Transcript The Confusion of Fitness - School of Computer Science

“The Confusion of Fitness”
André Ariew and Richard Lewontin
Biology and Computer Science
Workshop, Winsdor, Septembre 2007
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Darwinian fitness
• Fit, fittest, fitness – the degree to which the
organism matches a pattern of its environment
• What is to be explained:
– Fit between organism’s and species’ properties and
ecological niche they occupy
Organism’s properties  fitness to environment  reproductive
rates changes in representation in the population
• Problematic lock and key concept of ecological
niche, adaptive zones, causal independence
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Fitness in population genetics
• Organism’s properties  fitness to
environment  Reproductive rates 
reproductive fitness  changes in
representation in the population
• Reproductive fitness
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Fitness in population genetics –
problem 1°
• Reproductive fitness –
– no ecological account
– attribute in itself
• p. 350 and Lewontin: greater reproductive success
of an individual yet without fitness
– increase in number does not necessarily designate
increase in fitness
– more eggs example
– Reproductive fitness does not measure the adaptation,
is not associated to features we could call adaptations
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Fitness in population genetics –
problem 2°
•
Selective causes are not revealed by measuring
viability or fertility of the genotype of a given
generation, but are to be found in previous
generations
– Postponed reproductive fitness effect
•
Recessive grandchildless (gs) mutation in Drosophila
subobscure
1. Females homozygous for the mutation (gs, gs) normal fertility
and viability
2. Their offspring, irrespectively of their own genotype, do not
produce sperm of eggs
3. No grandchildren
•
Bird badly nourishing its offspring
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Fitness in population genetics –
problem 3°
• Fitness would measure the change in the relative
frequency of the classes over time
• Reproductive fitness – assigned to types not
tokens (p. 351)
• token causality (E. Sober, 1987)- referring to individuals
• property causality (E. Sober, 1987)- referring to properties of
populations (used by population genetics)
• Realism vs. Instrumentalism
– Objective vs. useful cutoffs points
– Problem: population’s property is not a property of
particular individuals from that population
• e.g. the average income of a family of four and the income of a6
particular family
Fitness in population genetics –
problem 3°
Example:
1. Forest and interbreeding moths
2. Forest after Industrial Revolution
• Melanic type is favored in industrial areas; brighter
wing color is favored in unpolluted areas.
• Within the same forest darker wing color at the
same time increases and decreases the fitness
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Fitness in population genetics –
problem 3°
3. Division into subpopulations
• context-dependency unacceptable for realists: the
‘real cause’ cannot be the cause in one context, and
not to be the cause in another (R. Lewontin, 1982)
• How to draw non arbitrary lines among different
selective situations? To what a feature constitutes
an adaptation? Function, evolutionary benefit, etc.
• Cladistic
– Problem of borders among populations, species
– Problem of incipient species (evolving entities) or of how
one splits into two (origin of discreteness)
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Answers to the problem 3°
• A. Ariew - instrumentalism: fitness can be associated
with equal validity to the level the most appropriate for the
experimenter’s aims  different selective explanations
whether:
• we analyze the dynamics of a population (macro-population level
• Or whether the study concerns individuals (micro-population level)
• “Are probabilities necessary for evolutionary explanations?”, 1998
• A. Ariew and R. Lewontin, 2004 – realism: critique of
reproductive fitness as assigned to types (population’s
properties) and not to tokens (individual features); p. 351
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Answers to the problem 3
• Probability liberates us from bimodality and
discreteness
– Individuals, embryology, and separate life cycles
• Probability concerns as well population property
(type) as individuals (tokens), at the same time,
given that the 50% probability of a coin to fall on
heads is as well valid for that particular coin as for
a set of coins (A. Ariew, 1998).
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Fitness and species
Microevolution
– Selective situations at
the level within
populations
and species
– variation
– phylogenetic rates –
rate at which features
replace one another
– incipient features
Macroevolution
– Selective situation
in congeneric species
and higher taxa
– diversity
– taxonomic rate –
rate at which taxes
replace one another
– incipient species
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Fitness and species
– (in reference to the problem 3°) How to draw non
arbitrary lines among different selective situations?
– speciation would be the consequence of « selection for »
– speciation would separate evolutionary trajectories
– Problem of discreteness
– origin of discreteness – from inexistent to existent; problem of
incipient species or of how one splits into two
– borders among species – where to put cutoff points?
– if Darwinian fitness then spatial border, allopatry, lock and key
concept of ecological niche
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Probabilistic Species Concept
1.
2.
Species - genotypic average of individuals, its parts
Two species - when the distance between two averages
lowers the probability of interbreeding below speciation
threshold.
•
3.
Conversely: new species arises when an individual mutation
raises the genetic distance between its bearer and the genotypic
average of his parental population above speciation threshold
Individual is a part of a species, when there is a high
probability that he interbreeds with other individuals,
parts of the same species
•
From inexistent to existent: an individual alone cannot constitute
a species (no possibility to interbreed); there is very low
probability for a species to be composed from only one
individual
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Probabilistic species concept
• Probabilistic definition of species offers
acceptable switch and overlap between the notion
of species as an individual or/and as a class
– Organisms are parts of the species and not its instances;
in rem
– No question of how species exists and whether species
makes sense as individuals rather than classes
(population’s property and types vs. tokens)
• Problem of borders: ring species and lock and key
concept of ecological niche
– Mode of speciation: allopatric and sympatric
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Ring species
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Thank you
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