Transcript Evidence for Evolution - University of Indianapolis

The Evidence for Evolution
Darwin’s Theory of Evolution by
Natural Selection
• Species have changed through time and
are related by descent from a common
ancestor
• The primary mechanism of Evolutionary
Change is Natural Selection
Darwin provided a mechanism for
evolutionary change  Natural Selection
1. Individuals within
a population or
species show
variation in some
features
2. There is hereditary
similarity between
parents and their
offspring
Darwin provided a mechanism for
evolutionary change --> Natural Selection
3. In every generation,
more offspring will
be produced than
can survive
1 starfish --> 1079 offspring in 16 years
4. Each variant has a
characteristic
survival and/or
reproductive success
An individual’s ability
to survive and reproduce
is called “fitness”
If the above postulates are met and the
environment remains constant, the
composition of the population/species
will tend towards an increase of the
variant with the highest reproductive
success.
Can selection produce
evolutionary change?
• Hypothesis: Natural selection is the primary mechanism
through which organisms have evolved over long periods
of time
• Prediction: selection can lead to small evolutionary
changes in short periods of time
-artificial selection
-direct observations: Darwin’s finches, Biston
moths, antibiotic resistance in bacteria, herbicide
resistance in weeds, apple maggot flies
Artificial Selection
Biston Moths: a Classic example
Selection in peppered moths in
England by H.B.D. Kettlewell
2 genetically determined
phenotypes: black, mottled white
Prior to 1600 (industrial revolution)
black form approximately 1%
white form approximately 99%
After 1600 (widespread pollution, smoke and soot)
black form approximately 90%
white form approximately 10%
Now (local pollution from smokestacks)
Near Pollution source
Away
black form
50%
10%
white form
50%
90%
An example of Natural Selection in Action:
Galápagos Finches
The case of the medium ground finch
Peter and Rosemary Grant
have been studying the
Galapagos finches
continuously since 1973
Postulate 1: Are populations variable?
Postulate 2: Is some of the variation
among individuals heritable?
Is there an excess of offspring?
In 1977: An extreme drought occurred
Instead of the normal 130mm of rain,
there was only 24mm of rain
Over 20 months, 84% of the population of finches died
Not only did the amount of seed decrease, the type of
seeds available changed as well
Portulaca:
Small soft seeds
Most frequent before the
drought
Tribulus:
large very hard seeds
Most frequent after the
drought
Is there differential survival an/or
reproduction among the variants?
1976 (Before the drought)
1978 (The survivors)
Average beak depth of
the population = 9.2 mm
Average beak depth of
the survivors = 10.1 mm
N = 751
N = 90
The offspring of these survivors
Average beak depth = 9.7 mm
Conclusion: Did evolution occur?
The offspring of the birds that survived the drought were
significantly larger than the population that existed before the drought
Natural selection is continually acting
on the population year after year
Implications of Natural Selection
• Natural selection acts on individuals, but its
consequences occur in populations
• Natural Selection Acts on Phenotypes, but
Evolution consists of changes in gene
frequencies
• Natural Selection is backward-, not forward
looking
Implications of Natural Selection
• Natural Selection acts on existing traits
• Natural Selection does not have a goal nor
is it "progressive”
• Natural Selection acts on individuals, not
groups
Apple Maggot Flies: The
evolution of a new species
Rhagoletis pomonella
Rhagoletis lays its eggs
in fruit to develop -->
Original host = hawthorn trees
Recently, the species R. pomonella shifted from its native host to
introduced, domestic apples (Malus pumila)
Now: two genetically distinct groups
that do not interbreed
The idea of evolution was developed from many
observations of life. It has been tested and challenged
many times and in many ways, and has survived in
great shape.
There are also many independent lines of evidence
which are consistent with evolution as a real process.
There is NO observed evidence against evolution.
Evolution therefore holds the high status of near
certainty.
Conclusion: Evolution is as good
as great science gets!
End
Is Evolution Weak Science, Good Science,
or Great Science?
How Does Evolution Compare with other Major
Scientific Theories such as General Relativity,
Atomic Theory, and Gravity?
How many independent lines of
evidence support the Theory?
-General Relativity is supported by only a few lines
There are three classic tests of General Relativity:
precession of the perihelion of Mercury
gravitational redshift
bending of starlight by gravity
The evidence showing that evolution has
occurred is stronger than the evidence
that shows the planets orbit the sun
If it is a fact that the planets go around the sun…
Then it is a stronger fact that evolution has occurred
How many previously unconnected areas of
knowledge does a theory unite?
Newton connected celestial motion with
that of terrestrial objects
Darwin connected evolutionary history
with Linnaean classification, geographic
patterns of distribution, etc.
If I have been able to see further, it
was only because I stood on the
shoulders of giants.
—Sir Isaac Newton
Darwin was the Newton of Biology
If Nature and Nature's laws lay hid in night:
God said, Let Newton be! and all was light.
—Alexander Pope
How clear are the causal
mechanisms?
Einstein attempted to unite different areas of Physics and explain
the dual nature properties of light
The ultimate causes of Gravity and wave-particle duality are still
unexplained
For Darwinism: heredity explains
the similarity between parent and
offspring; mutation explains
variation --> evolution inevitable?
Einstein was the Darwin of
Physics
Possible Weaknesses of the
Theory?
Does the Theory Explain the Ultimate
Origins of the System it Describes?
Quantum Mechanics --> for the universe
Plate tectonics --> for the Earth
Evolution --> for life on Earth
The answer for all of the above?
No
Is the Theory Widely Understood and
Accepted by the public?
General Relativity and Quantum Mechanics?
e = mc2
Why is evolution so
controversial?
If a Theory is Very Strong Scientifically, does that Mean One
Rationally Must or Even Should Accept it?
Metaphor of the Rusty Hand Grenade and the Idea of Consequences
How strong is your evidence that grenade is a
dud?
Should you pull the pin?
Bridging False Dichotomies
Parties in public controversies often disagree about consequences