Organizing Life’s Diversity

Chapter 17

How Classification Began In order to better understand organisms

scientists group them. Classification is the tool scientists use to group

organisms Taxonomy is the branch of biology that groups

and names organisms based on their characteristics.

Taxonomists are scientists who study taxonomy.

Early Systems1. Aristotle's System

a. Only included plants and animals.b. Did not group organisms by evolutionary history.c. Many organisms did not fit.

2. Linnaeus’s Systema. Based on physical and structural similarities.b. Still just plants and animals, but he further

subdivided these groups.c. Some scientists proposed that structural

similarities mirrored evolutionary relationships.

Today’s Classification System3. Modern system

a. Binomial nomenclature is a two name / word system that Linnaeus developed to identify species

b. Written in Latin because this language does not change and is universal.

c. The first word indicates the genus and the second the species (which is descriptive of the organism -sapiens means wise)

i. Ex. Homo sapiens, H. sapiens, Homo sapiens, H. sapiens

How Living Organisms are Classified1. Organisms are

ranked from very broad taxa containing lots of species to very specific taxa.

Example: Humans Domain: Eukaryota         Kingdom: Metazoa           Phylum: Chordata            

Class: Mammalia               Order: Primata                 Family: Hominidae                  

Genus: Homo                     Species: sapiens

The Six Kingdoms

How many species are there in each kingdom?

Archaebacteria = 500

Eubacteria = 10,000

Protista = 70,000

Fungi = 110,000

Plants = 510,000

Animals = 2,900,000

How Are Evolutionary Relationships Determined?

1. By looking at structural similarities2. Observing breeding behavior3. Geographic distribution4. Comparing chromosome number and

structures5. Biochemical analysis of organisms

(comparing DNA sequences).

Phylogenetic Classification: Models1. Phylogeny is the evolutionary history of an

organism (like your genealogy) and is depicted by a classification system

2. Cladistics is a system of classification based on phylogeny

a. Scientists who use cladistics assume organisms diverge and evolve from a common ancestor

b. Still retain some unique characteristics called derived traits.

c. A cladogram uses the derived traits of a group in the form of a branching diagram

Cladogram

Other Phylogenetic Models

1. Fan shapea. May depict time organisms became extinctb. Or relative number of species in a group

Identifying Organisms

1. Use a manual or field guide2. Ask a local expert3. Use a Key – a set of descriptive steps that

is subdivided into stepsa. Ex. Dichotomous Key – two descriptions at each

step. Just follow the steps until the key reveals the name of the organism.