1. Speciation Tempo of Speciation
Lack of evolutionary intermediates bothers some people
Traditionally interpreted as incompleteness of fossil record
Two models to explain evolution
Gradualism
Evolution proceeds at constant rate
New species evolve gradually, with distinct intermediate forms
Lack of intermediates in fossil record due to gaps

2. Speciation Tempo of Speciation Punctuated Equilibrium
First proposed in 1972 by Gould & Eldredge
Fossil record accurately reflects evolutionary history
Species evolve relatively rapidly
Long periods of stasis between evolutionary events
Lack of intermediates due to short time over which intermediates persist

3. Fig

4. Speciation Tempo of Speciation Proponents of punctuated equilibrium
Speciation events observed over years, not centuries
Proponents of gradualism
Periods of stasis result from accumulation of mutations without altering phenotype (preserved by fossil record)
Speciation may be reflected in physiology or behavior, which aren’t preserved
Pace of evolution may not be uniform in all instances
Most mutations may accumulate at constant rate without causing speciation
Major mutations may cause rapid speciation

5. Macroevolution Major changes over long periods
Often includes development of novel features
Ex: Increased brain size and upright gait in humans
Ex: Development of feathered, winged birds and mammals from reptiles (no feathers, no mammary glands)
Ex: Complex camera-type eye

6. Limpet
Slit-shell
Nautilus
Squid
Murex
Fig