How does mail end up in your
What is the purpose of an address?
Your address serves as a way to classify you
based on your location.
Your address is unique to your house and
differentiates your mailbox from all the other
mailboxes in the world.
Just as the mail system is set up in an orderly
fashion that allows you to identify a specific
mailbox, scientists have set up a classification
system that allows you to uniquely identify each
species on the planet.
Classification is the grouping of objects or
information based on similarities.
When you classify objects, you separate a large
group of objects into smaller and smaller sub-
groups based on similar characteristics until
each object is identifiable by its unique
With over 2 million species on Earth, scientists
needed to design a system if classification in
order to differentiate one species from another.
The branch of biology that deals with grouping
and naming organisms is called taxonomy.
The History of
The first method of classification
was developed around 350 B.C
by the Greek philosopher
Aristotle’s classification system
grouped plants according to their
size and structure, and grouped
animals according to where they
lived (land, air, or water).
However, Aristotle’s system failed
to show natural relationships
In the late 18th century, a Swedish
botanist named Carolus Linnaeus
developed a classification system
that is wisely used today.
Linnaeus analyzed physical
characteristics of organisms and
classified them based on close
Linnaeus designed a classification
system called binomial
nomenclature which classifies each
organism using two Latin names.
According to Linnaeus’ system of binomial
nomenclature, each organism is assigned two
He first name identifies the genus of the
A genus is a group of closely related species.
The second name identifies the species or
The species name usually describes the
Example: Canis familiaris = Dog
The two word name assigned to each species
through binomial nomenclature is called a scientific
-> Scientific Name: Belis perennis
However, people usually refer to organisms using
the organism’s common name.
-> Common name: Daisy
Common names do not tell how organisms are
related or classified, and they can also be
It is important that scientific names do not change,
so they are assigned in Latin, a language that is no
longer spoken (and therefore does not change).
Scientific names are either italicized or underlined,
and the first letter of the genus is capitalized, while
the first letter of the species is not.
In taxonomy, organisms are grouped in a series
of categories called taxa (singular = taxon)
When classifying an organism, biologists place
the organism in a broad group known as a
The organism is then placed in a series of sub-
groups (taxa) that becomes increasingly specific
until it is uniquely identifiable.
Progression of Taxa
Kingdom (most broad) Animalia Animalia
Phylum Chordata Chordata
Class Mammalia Mammalia
Order Carnivora Carnivora
Family Felidae Felidae
Genus Lynx Lynx
Species (most specific) Lynx rufus Lynx canadensis
(“King Phillip Came Over For Good Soup”)
There are four main ways
to determine relationships
1. Evolutionary history:
structure of modern-day life
forms with those found in
fossils to determine
The evolutionary history of
a species is called
Evolution: Change: All in the
Similarities in the
development stages of
animals help determine
relationships, and can
help determine if two
animals have a
3. Biochemical relationships:
Closely related species have
similar DNA sequences, and
therefore, similar proteins.
The more amino acid
sequences two species have in
common, the more closely
related they are to each other.
Example: Human and
Even though two species may look similar,
distinct differences in their behavior may
identify them as different species.
Example: Mating calls of frogs
Domains and Kingdoms
There are three domains
There are six kingdoms