Evolution

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Evolution

• Evidence and Ideas

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Evolution

• Change in populations over time

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Fossil Evidence

• remains or traces
• of past life forms
• most form from burial of plants animals in
  sediment
• soft parts are often consumed or decomposed but
  may leave imprints if buried rapidly

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How do we know how old it is?

• Relative dating is done by rock layers
• (top layers of rock are the youngest)
• Absolute dating uses radioactive isotopes
  (using half-lives and isotope amounts)

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Extinction

• death of all members of a species
• Mass extinction extinctions of many species
  in
  short time.
• There have been five mass extinctions so far and
• many agree we are in the middle of one NOW

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Mass Extinctions

• Following extinctions, remaining groups expand to
  fill habitats vacated by extinct species.
• Marine animal fossil record indicates mass
  extinctions occur every 26 million years--which
  corresponds to movement of our solar system
  within Milky Way galaxy.

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Biogeographical Evidence

• Biogeography is the study of the distribution of
  plants and animals throughout the world
• Current organism distribution reflects
  evolutionary history
• organisms evolve in one location and spread out
  into other regions
• no rabbits are found in South Americathey
  originated elsewhere and did not reach South
  America

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Biogeographical Evidence

• Physical factors limit population range
  (including location of continents)
• Continental drift continents have slowly moved
  over time
• distribution of early reptiles across many
  continents from time when land was attached
• divided distribution of mammals that evolved
  after continents parted

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Anatomical Evidence

• Organisms have homologous structures
• vertebrate forelimbs contain same sets of bones
  for different functions

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Anatomical Evidence

• Simplest explanation is a common ancestor whose
  basic forelimb plan was modified in succeeding
  groups as each continued along its own
  evolutionary pathway

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Anatomical Evidence

• Homologous structures are similar structures
  derived through descent from a common ancestor
  but may have different functions. (leg, wing,
  fin)
• Analogous structures have similar functions but
  differ in anatomy and did not derive from the
  same ancestral structure (insect wing and bird
  wing)

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Anatomical Evidence

• Vestigial structures are reduced and
  functionless anatomical features
• Flightless birds have wings.
• Snakes rear limb spurs.
• Humans have a tail bone.

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Anatomical Evidence

• Related species share embryological development.

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Biochemical Evidence

• Almost all living organisms use the same basic
  biochemicals
• DNA, ATP, same enzymes, DNA triplet code, 20
  amino acids

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Biochemical Evidence

• Similarity of biochemistry is explained by
  descent from common ancestor.
• Organisms show less difference in their DNA the
  more closely related they are
• 2.5 difference between humans chimpanzees
• 42 difference between humans lemurs.

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• END OF DAY 1