organisms in retrospect complexifying the picture of the Modenr Synthesis Philippe Huneman IHPST CNRSUniversité Paris I Sorbonne Nowadays two critiques of the Modern ID: 557737
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Slide1
Adaptation and organisms in retrospect: complexifying the picture of the Modenr Synthesis
Philippe Huneman
IHPST (CNRS/Université Paris I Sorbonne)Slide2
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)Slide3
-> The space of controversies is structured by these two issues – adaptationism,
genes
vs.
organisms.Slide4
The space of controversiesDawkins
Lyn
Mayr
Gould
Organisms
Not
only
natural selection (no
adptationnism
)Gould
Organisms Mostly natural selection ( adaptationnism)Mayr
GenesMostly natural selection ( adaptationnism)Dawkins
Genes
Not
only
natural selection (no
adaptationnism
)
Lynch
MichodSlide5
The space of controversiesDawkins
Lyn
Mayr
Gould
Organisms
Not
only
natural selection (no
adaptationnism
)Gould
Organisms Mostly natural selection ( adaptationnism)Mayr
GenesMostly natural selection ( adaptationnism)Dawkins
Genes
Not
only
natural selection (no
adaptationnism
)
LynchMichod
Optimisation line
Organismic
lineSlide6
Adaptation and the meaning and role of organisms: a genealogical enquiryQuestion :
what
does this owe to the « Modern Synthesis » (as a not necessarily synthetic
set of books,
papers
, etc.?)
Outline
Evolutionary organicism,
then and nowAdaptation and organismsThe MS’s take on organismsMayr’s organicismPopulation genetics and the Modern Synthese(s)Slide7
Evolutionary organicism, then and now ?I.Slide8
Adaptation and organismsI.ASlide9
A 2 decades-long critique of suborganismic/adaptationist biologyGould (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)Slide10
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 ? Slide11
Adaptation: Disentangling the conceptual issues Adaptation as a
process
, adaptation as a
productCurrentist vs historical concepts of adaptationsTraits as adaptations, adaptedness of organisms
Nature of the state;
ways
towards
itAdaptations; complex adaptations (Williams 1992)Explanatory importance (the adaptationist challenge)Issues not related to adaptationnism; yet included in all questions about adaptationism.Slide12
Adaptation as a process, adaptation as a productPhysiologyproducts
(
decreased pulse in altitude)/ process leading to it- > Phenotypic plasticity
Genetic
product
(
webbed
feet of ducks) / process leading to it (duck phylogeny)Slide13
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)Slide14
Traits as adaptations/ adapted organismsTraits 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)Slide15
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.)Slide16
Which pathway to adaptation? (Cc)NC vs. Natural selection (earthworms)
Niche construction
Natural selectionSlide17
Adaptation and complexityComplex 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?)Slide18
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)Slide19
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.
Slide20
Alternative viewNatural selection Plasticity/NC Developmental constraints
Adaptation
Diversity
Unity
Adaptive radiationSlide21
Adaptation as a multilayered conceptSlide22
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. Slide23
-> 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.Slide24
ORGanicism, another MS take on adaptationI.BSlide25
But: organismic critique is not newIndeed 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 hereIs this a last stage of the MS ? A first round of interpretation ?Slide26
Organicism, 60s.The level of organicism is emphasized as proper to biologyEspecially against the
rise
of
Molecular BiologySlide27
Arguments by Wright (levels) and Mayr (2 causes) were crucially influential …Slide28
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
precedingsSlide29
Wright, 1953Slide30
Mayr 1955Critique of « beanbag genetics » One- or two-loci model are
unable
to capture the
complexity of causal interactions in evolutionary dynamicsSlide31
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).Slide32
Essential idea, 2. (Mayr).What’s proper
to biology is
evolutionary style
explanations. (« ultimate »)« Nothing in biology
makes
sense
etc. » (Dobzhansky 1964.)
Explanatory
thesis Slide33
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 level-independent) 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 levelIn 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)Slide34
Mayr’s organicismII.2.Slide35
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)Slide36
Critique of genetic atomismTwo polemic stances: 1942-53,
downplay
the
role of geneticists in the founding of modern evolutionary biology1955-later (
after
the
discovery
of DNA):
vindicate
the specificity of evolutionary biology against molecular biologySlide37
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 naturalist
s,
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.”Slide38
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”Slide39
“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, 1985Slide40
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 realisticWhat causally accounts for speciation are changes in reproductive barriers
which imply whole genotypes and organismic behaviourSlide41
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)Slide42
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”)Slide43
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, West-Eberhardt etc.Defining a version of MS -> role of population genetics (viz. the result/cause
diff.).Slide44
ii. Population genetics and the versions of Modern SynthesisII. (the speculative part…)Slide45
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.)Slide46
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 ??Slide47
A parallel in quantitative geneticsLande-Arnold 1983, measurement of selection on correlated
characters
(i=1….n)G = variance-covariance matrix of breeding valuesP-1 s = set of partial regression
of relative fitnesses on
characters
(Corresponds to
univariate
breeder’s equation R=hs)Slide48
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). Slide49
Back: Two views of PGstatistical / causalAbstract
away
from causes in
generalThe content is pure maths (Price equ.) and statisticsHence 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 valueWhat causes evolution is differential replication, which is the explanandum of PGHence PG captures the process of Natural SelectionTherefore it is the core of evolutionary theoryAnd e.g. grounds its methodology
(FTNS -> optimisation methods).Slide50
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. (F
isher GTNS, 1930, 37.)Slide51
A sketch of a possible causal argument.Fisher’s parallel with statistical mechanics : FTNS and 2
nd
law as two main causal laws
StatMech
is a causal
knowledge
,
even
if statistically abstracting from many causal interactions, because it averages away too-fine-grained causesPG 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 backgroundSlide52
Note : About adaptationismPG as such is neutral about adaptationism – nothing entails
that
NS is the most important cause of evolutionHow to derive this darwinian claim ?Only
if the
fundamental
theorem
of NS is
trueFisher’s position : PG is a causal knowledge of evolution, FTNS grounds adaptationismFTNS (Frank &Slatkin 1992) is about the change in mean fitness caused directly by NS, hence assumes a causal understanding of population dynamics.Slide53
Two rhetorics of natural selectionHullDifferential replication of replicators according to interactions of
interactors
“
Interactors” is the level where causation isDawkins
Differential replication of
replicators
embedded in
vehicles
(Differential) “
replication” is where causation takes placeSlide54
A by-product of this alternativeDebates 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)Slide55
ConclusionAt least two versions of MSMS 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…)Slide56
The space of controversiesDawkins
Lyn
Mayr
Gould
Organisms
Not
only
natural selection (no
adptationnism
)Gould
Organisms Mostly natural selection ( adaptationnism)Mayr
GenesMostly natural selection ( adaptationnism)Dawkins
Genes
Not
only
natural selection (no
adaptationnism
)
LynchMichod
MS F
MS MSlide57
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 theoryc.
Extending
(resp.
expanding
,
overcoming
, etc.) the Modern Synthesis can’t make sense except if one specifies which Synthesis.