Systematics • Branch of Biology that deals with classifying

living things both current and prehistoric.

3 components:

1. Taxonomy:

– Branch describing and naming new taxonomic

groups (species)

2. Classification

– Branch organizing information about organisms by

arranging them into a hierarchical system

3. Phylogenetics

– Branch determining the evolutionary history and

relationships among the various forms of life through

time

Current Taxonomic Model

Family

Kingdom

Phylum / Division

Class

Order

Genus

Species

Domain

Species

Genus

The smallest group of organisms classified

• Difficult to determine the criteria for what a species is.

– Example: is a mule it’s own species?

• A species is a population which can interbreed with each other (share a gene pool) to produce fertile offspring

• This makes them a distinct biological unit

• Part of the scientific name

• e.g. scientific name of human : Homo sapien

Scientific name of a cat: Felis domesticus

• Group of closely related species

• All the species in a genus share common

characteristics

– Ex: a house cat, Felis domesticus, and a mountain lion, Felis

concolor, share many similar characterisitcs, but are clearly

different organisms

Binomial Nomenclature

• Naming system developed by Swedish botanist

Carolus Linneaus

• Each organism has a two part name

• First the genus and then the species

– Ex: Acer rubrum (red maple tree)

Acer is the genus name

rubrum is the species name

• The species name is usually a Latin word

describing a characteristic

• Notice: genus name is capitalized, species

name is not!

Family

Order

Class

• A family is a larger classification than genus

and groups similar genera (plural for genus)

together

– Ex: all genera of cat-like animals are grouped in the

family Felidae

– Felis, Panthers, Acinonyx

• The next largest classification (taxon) groups

similar families together

– Ex: Cats (family Felidae) and Dogs (family Canidae)

are in the order Carnivora (carnivores)

• Orders are grouped into classes, again based

on common characteristics

– Ex: all order of Carnivora are warm-blooded, have

body hair and produce milk, so they are placed with

the order Primates (incl. humans) in the class

Mammalia

Phylum

(Division)

• Classes are grouped into a phylum

– Ex: mammals are placed in the phylum Chordata with

birds, fish, and reptiles because they share a similar

characteristic (of nervous system development)

Cladogram

Phylogenetic

Tree

Kingdom

Domain

• Closely related Phyla are grouped into

Kingdoms

• There are six kingdoms:

– Animalia, Plantae. Fungi, Protista, Eubacteria,

Archaebacteria

• In 1990 a system of 3 Domains was introduced

– Domain Eukaraya (includes Protists, Fungi, Plantae

and Animalia Kingdoms)

– Domain Bacteria (includes Kingdom Eubacteria)

– Domain Archaea (includes Kingdom Archaebacteria)

So where did this system come from?(the history)

Aristotle (384 – 322 BCE)

• Created the first widely used system of

classification by dividing organisms into

Animals and Plants

Carolus Linnaeus (1707 – 1778)

• Developed a hierarchical categorization

system (kingdom, phylum, class, order, family,

genus, species)

• Grouped organisms based on their resemblance

to other life forms

• Developed the Binomial Nomenclature system

(still in use today)

1850’s

• Improvements in light microscope led to the

discovery of a large number of organisms

Ernst Haeckel (1866)

• Proposed 3rd Kingdom Protista which includes

all single celled organisms

1900’s

• Invention of electron microscope and

advancements in biochemistry

• Discovery of Eukaryotic and Prokaryotic cells

Robert Whitaker (1959)

• Proposed 5 kingdom system (Plants, Animals,

Fungi, Bacteria and Protists)

Carl Woese (1970’s)

• Analyzed base sequences of RNA in bacteria

and protists and suggested that bacteria should

be separated into two groups Eubacteria and

Archaebacteria

• Led to a Six Kingdom system in which

Kingdom Bacteria (Monera) was separated into

the Eubacteria and Archaebacteria kingdoms

• 1990 Woese proposed a Three Domain

scheme of clasification

Life as we Know it

(right now)