18.2 Modern Evolutionary Classification

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18.2 Modern Evolutionary Classification

• Which similarities are most important?
• Evolutionary classification
• Classification using cladograms
• Similarities in DNA and RNA
• Molecular clocks

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Which similarities are most important?

• Based on how Linnaeus grouped organisms (physical
  characteristics), it would be difficult to
  determine which characteristics you base their
  name off of.
• For example, would he group dolphins with fish
  because they live in water and have fins, or
  would they be mammals because they breath air and
  feed their young milk?

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Evolutionary Classification

• Phylogeny the study of evolutionary
  relationships among organisms, Darwin gave rise
  to this study.
• Biologists now group organisms into categories
  that represent lines of evolutionary descent, or
  phylogeny, not just physical similarities.
• Evolutionary classification the strategy of
  grouping organisms together based on their
  evolutionary history.

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Classification Using Cladograms

• Cladistic analysis identifies and considers
  only those characteristics of organisms that are
  evolutionary innovations
• Derived characters characteristics that appear
  in recent parts of a lineage but not in its older
  members.
• Cladogram a diagram that shows the evolutionary
  relationships among a group of organisms.

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Cladograms, cont.

• They are useful tools that help scientists
  understand how one lineage branched from another
  in the course of evolution, kind of like a family
  tree.

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Similarities in DNA and RNA

• The genes of many organisms show important
  similarities at the molecular level.
  Similarities in DNA can be used to help determine
  classification and evolutionary relationships.
• The more similar the DNA sequence in two species,
  the more recently they had a common ancestor.

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Molecular Clocks

• Molecular clock uses DNA comparisons to
  estimate the length of time that two species have
  been evolving independently.
• This process relies on mutations that occur.
• The degree of dissimilarities is an indication of
  how long ago species shared a common ancestor.
• This process can be difficult because each genome
  contains more than one clock because of the
  many different genes.