1

The Origin of Species

Chapter 22

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The Origin of Life

Alexander Oparin and coacervates• Theory that extends evolution back to

the Earth’s beginning to explain how life began.

The Biological Species Concept

• Species – Individuals in the

population can mate and produce fertile offspring

– Individuals in different populations would mate and produce fertile offspring if they came in contact naturally.

3

Liger

4

The Nature of Species

• Two types of speciation:– Sympatric– Allopatric

Within species you also have subspecies.

There are two types:

1.Prezygotic isolating mechanismsoGeographic isolationoEcological isolationoBehavioral isolationoTemporal isolationoMechanical isolation

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Reproductive Isolating Mechanisms

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Behavioral isolation

Breeds Jan - March

Breeds late March - May

Temporal Isolation

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Mechanical Isolation

2. Postzygotic Isolating Mechanisms -

“Processes that prevent hybrid zygotes

from developing into normal, functioning,

fertile adults”.

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Reproductive Isolating Mechanisms

1. How reproductively isolated are the species?

2. Difficult to apply to allopatric populations.

3. Doesn’t apply to asexual species.

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Problems with the Biological Concept

Alternative:

Ecological Species Concept

Geography of Speciation• Speciation is a 2-part process

– Initially identical populations must diverge– Reproductive isolation must evolve to

maintain these differences

10a. b. c.

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Isolated islandpopulation

of kingfishers

Isolated islandpopulation

of kingfishers

Mainlandpopulation

of kingfishers

Mainlandpopulation

of kingfishers

Isolated islandpopulation

of kingfishers

PACIFICOCEAN

NEWGUINEA

Allopatric Speciation

Sympatric speciation

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Speciation

Adaptive Radiation:• “Closely related

species that have recently evolved from a common ancestor by adapting to different parts of the environment”

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Character Displacement:

• “Natural selection favors those individuals that use resources not used by other species”

Adaptive Radiation

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Character Displacement

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Adaptive Radiation and Darwin’s finches

• Ancestors reached these islands before other land birds.

Ground finches Tree finchesVegetarian finch Warbler finches

16

17

The Pace of Evolution

Speciation and Extinction

• Speciation, through time, has surpassed extinction

• Five mass extinctions have occurred.

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• Not all groups are affected equally by mass extinctions.

• Previously dominant groups may perish, changing the course of evolution.

• The 6th extinction is currently underway.

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Speciation and Extinction