Chapter 24The Origin of

Species

Question?

What is a species? Comment - Evolution theory

must also explain how species originate.

Two Concepts of Species

Morphospecies

Problem Where does extensive

phenotype variation fit?

Two Schools

Biological Species

Key Points

Heaven Scent

an F1 hybrid between 2 species, but sterile.

Speciation Requires:

Reproductive Barriers

Main Types of Barriers

Prezygotic - Types

Habitat Isolation

Behavioral Isolation

Temporal Isolation

Mechanical Isolation

Gametic Isolation

Postzygotic Types

Reduced Hybrid Viability

Reduced Hybrid Fertility

Hybrid Breakdown

Modes of Speciation

Allopatric Speciation

Example

Another Example

Conditions Favoring Allopatric Speciation

Conditions Favoring Allopatric Speciation

Result

Adaptive Radiation

Mechanism

When the Environment Saturates

Sympatric Speciation

Plants

Polyploid Types

Autopolyploid

Allopolyploid

Animals

Gradualism Evolution

Gradualism Predicts:

Problem

Punctuated Evolution

Punctuated Equilibrium

Predictions

Predictions

Possible Mechanism

Comment

Origin of Evolutionary Novelty

Ex - Homeosis

Gene Duplications

Future of Evolution ?

Look for new theories and ideas to be developed, especially from new fossil finds and from molecular (DNA) evidence.

Evolutionary Trends

Evolution is not goal oriented. It does not produce “perfect” species.

Remember – species survive because of their adaptations. They don’t adapt to survive.

Summary

Be able to discuss the main theories of what is a “species”.

Know various reproductive barriers and examples.

Summary

Know allopatric and sympatric speciation.

Be able to discuss gradualism and punctuated equilibrium theories.

Summary

Recognize various ideas about the origin of evolutionary novelties.