Download P(O/H 2 )

Lecture 3
1.
2.
3.
4.
Leftovers…
Kinds of evidence and reasoning at work in
evolutionary theorizing.
Anticipating next readings (by A.J. Ayer and
Karl Popper) and topic.
Introduction to The Elegant Universe (film
today)
Leftovers
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The evidence for subatomic particles – and
the same turns out to be true for evidence for
evolutionary processes and events – is
indirect
We draw inferences from what we can
observe to what we cannot
Leftovers
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We bring metaphysical or ontological
assumptions about what there is and about
causes at work
We bring epistemological assumptions about
the nature and limits of our knowledge in a
given domain – including what justifies the
way we are reasoning, our technology, etc.
We bring aesthetic (and quasi-metaphysical)
assumptions: e.g., that the universe is simple
or elegant
Leftovers
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For a great episode on the discovery of and
years of work to put Ardi together:
www.pbs.org/newshour/videos
For a great read every Tuesday:
www.nytimes.com: Science Times
How did Lucy get her name?
Evolutionary theorizing
The late great Stephen Jay
Gould
(1941-2002)
Harvard paleontologist and
evolutionary theorist
One of the strongest defenders
of Darwin and evolutionary
theory
One of the strongest critics of
some aspects of
evolutionary theory.
Natural Selection

Darwin’s “great discovery”
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A mechanism by which evolution could occur.
Similar to the revolution that brought us “Continental Drift”
given the mechanism of “Plate Tectonics” …
What it is…
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1. There is intra-species variation.
2. There is a struggle for existence.
3. If some variation provides an advantage (however small…)
in terms of survival and/or reproductive success, those
organisms with it will tend to survive better and reproduce
more successfully and tend to pass on the trait to their
offspring.
The Likelihood Principle
O: an observation or set of observations
H: a hypothesis proposed as an explanation of O
The likelihood principle asks
“What is the likelihood of O (observations) given
H (hypothesis)?”
P(O/H)
NOT “What is the probability of H given O?
P(H/O)
The Likelihood Principle
O: There is noise in the attic.
H: Gremlins are bowling in the attic.
“What is the likelihood of O given H?”
P(O/H)
VERY HIGH!
“What is the probability of H given O?
P(H/O)
VERY LOW (if any probability at all)!
Paley’s argument from design
O: Organisms are perfectly fit relative to their
environments, and their parts (e.g., eyes) are
perfectly designed for their functions.
 H1: Organisms and their parts were produced by
a Designer.
 H2: Organisms and their parts are the result of
random, physical processes.
 “Obviously”, Paley concluded,
P(O/H1) >> P(O/H2)
 The likelihood of O is much higher if H1 than if
H 2.

Paley’s reasoning updated…
O: Organisms are perfectly fit to their environments and
their parts (e.g., eyes) are perfect designed for their
functions.
No. It turns out there are many imperfections, and a
change in environment can easily wipe out a population
or species however well suited they were to an earlier
environment
H1: All was produced by a Designer
H2: All are the results of random, physical changes
Paley could only think of two possibilities but now we
have:
H3: Natural selection, which doesn’t require supernatural
intervention and is also not random.
Paley’s reasoning updated…
 Not
random?
 After
all, mutations are often random… and
they underlie
phenotypic/morphological/behavioral
change…
 True, but NS is not itself a random process.
 Consider it to be an algorithm…
 Like long division?
 No.
 More like an elimination tournament in tennis.
The Panda’s Thumb
O: the panda’s “thumb” (TPT) and what it actually
is (an enlarged wrist bone)
H1: TPT came about through natural selection: the
(blind) tinkering with available parts that gave
those ancestors with it an advantage and, thus,
the trait spread.
H2: TPT was designed by perfect engineer.
Gould:
P(O/H1) >> P(O/H2)
The Panda’s Thumb
Gould: P(O/H1) >> P(O/H2)
What is the evidence?
Comparative anatomy:
Both the radial sesamoid, which in its elongated
form constitutes this false “digit”, and the
relevant musculature that gives the digit its
relative rigidness and relative flexibility, are
common to other species, including other bears.
The (perhaps single) genetic change producing a
larger radial sesamoid, would given their spatial
locations, force the change in the musculature.
The Panda’s Thumb
Gould: P(O/H1) >> P(O/H2)
What is the evidence?
Comparative anatomy:
In many other bears, the radial sesamoid is also
somewhat enlarged.
This is by no means a “perfect” thumb (it is neither
opposable nor able to manipulate objects by
itself).
It is, rather, the result of tinkering with parts
available to the panda’s ancestors.
Darwin’s orchids
Non-sexual reproduction is cheaper, but sexual
reproduction insures that an organism’s progeny
are varied (and thus will have a better chance of
survival if conditions change).
 From the same relatively primitive petal of its
ancestor, varieties of orchids have different
“contraptions” for insuring cross-pollination
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QWERTY PHENOMENA
Like the arrangements of the keys on a keyboard,
QWERTY phenomena are phenomena that show
signs of history: a history of R&D (research and
development) using what’s available, and limited
or directed by contingencies and constraints…
Francis Crick called them “frozen accidents”
QWERTY phenomena abound in the organic
world.
QWERTY PHENOMENA
In our case:
wisdom teeth, the blank spot in the center of each of our
eyes, the possibility of retinal detachment, our “tail
bone”, our back problems, (perhaps) our appendix,
relatively short gestational period, male nipples….
Other cases:
blind fish in dark caves, with eyes that don’t function,
but whose ancestors had functioning eyes
blind fish in dark caves, without eyes, whose ancestors
did have eyes
“toothless” species of whales in which embryos have
teeth and lose them during natal development
Part III
Next readings
What distinguishes science from pseudo-science?
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Logical Positivism:
 Science
should and must be a positive force for
human wellbeing

Logical Empiricism (same movement):
 Working
to identify the role of logic and that of
experience in the workings of genuine science.

Both emphases underlie the work to identify the
criterion (or criteria) that demarcate science (i.e.,
distinguish it from) “pseudo-science” and “nonscience”.
What distinguishes science from pseudo-science?
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A.J. Ayer (first reading)
A Logical Positivist (aka Logical Empiricist)
His target as “pseudo-science” (“nonsense” or
without meaning): statements that cannot be verified
by experience.
He terms them ‘metaphysical’ but as he uses it, the
term has a different sense than that we discussed as
“philosophical metaphysics or ontology”
It concerns efforts to identify a reality that allegedly
“transcends” our experiences.
His criterion: verifiability
What distinguishes science from pseudo-science?
Sir Karl Popper (second reading)
 Rejects “Verifiabiliity” (too many pseudoscientific theories can be claimed to “fit” the
evidence)
 Offers “Falsifiability” as an alternative criterion
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Part IV
The Elegant Universe
The Elegant Universe
Note the title! The universe is “elegant”!
 String Theory: everything there is is made of
tiny vibrating strings of energy… (not some
one or more particles!)
 Goals: a grand theory of everything!
 Unifying physics
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 Resolving
the contradictions between the 2 pillars
of contemporary physics:
 Quantum theory
 Relativity