Transcript Slide 1

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.
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
A Simpler System
A simpler system for naming organisms
was developed by the Swedish biologist
Carl Linnaeus
Linnaeus’s 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
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
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.
Classifying Organisms
Linnaeus worked out a broad system of
classification for plants and animals in
which an organism’s 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
Similar genera are grouped into a family
Similar families are combined into an
order
Orders with common properties are
united in a class
Classes with similar characteristics are
assigned to a phylum
Similar phyla are collected into a kingdom
Similar kingdoms are grouped into
domains
Classification of the Honeybee
Each level of classification is based on
characteristics shared by all the
organisms it contains
The honeybee’s 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
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
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
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 organism’s
features
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
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
Evolutionary History
Classification based on similarities should
reflect an organism’s 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
Similarities that arise through
convergent evolution are called analogous
characters
Phylogenic Diagram of Mammals
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
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
Cladogram: Mammals,
Reptiles, and Birds
Cladogram: Major Groups of Plants
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
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
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.
Evolutionary Systematics and
Cladistic Taxonomy