The Origin of Species 1859

1
Charles Darwin

• The Origin of Species (1859)
• Scientific evidence for evolution
• Proposed a mechanism of adaptive evolution
  Natural Selection

Goldman, 2003
2
ONTHE ORIGIN OF SPECIESBY MEANS OF NATURAL
SELECTION,OR THEPRESERVATION OF FAVOURED RACES
IN THE STRUGGLE FOR LIFE.
3
Darwins evidence for evolution

• The Fossil Record
• Transitional fossils
• Simpler forms lower/earlier
• Gradual transitions seen

4
Darwins evidence for evolution

• Homology
• Distantly related organisms share structural
  similarities
• Cannot be explained because the structures are
  optimal

5
Vestigial structures

• Animals appendix pythons hind legs whale
  pelvic bones
• Plants Plastids in non-photosynthetic plants
  sterile stamens (staminodes)

6
Hallmarks of history

• Satyrium flowers twist 360 degrees during
  development
• Other orchid flowers rotate 180 degrees

7
Natural classification

• It was long recognized that some classifications
  were natural
• Supported by many traits
• Hierarchical groupings of traits
• This is consistent with species being branches of
  an evolutionary tree natural classification is
  based on evolutionary relatedness

8
Hierarchical classification
Vascular plants
Lycophytes
Euphyllophytes
Moniliforms
Seed plants
Angiosp.
Gymnosp.
9
Classification of embryophytes

• Land plants (land, alternation of generations,
  embryo, etc.)
• Vascular plants (branched sporophyte, sporophte
  dominance, xylem, phloem)
• Lycophytes (microphylls, lateral sporangia,
  protostele)
• Euphyllophytes (megaphylls)
• Ferns
• Seed plants (bipolar embryo, secondary
  thickening, seed habit, integuments)
• Gymnosperms
• Angiosperms (flowers, double fert., stamens,
  carpels..)

10
Hierarchy and natural classification makes sense
given descent from common ancestry
Seed plants
lycophytes
Ferns
gymnosperms
angiosperms
lycophytes
Ferns
gymnosperms
angiosperms
Flowers
Seed plants
Seeds
Euphyllophytes
Vascular plants
Vascular system
11
Strengthened with molecular data

• When we estimate a phylogeny for the same
  organisms from multiple genes we get the same (or
  very similar) trees
• The odds of this happening by chance are VERY low
• Suggests tree like relationships are real

12
Geographical patterns

• Species usually live near their close relatives
• Cacti restricted to the new world

13
Geographical patterns

• Species usually live near their close relatives
• Hummingbirds restricted to the new world

14
We see evolution in action

• Artificial selection
• Rapid evolution in nature

Brassica oleracea
Ear of maize and its wild relative
15
What happens during evolution?

• Individual organisms change (adapt) in response
  to their environment
• The genetic composition of populations changes
• The physiology of the organisms changes

16
How many of the following are evolution?

• A plant growing in bright light produces
  accessory pigments to protect its chloroplasts
  from damage
• A population of plants living in poor soils
  becomes much larger upon being transplanted to
  rich soils
• Over a few generations, a population subject to
  attack by insects shows an increase in the
  frequency of an allele conferring resistance to
  attack

17
Evolution

• A change in the genetic composition of
  populations over time
• Change occurs in populations not organisms
• Over multiple generations
• Genetic differences - not just environmental
  response
• Two mechanisms of evolution
• Selection
• Genetic drift (no time to cover)

18
Selection

• Genetic variation in traits that affect fitness
• Fitness the expected lifetime reproductive
  output of an organism
• Heritable traits conferring higher fitness will
  tend to increase in frequency in a population

19
Where does variation come from?
20
If mutation is random with respect to needs how
come populations tend to get better adapted?
21
Ancestral population fixed for blue
22
What determines which allele will increase in
frequency?
The effect of that allele on fitness the
expected lifetime reproductive output of
organisms with allele
23
Can evolution by natural selection explain plant
diversity?

• The fact of evolution is well supported
• Selection is shown to be very powerful given
  enough time
• Artificial selection
• Mathematical simulation
• Life on earth is old
• Selection is the only viable scientific
  explanation for adaptive evolution