Diapositiva 1

1
History of a concept in complexity studies
The origins of natural design
The origins of particularly complex and perfect
organs (analogy with artifacts)
There cannot be design without a designer
contrivance, without a contriver order, without
choice
Young Darwin impressed by Paleys descriptions of
adaptations
Natural Theology, 1802
2
Charles Darwins Transmutation Notebooks
1836 - 1839
3
SOME RADICAL DOUBTS (1837-1838)
Imperfection When one sees nipple on mans
breast, one does not say some use. So with
useless wings under elytra of beetles, born from
beetles with wings and modified. If simple
creation, surely would have been born without
them (Not. B, Sept. 1837)
Evolution is not superiority It is absurd to
talk of one animal being higher than another. We
consider those, where the cerebral structure, or
intellectual faculties, most developed, as
highest. A bee doubtless would when the instincts
were (Not. B, Sept. 1837)
Adaptive contingency of characters Chance and
unfavourable conditions to parent may become
favourable to offspring (Notebook E, 19 Oct.
1838)
Every species is due to adaptation AND
hereditary structure (Not. B, 1837)
4
The tree (or coral) of life (branching evolution)
as description Natural selection (differential
survival and reproduction) as explanation
Notebook B, July 1837
5
ADAPTATION WITHOUT FINALISM (Notebook E, Dec. 1,
1838)
No adaptation to an end, but adaptation to
varying circumstances owing to external
contingencies and relations with other species,
not owing to mandate of God (commenting William
Whewells History of the Inductive Sciences and
his idea of a providential adaptation)
Structure is due to external agency and
circumstances, without final cause, either in
present, or past generation
(Notebook E, Dec. 14 1838)
6
A pessimistic passage in Notebook C, July 1838
We never may be able to trace the steps by which
the organization of the eye, passed from simpler
stage to more perfect, preserving its relations.
The wonderful power of adaptation given to
organization. This really perhaps greatest
difficulty to whole theory (CD)
DIFFICULTY is there any contradiction between
continuity of change, by natural selection, and
the need of a persistent (even infinitesimal)
functional advantage?
7
CD is quoting Henri Milne-Edwards (Histoire
naturelle de crustacés, 1834, paper 1838)
Il est aussi digne de remarque que linstrument
affecté à cet usage insolite nest pas un organe
nouveau introduit ad hoc dans la structure des
Crustacés à brachies infèrieures, mais un
appendice qui existe dans tous les animaux de
cette catégorie, et qui est seulement en partie
détourné de sa destination ordinaire et
lègérement modifié dans sa conformation pour
devenir apte à remplir ses fonctions nouvelles
(in, Notebook E, Oct. 19, 1838)
8
The five percent of a wing Problem
How can evolution ever make a wing in Darwins
gradualist and functionalist way if the five
percent of a wing cannot possibly provide any
benefit for flight?
George Mivarts objection to Darwin (1871) the
incompetency of natural selection to account for
the incipient stages of useful and complex
structures
9
Risky predictions
To suppose that the eye with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of
light, and for the correction of spherical and
chromatic aberration, could have been formed by
natural selection, seems, I freely confess,
absurd in the highest degree
(CD, Origin, Sixth Edition, 1872, p.)
10
Mivarts objection answer 1 GRADUAL
IMPLEMENTATION
When it was first said that the sun stood still
and the world turned round, the common sense of
mankind declared the doctrine false but the old
saying of Vox populi, vox Dei, as every
philosopher knows, cannot be trusted in science.
Reason tells me, that if numerous gradations from
a simple and imperfect eye to one complex and
perfect can be shown to exist, each grade being
useful to its possessor, as is certainly the
case if further, the eye ever varies and the
variations be inherited, as is likewise certainly
the case and if such variations should be useful
to any animal under changing conditions of life,
then the difficulty of believing that a perfect
and complex eye could be formed by natural
selection, though insuperable by our imagination,
should not be considered as subversive of the
theory (p. 144)
11
Mivarts objection answer 2 FUNCTIONAL SHIFT
Natural selection might specialise, if any
advantage were thus gained, the whole or part of
an organ, which had previously performed two
functions, for one function alone, and thus by
insensible steps greatly change its nature.
Again, two distinct organs, or the same organ
under two very different forms, may
simultaneously perform in the same individual the
same function, and this is an extremely important
means of transition. In all such cases one of the
two organs might readily be modified and
perfected so as to perform all the work, being
aided during the progress of modification by the
other organ and then this other organ might be
modified for some other and quite distinct
purpose, or be wholly obliterated (p. 147)
12
Mivarts objection answer 12 PRE-ADAPTATION
The illustration of the swimbladder in fishes is
a good one, because it shows us clearly the
highly important fact that an organ originally
constructed for one purpose, namely, flotation,
may be converted into one for a widely different
purpose, namely, respiration. The swimbladder
has, also, been worked in as an accessory to the
auditory organs of certain fishes. All
physiologists admit that the swim bladder is
homologous, or "ideally similar" in position and
structure with the lungs of the higher vertebrate
animals hence there is no reason to doubt that
the swim bladder has actually been converted into
lungs, or an organ used exclusively for
respiration (p. 148)
Flexibility Redundancy
Structure/Function
13
PRE-ADAPTATION (Ernst Mayr) continuity in
differential reproductive success, not in the
same function

• CURRENT USE not always gt HISTORICAL ORIGIN
• SUB-OPTIMALITY of adaptation (CONSTRAINTS)

Natural selection tends only to make each
organic being as perfect as, or slightly more
perfect than, the other inhabitants of the same
country with which it comes into competition. And
we see that this is the standard of perfection
attained under nature. Natural selection will not
produce absolute perfection, nor do we always
meet, as far as we can judge, with this high
standard under nature (p. 163)
I am convinced that Natural Selection has been
the most important, but not the exclusive, means
of modification (CD, Origin, p. 4)
14
XX Century vulgata ADAPTATIONISM (strong)

• A) power of natural selection as an optimizing
  agent, at the genetic level
• - B) breaking an organism into unitary "traits"
  and proposing an adaptive story for each one
  considered separately
• - C) Trade-offs among competing selective demands
  exert the only brake upon perfection
  (non-optimality is thereby rendered as a result
  of adaptation as well)

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A PANGLOSSIAN PARADIGM?
(Gould-Lewontin, 1979)
Criticisms

• 1) SELECTION ACTING ON CONSTRAINTS
• 2) DISTINCTION BETWEEN CURRENT UTILITY AND
  REASONS FOR ORIGIN
• 3) INFALSIFICABILITY OF ADAPTIVE STORIES
• 4) failure to consider adequately such competing
  themes as random fixation of alleles, production
  of non-adaptive structures by developmental
  correlation with selected features (allometry,
  pleiotropy, material compensation, mechanically
  forced correlation) and current utility as an
  epiphenomenon of nonadaptive structures.

- Coming back to Darwin
16
Daniel Dennetts Reverse Engineering (Darwins
dangerous idea)
EXPLANATORY ADAPTATIONISM

• Not only adaptations in nature, but adaptations
  explain evolution
• Adaptive problems in the past adaptations
  evolved to solve them
• Evolutionary problem-solving based on the
  universal darwinian algorithm

Hypothesis of optimality
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QUIRKY FUNCTIONAL SHIFT
Exaptation a missing term in the science of form
(S.J. Gould, E. Vrba, 1982)
APTATION any features now contributing to
fitness - AD-APTATION a feature directly crafted
for a current utility by natural selection -
EX-APTATION a feature coopted for a current
utility following an origin for a different
function, or for not function at all.
Exaptation character useful (aptus) as a
consequence of (ex) its form
18
1941 - 2002
To paraphrase Mr. Huxley in a famous context, I
am prepared to go to the stake for exaptation
for this new term stands in important contrast
with adaptation, defining a distinction at the
heart of evolutionary theory, and also plugging
an embarassing hole in our previous lexicon for
basic processes in the history of life (S.J.
Gould, The Structure of Evolutionary Theory,
2002, p. 1234)
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THE END OF ADAPTATIONISM - A NEW TAXONOMY OF
FITNESS (Gould-Vrba 1982 Gould, 2002)
Natural Selection shapes the character for
a current use
Adaptation
A character, previously shaped by natural
selection for a particular function (an
adaptation), is coopted for a new use
Exaptation 1 (by cooptation) preadaptation
A character whose origin cannot be ascribed to
the direct action of Natural Selection (a
non-aptation), is coopted for a current use
Structural Effect
Exaptation 2 (by nonaptation)
20
Ichthyosaurus
21
TAXONOMY OF THE EXAPTIVE POOL
as structural basis of
evolvability in lifes history
(S.J. Gould, 2002)
A Inherent potentials (unexploited) B
Available things (spandrels) B1) As
architectural consequences (structural and
non-adaptive origin) B2) As
historical unemployments (historical,
non-adaptive origin) (ex. vestigia)
B3) As invisible introductions (historical,
non-adaptive origin) (ex. neutral
drifts, founder effects)
22
The Spandrels of San Marco
A character whose origin cannot be ascribed to
the direct action of Natural Selection (a
non-aptation), could be coopted for a current use
23
Imperfections in human physiology

• Due to
• Previous adaptations
• Selective trade-offs
• Exaptations
• Spandrels and vestigia

24
The Five Percent of a Wing Problem - 2011
Archaeopteryx lithographica
Solnhofen, 1861 (Richard Owen)
ADAPTIVE STORIES? Protowings? Transitional stages?
25
Dinosaurs with plumage?
1996-2006 AMNH of NY
A) Arboreal Theory (for gliding in tree-dwelling
ancestors) B) Cursorial Theory (from running
terrestrial dinosaurs) C) Wing-assisted incline
running in avian ancestors (Dial, Randall, Dial,
BioScience, 56, n. 5, May 2006) Anyway
Exaptation (type 1) of avian flight
Velociraptor mongoliensis with Mononykus olecranus
26
A firm step from water to land (Nature, 440,
April 2006)
Tiktaalik roseae Ellesmere Island, Nunavut,
Arctic Canada (Shubin, Daeschler, Jenkins,
Nature, 440, 2006)
Tetrapods
359 M
Single intermediate fossil? Missing link?
365 M
What is the right pattern for vertebrate
transition from water to land?
Fishes
385 M
Classic picture DevonianCarboniferous LINEAR
ANAGENESIS?
27
Cladogram of the pectoral fins of taxa on the
tetrapod stem
Life in shallow water

• Multiple adaptive solutions (different
  combinations of retained and modern
  characters)
• Exaptation fins-limbs
• Not always the present is the key for the past
  (Henry Gee)

28
EVO-DEVO HOX-MUTATIONS IN PHYLOGENY
- Same Hox genes for the entire animal kingdom
- Nat. Selection and Dev. Constraints
- Traits without adaptation (structural effects)
Evolution and bricolage functional shifts and
cooptations
29
Extensive application of exaptation today

• Palaeontology (primary/secondary adaptations)
• Evo-Devo (selection on developmental
  constraints)
• Genetics (molecular cooptations symbioses)
• Multilevel selection (adaptations at one level
  could be exaptations at another)
• Niche construction (the active role of
  organisms shaping the frame of selective
  pressures triggers for new niches)
• Evolution of unselfish behaviours (selective
  triggers and then exaptations or exaptations and
  then selective reinforcement)
• Human evolution (evolution of mind cultural
  evolution)
• Evolutionary psychology (where the strong
  adaptationist approach is more and more failing)
• Theoretical biology and complexity (adjacent
  possible)

30
What exaptation does not mean

• A CONFUTATION OF THE AGENCY OF NATURAL SELECTION
  IN EVOLUTION, but a) trade-offs between
  functions and structures b) non-adaptive
  structures.
• 2) A BREAK IN THE CONTINUITY OF EVOLUTIONARY
  PROCESSES (it could allow major and rapid
  novelties, but without statements about
  saltations in evolution)
• 3) THE AD HOC HYPOTHESIS WHEN ALL THE OTHER
  ONES FAILED (exaptation needs observative and
  experimental supporting data)
• 4) A UNIVERSAL EVOLUTIONARY PROCESS (but a
  prominent pattern in a pluralistic framework of
  evolutionary processes)

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AN EXTENDED NEO-DARWINIAN SYNTHESIS

Understanding the phenotype (phenotypic
plasticity, macroevolution, origins of form)
Advances of Neo-Darwinism (population genetics,
drift, speciation)
Evo-Devo (innovation, modularity,
evolvability)
New views on inheritance (epigenetic inherit.,
niche inherit.)
Selection and adaptation reformed (neutralism,
multilevel selection, niche construction,
exaptation)
The evolution of the structure of Neo-Darwinian
Research Program