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Chapter 5
The Forces of Evolution And The
Formation of Species
Copyright © 2013 Pearson Education, Inc. All rights reserved.
How Evolution Works
• Where Does Variation Come From?
– Mutations
• Point mutation
• Chromosomal mutation
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How Evolution Works (cont’d)
• How Natural Selection Works
– Phenotypes in environments
– Changes in gene frequencies
– Directional Selection/ Stabilizing Selection
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How Evolution Works (cont’d)
• Other Ways By Which Evolution Happens
– Gene Flow: movement of genes between populations
– Genetic Drift: random changes in gene frequency in a
population
– Founder Effect: genetic bottleneck
– Sexual Selection: Differential reproductive success
within one sex of any species
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Classification and Evolution
• Taxonomy and Speciation
– Systematics: branch of biology that describes
organismal variation (what used to be called
taxonomy)
– Homology: the notion that similar features in two
related organisms look alike because of a shared
evolutionary history
– Analogy: the notion that similar features in two
unrelated organisms look alike because of adaptations
to similar functions. (Convergent (parallel) evolution)
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Classification and Evolution (cont’d)
– Cladistics
• Cladograms
– Phenetics: numerical taxonomy
What is a Species?
• An interbreeding group of animals or plants
that are reproductively isolated through
anatomy, ecology, behavior, or geographic
distribution from all other such groups
(Mayr, 1942)
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Classification and Evolution (cont’d)
Species Concepts
• Biological species concept
• Evolutionary species concept
• Ecological species concept
• Recognition species concept
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Classification and Evolution (cont’d)
• Reproductive Isolating Mechanisms (RIMs)
– Any factor that prevents a male and female of two
different species from hybridizing
• Premating RIMs
• Postmating RIMs
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Classification and Evolution (cont’d)
• Premating RIMs
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Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical incompatibility
• Postmating RIMs
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Sperm-egg incompatibility
Zygote inviability
Embryonic or fetal inviability
Offspring inviability
Offspring sterility
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Classification and Evolution (cont’d)
• The Origin of Species: how species are formed
– Anagenesis (whole group, no branching)
– Cladogenesis (splitting events; branching)
– Allopatric speciation (geographic isolation)
– Parapatric speciation (separate habitats)
– Sympatric speciation (form of anagenesis)
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Classification and Evolution (cont’d)
• The Tempo of Speciation
– Gradualism
• Darwinian
• Gaps?
• Macroevolution
– Punctuated equilibrium
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Classification and Evolution (cont’d)
• Adaptation
(Is everything adaptive?)
Adaptations are evolved phenotypic traits that
increase an organism’s reproductive success
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Classification and Evolution (cont’d)
Hardy-Weinberg Equilibrium
(p + q)2 = p2 + 2pq + q2 = 1
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Levels of Selection
• Group selection
• Inclusive Fitness
– Behavioral ecology
• Kin selection
• Coefficient of relatedness rb > c
– Hamilton’s Rule
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