Theory of Natural Selection

What are the four postulates of natural selection?

Variation among individuals; variation is heritable; individuals differ in survival/reproduction; reproduction is non-random.

Postulate 1 of natural selection

Individuals vary in an almost infinite number of ways.

Postulate 2 of natural selection

Variation is heritable (traits/genes can be passed on).

Postulate 3 of natural selection

Individuals vary in their success at surviving and reproducing.

Postulate 4 of natural selection

Reproduction is non-random; some individuals leave more offspring than others.

If all four postulates are true for a trait, what happens?

Evolution by natural selection occurs.

What does “postulate” mean?

A basic assumption accepted without proof.

How can Darwin’s finches be used to test Postulate 1?

Measure variation in traits such as beak depth.

What finch trait is commonly measured to show variation?

Beak depth.

What island were most finch studies conducted on?

Daphne Major.

Why was Daphne Major ideal for study?

Researchers could track most individuals over their lifetimes.

How is Postulate 2 tested in finches?

By comparing parent and offspring beak sizes.

What does a positive correlation between parent and offspring traits indicate?

Heritability.

What environmental event tested Postulate 3 in finches?

The 1977 severe drought.

How did the 1977 drought affect seed availability?

Seeds became scarcer and harder.

Which finches survived better during the drought?

Those with larger, deeper beaks.

Why did larger beaks increase survival?

They could crack larger, harder seeds.

How does survival affect lifetime reproduction?

Survivors produce more offspring over their lifetime.

What does Postulate 4 focus on?

Non-random reproduction based on trait differences.

Why is reproduction considered non-random in finches?

Individuals with advantageous traits survive and reproduce more.

Is survivorship alone evolution?

No, evolution requires heritable traits passed to offspring.

Why must traits be heritable for evolution to occur?

Otherwise advantageous traits are not passed on.

What gene is associated with beak morphology in finches?

BMP4 (bone morphogenetic protein 4).

What does BMP4 influence?

Beak shape and depth during development.

What increases heritability of a trait?

More additive genetic variation.

What does “additive genetic variation” mean?

Effects of alleles add together to influence phenotype.

What did 30 years of finch data show?

Evolution can occur rapidly and is not always directional.

Is evolution always progressive?

No.

What is population thinking?

Selection acts on individuals, but evolution occurs in populations.

Does natural selection act on individuals or populations?

Selection acts on individuals.

Does evolution occur in individuals or populations?

Evolution occurs in populations across generations.

What happens if a trait is not heritable?

Selection does not cause evolutionary change.

Natural selection works with what kind of variation?

Only the genetic variation already available.

Does natural selection lead to perfection?

No.

Why doesn’t natural selection lead to perfection?

It is limited by existing variation and trade-offs.

What flatfish example illustrates limits of natural selection?

Asymmetrical flounder vs symmetrical skate.

What fish example shows non-optimal outcomes of selection?

Mosquitofish gonopodium.

What does eye evolution illustrate?

Even partial structures can be favored by selection.

What does “half an eye is better than no eye” mean?

Intermediate forms can still increase fitness.

Do all eyes evolve the same way?

No, different lineages evolve different solutions.

Is natural selection random?

No, it is non-random.

Is mutation random with respect to fitness?

Yes.

Is natural selection goal-directed?

No.

Why is “survival of the fittest” misleading?

It is tautological and uninformative.

How is fitness properly defined?

Reproductive success relative to others.

Is natural selection “for the good of the species”?

No.

Can natural selection favor traits harmful to others?

Yes.

Give an example of harmful traits favored by selection

Cannibalism or increased virulence.

How can altruism evolve under natural selection?

Through kin selection.

What is kin selection?

Behaviors that increase the fitness of relatives.

What is a vestigial structure?

A reduced structure inherited from ancestors.

The human coccyx is an example of what?

A vestigial structure.

Archaeopteryx is a transitional fossil between which groups?

Dinosaurs and birds.

What makes a fossil “transitional”?

It shows a mix of ancestral and derived traits.

In the moth example, what is the agent of natural selection?

Bird predation.

How does environmental change affect selection?

It changes which traits are advantageous.

What does the moth example teach about evolution?

Fitness depends on environment.

If all individuals have low fitness, what does NOT explain it?

Unusually short generation time.

Why can a lack of genetic variation limit evolution?

Selection has nothing to act on.

Why can recent environmental change reduce fitness?

Populations may not yet be adapted.

Why can small population size reduce fitness?

Inbreeding and drift reduce adaptive potential.