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Evolution
• What is evolution?
• What lead Darwin to his thoughts
• 4 Premises of Evolution by Natural
Selection
• Evidence supporting Evolution
Pre-Darwin
• Aristotle (348-322 BCE)
Scale of Nature – moving towards perfection
Jean Baptiste Lamarck (1744 - 1829)
• Proposed that organisms
– change over time by natural phenomena
– vital force moved toward greater complexity
over time
– could pass traits acquired during lifetime to
offspring
2. Observations of artificial
selection
• Genetic change in a population over
time.
• Unifying concept of biology
– links all fields of life sciences into a unified
body of knowledge
Charles Darwin (1809 – 1882)
• Theory of evolution
– Based on observations:
1. Found similarities between organisms
– on Galápagos Islands and South American
mainland
Darwin
3. Applied Thomas Malthus’s ideas
– on human populations to natural populations
4. Influenced by geologists
– idea that Earth was extremely old
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4 Premises of Evolution
by Natural Selection
4 Premises of Evolution
by Natural Selection
• 1. Variation
– Variation exists among individuals in
population (heritable variation)
4 Premises of Evolution
by Natural Selection
3. There are limits on population growth
Organisms compete with one another for
resources: food, living space, water, light
Predators, disease, weather,
Thus, not all individuals survive to reproduce
4. Differential reproductive success
Offspring with most favorable characteristics
likely to survive and reproduce
pass favorable characteristics to next gen.
• Leads to accumulation of favorable traits in the
population over generations
Galapagos Finches
2. Overproduction
Reproductive potential of a species is great
– BUT – Not all survive
Natural Selection
• Results in adaptations
– evolutionary modifications from environmental
pressure
– improve chances of survival and reproductive
success in a particular environment
• Over time
– accumulated changes in geographically separated
populations can produce new species
Modern Synthesis
• Or synthetic theory of evolution
– combines Darwin’s theory of evolution by natural
selection with modern genetics
- incorporates our understanding of genetics/DNA
• Explains:
– why individuals in a population vary (genetic
variation in a population)
– how species adapt to their environment
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Important points to remember:
1. Differential reproduction
Evidence for Evolution
• Fossils
2. Evolution occurs in populations not
individuals (but the environment
selects traits at the individual level).
3. Mutation is important (provides genetic
variation - synthetic theory of evolution)
4. Don’t’ think of evolutionary change as
purposeful
- Panda’s thumb
Fossil Record
• Sedimentary rock
– layers occur in sequence of deposition
• Index fossils
Transitional
fossils:
E.g., Whale
Evolution
– characterize specific layer
• Radioisotopes
– in rock accurately measure rock’s age
Homologous Features
Homology in Plants
• Features derived from the same structure in a
common ancestor
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Homoplastic Features
• Structural features that are not homologous
but have similar functions that evolved
independently
Result in convergent evolution
– organisms with separate ancestries
develop similar adaptations in response to
similar selective pressures (environments)
Fig. 18-12a, p. 402
Homoplasy
Biogeography: Past and present
distribution of organisms
• Geographic distribution of organisms
– affects evolution (remember the
environment selects traits)
Vestigial Structures
• Nonfunctional/degenerate structures
- were present and functional in ancesters
organisms
Continental Drift
• At one time, continents were joined to form
a supercontinent
• Continental drift
• Isolated land masses
– contain organisms that evolved in
isolation
– unique to those areas
– caused landmasses to separate
– played major role in evolution
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Cynognathus
Lystrosaurus
(a)
(b)
Continental Drift
Africa
India
South
America
Australia
Antarctica
(c)
Mesosaurus
Glossopteris
(d)
Fig. 18-16, p. 405
Evidence provided by Developmental Biology
Molecular evidence for evolution
• We note that gene mutations can affect events in
development (snakes hind limbs)
Universal nature of genetic code
Only 4 nucleotides!!!!!!!
Development in different animals controlled by same kinds of
genes indicates shared evolutionary history
DNA
Genetic Changes
• Accumulation of genetic changes
– since organisms diverged
– modified development patterns in more
complex vertebrate embryos
3 billion pairs in humans
Human - chimp 95%
same
Genetic evidence
Species A
Species B
Species C
Amino acid sequences on proteins (cytochrome c)
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Cetaceans
(whale, dolphin)
Hippopotamus
Ruminants
(cow, sheep,
giraffe)
Pig
Camel
Artiodactyls
• Can evolutionary hypotheses be tested
experimentally?
Common
ancestor of
hippos and
whales
Common ancestor of
artiodactyls and
cetaceans
Fig. 18-17, p. 407
Reznick Experiment
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