How Evolution Works
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Transcript How Evolution Works
How Evolution Works
Genes, Germs, Geography and Sex
Step 1: Raw Material
Genes are raw material
Forms of genes = alleles
Polygenic vs. Single gene trait
Selection on a Single Gene:
The Peppered Moth
Before Industrial
Revolution
After Industrial
Revolution
Single gene
controlling a trait
will have only a few
(usually 2 or 3
phenotypes)
Variation and Selection
Variation from two sources
1) New mutations = new allele types
2) Gene shuffling = new allele
combinations
Any change in allele frequency =
Evolution
Peppered Moth Simulation
Polygenic Traits
More than one gene controls a trait
Selection and Changing the
Norm
Most traits are polygenic
The normal trait is the average or
mean in the population
More variation=more selection
Selection will adjust mean
Stabilizing Selection
Disruptive Selection
Can lead to new species
Does Evolution Ever Stop?
YES, but only if the following conditions
are met
1) Random mating
2) Large Population
3) No movement in or out of
population
4) No Mutations
5) No Natural Selection
Hardy Weinberg Equilibrium
How New Species Are Formed
Two populations must become
reproductively isolated
Behavioral Isolation
Groups differ in mating, feeding,
sleep/awake cycles so members of
populations do not meet to mate
Rana aurora (Redlegged frog)
Breeds in fast moving
streams
call
Rana catesbiana
(Common bullfrog)
Breeds in still ponds
call
Geographic Isolation
Geological Time and Evolution
First fossils 3.5 bya
Stromalites
550 mya =
Cambrian Explosion
(by fossil evidence)
Dating Fossil Age
Relative Dating
Radioisotope Dating
Known decay times
of isotopes can be
used
Vestigial Structures
Structures
possessed by
ancestors but no
longer necessary
- whale pelvis
- human coccyx
- human appendix
Extinction and Adaptive
Radiation
Most species cannot
adapt
Those that can
radiate into open
niches
Evolution Patterns
Convergent Evolution
Coevolution