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Objectives
• 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
Evolution
• 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)
• Darwin made some observations!!!!!
• H.M.S. Beagle
– 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
resulting from Darwin’s observations
4 Postulates of Evolution
by Natural Selection
1. Variation exists among individuals in populations.
(and the variation is heritable)
3. In a population not all individuals survive to
reproductive age
i.e., 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
2. Variation that exists in population is heritable
4 Postulates of Evolution
by Natural Selection
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
Important points to remember:
1. Differential reproduction
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
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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Evidence for Evolution??
• Fossils
Fossil Record
• Sedimentary rock
– layers occur in sequence of deposition
• Unicellular deeper than multicellular
– - simpler towards more complex
– - fossils show series of changes in many
organsims
• Radioisotopes
– in rock accurately measure rock’s age
Transitional
fossils:
Homologous Features: Similar features in different
species. Natural selection modified for a particular
Strongly
suggests
a common
ancestorin a
•function.
Features
derived
from the
same structure
common ancestor
E.g., Whale
Evolution
Homologous Features in Plants
Analogous Structures
Structural features that have similar functions
that evolved independently
– i.e. they are not homologous structures!!!!!
Result in convergent evolution
– organisms with separate ancestries
develop similar adaptations in response to
similar selective pressures (environments)
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Analogous Features
Fig. 18-12a, p. 402
Vestigial Structures
• Nonfunctional/degenerate structures
were present and functional in ancestors
organisms
Evidence provided by Developmental Biology
• We note that gene mutations can affect events in
development (snakes hind limbs)
Development in different animals controlled by same kinds of genes indicates
shared evolutionary history
Continental Drift
Biogeography: Past and present distribution of
organisms
• Geographic distribution of organisms
– affects evolution (remember the environment
selects traits)
• Isolated land masses
– contain organisms that evolved in isolation
– unique to those areas
•At one time, continents were joined
to form a supercontinent
•Continental drift
caused landmasses to separate
played major role in evolution
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Cynognathus
Lystrosaurus
(a)
(b)
Molecular evidence for evolution
Africa
India
Universal nature of genetic code
South
America
Australia
Only 4 nucleotides!!!!!!!
Antarctica
3 billion pairs in humans
Human - chimp 95%
same
(c)
DNA
Mesosaurus
Glossopteris
(d)
Fig. 18-16, p. 405
Genetic Changes
Genetic evidence
• Accumulation of genetic changes
Species A
– since organisms diverged
Species B
Species C
Amino acid sequences on proteins (cytochrome c)
Cetaceans
(whale, dolphin)
Hippopotamus
Ruminants
(cow, sheep,
giraffe)
Pig
Camel
Artiodactyls
• Can evolutionary hypotheses be tested
experimentally?
Common
ancestor of
hippos and
whales
Hypothesis : based on DNA sequences
Who is more closely related to who.
Common ancestor of
artiodactyls and
cetaceans
Fig. 18-17, p. 407
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