How Biologists Classify Organisms
Chapter 14 Section 2
Grade 10 BiologySpring 2011
What is a Species?Biological species: a group of natural
populations that are interbreeding or that could interbreed, and that are reproductively isolated from other such groups
What is a Species?Hybrids: sometimes individuals of
different species interbreed and produce offspring Species are closely related when they can
interbreed and produce fertile hybrids
Evaluating the Biological Species ConceptWorks well for most members of kingdom
AnimaliaSome species are able to form fertile
offspring with closely related speciesFails to describe species that reproduce
asexually Biologist recognize species by studying an
organism’s features
Evolutionary HistoryClassification based on similarities should
reflect an organism’s phylogeny Its evolutionary history
This can be misleading, not all characters are inherited from a common ancestor Wings of bird vs. wings of insect
Evolutionary HistoryConvergent evolution: similarities evolve
in organisms not closely related to one another, often because the organisms live in similar habitats
Analogous structures: similarities that arise through convergent evolution
Evolutionary HistoryDivergent evolution: similarities evolve
in organisms not closely related to one another
CladisticsCladistics: method of analysis that
reconstructs phylogenies by inferring relationships based on shared characters Can be used to hypothesize the sequence in
which different groups of organisms evolved
CladisticsAncestral character: with respect to two
different groups, a character is defined as an ancestral character if it evolved in a common ancestor of both groups Ex. Birds and mammals, backbone is an
ancestral character
CladisticsDerived character: evolved in an
ancestor of one group but not of the other Ex. Feathers evolved in an ancestor of birds
that was not also ancestral to mammals
CladisticsCladogram: branching diagram, shows the
evolutionary relationships among groups of organisms
Evolutionary SystematicsEvolutionary systematics: taxonomists give
varying degrees of importance to characters and thus produce a subjective analysis of evolutionary relationships
Phylogenetic tree: branching diagram based on evolutionary systematics
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