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Early Systems 1. Aristotle's System a. Only included plants and animals. b. Did not group organisms by evolutionary history. c. Many organisms did not fit. 2. Linnaeus’s System a. Based on physical and structural similarities. b. Still just plants and animals, but he further subdivided these groups. c. Some scientists proposed that structural similarities mirrored evolutionary relationships.
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Organizing Life’s Diversity
Chapter 17
How Classification Began In order to better understand organisms
scientists group them. Classification is the tool scientists use to group
organisms Taxonomy is the branch of biology that groups
and names organisms based on their characteristics.
Taxonomists are scientists who study taxonomy.
Early Systems1. Aristotle's System
a. Only included plants and animals.b. Did not group organisms by evolutionary history.c. Many organisms did not fit.
2. Linnaeus’s Systema. Based on physical and structural similarities.b. Still just plants and animals, but he further
subdivided these groups.c. Some scientists proposed that structural
similarities mirrored evolutionary relationships.
Today’s Classification System3. Modern system
a. Binomial nomenclature is a two name / word system that Linnaeus developed to identify species
b. Written in Latin because this language does not change and is universal.
c. The first word indicates the genus and the second the species (which is descriptive of the organism -sapiens means wise)
i. Ex. Homo sapiens, H. sapiens, Homo sapiens, H. sapiens
How Living Organisms are Classified1. Organisms are
ranked from very broad taxa containing lots of species to very specific taxa.
Example: Humans Domain: Eukaryota Kingdom: Metazoa Phylum: Chordata
Class: Mammalia Order: Primata Family: Hominidae
Genus: Homo Species: sapiens
How many species are there in each kingdom?
Archaebacteria = 500
Eubacteria = 10,000
Protista = 70,000
Fungi = 110,000
Plants = 510,000
Animals = 2,900,000
How Are Evolutionary Relationships Determined?
1. By looking at structural similarities2. Observing breeding behavior3. Geographic distribution4. Comparing chromosome number and
structures5. Biochemical analysis of organisms
(comparing DNA sequences).
Phylogenetic Classification: Models1. Phylogeny is the evolutionary history of an
organism (like your genealogy) and is depicted by a classification system
2. Cladistics is a system of classification based on phylogeny
a. Scientists who use cladistics assume organisms diverge and evolve from a common ancestor
b. Still retain some unique characteristics called derived traits.
c. A cladogram uses the derived traits of a group in the form of a branching diagram
Cladogram
Other Phylogenetic Models
1. Fan shapea. May depict time organisms became extinctb. Or relative number of species in a group
Identifying Organisms
1. Use a manual or field guide2. Ask a local expert3. Use a Key – a set of descriptive steps that
is subdivided into stepsa. Ex. Dichotomous Key – two descriptions at each
step. Just follow the steps until the key reveals the name of the organism.