Biological Classification

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Biological Classification
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Why Do We Classify Organisms?

• Biologists group organisms to organize and
  communicate information about their diversity,
  similarities and proposed relationships.
• Classification systems change with expanding
  knowledge about new and well-known organisms.
• Approximately 1.75 million species have been
  classified so far.

Tacitus bellus
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History of Classification

• Aristotle (2000 y.a.) classified organisms as
  either plants (by size) or animals (red-blooded
  or not).

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History of Classification

• In the 1700s and 1800s
• Carolus Linnaeus, a Swedish botanist, used
  similarities and differences in morphology and
  behavior to classify birds.
• Linnaeus developed the first taxonomy system and
  made it possible to include evolutionary
  principles in classification in the 1800s.
• Jean-Baptiste Lamarck, Charles Darwin, and Ernest
  Haeckel introduced classification systems based
  on evolutionary relationships to organize
  biological diversity.

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Scientific Names

• Carolus von Linnaeus devised the currently used
  binomial nomenclature.
• Two-word naming system
• Genus
• Noun, Capitalized, Underlined or Italicized
• Species
• Descriptive, Lower Case, Underlined or
  Italicized
• Ex.
• Genus Homo or Homo
• Species sapiens or sapiens
• Complete scientific name of species
• Homo sapiens or Homo sapiens
• Abbreviated form H. sapiens or H. sapiens

Carolus von Linnaeus(1707-1778) Swedish
scientist who laid foundation for modern taxonomy
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Hierarchical Classification into Taxa

• Taxonomists classify organisms by dividing them
  into smaller groups based on more specific
  criteria. A named groups of organisms is a
  taxon.
• Taxonomic categories (taxa)
• Kingdom King
• Phylum Philip
• Class Came
• Order Over
• Family For
• Genus Green
• Species Spaghetti
• Beginning with species, each category becomes
  progressively more comprehensive. Ex. while the
  leopard, tiger and domestic cat all belong to
  different genera, they are grouped together in
  the same family.

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Modern Classification - Species Concepts
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Modern Classification Systems / Disciplines of
Biology

• Systematics is the branch of biology concerned
  with the study of biological diversity.
• Taxonomy is the part of systematics concerned
  with identifying, naming, and classifying species
  based on morphological and behavioral
  similarities and differences.
• Binomial Nomenclature is used to name species
  using two words, genus and species.

Populus tremuloides Quaking Aspen
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SystematicsEvolutionary Classification of
Biodiversity

• Systematics is the study of the evolution of
  biological diversity, and combines data from the
  following areas
• Fossil record
• Comparative homologies, morphological characters
  (traits) derived from common ancestry
• Cladistics, the study of evolutionary
  relationships between species based on shared
  characters (inherited traits)
• Biochemical characters, such as comparative
  sequencing of DNA/RNA among organisms
• Molecular clocks

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Comparing Morphological Characters
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A Molecular Clock

• The rate at which mutations occur varies
  depending on
• Type of mutation
• Location of mutation in the genome
• Type of protein affected
• Population in which the mutation occurs
• This inconsistency makes molecular clocks
  difficult to read.
• Molecular clocks are often used along with the
  fossil record and help determine when a species
  evolved.

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Taxonomic Diagrams based on Phylogeny
Mammals
Turtles
Lizards and Snakes
Crocodiles
Birds
Mammals
Turtles
Lizards and Snakes
Crocodiles
Birds
Cladogram a branched diagram that shows the
proposed phylogeny (evolutionary history) of a
species nodes represent common ancestors
Phylogenetic Tree a form of cladogram nodes
represent common ancestors
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Lily Cladogram
The closer two groups are, the larger the number
of characters they share.
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Dichotomous Keys Identify Organisms

• Dichotomous keys are tools used to identify
  organisms field guides contain dichotomous keys.
• Dichotomous keys contain pairs of contrasting
  descriptions - choices between two options.
• After each description, the key directs the user
  to another pair of descriptions or identifies the
  organism.
• Example (identifying a plant using its leaf)
  1. a) Is the leaf simple? Go to 2 b) Is the
  leaf compound? Go to 3
• 2. a) Are margins of the leaf jagged? Go to
  4 b) Are margins of the leaf smooth? Go to 5

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Kingdoms and Domains
The three-domain system
Bacteria
Archaea
Eukarya
The six-kingdom system
Bacteria
Archaea
Protista
Plantae
Fungi
Animalia
The traditional (now outdated) five-kingdom system
Monera
Protista
Plantae
Fungi
Animalia
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Classification All in the Family at pbs.org