EvolutionThe Theory and Its Supporting Evidence

1
EvolutionThe Theory and Its Supporting Evidence
2
How to explain fossil record?

• tremendous variation and diversity in the rock
  record of life.

3
Organisms in the same species share a common DNA
pool

• DNA defines the species
• there is variation within species
• gene pool
• total sum of genetic information present in all
  members of a species
  
• a species gene pool changes slightly with each
  organisms birth and death

4
How gene pools can vary

• DNA can be changed by
• mutation
• sex (recombination)
• changes can be
• neutral, advantageous, or deleterious
• natural selection
• advantageous mutations aid reproduction and are
  eventually amplified within the gene pool.

5
Organic Evolution

• All life on Earth is descended from other,
  earlier life
  
• All life is interrelated
• Natural selection is the mechanism which drives
  changes in species.

6
Charles Darwin

• H.M.S. Beagle cruise 1831-1836

www.rit.edu/rhrsbi/GalapagosPages/Darwin.html
7
Precursor ideas to Darwin

• Organisms present in fossil record are different
  from those alive today
  
• Geologic time might be long (uniformitarianism)
• Organisms can be classified by shared
  characteristics
  
• Inheritance of acquired characteristics
• Continuous, spontaneous generation of life.

8
Charles Darwin

• H.M.S. Beagle cruise 1831-1836
• Natural selection through time, populations
  become better fitted to their environments as
  poorly-adapted members fail to reproduce
  offspring as successfully (mechanism)
• The best adapted are most likely to survive

9
Galapagos Finches

• Helped form Darwins theory of natural selection
• Variety between populations of different islands
• Adapted to exploit different food sources

10
Galápagos Finches

• Beak shape varies depending on diet

Berry eater
Seed eaters
Cactus eaters
11
More on Darwin

• On the Origin of Species by Means of Natural
  Selection published in 1859
  
• 4 main arguments for evolution
• Branching organization of life
• Homology
• Vestigial structures
• Embryonic history

12
Branching organization of life

• Nature organized into hierarchy of groups
  (Linnaeus)
  
• Kingdom Phylum Class Order Family Genus
  Species
  
• Confirmed by modern genetics

13
What does species mean?

• Most specific classification
• Organisms capable of interbreeding

14
Species

• Individuals that in nature interbreed and produce
  fertile offspring
  
• Goats and sheep do not interbreed in nature, so
  they are separate species
  
• Yet in captivity they can produce fertile
  offspring
  

15
Homology

• Similarity in structure between parts of
  different organisms due to evolutionary
  differentiation from the same part
  
• Similarity attributable to common origin
• Legs, hands, wings, flippers

16
Homology

• Homologous similar elements derived from common
  ancestor (eg. wings of bats and our finger
  bones)
  
• Analogous similar elements without common
  ancestor (eg. wings of bats and wings of insects)

17
Homologous Structures

• Forelimbs of humans, whales, dogs, and birds are
  made up of the same bones
  

• Also have similar arrangement of muscles, nerves
  and blood vessels

18
Analogous Structures

• Wings of insects and bats serve the same function
  but differ considerably in structure and
  embryological development

19
Vestigial Structures

• Remnants of features no longer used

Human tail bones Whale hip and leg bones Hor
se splint bones (ancient side toes)
20
Vestigial Structures

• Vestigial structures are nonfunctional remnants
  of structures in organisms that were functional
  in their ancestors

• Why do dogs have tiny, functionless toes on their
  feet (dewclaws)?

• Ancestral dogs had five toes on each foot

• As they evolved they became toe-walkers with only
  four toes on the ground
  
• Big toes and thumbs were lost or reduced to their
  present state

21
Remnants of Toes in Horses

• Normally a horses back foot has only one
  functional toe, the third
  

• Splints are small remnants of toes 2 and 4 that
  remain as vestiges

22
Embryonic History (Ontogeny)

• All vertebrate embryos start out very similar
• Gill slits
• Long tail
• One idea organisms evolve by adding stages to
  their embryonic development

23
Embryonic History (Ontogeny)
24
Embryonic History (Ontogeny)

• YES We can learn about evolutionary history by
  looking at how embryos develop
  
• NO organisms do not evolve by adding stages to
  their embryonic development

25
Example of the Peppered Moths
26
Phyletic Gradualism vs. Punctuated Equilibrium

• Gradual transformations from one species to
  another
  
• Rare and sudden speciation events
• Evidence of both
• Horse example first thought to be example of
  gradualism, but many species living at same time
  
• Still debated

27
Patterns of Evolution

• Divergence new species develop traits that
  differentiate them from their ancestors
  
• Adaptive radiation mammals filled ecological
  niches vacated by dinosaurs
  
• Convergence unrelated animals develop similar
  body forms to fill same niche

28
Divergent Evolution

• Divergent evolution of a variety of placental
  mammals from a common ancestor
  
• Divergence accounts for descendants that differ
  from their ancestors and from one another

29
Convergent Evolution

• Convergent evolution takes place when distantly
  related organisms give rise to species that

• resemble one another because they adapt in
  comparable
  
• ways

30
Recent Ideas

• Neutralism most genetic changes are adaptively
  neutral
  
• Inheritance of acquired characteristics (e.g.,
  immunity passed on to offspring)?
  
• Can natural selection account for macroevolution
  (major evolutionary changes, complex
  structures)?
  

31
Background and Mass Extinction

• Perhaps as many as 99 of all species that ever
  existed are now extinct
  
• The continual extinction of species is referred
  to as background extinction
  
• Different from mass extinction during which
  accelerated extinction rates sharply reduce
  Earths biotic diversity
  

32
Mass Extinction

• The mass extinction of dinosaurs is well known
• Greatest mass extinction occurred millions of
  years before
  
• More than 90 of all species died out
• we will discuss these extinctions and their
  possible causes later in the term