Classification systems help biologists organize living things into groups based on shared characteristics. Biologists use a seven-level system of classification that includes kingdom, phylum, class, order, family, genus, and species. This system was developed by Carolus Linnaeus in the 1700s and is still used today. Each level provides more specific details about an organism's characteristics and evolutionary relationships. Scientific names provide a standardized way to identify organisms worldwide.

1. CLASSIFICATION!
Sorting It All Out

2. Why Classify?
 Classification: the division of organisms
into groups, or classes, based on specific
characteristics
 For thousands of years, humans have
classified things based on usefulness
 Biologists use system to classify things—
this system groups organisms according
to their shared characteristics

3.  Classification of living things
makes it easier for biologists to
answer many important
questions, such as:
How many known
species are there?
What are the defining
characteristics of each
species?
What are the
relationships between
these species?

4. How Do Scientists Classify
Organisms?
 Great Greek
philosopher and
scientist Aristotle
(384-322 BCE)
began classifying
animals into
logical groupings
more than 2000
years ago

5. – He arranged all living
things in an ascending
ladder with humans at
the top
– Animals were
separated into two
major groups—those
with red blood and
those without red blood
(very similar to our
modern classification of
invertebrates and
vertebrates )

6.  In 1700s, Swedish
scientist Carolus
Linnaeus founded
modern taxonomy
 Taxonomy : the
science of describing,
naming, and
classifying organisms
 Linnaeus tried to
classify all living things
based on their shape
and structure

7. – Species were given
distinctive two-word
names
 Described a seven -
level system of
classification, which is
still used today,
although it has gone
through many
changes.

9. Classification Today
 Taxonomists use the 7-level system to
classify living things based on shared
characteristics
 Also use shared characteristics to
hypothesize how closely related living
things are
 The more characteristics they share, more
closely related the organisms are

10. Example: platypus, brown bear, lion, and house cat are
thought to be related because they share many
characteristics. These animals have hair and mammary
glands, so they are grouped together as mammals.
They can be further classified into more-specific
groups.

11. Branching Diagrams
 Each characteristic on the lines of the branch are
shared by the animals to the right of it
 As you move up the line, the animals are more
closely related to each other

12. Levels of Classification
 Every living thing is classified into one of six
kingdoms:
1. KINGDOM: largest, most general group
2. PHYLUM: sorted from the kingdom
3. CLASS: all living things in a phylum are sorted
into classes
4. ORDER: each class includes one or more
orders
5. FAMILY: one or more orders
6. GENUS: families are broken into genera

13.  Genera are sorted into
species
 A species is a group of
organisms that are
closely related and can
mate to produce fertile
offspring
 Let’s see the
classification of a
housecat from kingdom
Animalia to genus and
species, Felis domesticus

14. Kingdom Animalia
All animals are in the kingdom animalia

15. Phylum Chordata
All animals in the phylum Chordata have a
hollow nerve cord. Most have a backbone.

16. Class Mammalia
Animals in the class Mammalia have a
backbone. They also nurse their young.

17. Order Carnivora
Animals in the order Carnivora have a
backbone and nurse their young. They also have
special teeth for tearing meat.

18. Family Felidae
Animals in the family Felidae are cats. They have a
backbone, nurse their young and have special teeth for
tearing meat. The Felidae have five toes on the front feet,
four on the hind ones, all armed with strong "retractile
claws”.

19. Genus Felis
Animals in the genus Felis have traits of
other animals in the same family. However,
these cats cannot roar; they can only purr.

20. Species Felis domesticus
the species Felis domesticus is the
common house cat. The house cat shares
traits with all of the organisms in the levels
above the species level, but it also has
unique traits.

21. Scientific Names
 A scientific name is always the same for a
specific kind of organism no matter how
many common names there might be
 Before Linnaeus, different scientists
named organisms differently, so an
organism could have more than one name
Example on next slide…

22. Example:
What do the mountain lion, cougar, and puma all
have in common? They are ONE ANIMAL with
several common names! The scientific name for
all three common names is Felis concolor, no
matter where you go in the world!

23. Two-Part Names
 Linnaeus simplified the naming of
living things by giving each species
a two-part scientific name
 For example, the scientific name for
the Asian elephant is Elephas
maximus. First part of name
Elephas is genus name. Second
part, maximus, is species name.
 No other species has both this
genus name and species name.

24.  All genus names begin with a
capital letter
 All species names begin with a
lowercase letter
 Usually, both words are
Equus caballus
underlined or italicized
 Scientific names are usually in
Greek or Latin, and contain
information about the organism

25. Dichotomous Keys
 Dichotomous key: an aid that is used to
identify organisms and that consists of the
answers to a series of statements
 There are only 2 alternative responses to
each statement
 Either the chosen statement identifies the
organism or the person is directed to
another pair of statements

26.  By working through
the statements in the
key in order, the
person can eventually
identify the organism
Dichotomous Key for Identifying Candy

28. A Growing System
 People are still discovering and classifying
organisms
 Some newly discovered organisms fit into
existing categories
 Sometimes, someone discovers new
evidence or an organism is so different
from other organisms that it doesn’t fit into
a category.