Classification

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Chapter 15 Classification of Organisms
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15-1 Categories of Biological Classification
Until more recent times, scientists named Things
with crazy long names that Just described the
organism.
Apis pubescens, thorace subgriseo, abdomine
fusco, pedibus posticis glabis, untrique margine
cilatus.
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Taxonomy
The science of naming and classifying organisms
is called taxonomy.
Until the mid-1700s, biologists named a
particular type of organism by adding descriptive
phrases to the name of the genus
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A Simpler System
A simpler system for naming organisms was
developed by the Swedish biologist Carl Linnaeus
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Linnaeuss two-word system for naming organisms
is called binomial nomenclature
Over the past 250 years since Linnaeus first used
two-part binomial species names, his approach has
been universally adopted
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Scientific Name
The unique two-part name for a species is now
referred to as its scientific name
The first word is the genus to which the organism
belongs. A genus is a taxonomic category
containing similar species
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The second word in a scientific name identifies
one particular kind of organism within the genus,
called a species. A species is the basic
biological unit in the Linnaean system of
classification
With Linnaeus system, the honey bee Is now
called Apis mellifera.
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Classifying Organisms
Linnaeus worked out a broad system of
classification for plants and animals in which an
organisms form and structure are the basis for
arranging specimens in a collection
The genera and species that he described were
later organized into a ranked system of groups
that increase in inclusiveness
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Similar genera are grouped into a family
Similar families are combined into an order
Orders with common properties are united in a
class
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Classes with similar characteristics are assigned
to a phylum
Similar phyla are collected into a kingdom
Similar kingdoms are grouped into domains
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Classification of the Honeybee
Each level of classification is based on
characteristics shared by all the organisms it
contains
The honeybees scientific name, Apis mellifera,
indicates that it belongs to the genus Apis,
which is classified in the family Apidae
All members of the family Apidae are bees that
live either alone or in hives, as does Apis
mellifera
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15-2 How Biologists Classify Organisms
What Is a Species?
In 1942, the biologist Ernst Mayr of Harvard
University proposed a biologically based
definition of species, which is called the
biological species concept
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Mayr defined a biological species as a group of
natural populations that are interbreeding or
that could interbreed, and that are
reproductively isolated from other such groups
Sometimes individuals of different species
interbreed and produce offspring called hybrids
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Evaluating the Biological Species Concept
The biological species concept works well for
most members of the kingdom Animalia, in which
strong barriers to hybridization usually exist
In practice, modern biologists recognize species
by studying an organisms features
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But the biological species concept fails to
describe species that reproduce asexually, such
as all species of bacteria and some species of
protists, fungi, plants, and even some animals
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Number of Species
The number of species in the world is much
greater than the number described
Only about 1.5 million species have been
described to date
Scientists estimate that 5 million to 10 million
more species may live in the tropics alone
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Evolutionary History
Classification based on similarities should
reflect an organisms phylogeny, that is, its
evolutionary history
Through the process called convergent evolution,
similarities evolve in organisms not closely
related to one another, often because the
organisms live in similar habitats
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Similarities that arise through convergent
evolution are called analogous characters
Phylogenic Diagram of Mammals
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Cladistics
Cladistics is a method of analysis that
reconstructs phylogenies by inferring
relationships based on shared characters
With respect to two different groups, a character
is defined as an ancestral character if it
evolved in a common ancestor of both groups
A derived character evolved in an ancestor of one
group but not of the other
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Cladistics is based on the principle that shared
derived characters provide evidence that two
groups are relatively closely related
A biologist using cladistics constructs a
branching diagram called a cladogram, which shows
the evolutionary relationships among groups of
organisms
Organisms that share derived characters, are
grouped together on the cladogram
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Cladogram Mammals, Reptiles, and Birds
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Cladogram Major Groups of Plants
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Considering Characters
The great strength of cladistics is objectivity.
If a computer is fed the same set of data
repeatedly, it will make exactly the same
cladogram every time
The disadvantage of cladistics is that the degree
of difference between organisms is not considered
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Cladistic analysis does not take into account
variations in the strength of a character, such
as the size or location of a fin or the
effectiveness of a lung. Each character is
treated equally
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Evolutionary Systematics
In evolutionary systematics, taxonomists give
varying degrees of importance to characters and
thus produce a subjective analysis of
evolutionary relationships
In this type of analysis, evolutionary
relationships are displayed in a branching
diagram called a phylogenic tree
Evolutionary systematics involves the full
observational power of the biologist, along with
any biases he or she may have.
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Evolutionary Systematics and Cladistic Taxonomy
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THE END