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Development of Darwin’s idea

Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

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Page 1: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

Development of Darwin’s idea

Page 2: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation
Page 3: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

An example of natural selection

• The premises• 1. Populations exhibit phenotypic variation.• 2. The phenotypic variation has a genetic component

(can be inherited).• 3. Differential reproductive success among members of

the population.• Survival and reproduction is, on-average, nonrandom

• 4. Phenotypic variation shifts between generations in response to a changing environment.

Page 4: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

Adaptive radiationGalapagos finches

Page 5: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

Medium ground finchGeospiza fortisgeneration time: 4.5 yearslife span c. 16 years

Page 6: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

120 mN = c. 1,200

Research of Peter and Rosemary Grant: 1973 - present

Hot spot

7 cm/yr

4-5 my

2-3 my

1 my

Page 7: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

1: Is the population phenotypically variable?

Geospiza fortis

Page 8: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

2: Is the variation heritable?(heritability: proportion of phenotypic variation due to genetic variation; c. 65%)

Evolution!

Page 9: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

1977: drought130 mm precipitation droppedto 24 mm The base level natural selector

Was there differential survival?

Effect of naturalselection

Page 10: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

1.

2.

3.

The interplay

Seed abundance

Number of finches

The second level natural selectorSeed characteristics of survivingplants

Page 11: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

Had evolution taken place? Significant difference in beak size.

Note: naturalselection is alwaysone generationbehind theexpression of modifiedphenotypes

Page 12: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

Natural selection cannot anticipate future “needs” of a population

• Evolutionary change is based selection in the previous generation.

• 1. Parental population + environment (natural selectors)

• 2. Part of population selected to reproduce• 3. Transmission of heritable characteristics to the

new generation (e.g., size of the beak).– But the change was based on phenotypic variation among

their parents.

Page 13: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

: species originate by divergence from common ancestors

Evolution tends to take a branching form.

Page 14: Development of Darwin’s idea. An example of natural selection The premises 1. Populations exhibit phenotypic variation. 2. The phenotypic variation

Darwin’s 1859 illustration (On the Origin of Species by Means of Natural Selection)