Evidence for Evolution

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Chapter 22

• Evidence for Evolution

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Evolution occurs by natural selection

• Darwins finches
• Found on Galapagos
• Descent with modification

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Natural selection has 3 conditions that must be
met

• 1.) variation within the population
• 2.) variation must lead to differences among
  individuals in survival and reproductive success
• 3.) variation must be genetically inheritable

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Found with finches

• variation is within the population
• changed from one year to the next depending on
  the weather and plant seed production
• drought fewer seeds, birds with large beaks
  survived b/c could eat bigger seeds
• wet many more small seeds, birds with small
  beaks survived ok
• Traits were passed down according to those who
  survived fluctuated within the population

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Peppered moths and industrial melanism

• Industrial melanism is the darkening of a species
  due to industry
• Two main forms peppered and melanic
• In areas of industry, the tree bark is darker
  the dark moths do better
• Non-industrial areas, the light moths do better

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• Kettlewell did experiment with industrial
  melanism
• Raised both colors of moths
• Marked their abdomens and released equal amounts
  of each color into an area of industry and a
  rural area.
• Waited a a few weeks and recaptured as many moths
  as possible in each area.
• Results
• light moths more in rural area
• dark moths more in industrial area

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Artificial Selection

• Lab experiments
• Used to test if selection can produce
  evolutionary change
• Used fruit flies
• Chose flies with many bristles - Only bred the
  ones with the most
• Over 86 generations, increased the bristle from
  9 to over 40!!

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In Agriculture

• Only allow the plants that produce the best seeds
  to breed
• Ex corn, wheat, strawberries

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Domestication

• Taking a once wild animal and breeding those with
  desirable traits to eventually spawn a desirable
  offspring
• Has been done with wolves, foxes, cats and more!

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The fossil record

• Most direct evidence for evolution
• Can get from rock, amber, permafrost, dry caves
  or deserts
• Problem fossilization does not occur easily!
• Must have very specific conditions
• Usually the remains are scavenged or eroded
  before the process can be completed

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• Must have very specific conditions
• Usually the remains are scavenged or eroded
  before the process can be completed
• Heres a bird in the process of being fossilized!

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Dating fossils

• Date the rocks in which they are preserved
• Absolute dating uses U238
• Relative dating uses rock layers in respect to
  one another

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Gaps in the record

• Even though gaps exist, links have been found
  between
• Reptiles and birds
• Ex Archaeopteryx

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• Snakes and lizards
• - pelvic girdles still visible in snakes
• Whales and land mammals
• - flippers with homologous structures, pelvic
  girdle

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Anatomical record

• Homology homologous structures are structures
  with different appearances and functions that are
  all derived from the same body part in a common
  ancestor
• Ex forelimbs of mammals

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• Vestigial Organs - Rudimentary structures of
  marginal, if any, use.

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Human Example
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Evolution Viewpoint

• Remodeling of ancestral structures as their
  functions or adaptations changed.

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Comparative Embryology

• Problem - closely related organisms go through
  similar stages in their embryonic development.
• Ex Gill pouches in vertebrates

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Molecular Biology

• Study of Evolution at the DNA or protein levels.
• Problem - related species have similar DNA
  sequences.

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Evolution Viewpoint

• Related species share a common ancestrial DNA.
  The closer the relationship, the more similar the
  DNA sequences should be.

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Convergent evolution
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Horse evolution

• For example, we can trace the evolution of the
  modern horse through fossils.
• First horses
• small, short legs, broad feet
• lived in woods and ate leaves and berries
• We will look at the changes in these animals

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Size

• First horses were the size of dogs or smaller
• Now they weigh on average about 1000 lbs!
• Lets see the fossils for this change
• http//chem.tufts.edu/science/evolution/HorseEvolu
  tion.htm

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Toe reduction

• Primitive horses had 4 toes with fleshy pads like
  a dogs
• Modern horses have one toe encased in bone and
  keratin
• This allowed the horse to run faster for longer
  distances
• First row forefoot
• Bottom row hindfoot

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Tooth size and shape

• Primitive horses had small and simple teeth for
  the vegetation of the time
• Modern horses now have more complex teeth that
  are longer and have ridges for chewing grasses
  which evolved along with the horse
• The grasses are tough and the teeth need to tough
  to withstand the chewing of these materials

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• Only one genus of horse still exists todayEquus
• All others died out long ago naturally selected
  against in the changing environment

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Summary

• Know Darwins facts and inferences.
• Be able to discuss the various evidences of
  Darwinian evolution.