CLASSIFICATION

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CHAPTER 15.4

• CLASSIFICATION

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Why Classify ?

• The world is populated by at least 10 M
  organisms.
• To ensure accurate communication about organisms,
  biologists use classification systems.
• Taxonomy is the branch of biology that names and
  groups organisms according to their
  characteristics and evolutionary history.

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Early Classification Systems

• Aristotle (over 2000 yrs ago) devised the first
  classification system.
• grouped plants by size (small, med, large)
• grouped animals by habitat land, water, air
  dwellers
• This was not a great system but it persisted
  until Linnaeus (Swedish botanist) came up with
  another one in the mid-1700s

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Linnaeuss System

• Linnaeuss system relied upon hierarchical
  categories using mainly the organisms morphology
  (form and structure).

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Levels of Classification

• Scientists classify organisms into seven basic
  levels in the hierarchy (expanded since
  Linnaeus) kingdom, phylum, class, order, family,
  genus, and species.
• Kingdom is the largest category species, the
  smallest grouping.
• The placement of species is meant to indicate how
  closely related species are to each other.

KPCOFGS
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Biological Naming of Species

• Binomial nomenclature is a system developed by
  Linnaeus that consists of two-part names for each
  organism.
• The scientific name consists of the genus and
  species. It is italicized or underlined.
  (Species is sing/plural.)
• genus - capitalized species - not capitalized
• standard throughout the world (unlike common
  name)
• in Latin - the scientific
• language of the day
• unique to the organism

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Why Binomial Nomenclature?

• There is confusion about common names
• Ex. This cats common name
• mountain lion puma cougar panther
• These two birds are both called robins
• To avoid this confusion scientists assign each
  species a unique scientific name.

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Classification Example
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Problems with Classification

• Because of convergent evolution, analogous
  characters sometimes make it seem like unrelated
  organisms are related
• Ex. These vultures and plants are unrelated and
  from different continents.
• To solve this problem, taxonomists now make use
  of biochemistry, DNA sequences, embryology etc.

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Cladistics

• Taxonomists have developed a way to build family
  trees (called cladograms) which show the
  evolutionary relationship between species.
• These are made by finding shared derived
  characteristics between species.
• These characteristics are placed on the cladogram
  where they first developed all organisms that
  evolved after that point have the characteristic.

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Kingdoms and Domains

• As biologists learned more about the natural
  world, they realized that two kingdoms did not
  adequately represent all the diversity of life.

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Three Domain System

• More recently, comparing sequences of ribosomal
  RNA in different organisms has helped scientists
  determine that living organisms seem to fall into
  three broad groups or domains.