1. Aristotle
natural history
essentialism
species are fixed and unchanging
concept of the “type”

2. Lamarck ( )
Philosophie Zoologique
tried to explain two phenomena:
1. diversity of form
2. trend of increasing complexity
how is one species transformed into another ?

3. Lamarck, con’t
mechanisms:
1. possible to increase complexity (forever)
1st notion of adaptation
2. organisms respond to environment
inheritance of acquired characteristics
consequences of environment and environmental
change for the phenotype

4. Georges Cuvier ( )
paleontology, comparative
anatomy
catastrophism: total
destruction and replacement
of flora/fauna
species didn’t change; only
non-essential features varied

5. Richard Owen
Louis Agassiz

6. Charles Lyell
species die out and are replaced
how? - singly or all at once?
why? - senescence?
- environmental change?

7. Charles Darwin
( )
Alfred Russell Wallace
( )

8. Charles Darwin
ship’s naturalist on the HMS Beagle ( )
-- fauna of Galapagos Islands: each island had
similar physical conditions but distinct species
of mockingbirds, finches, tortoises
divergence in isolation from a common ancestor
--fossils of Patagonia: similarity of fossil and
living forms (e.g., armadillos)
descent with modification

9. derivation of natural selection
reproductive capacity and population increase
(Malthus Essay on the principle of popn)
population size is ~stable (most species)
resources (food, space) are limited;
“struggle for existence”
no two individuals are identical
much variation is heritable
unequal survival; depends on genotype
gradual changes over time in popns

10. 1859 Origin of Species
species are not fixed or constant
1. gradual descent with modification from
a common ancestor
(transformation and diversification)
2. modification via natural selection on
individual variation
Natural Selection = differential survival or
reproduction of some individuals under
current environmental conditions

11. Evolution by natural selection
individuals within a species are variable
some of the variations are passed to
offspring (heritable)
in every generation more offspring are
produced than can survive
Survival and reproduction are not random;
individuals that survive +/or reproduce the
best have the variations most favored in
the current environment

12. AZT resistance is an example of evolution by
Natural Selection
1. mutations by reverse transcriptase produce
variant HIV molecules
2. mutants differ in enzyme function
3. differential survival in AZT environment
resistance is costly (slow growth)
4. mutants are passed to ‘offspring’ of resistant
genotypes
effectiveness and speed of process
-- rate of mutation (m ~1%/yr)
-- strength of selection

13. Sewell Wright R. A. Fisher J. B. S. Haldane

16. natural selection in action:
morphological evolution of Geospiza fortis
Peter & Rosemary Grant and colleagues
long-term study of G. fortis population on Daphne Is.
two episodes of natural selection:
severe drought
extreme El Nino event

18. beak depth in G. fortis is highly variable

19. beak depth is highly heritable in this population

20. ENSO
drought

21. normal
vegetation on
Daphne Is.
drought

22. fewer seeds
harder seeds
Tribulus

23. a decline in food results in a decline in finches

25. survival is not random; larger birds are more likely
Evolutionary response of Geospiza fortis to selection in
before selection next generation
Mean (SE) Mean (SE) D
Weight (g) (0.06) (0.13) +1.07
Wing length (mm) (0.10) (0.20) +0.99
Tarsus length (mm) (0.03) (0.07) +0.21
Bill length (mm) (0.03) (0.06) +0.32
Bill depth (mm) (0.03) (0.06) +0.49
Bill width (mm) (0.02) (0.05) +0.25
Sample size
survival is not random; larger birds are more likely
to survive than small birds

27. birds with deeper bills have higher survival

29. ENSO
drought

30. normal wet season
vegetation on
Daphne Is.
El Nino event

31. the direction of selection is not constant

33. Natural selection acts on individuals, but the
consequence is a change in the population
phenotypic distribution
Natural selection acts on phenotypes, but changes
the genotypic distribution (without underlying
genetic variation, evolution will not occur
Each generation is the product of selection on their
parents
Natural selection acts on existing traits. New traits
arise as a modification of old features and in
combination with new mutations
Natural selection is non-random, but not progressive