CLASSIFICATIONQ: WHAT IS THE GOAL OF

BIOLOGISTS WHO CLASSIFY LIVING THINGS?

Why classify organisms?How do evolutionary relationships affect the way scientists classify organisms?What are the major groups within which all organisms are currently classified?

A: TO FIND ORDER IN DIVERSITYQ: What is one thing we can do to “find order

in a diverse world”?A: Give it a name and describe itThis is one of the most basic skills a scientist

does, but exactly how do scientists name things?

COMMON NAMES Depending where you live, common names

are assigned to living things—but this presents a problem because common names may vary from place to place and among languages

Examples: bobcat, cougar, puma, mountain lion all refer to

the same type of cat In the UK a buzzard is a hawk, while in the US it

is a vulture Maryland’s state flower—black eyed Susan,

yellow cornflower

ASSIGNING SCIENTIFIC NAMES To be useful, each scientific name must refer

to one and only one species, and everyone must use that same name for that species.

It must be written in Latin

DICHOTOMOUS KEYS One of the earliest classification systems Consists of a series of paired statements or

questions that describe alternative possible characteristics of an organism.

The paired statements usually describe the presence or absence of a certain visible characteristics or structures.

Each set of choices is arranged so that each step produces a smaller subset.

USING A DICHOTOMOUS KEY

How would you describe this leaf?

Step Leaf Characteristics Tree

1a 1b

Compound leaf (leaf divided into leaflets)…go to step 2Simple leaf (leaf not divided into leaflets)…go to step 4

2a2b

Leaflets all attached at a central point Leaflets attached at several points…go to step 3

Buckeye

3a3b

Leaflets tapered with pointed tips Leaflets oval with rounded tips

PecanLocust

4a4b

Veins branched out from one central point…go to step 5Veins branched off main vein in middle of the leaf…go to step 6

5a5b

Heart-shaped leaf Star-shaped leaf

RedbudSweet gum

6a6b

Leaf with jagged edges Leaf with smooth edges

BirchMagnolia

BINOMIAL NOMENCLATURE Definition: having a two-part scientific name Written in italic if typing or underlined if

hand-written First word (of name) is capitalized and the

second word (of name) is lower-cased Example: Felis concolor or Homo saphien Created by a Swedish botanist named

Carolus Linnaeus

BINOMIAL NOMENCLATURE CONT. Polar bear’s scientific name is Ursus maritimus Ursus is the genus (plural: genera) to which the

polar bear belongs A genus is a group of similar species The genus Ursus contains 4 species of bears

including Ursus arctos—the brown bear or “grizzly”

The second part of the name is the species A species is defined as a group of individuals

capable of interbreeding and producing fertile offspring

The species name is often a description of an important trait or the organism’s habitat.

Species and subspecies of UrsusAmerican Black Bear, Ursus americanus

Cinnamon Bear, Ursus americanus cinnamomumKermode Bear, Ursus americanus kermodei

Brown Bear, Ursus arctos Grizzly Bear, Ursus arctos horribilisKodiak Bear, Ursus arctos middendorffi

Polar Bear, Ursus maritimus (earlier Thalarctos maritimus) Asiatic Black Bear, Ursus thibetanus, or Selenarctos thibetanus

A hybrid between grizzly bears and polar bears has also been recorded (known commonly as a pizzly bear). The official name is a grizzly-polar bear hybrid.

CLASSIFYING SPECIES INTO LARGER GROUPS The science of naming and grouping

organisms is called systematics The goal of systematics is to organize living

things into groups (called taxa; singular: taxon) that have biological meaning

HOW DID LINNAEUS GROUP SPECIES INTO LARGER TAXA? Classification System based on a hierarchy or

set of ordered ranks (smallest to largest): Species Genus Family Order Class Phylum (Division) Kingdom

PROBLEMS WITH TRADITIONAL (LINNAEAN) CLASSIFICATION Linnaean classification emphasized the

overall similarities and differences to classify an organism

Modern systematists apply Darwin’s ideas (descent with modification) to classification and try to look beyond simple similarities and differences to ask questions about evolutionary relationships (i.e. who is more closely related to each other)

LESSON ASSESSMENT1. Identify two goals of systematics.2. Why do the common names of organisms—like

daisy or mountain lion—often cause problems for scientists?

3. The scientific name of the sugar maple is Acer saccharum. What does each part of the name designate?

4. List the ranks of the Linnaean system of classification from largest to smallest.

5. In which group of organisms are the members more closely associated—kingdom or order. Explain your answer.

6. Why might modern biologists have a problem with the term “species”?

TODAY’S MAIN QUESTION:HOW DO EVOLUTIONARY RELATIONSHIPS AFFECT THE WAY SCIENTISTS CLASSIFY ORGANISMS?

Guiding Questions: What is the goal of evolutionary classification? What is a cladogram and how do you interpret a

cladogram? How are DNA sequences used in classification?

MODERN EVOLUTIONARY CLASSIFICATION Remember: Linnaean classification system is

based on similarities and differences Remember: Darwin’s “Tree of Life” suggests

that all living things are related to each other through evolutionary relationships back to a common ancestor

This presents some problems in how we classify living things.

Example: Birds and Reptiles

WHAT IS THE GOAL OF EVOLUTIONARY CLASSIFICATION? The concept of descent with modification (by

Darwin) led to the study of phylogeny—the evolutionary history of lineages—which led to phylogenetic systematics (aka evolutionary classification).

The goal of phylogenetic systematics is to group species into larger categories that reflect lines of evolutionary descent, rather than overall similarities and differences.

EVOLUTIONARY CLASSIFICATION Places organisms into higher taxa whose

members are more closely related to one another than they are to members of any other group. The larger the taxon is, the farther back in time all of its members shared a common ancestor.

Classifying organisms according to these above rules places them into groups called clades.

A monophyletic clade is a group of species that includes a single common ancestor and all descendants of that ancestor—living and extinct.

Paraphyletic clades include a common ancestor but are missing one or more descendants.

WHAT IS A CLADOGRAM? A diagram that links groups of organisms by

showing how evolutionary lines or lineages branched off from common ancestors.

BUILDING CLADOGRAMS Speciation

The process by which one ancestral species splits into two new ones

This is the basis by which each branching point or node is made in a cladogram

The node represents the last point at which the two new lineages above the node shared a common ancestor

The bottom or “root” of a cladogram represents the common ancestors shared by all organisms in the cladogram

Derived Character:A trait that arose in the most recent common ancestor or a particular lineage and was passed along to its descendants.