15'3 Evolution in Process

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15.3 Evolution in Process

• Biology

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Evidence of evolution

• Homologous similar features that originated in
  a shared ancestor
• Can result from modification that change an
  original feature to two extremely different
  types, such as a wing and an arm
• Analogous features serve identical functions,
  and they look somewhat alike
• Have very different embryological development,
  however, and may be very different in internal
  anatomy

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Forelimbs of the penguin, alligator, bat and
human all derive from the same embryological
structures
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Vestigial structures

• Many organisms have features that seem to serve
  no useful function.
• Humans have a tailbone at the end of the spine
  that is of no apparent use. The human appendix
  also has no known current function
• These apparently useless features are said to be
  vestigial

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Vestigial structures

• What sort of evolutionary clues can vestigial
  features provide?
• Consider that normal sperm whales, like all
  whales, have small pelvic bones but no hind legs.
  
• Very small percentage of sperm whales have
  vestigial leg bones, and some sperm whales even
  have bone-supported bumps protruding from their
  body
• In the whales genome, many of the genes needed
  to make hind legs have been conserved, or have
  remained unchanged.

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Vestigial structures

• Vestigial features were useful to an ancestor,
  but are not useful to modern organisms that have
  them.
• An organism with a vestigial feature probably
  shares a common ancestry with an organism that
  has a functional version of the same feature.

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Similarities in embryology

• Embryological development repeats evolutionary
  history.
• All vertebrate embryos are similar but those
  similarities fade as development proceeds

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Similarities in macromolecules

• Darwin hypothesized that more-similar forms of
  organisms have a more recent common ancestor than
  do less-similar forms
• Amino acid sequence in the hemoglobin molecules
  of different species are similar, but not
  identical.

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Similarities in macromolecules continued

• Thus, the more-similar the homologous proteins
  are in different species, the more closely
  related the species are thought to be

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coevolution

• The change of two or more species in close
  association with each other
• One example of coevolution is plants and animals
  that pollinate them.
• In tropical regions, some species of bats feed on
  the nectar of flowers. These bats have a slender
  muzzle and a long tongue with a brush-like tip,
  which aid them in feeding.
• The fur on the bats face and neck picks up
  pollen, which the bat takes to the next flower

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Convergent evolution

• Appear to be very similar, such as a shark and a
  porpoise, but are not closely related at all is
  convergent evolution
• Occurs when the environment selects similar
  phenotypes, even though the ancestral types were
  quite different from each other

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Divergent evolution

• Two or more related populations or species become
  more and more dissimilar
• Divergence is nearly always a response to
  differing habitats and it can ultimately result
  in new species

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Adaptive radiation

• Many related species evolve from a single
  ancestral species
• The Galapagos finches are an example of adaptive
  radiation. They diverged in response to the
  availability of different types of food in their
  different habitats

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Artificial selection

• Sometimes the process of divergence can be sped
  up artificially through artificial selection
• All domestic dogs are the same species, Canis
  familiaris but different breeds with different
  traits
• Divergent evolution operating over very long
  periods of time has produced the seemingly
  endless variety of species alive today