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BIO120H1 Chapter Notes -Mutationism, Common Descent, Ginkgo

2 pages1835 viewsFall 2012

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James Thomson

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Chapter 1 What is Evolution?
Paley argued that the existence of well adapted organisms was similar to the existence of a watch there is a
designer just as there is a watchmaker
The theory of evolution: life in earth evolved gradually beginning with one primitive species that lived more than 3.5
billion years ago - it branched over time, resulting in new and diverse species; the mechanism for most of evolutionary
change is natural selection
- Evolution
- Gradualism
- Speciation
- Common ancestry
- Natural selection
- Other mechanisms of evolutionary change
Species undergoes genetic change over time due to changes in the DNA, which originate as mutations
Theory does not predict that species will be constantly evolving or how fast they evolve
Takes many generations to produce a substantial evolutionary change
Strong natural selection leads to fast evolutionary change paces are dependent on evolutionary pressures
Speciation is the evolution of one species into two
different groups that can‟t interbreed
- Group was split, and over time, developed
The common ancestor “X” between species is called
the missing link
Vast majority of species go extinct, others can live
millions of years without speciation (gingko trees)
Common Ancestry
Flip of speciation: all species trace back to a
common ancestor. Those that are modernly more closely
related have more recent common ancestors
Such nested arrangement only arrives with objects
that have arisen from evolutionary processes
Nowadays, by comparing DNA, we see that species
with similar DNA are more closely related (i.e. they have
common ancestors that lived more recently
Natural Selection
When there are differences in one species, „good genes‟ will lead to higher reproduction rates
- Creates species that are best adapted for their habitats
Natural selection cannot produce from scratch it can only alter what‟s already existent
- Creates „fitter‟ not the „fittest‟
Because natural selection must work with organism as a whole, there are tradeoffs
New species are created by mutations of old species
Mutationism: new groups should arise instantly from old one, without transitions in fossil records
- E.g. the first bird came from a reptile egg
Mystical and teleological force: organisms have an „inner drive‟ that made them change
Testing the Theory
Two types of evidence: testable predictions and retrodictions
Testable predictions: predicts what we should find in living or ancient species when studied
- Find evidence of evolutionary change in fossils
- Find speciation in fossils
- Species should show genetic variation for many traits
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