Geology 105: History of Life
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Lecture Notes
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Introduction and Overview
Fossils 1
Fossils 2
Geologic Principles
Relative Time
Absolute Time
Diversity of Life
Evolution
Evolution and Diversity
Rates of Evolution
Extinction
Plate Tectonics
Origin of the Earth
Origin of Life
Early Precambrian (Archean) Life
Late Precambrian (Proterozoic) Life
The Cambrian Explosion
Early Paleozoic Life
Late Paleozoic Marine Life
The Invasion of Land 1
The Invasion of Land 2
The Permo-Triassic Extinctions
Mesozoic Marine Life
Mesozoic Terrestrial Life
Cretaceous-Tertiary Extinctions
Cenozoic Life

Rates of Evolution

Lecture 10
2/27/98

Introduction
 Today, we continue our investigation of evolution by focusing on the rates of speciation.
 We will use this discussion as a back drop for looking at the Cambrian Explosion
Key Points
 Earths history shows periods of slow evolution punctuated by periods of rapid evolution
 The rate of evolution is dependent on at least three different things
 rate of mutation
 rates of selection
 rate of environmental change
 Once structures and/or behaviors evolve it is difficult to change them radically
The Cambrian Explosion
 Seven major animal groups appear in short period of geologic time
 Additional groups appear, but do not survive long
 By comparison, the rest of the earths history is one of slow evolution
 Why the explosion?
Speciation
 Speciation typically occurs when a small population is isolated from the main gene pool
 Selection that each population experiences varies.
 Over time genetic variability between the two populations grows to a point of where they can no longer interbreed
Rate of Speciation
 Two primary factors govern the rate of speciation
 Mutation Rates
 a positive force, providing new genetic material
 Selection Rates
 a negative force, removing mutations that are not beneficial
 Competition
 Selection can be viewed as competition between individuals
 Competition between members of the same species
 Competition between members of different species
Speciation patterns
 "Normal"
 new species form in a "filled" environment
 leads to normal rates of evolution
 Explosive
 new species form in an empty environment
 competition between species is minimal but increases with time.
 differences are preferentially selected for
The role of environmental change
A look back at the Cambrian Explosion
 Development of the SuperWorms
 Oxygenation of the upper sediments
 Escape to the surface (Base of the Cambrian)