Classification of Organisms

What’s in a name?

I. Species

II. Origins of taxonomy

III. Modern criteria for classification

VI. The changing classification system

V. Biodiversity and total species

OutlineOutline

Species - A group of organisms that share common characteristics and can interbreed.

Species

A. Aristotle (384-322 B.C.)-simple classification using structural complexity, behavior and degree of development at birth.

B. Carolus Linnaeus (1707-1778) Classification based on resemblance to other life forms

C. Charles Darwin (1809-1882)-categories reflect evolutionary relationship

Origins of taxonomy

In the Linnean System of Classification, eachIn the Linnean System of Classification, each

specific type of organism has a unique name. specific type of organism has a unique name.

Known as the Known as the binomial namebinomial name, it is unique for , it is unique for

each recognized species.each recognized species.

This binomial name consists of a This binomial name consists of a genusgenus name, name,

usually derived from a group of related usually derived from a group of related

organisms...organisms...

and a and a speciesspecies name which is unique to a name which is unique to a

specific group of similar organisms specific group of similar organisms

found within the larger genus grouping. found within the larger genus grouping.

Texas BluebonnetLupinus texensis / Lupinus texensis

Evolution and Natural Selection Evolution and Natural Selection

DarwinDarwinEvolution

Change occurring in a line of descent over time

Natural SelectionSome traits are favored over others

Individuals vary in a population

Some heritable traits are more adaptive than

others

The outcome of differences in survival and

reproduction of individuals

Adaptive traits become more common in a particular environment

ClassificationClassification should reflect the should reflect the Evolutionary relationship:Evolutionary relationship:

Today, the process of classification focuses on

reconstructing phylogeny, or evolutionary history

All species that have ever lived are related

Fossil and geologic records give evidence of

evolution

Tree fern dated 250 mya

A sycamore leaf dropped 50 mya

Categories of ClassificationCategories of Classification

Species

Genus

Family

Order

Class

Phylum

Kingdom

Domain

III. Modern criteria for classification

Anatomy-homologous structures and analogous structures

Developmental stages-embryology

Biochemical comparisons also provide

evidence of evolution

Fossil dating

Evidence of Evidence of Morphological DivergenceMorphological Divergence

Homologous structures vs Analogous structures

Evidence From Evidence From Comparative EmbryologyComparative Embryology

Ontogeny Recapitulates Phylogeny

Evidence from Evidence from Comparative BiochemistryComparative Biochemistry

Molecular clocks

Mutations

Nucleic Acid comparisons

Protein comparisons

Primary structure of three versions of cytochrome C, a major protein component of electron transport systems in cells: yeast (top row), wheat (middle row) & primate (bottom row).

Protein comparisonsProtein comparisons

RACCOON RED PANDA GIANT PANDA

DIVERGENCE

approximately

40 million years ago

DIVERGENCE

15-20 million years ago

SPECTACLED

BEAR

SLOTH

BEAR

SUN

BEAR

BLACK

BEAR

POLAR

BEAR

BROWN

BEAR

Fig. 20.13, p. 322-23

GREEN PYTHON NILE CROCODILE

SEA TURTLE CHAMELEON DINOSAURS

OWL

VI. The changing classification systemVI. The changing classification system

1 Prior to 1970: two-kingdom system

Plants and animals

2 1969: Roger Whittaker-five-kingdom system

Monera, Protista, Fungi, Plantae, Animalia

3 Recent proposal: Carl Woese-three-domain system

Bacteria, Archaea, Eukarya

How Many Kingdoms?How Many Kingdoms?

Whittaker’s Five-Kingdom Scheme

Monera

Protista

Fungi

Plantae

Animalia

Six Kingdom SchemeSix Kingdom Scheme

Carl Woese

Includes the Archaebacteria

eukaryotic organisms that are not animals, plants, or fungi put into Protist

V. Biodiversity and total speciesV. Biodiversity and total species

How many species exist?

1. 1.5 million species categorized

2. Up to 30 million species may exist

7000 to 10,000 new species identified

annually

Many classified species are becoming extinct

as their habitats are destroyed