factors
and not in the modelling itself.
– Heuristic value?
• Mismatch reveals unsuspected constraints
– Adaptionism as a research program: adaption is
ubiquitous, important and optimal.
• Core ideas not tested, “extra” theories are.
Definitions - Methodological Problems - Alternative Theory - New Methods
• 10.7 Adaptation and the Comparative
Method
– The historical problem in testing adaptionist’s
hypothesis
• Optimality is local
• Chance (drift) may have a big effect in small
populations
• Modelling “best explanations” (abduction) require
some historical assumptions
– there are many “good explanations”
Definitions - Methodological Problems - Alternative Theory - New Methods
• Advantages:
– test historical premises in adaptionist
hypothesis
• low birthweight for hibernation.
– test link between trait and habitat factors
• finding covariations (flightless bird in island)
• convergence
– test the priority of selection
• history is constant
• selection gives the variance
– Dunbar’s theory on brain size and group size
Definitions - Methodological Problems - Alternative Theory - New Methods