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Modern Taxonomy
How organisms are classified:
• Each organism is classified into a series of
categories (kingdom, phylum…), called taxa
– Organisms of the same species look alike
and can reproduce fertile offspring
– The more categories 2 species have in
common, the closer they’re related
• Ex: Lynx and Bobcat
Lynx vs. Bobcat
Lynx canadensis
Lynx rufus
*Kingdom thru Genus is the same
Evolutionary History
• The evolutionary
history of a species
is its phylogeny
• Phylogeny shows a
characteristic that
is unique to related
species
– ex: retractable
claws = the cat
family
Phylogenic Trees or Cladograms
• Phylogenic Tree: a tree that represents
evolutionary relationships, using unique
characteristics, from a common ancestor
• We use structures, development,
biochemistry, behavior, and evolutionary
history to determine evolutionary
relationships
Cladogram
How evolutionary relationships
are determined:
• By structure
– Structure is how something is built, NOT
what function it performs
• Ex: Human arms/hands are
structurally the SAME as a bat’s wing
(but they do different jobs)
Structures
• Homologous Structures – similar structures
in different species
– If different species have similar
structures, then they must have a
common ancestor
• Vestigial structures: a body structure that
has no apparent function but is similar to
another structure in another organism
– Ex: appendix in humans vs. the caecum of
herbivores
• Analogous Structures: structures that
are alike in function, but are different and
DO NOT share a common ancestor
– Ex: wings of a bat vs. wings of birds
Bat vs. Bird wings
• The wings have separate evolutionary
origins but evolved to serve the same
function
How evolutionary relationships
are determined:
• By development (animals only)
– Taxonomists study developmental
stages from embryos to adults
(Embryology)
– Similarities in a particular stage of
development could mean that there’s a
common ancestor
• Ex: Adults of certain species may look
different, but the larval stage may resemble
another species…suggesting a relationship
• By biochemistry
– Closely related species have similar DNA
patterns and similar proteins
– The more nucleotides (or amino acids)
sequences in common, the closer the relation
• By behavior
– Behavioral patterns provide important clues to
relationships
– Ex: mating calls
• By evolutionary history
– Species that share many characteristics
indicates they have evolved from a
common ancestor (ex: Lynx & Bobcat)
– We can compare modern-day
organisms with the fossil records to look
at common structure
Dichotomous Key
• A tool that uses pairs of contrasting,
descriptive statements to identify an
organism (Ex. a field guide)
– Constructed of a series of 2 contrasting
statements
– A user works through the set of
statements in order to identify the
organism