The Evidence for Evolution

• Species have changed through time and are related by descent from a common ancestor

• The primary mechanism of Evolutionary Change is Natural Selection

Darwin’s Theory of Evolution by 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

4. Each variant has a characteristic survival and/or reproductive success

An individual’s ability to survive and reproduce is called “fitness”

1 starfish --> 1079 offspring in 16 years

Darwin provided a mechanism for evolutionary change --> Natural Selection

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 exampleSelection 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

Tribulus: large very hard seeds

Most frequent before the drought

Most frequent after the drought

Is there differential survival an/or reproduction among the variants?

1976 (Before the drought)

Average beak depth of the population = 9.2 mm

N = 751

1978 (The survivors)

Average beak depth of the survivors = 10.1 mm

N = 90

The offspring of these survivorsAverage 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

Recently, the species R. pomonella shifted from its native host to introduced, domestic apples (Malus pumila)

Rhagoletis lays its eggs in fruit to develop -->Original host = hawthorn trees

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

How Does Evolution Compare with other Major Scientific Theories such as General Relativity, Atomic Theory, and Gravity?

Is Evolution Weak Science, Good Science, or Great Science?

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 historywith 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 stillunexplained

For Darwinism: heredity explains the similarity between parent andoffspring; 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

Bridging False Dichotomies

How strong is your evidence that grenade is a dud?

Should you pull the pin?

Parties in public controversies often disagree about consequences