Transcript pittsburgh embodiement adaptation workshop

Adaptation and organisms in
retrospect: complexifying the
picture of the Modenr Synthesis
Philippe Huneman
IHPST (CNRS/Université Paris I
Sorbonne)
Nowadays: two critiques of the Modern
Synthesis that concern adaptation:
Critique of adaptationism.
not all traits are resulting
from natural selection;
natural selection is not
the exclusive cause of
evolutionary change, etc.
(Gould-Lewontin, 1979; Godfrey
Smith 1996; Lewens 2008)
-
The active role of
organisms: adaptation
starts from the activity of
organisms:
– Phenotypic plasticity (West
Eberhardt, 2005): « Genes
are followers, not
leaders »;
– Niche construction (Odling
Smee et al. 2003)
-> The space of controversies is structured by
these two issues – adaptationism, genes vs.
organisms.
The space of controversies
Genes
Mostly natural selection ( adaptationnism)
• Dawkins
Dawkins
• Lyn
Genes
Not only natural selection (no adaptationnism)
Organisms
Mostly natural selection
( adaptationnism)
Mayr
Lynch
Michod
Mayr
Organisms
• Gould
Not only
natural selection (no adptationnism)
Gould
The space of controversies
Genes
Mostly natural selection ( adaptationnism)
• Dawkins
Dawkins
Optimisation line
• Lyn
Organisms
Mostly natural selection
( adaptationnism)
Mayr
Genes
Not only natural selection (no adaptationnism)
Mayr
•
Lynch
Michod
Organisms
Not only natural selection (no
Gould
adaptationnism)
Gould
Organismic
line
Adaptation and the meaning and role
of organisms: a genealogical enquiry
• Question : what does this owe to the « Modern
Synthesis » (as a not necessarily synthetic set of
books, papers, etc.?)
• Outline
– Evolutionary organicism, then and now
• Adaptation and organisms
• The MS’s take on organisms
• Mayr’s organicism
– Population genetics and the Modern Synthese(s)
I.
EVOLUTIONARY ORGANICISM,
THEN AND NOW ?
I.A
ADAPTATION AND ORGANISMS
A 2 decades-long critique of
suborganismic/adaptationist biology
- Gould (1983): the « hardening of the
Synthesis »
- Walsh (2010) The triumph of « suborganismal
biology » (= MS) and the recent prospects for
« organismal » biology (phenotypic plasticity,
adaptivity of organisms)
What is crucial : the status of adaptation.
(Depew 2010, on the duality (UK /US) of the Synthesis;
the « hardening » is the triumph of the former)
Received view : an adaptation = a (trait) result(ing) from
natural selection
Challenges : adaptation as changing the environment
(Odling-Smee et al. 2003); adaptation as adaptive
plasticity (Walsh 2003, 2010, West-Eberhardt...)
Old problem : how to get the adaptedness of organisms ?
Adaptation: Disentangling the
conceptual issues
a.
b.
c.
d.
e.
f.
Adaptation as a process, adaptation as a product
Currentist vs historical concepts of adaptations
Traits as adaptations, adaptedness of organisms
Nature of the state; ways towards it
Adaptations; complex adaptations (Williams 1992)
Explanatory importance (the adaptationist challenge)
Issues not related to adaptationnism; yet included in all questions about
adaptationism.
Adaptation as a process, adaptation as a
product
Physiology
products (decreased pulse in altitude)/ process
leading to it
- > Phenotypic plasticity
Genetic
product (webbed feet of ducks) / process
leading to it (duck phylogeny)
Currentist vs historical concepts of
adaptations
« X is an adaptation » is a
historical statement
(Brandon 1996, Sober 1984,
etc.)
(In the case of
maintenance questions)
adaptation is a
currentist concept, i.e.
the highest fitness
variants in a population
(as opposed to origin
questions, e.g.
paleontology) (Reeve &
Sherman 1993)
Traits as adaptations/ adapted
organisms
Traits are adaptations.
« The expression of conditions of
existence, so often insisted on by the
illustrious Cuvier, is fully embraced by
the principle of natural selection. For
natural selection acts by either now
adapting the varying parts of each
being to its organic and inorganic
conditions of life; or by having
adapted them during past periods of
time: the adaptations being aided in
many cases by the increased use or
disuse of parts, being affected by the
direct action of external conditions of
life, and subjected in all cases to the
several laws of growth and variation.”
Darwin – OS – 6; summary
MS – traits are tied to genes (that’s why
natural selection acts on them)
But: organisms are « adapted. »
Formerly (Cuvier, etc. – see Ospovat
1980)– adaptation was a quantitative
property of organisms…
Double issue :
« Adaptedness » of organisms is involved in
fitness, which is explanatoy of
adaptation;
An organims is a « bundle of adaptations »
(Huxley, 1942) ? Or not ? (adaptations
can be conflicting; « trade-off » may not
be the solution)
Which pathway to adaptation?
« Adaptation » connotes a kind of
fit; what does produce such fit ?
(one or several pathways?)
-> externalism vs. (constructive)
internalism
• The Niche Construction challenge
• Is natural selection the cause of
adaptation or of its spreading (Walsh
2003; Sober 1999, Neander 1995, etc.)
Which pathway to adaptation? (Cc)
NC vs. Natural selection (earthworms)
• Niche construction
•
Natural selection
Adaptation and complexity
Complex adaptation is a problem (eye, bats radar,
vertebrate immune system, etc.); but many
adaptations are not complex (e.g. fur colour etc.).
Link: The criterion of adaptation = complexity. (Paley,
quoted in Williams 1992; « exquisite contrivances »:
Gardner 2009)
Evolutionary biology may be determined either by an
interest in complex adaptations (Dawkins’ problem) or
by a question about in the pervasiveness of
adaptations (but what are the criteria?)
Explanatory relevance
-> what is the main explanatory project of evolutionary
biology ? Adaptations ? Complex adaptations ?
Not just adaptation (but diversity; or unity in diversity,
etc.)?
Lewontin 1971: « Evolutionary theory explains adaptation and
diversity in the living world. ».
• Are all explananda compatibles?
• Is the explanation of diversity (resp. Unity in diversity),
deducible from the explanation of adaptation ?
(Darwin’s finches)
•
Natural
selection
Adaptation
Adaptive
radiation
Diversity
Analogies ->
Unity
Common
descent homology
« Unity of
type »
On my theory, unity of type is
explained by unity of descent. The
expression of conditions of existence,
so often insisted on by the illustrious
Cuvier, is fully embraced by the
principle of natural selection. For
natural selection acts by either now
adapting the varying parts of each
being to its organic and inorganic
conditions of life; or by having
adapted them during past periods of
time: the adaptations being aided in
many cases by the increased use or
disuse of parts, being affected by the
direct action of external conditions of
life, and subjected in all cases to the
several laws of growth and variation.
Hence, in fact, the law of the
Conditions of Existence is the higher
law; as it includes, through the
inheritance of former variations and
adaptations, that of Unity of Type.
Alternative view
Natural selection
Plasticity/NC Developmental constraints
Adaptation
Adaptive radiation
Diversity
Unity
Adaptation as a multilayered concept
Traits
product ?
Vs
organisms
Historical
concepts
Process ?
Currentist
concept
One or
many
pathways?
Role of
complexity
Etxplanaory
relevance
summarizing…
The MS (or supposed so…) view :
an adaptation is a result of
natural selection; adaptedness
of organisms results from the
set of adaptations (« bundles
of adaptations »); adaptation
is historical (monism) or we
can admit currentist concept
(pluralism); adaptation
explained leads to explaining
other explananda; adaptations
may be complex or not
(neutral) – but complex
adaptations are (one of ) the
Big Problem(s)
Challenge : the « fit » within
adaptation results from
something else than selection;
it involves organisms; the
traits as adaptations can’t give
us adaptedness of organisms;
the explananda of EB are not
all yielded by the explanation
of adpatation, which maynot
be the main important thing;
complex adaptations are not
THE problem of evo bio.
-> Challenging the conception of adaptation in
MS leads to thinking differently about
organisms and their role in producing
adaptation, as well as diversity and evolution.
But : different from what?....
Claim – this was an issue within the MS.
I.B
ORGANICISM, ANOTHER MS TAKE
ON ADAPTATION
But: organismic critique is not new
Indeed it was a crucial moment in the
consolidation/ aftermath of the MS:
Ernst Mayr, “Where Are We?” Cold Spring Harbor Symposium on Quantitative
Biology 24 (1959): 1–14.
Ernst Mayr, “Cause and Effect in Biology” Science 134 (1961): 1501–06;
Theodosius Dobzhansky, “Biology, Molecular and Organismic,” American Zoologist
4 (1964): 443–52.
Sewall Wright, “Gene and Organism,” The American Naturalist 87, no. 832 (1953):
5–18.
George Gaylord Simpson, “The Status of the Study of Organisms,” American
Scientist 50, (1962): 36–45.
case of Waddington left aside here
Is this a last stage of the MS ? A first round of interpretation ?
Organicism, 60s.
• The level of organicism is emphasized as
proper to biology
• Especially against the rise of Molecular
Biology
Arguments by Wright (levels) and Mayr (2
causes) were crucially influential …
Essential idea, 1.
• Biology is hierarchised.
Reduction, in Nagel’s
sense (Dobzhansky,
Mayr cite Nagel 1961)
does not work.
Each level is not deducible
from the precedings
Wright, 1953
Mayr 1955
• Critique of « beanbag genetics »
One- or two-loci model are unable to capture the
complexity of causal interactions in evolutionary
dynamics
Evolutionary thinking is holistic and
interactionist - Dobzhansky
• “Talking about traits as though they were independent
entities is responsible for much confusion in biological
and especially in evolutionary thought” (1970, 65).
• “A change in the genotype alters the reaction norm,
and some of the alterations may enable the new
genotype to produce a harmonious response where
the ancestral has been a failure … Selection deals not
with the genotype as such, but with its dynamic
properties, its reaction norm, which is the sole
criterion of fitness in the struggle for existence.” (1937,
170).
Essential idea, 2. (Mayr).
• What’s proper to biology is
evolutionary style
explanations. (« ultimate »)
• « Nothing in biology makes
sense etc. » (Dobzhansky
1964.)
Explanatory thesis
The strategy.
(1) + (2) = the proper biological (= evolutionary)
level is organism (and beyond).
MAYR
Notice : curiously, evolutionary
explanation and organicism are tied
(whereas, one could think that
evolutionary explanations are levelindependent)
•
•
A first reason : genes are too close
to chemistry (via molecular biology)
A second reason : critique of
genetic atomism (as misleading
abstraction); interactionism:
concrete complexity occurs at the
organismic level
In biology, a second kind of
explanation may be added to the
first, or reductionist explanation,
made in terms of physical,
chemical and mechanical
principles. This second form of
explanation, which can be called
compositionist in contrast to
reductionist, is in terms of
adaptive usefulness of structures
and processes to the whole
organism and to the species of
which it is a part, and still further,
in terms of ecological function in
which the species occurs.
(Simpson 1964)
II.2.
MAYR’S ORGANICISM
Mayr ?
“It is hard to exaggerate the significance of Mayr's
defense of the proximate/ultimate distinction in
establishing philosophy of biology as a legitimate
special area of inquiry”
(Beatty 1994)
Most quoted author in Hull’s classical « What
philosophy of biology is not ? » (19 occurrences)
Critique of genetic atomism
Two polemic stances:
1942-53, downplay the role of geneticists in the
founding of modern evolutionary biology
1955-later (after the discovery of DNA): vindicate
the specificity of evolutionary biology against
molecular biology
Historical sketch of MS by Mayr
« Several historians have mistakenly thought that this synthesis within genetics had solved
all the problems of Darwinism. That assumption, however, failed to take account of an
important gap. One of the two major branches of evolutionary biology, the study of the
origin of biodiversity, had been left out of the major treatises of Fisher, Haldane, and
Wright. Actually, unknown to these geneticists, the problems of the origin of biodiversity
had already been solved in the 1920s by several European naturalists, most important
among them, Moritz Wagner, Karl Jordan, Poulton, Chetverikov and Stresemann. Thus,
evolutionary biology around 1930 found itself in a curious position. It faced two major
seemingly unsolved problems: the adaptive changes of populations and
the origin of biodiversity. Two large and very active groups of evolutionists worked
on these problems. One of these groups consisted of the population geneticists. As
summarized in the works of Fisher, Haldane, and Wright, this group had solved the
problem of gradual evolution of populations through natural selection. But they had
not made any contribution to the problem of how species arise (speciation) - that is, to
the problem of the origin of biodiversity. The other group of evolutionists consisted of
the naturalists taxonomists.”
• The two explananda of evolution : adaptation,
diversity
(notice how it differs from Dobzhansky, quoted above)
About Systematics and the origins of species (1942): “The real
objective of my volume was to explain a whole set of
phenomena,—such as species and speciation, as the effects of
selection on populations, as the role of geography at the level of
species and populations, and as the role of species in
macroevolution,— that were omitted in the accounts of the
geneticists or that were based on the findings of the systematists,
such as in the volumes of Dobzhansky, Timoféeff-Ressovsky and
Huxley”
“It is now understood that evolution consists in two major processes,
the changes (usually adaptational) of populations in time, and the
multiplication of species in space that is the origin of new organic
diversity. The latter process, more often called speciation, has been
clouded with confusion ever since 1859. Darwin in his early
unpublished writings (1837 to 1844) had come to the conclusion
that geographic isolation was a necessary prerequisite for
speciation and that therefore allopatric speciation was the
prevailing, if not the only, form of speciation (Kottler 1978; Sulloway
1979). However, by 1859 when he published the Origin, Darwin had
concluded that sympatric speciation, the splitting of a single
population without geographic isolation, was at least equally
common.”
Mayr, JHB paper on Weissmann, 1985
What’s the trouble with population
genetics ??
Speciation appears when genetic environment of
the genes change (e.g. at boundaries of
territories). (« Change of environment and speciation » (1954))
• This assumes that the effect of genes is
(organsims- and gene-contextual) dependent.
• Usual PG models (atomistic etc.) are not realistic
• What causally accounts for speciation are
changes in reproductive barriers which imply
whole genotypes and organismic behaviour
Consequences
« Population » is not exemplarily represented by
population genetics !
A population is indeed biological : it reproduces itself through
the reproduction of some organisms.
« In the study of biological species one deals with biological populations. (…)
Only a small fraction of any biological population reproduces, because not
every individual in a population survives up to the reproductive age and
reproduces successfully. This is true on the average of only two of the
total number of a prenatal pair in a sexually reproducting species. »
(« What is a species and what it is not », Phil Sci 1996)
From the viewpoint of diversity questions, the causal consistency
of population is due to organisms (and not genes)
Consequences, 2
-> Population genetics does not exemplify the
evolutionary style of explanation:
“Evolutionary biology dealing with highly complex
systems [not genes, PH] operated by historically
evolved genetic programs, must pursue a very different
strategy of research in order to provide explanations.
Its most productive method is the comparative
method, for which the taxonomists have laid the
foundation. Indeed I can hardly think of a evolutionary
problem that has not developed out of some findings of
taxonomy.” (“the role of systematics in biology”)
• Hence Mayr rejects the
textbook definition of
evolution as « changes in
allele frequencies in a
population ».
– “Evolution is not a change in
gene frequencies, as is claimed
so often, but the maintenance
(or improvement) of
adaptedness and the origin of
diversity. Changes in gene
frequency are a result of such
evolution, not its cause.” (Mayr
1997, 2093).
• Mayr would subscribe to
Walsh’s idea that it
providses only a shadow
(« pseudo-process » sensu
Salmon) of the evolutionary
process.
• This is not at all the MS
targeted by Walsh,
Muller, Gerhardts and
Kirschner, WestEberhardt etc.
• Defining a version of MS
-> role of population
genetics (viz. the
result/cause diff.).
II. (the speculative part…)
II. POPULATION GENETICS AND THE
VERSIONS OF MODERN SYNTHESIS
• Claim 1, weak. Population genetics is central in
evolutionary biology because it mathematically
explains why evolution by NS is possible (eg
Gayon 1998) (assuming particular inheritance)
• Claim 2, strong. Population genetics provides the
fine-grained knowledge of the process of
evolution as a population level phenomenon
(Hamilton, Maynard-Smith, Williams, Price, Grafen, Michael Lynch,
etc.)
The call for an extended MS often rejects 2.
Especially : « PG is not a causal knowledge of
evolution. »
The issue : is PG a statistical or a causal
understanding of evolutionary dynamics ??
A parallel in quantitative genetics
• Lande-Arnold 1983,
measurement of selection
on correlated characters
(i=1….n)
• G = variance-covariance
matrix of breeding values
• P-1 s = set of partial
regression of relative
fitnesses on characters
(Corresponds to univariate
breeder’s equation R=hs)
• Major idea: G represents how the genic
architecure constrains the response to
selection
• Yet major problems to get causal explanations
out of it (Pigliucci 2005; Barton and Turelli
1989).
Back: Two views of PG
statistical
• Abstract away from causes
in general
• The content is pure maths
(Price equ.) and statistics
• Hence causes have to be
plugged in from the outside
• They are the causes of
fitness (pertaining to
ecology, physiology, etc.)
• It is not the core of MS but
has instrumental value
/
causal
• What causes evolution is
differential replication,
which is the explanandum
of PG
• Hence PG captures the
process of Natural Selection
• Therefore it is the core of
evolutionary theory
• And e.g. grounds its
methodology (FTNS ->
optimisation methods).
Fisher’s take on PG.
The statement of the principle of Natural Selection in the form of a theorem
determining the rate of progress of a species in fitness to survive (this
term being used for a well-defined statistical attribute of the population),
together with the relation between this rate of progress and its standard
error, puts us in a position to judge of the validity of the objection which
has been made, that the principle of Natural Selection depends on a
succession of favourable chances. The objection is more in the nature of
an innuendo than of a criticism, for it depends for its force upon the
ambiguity of the word chance, in its popular uses. The income derived
from a Casino by its proprietor may, in one sense, be said to depend upon
a succession of favourable chances, although the phrase contains a
suggestion of improbability more appropriate to the hopes of the patrons
of his establishment. It is easy without any very profound logical analysis
to perceive the difference between a succession of favourable deviations
from the laws of chance, and on the other hand, the continuous and
cumulative action of these laws. It is on the latter that the principle of
Natural Selection relies. (Fisher GTNS, 1930, 37.)
A sketch of a possible causal argument.
Fisher’s parallel with statistical mechanics : FTNS and 2nd law as
two main causal laws
StatMech is a causal
knowledge, even if
statistically abstracting
from many causal
interactions, because it
averages away too-finegrained causes
PG is possible because
many interactions
between genes in the
genetic background of
one or two loci in a
population can be
averaged out, and by
tracing the dynamics of
the focal loci one
captures its dynamics
on any background
Note : About adaptationism
• PG as such is neutral about adaptationism –
nothing entails that NS is the most important
cause of evolution
• How to derive this darwinian claim ?
• Only if the fundamental theorem of NS is true
• Fisher’s position : PG is a causal knowledge of
evolution, FTNS grounds adaptationism
• FTNS (Frank &Slatkin 1992) is about the change in
mean fitness caused directly by NS, hence
assumes a causal understanding of population
dynamics.
Two rhetorics of natural selection
Hull
• Differential replication
of replicators according
to interactions of
interactors
“Interactors” is the level
where causation is
Dawkins
• Differential replication
of replicators
embedded in vehicles
(Differential) “replication”
is where causation
takes place
A by-product of this alternative
Debates on gene selectionism:
Classical counter-argument (Sober 1982): gene
selection is bookkeeping, does not capture
causal processes.
(whereas gene selectionists would say that causal
dispositions are in the relatedness value r, e.g.
West et al. 2007)
Conclusion
At least two versions of MS
MS M : organicism; PG not the central core
MS F : PG = science of the process of ENS; core of
the evolutionary theory (Lynch’s dictum)
(may be analogous to Depew’s distinction, UK and US
styles in MS…)
The space of controversies
Genes
Mostly natural selection ( adaptationnism)
• Dawkins
Dawkins
• Lyn
MS F
Genes
Not only natural selection (no adaptationnism)
Organisms
Mostly natural selection
( adaptationnism)
Mayr
Lynch
Michod
Mayr
MS M
Organisms
• Gould
Not only
natural selection (no adptationnism)
Gould
a. Calls for « organismal » biology target MS F
Issues about the causal nature of PG seem
unavoidable.
b. In terms of interpreting the models (especially
PG) MS is NOT a synthetic theory
c. Extending (resp. expanding, overcoming, etc.)
the Modern Synthesis can’t make sense
except if one specifies which Synthesis.