Download Adaptation, perfection, and function

Adaptation,
optimality, and
function
Adaptive vs. Adaptation
•• Traits
Traits are
are adaptive
adaptive ifif they
they are
are beneficial
beneficial to
to an
an
organism
organism in
in the
the here
here and
and now
now
•• Traits
Traits are
are adaptations
adaptations ifif they
they are
are the
the product
product of
of
natural
natural selection
selection
–– They
They benefited
benefited the
the ancestors
ancestors of
of the
the organism
organism and
and
figured
figured in
in their
their selection
selection
•• All
All combinations
combinations are
are possible
possible
–– Some
Some traits
traits are
are both
both adaptive
adaptive and
and adaptations
adaptations
–– Some
Some traits
traits are
are neither
neither adaptive
adaptive nor
nor adaptations
adaptations
–– Some
Some traits
traits are
are adaptive
adaptive but
but not
not adaptations
adaptations
–– Some
Some traits
traits are
are not
not adaptive
adaptive but
but adaptations
adaptations
Biological niches change
•• Traits
Traits that
that were
were adaptive
adaptive may
may cease
cease to
to be
be
–– Vestigial
Vestigial organs
organs such
such as
as the
the appendix
appendix
•• Traits
Traits that
that were
were adaptations
adaptations may
may come
come to
to serve
serve aa
different
different adaptive
adaptive role
role
–– Preadaptations
Preadaptations or
or exaptations
exaptations
Teleology and functions
•• For
For Aristotle,
Aristotle, natural
natural phenomena
phenomena were
were teleological
teleological
–– Events
Events happened
happened to
to produce
produce results
results
•• The
The scientific
scientific revolution
revolution seemed
seemed to
to remove
remove purpose
purpose
from
from the
the world
world
–– Events
Events happened
happened solely
solely because
because of
of prior
prior causes
causes
•• But
But teleological
teleological talk
talk is
is preserved
preserved in
in the
the language
language of
of
functions
functions
–– The
The heart’s
heart’s function
function is
is to
to pump
pump the
the blood
blood
–– The
The kidney’s
kidney’s function
function is
is to
to filter
filter and
and remove
remove waste
waste
–– The
The function
function of
of the
the ribosome
ribosome is
is to
to synthesize
synthesize
proteins
proteins
Functions and natural selection
•• One
One strategy:
strategy: explain
explain the
the function
function of
of something
something in
in
terms
terms of
of what
what itit was
was selected
selected for
for
–– Treat
Treat itit as
as an
an adaptation
adaptation
–– Function
Function explained
explained etiologically
etiologically
•• Another
Another strategy:
strategy: explain
explain the
the function
function of
of something
something in
in
terms
terms of
of what
what role
role itit is
is playing
playing today
today
–– Treat
Treat itit as
as adaptive
adaptive
–– Function
Function treated
treated as
as aa propensity
propensity
•• Third
Third alternative:
alternative: explain
explain the
the function
function in
in terms
terms of
of the
the
contribution
contribution something
something makes
makes to
to an
an operating
operating system
system
–– Detach
Detach function
function from
from natural
natural selection
selection
–– Function
Function in
in terms
terms of
of contributions
contributions to
to the
the
operations
operations of
of aa mechanism
mechanism
When is a trait an adaptation?
•• To
To be
be an
an adaptation,
adaptation, aa trait
trait must
must have
have figured
figured in
in the
the
reproductive
reproductive success
success of
of ancestors,
ancestors, thereby
thereby providing
providing
an
an explanation
explanation of
of the
the presence
presence of
of the
the trait
trait in
in current
current
organisms
organisms
•• How
How common
common are
are adaptations?
adaptations?
–– Adaptationism:
Adaptationism: the
the default
default assumption
assumption when
when
identifying
identifying aa trait
trait is
is that
that itit is
is an
an adaptation
adaptation to
to some
some
selection
selection forces
forces
•• Heuristic
Heuristic for
for evolutionary
evolutionary biology—find
biology—find the
the
selection
selection forces
forces which
which selected
selected the
the trait
trait and
and
made
made itit an
an adaptation
adaptation
–– Alternative:
Alternative: only
only some
some traits
traits are
are adaptations
adaptations
Adaptationism: Three accounts
•• Empirical
Empirical adaptationism
adaptationism
–– Most
Most biological
biological traits
traits are
are adaptations
adaptations
•• Natural
Natural selection
selection is
is the
the primary
primary shaper
shaper of
of the
the
traits
traits of
of organisms
organisms
•• Explanatory
Explanatory adaptationism
adaptationism
–– Apparent
Apparent design
design is
is biology’s
biology’s central
central problem
problem and
and
natural
natural selection
selection is
is the
the fundamental
fundamental answer
answer
•• Methodological
Methodological adaptationism
adaptationism
–– As
As aa strategy,
strategy, view
view traits
traits as
as adaptations—optimal
adaptations—optimal
designs
designs promoted
promoted by
by natural
natural selection
selection
Spandrels of San Marco
•• Spandrels
Spandrels are
are an
an
inevitable
inevitable consequence
consequence
of
of mounting
mounting aa dome
dome on
on
top
top of
of rounded
rounded arches
arches
•• Once
Once spandrels
spandrels existed,
existed,
they
they became
became places
places on
on
which
which to
to present
present art
art
•• BUT,
BUT, they
they were
were not
not
included
included in
in the
the design
design as
as
aa place
place to
to put
put art
art
Gould and Lewontin’s
Critique of Adaptationism
•• Traits
Traits might
might be
be adaptive
adaptive without
without being
being adaptations
adaptations
•• Traits
Traits can
can evolve
evolve without
without being
being adaptations
adaptations
–– As
As consequences
consequences of
of other
other traits
traits that
that are
are adaptive
adaptive
–– As
As conserved
conserved traits
traits due
due to
to existing
existing bauplan
bauplan
–– As
As product
product of
of developmental
developmental constraints
constraints
•• Adaptationist
Adaptationist explanations
explanations run
run the
the risk
risk of
of being
being justjustso
so stories
stories
–– Typically
Typically are
are not
not empirically
empirically vindicated
vindicated
Optimizing and Game Theory
•• Find
Find the
the item
item amongst
amongst all
all the
the alternatives
alternatives that
that
optimally
optimally meets
meets stated
stated criteria
criteria
•• Search
Search the
the state
state space
space for
for the
the best
best solution
solution
–– Search
Search costs
costs resources,
resources, so
so must
must factor
factor in
in the
the cost
cost
of
of searching
searching
–– Search
Search until
until reach
reach aa maximum
maximum value
value of
of
•• Outcome
Outcome –– cost
cost of
of searching
searching
•• Evolution
Evolution interpreted
interpreted as
as aa search
search for
for optimal
optimal
solutions
solutions
–– Generate
Generate many
many variants
variants
–– Those
Those that
that solve
solve the
the problem
problem best
best leave
leave more
more
offspring
offspring
–– Win
Win the
the competition
competition in
in the
the long-run
long-run
Satisficing: Herbert Simon
••
••
••
Human
Human rationality
rationality is
is bounded
bounded
Set
Set aa criterion
criterion for
for aa decision
decision being
being “good
“good enough”
enough”
Search
Search until
until an
an option
option is
is found
found that
that meets
meets this
this
criteria,
criteria, then
then stop
stop
•• Apply
Apply to
to nature:
nature:
–– “It
“It appears
appears probable
probable that,
that, however
however adaptive
adaptive the
the
behavior
behavior of
of organisms
organisms in
in learning
learning and
and choice
choice
situations,
situations, this
this adaptiveness
adaptiveness falls
falls far
far short
short of
of the
the
ideal
ideal ‘maximizing’
‘maximizing’ postulated
postulated in
in economic
economic theory.
theory.
Evidently,
Evidently, organisms
organisms adapt
adapt well
well enough
enough to
to
‘satisfice’;
‘satisfice’; they
they do
do not,
not, in
in general,
general, ‘optimize’.”
‘optimize’.”
Canalization: C. H.
Waddington
•• State
State space
space of
of possible
possible designs
designs
•• Development
Development is
is aa trajectory
trajectory
through
through such
such aa space
space
•• Options
Options are
are limited
limited
–– Once
Once aa given
given decision
decision is
is
made
made in
in the
the development
development of
of
an
an organism,
organism, the
the range
range of
of state
state
space
space to
to which
which itit can
can go
go is
is
constrained
constrained
•• Development
Development is
is canalized—it
canalized—it is
is limited
limited to
to the
the options
options
available
available in
in the
the particular
particular canal
canal itit has
has entered
entered
Boolean Attractor Networks:
Stuart Kauffman
A
B
C
B
C
A
0
0
0
0
1
0
1
0
0
1
1
1
000
010
001
100
A
C
B
A
B
C
0
0
0
0
0
0
0
1
1
0
1
1
1
0
1
1
0
1
1
1
1
1
1
1
110
011
101
111
Generative Entrenchment:
William Wimsatt
•• Three
Three designs
designs for
for aa lock
lock
–– Standard
Standard (no
(no clues
clues for
for any
any partial
partial answers)
answers)
10 =
»» .5
.5 xx 10
1010
= 5,000,000,000
5,000,000,000 tries
tries to
to crack
crack
–– Cracker’s
Cracker’s delight
delight (each
(each wheel
wheel clicks
clicks when
when in
in
the
the right
right position)
position)
»» 55 xx 10
10 == 50
50 tries
tries to
to crack
crack
–– Developmental
Developmental lock
lock (Cracker’s
(Cracker’s delight
delight when
when
solved
solved from
from left
left to
to right,
right, otherwise
otherwise clicks
clicks are
are
misleading)
misleading)
Ernst von Baer
»» Wheels
Wheels to
to the
the right
right are
are dependent
dependent on
on
settings
settings of
of wheels
wheels to
to the
the left
left
Testing for adaptations
•• Even
Even ifif the
the critics
critics of
of adaptationism
adaptationism are
are right,
right, there
there are
are
adaptations
adaptations
•• Challenge:
Challenge: how
how to
to test
test the
the claim
claim that
that aa trait
trait is
is an
an
adaptation
adaptation
–– Both
Both the
the selection
selection forces
forces and
and alternative
alternative traits
traits are
are
usually
usually hypothesized
hypothesized
–– Seek
Seek best
best explanation
explanation for
for the
the observed
observed
phenomena
phenomena
•• Problem:
Problem: to
to many
many free
free parameters
parameters
–– Can
Can always
always fit
fit the
the phenomena
phenomena
•• Using
Using the
the comparative
comparative method
method to
to achieve
achieve further
further
constraint
constraint
Comparative Method
•• Comparisons
Comparisons with
with other
other branches
branches in
in
the
the phylogenetic
phylogenetic tree
tree can
can provide
provide
evidence
evidence regarding
regarding aa claims
claims as
as to
to
what
what has
has been
been selected
selected (and
(and so
so is
is an
an
adaptation
adaptation
•• Do
Do the
the proposed
proposed selection
selection events
events fit
fit the
the
phylogenetic
phylogenetic pattern?
pattern?
–– IfIf two
two alternatives
alternatives (one
(one vs.
vs. two
two horned
horned
rhinoceroses)
rhinoceroses) are
are both
both evolutionarily
evolutionarily stable
stable
strategies,
strategies, then
then neither
neither can
can be
be invaded
invaded by
by the
the other
other
•• But
But the
the one-horned
one-horned species
species evolved
evolved from
from the
the
two-horned
two-horned one
one
•• Are
Are there
there regular
regular relationships
relationships between
between changes
changes in
in
traits
traits and
and changes
changes in
in habitat
habitat in
in aa lineage?
lineage?