Lecture 3. Evolution
Alfred Russel Wallace
“On the Origin of Species
by Means of Natural
Selection, or the
Preservation of Favoured
Races in the Struggle for
Life”
(1859)
Darwin’s Theory of
Evolution
• Variation: There is variation among
the individuals of most natural populations
• Inheritance: Some of that variation is inherited
• Competition: Populations tend to produce more
offspring than the evolution can support
• Survival of the Fittest: Those individuals whose
traits best adapt them to the environment will survive
better and leave more offspring than those with less
adaptive traits
Key forces which influence
the evolution of species
• Environmental changes (e.g. geographic
isolation of marsupials)
• Random factors (e.g. Genetic drift due to
the founder effect)
CONVERGENT
EVOLUTION
*
*
•Different species come
to resemble each other
due to the similarities in
their habitats
(ecological niches)
*
DIVERGENT
EVOLUTION
•Increasing separation
between related species
due to the process of
adaptive radiation
*
Analogous
structures
• Structures that are
similar in the way they
look because they
share similar function
but evolved
independently
Homologous
structures
• Structures that share
the same origin (e.g.
ancestral mammalian
limb) but serve
different function in
different species
Analogous structure
VESTIGIAL ORGAN: no longer useful but still retained
A vestigial structure in the skeleton of a baleen whale.
The pelvic bones have no apparent function.
Common Fallacies about Evolution
<-HUMAN
• Progressivism Fallacy
• Teleology Fallacy
(Purposivism Fallacy)
How Fast is Evolution?
• Gradualism Hypothesis
(Charles Darwin)
• Punctuated Equilibrium Hypothesis
(Stephen Jay Gould and Niles Eldrege)
DARWIN’S FINCHES
Natural Selection in Action
*
Daphne Major
Normal year
Drought year
The story of the ground finch
• Medium Ground Finch
(Geospiza fortis)
• Seed Eater
• Every year on Daphne all
the birds are caught and
measured
• Their food size is measured
Ground finch
Beak Depth is Inherited
What happened to the food ?
Drought
Seed size
and
hardness
Figure 01.08
Year
What happened to the finches?
Drought
Beak
size
Year
Finch Summary
• Beak depth is a trait that responds to
changing environmental conditions
• Beaks appear to be an adaptation for
feeding
• Evolution is a process-continually in
operation
– Sometimes measurable in real time
Darwin’s Theory of
Evolution
• Variation
• Inheritance
• Competition
• Survival of the Fittest