Why do scientists

classify?

TAXONOMY – branch of biology that

names organisms according to their

characteristics

Why classify? › How many known species are there?

› What are the defining characteristics?

› What are the relationships between these species?

ARISTOTLE

› Greek philosopher/teacher

› 1st person to group/classify organisms

Problems with

Aristotle’s

classification

system.

Not all organisms fit into Aristotle’s

2 groups (plants or animals)

Common names can be misleading

Common names vary from place to

place

Same organisms have different names in

different countries

Fungi & Bacteria

Not all organisms fit into Aristotle’s 2

groups (plants or animals)

Common names can be

misleading

Common names vary from place to

place

Same organisms have different names in

different countries

A jellyfish isn’t a fish but a seahorse is a fish, a sea cucumber sounds like a plant but its an animal

Not all organisms fit into Aristotle’s 2

groups (plants or animals)

Common names can be misleading

Common names vary from place

to place

Same organisms have different names in

different countries

Puma, catamount,

mountain lion,

cougar = the same

animal!

Not all organisms fit into Aristotle’s 2

groups (plants or animals)

Common names can be misleading

Common names vary from place to

place

Same organisms have different

names in different countries

Chipmunk

Streifenhornchen

(German)

Tamia

Ardilla listada

(Spanish)

Description using Latin names

Red Oak – Quercus foliis obtuse-sinuatis

setaceo-mucronatis

Which means – oak with leaves with

deep blunt lobes bearing hairlike

bristles… so what’s the problem?

The name is TOO LONG!

The name doesn’t show evolutionary

relationships.

Hierarchy of seven

levels

Devised a new system based on

morphology (organisms form & structure)

Linnaeus’s Classification System

› Organisms grouped in a hierarchy of seven

different levels

› Each organism has a 2 part name (binomial

nomenclature)

Kingdom

Phylum

Class

Order

Family

Genus

Species

Mneumonic device suggestions…?

WH

ITE P

INE

AFR

ICA

N L

ION

Kingdom -

Phylum -

Class -

Order -

Family -

Genus -

Species -

Kingdom –

Phylum –

Class –

Order –

Family –

Genus –

Species –

Trace the Ancestry

Binomial nomenclature – a two-name

naming system

› ALWAYS italicized or underlined

1st Name: Genus

› First letter CAPITALIZED

2nd Name: Species Identifier

› lower case

EXAMPLE: Homo sapiens (humans)

How scientists use

information to

classify organisms

Uses Linnaeus’s system, but

with additional kingdoms.

Organizes in the context of

evolution.

Scientists classify organisms according to…

1. Fossil Record

2. Morphology

3. Embryology

4. Chromosomes

5. Macromolecules (DNA & Proteins)

We can trace changes over time through

the fossil record

PHYLOGENY = evolutionary history

Shape & Function

Homologous Characteristics

› Same embryological origin, similar structure

and function

› Ex: bat wing & human arm

Analogous Characteristics

› Different embryological origin, similar

structure and function

› Ex: bird wing & butterfly wing

Homologous Structures Analogous Structures

Animals whose embryos develop in a

similar pattern may be related…

Similar karyotypes suggest closer

relationships…

Human –

46 Chromosomes

Chimpanzee –

48 Chromosomes

Comparison of macromolecules such as

Proteins & DNA

Organisms with similar sequences are

(thought to be) more closely related