The Origin of Species

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Slide 1

The Origin of Species

Speciation, the origin of new species, is at the focal point of Darwin’s evolutionary theory.

Evolutionary theory must explain how new species originate and how populations evolve.

Microevolution consists of adaptations that evolve within a population, confined to one gene pool.

Macroevolution refers to evolutionary change above the species level.

Slide 2

In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth

Slide 3

The Biological Species Concept emphasizes reproductive isolation

Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms.

The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations.

Slide 4

Fig. 24-2

(a) Similarity between different species

(b) Diversity within a species

Slide 5

Gene Flow Between Populations

EXPERIMENT

RESULTS

Example of a gene tree for population pair A-B

Allele

Population

Gene flow event

1

B

B

B

B

5

6

7

2

3

4

A

A

A

Allele 1 is more closely related to

alleles 2, 3, and 4 than to

alleles 5, 6, and 7.

Inference: Gene flow occurred.

Alleles 5, 6, and 7 are more closely

related to one another than to

alleles in population A.

Inference: No gene flow occurred.

Pair of

populations

with detected

gene flow

Estimated minimum

number of gene flow

events to account for

genetic patterns

Distance between

populations (km)

A-B

K-L

A-C

B-C

F-G

G-I

C-E

5

3

2–3

2

2

2

1–2

340

720

1,390

1,190

1,110

760

1,310

Slide 6

Reproductive Isolation = Barriers to Interbreeding

Reproductive isolation is the existence of biological factors (barriers) that impede two different species from producing viable, fertile offspring.

Hybrids are the offspring of crosses between different species.

Reproductive isolation can be classified by whether factors act before or after fertilization.

Slide 7

Prezygotic barriers block fertilization from occurring by: