Honors Biology

Mrs. Toner

Chapter 17: Organizing Life’s Diversity

1. How is classification used every day?2. Why do scientists organize or classify

living things?3. Do you know the scientific names of any

species?

Biologists use a system of classification to organize information about the diversity of living things.

Just as stores group CDs according to type of music and artist, biologists group living things by their characteristics and evolutionary relationships.

Section 17.1 – The History of Classification

Classification – is the grouping of objects or organisms based on a set of criteria.

Biologists find it easier to communicate and retain information about organisms when the organisms are organized into groups.

One of the principal toolsfor this is biological classification.

Early Systems of Classification

Aristotle’s SystemGreek philosopher , Aristotle (394-322 B.C.)Developed the first widely accepted system.Classified organisms as either plants or

animals.

Early Systems of Classification (cont.)

See page 484Table 17.1Aristotle’s Classification System

Limitations of Aristotle’s System:Viewed systems as being distinct, separate,

and unchanging.This was a common view until Darwin

presented his theory of evolution which stated that organisms are always changing. Organisms share evolutionary relationships.

Nevertheless, many centuries passed before Aristotle’s System was replaced by a new one that was better suited to the increased knowledge of the natural world.

Early Systems of Classification (cont.)

Linnaeus’s System:Linnaeus (Swedish Naturalist, 1707-1778)Broadened Aristotle’s classification methodConcentrated on morphology and behavior of

organismsCategorized birds into three major groups (see

page 485, Figure 17.1)Linnaeus’s system of classification was the first

formal system of taxonomic organization.Taxonomy – is a discipline of biology primarily

concerned with identifying, naming, and classifying species based on natural relationships.

Early Systems of Classification (cont.)

Linnaeus’s method of naming organisms called binomial nomenclature – gives each species a two-part name: genus and species

LatinCardinalis cardinalis

Early Systems of Classification (cont.)

Species and GenusTaxon – a named group of organisms (plural,

taxa).Range from having broad diagnostic characteristics

to having specific characteristics.Think of taxa as a set of nesting boxes – one

fitting inside the other. (See page 488, Fig. 17.4)

DomainKingdomPhylumClass OrderFamilyGenusSpecies

Taxonomic Categories(Created by Linnaeus)

Species – a group of organisms that can interbreed and produce offspring. [Ursus americanus (American black bear), Ursus thibetanus (Asiatic black bear)]

Genus – (pl. genera) a group of species that are closely related and share a common ancestor. (Ursus = black bear)

Family – is the next higher taxon, consisting of similar, related genera. (Ursidae = all bears, both living and extinct; brown bears, polar bears, giant pandas)All members of the bear family share certain

characteristics. They walk flatfooted, have forearms that can rotate to clasp prey.

The Taxonomic Categories

Order – contains related familiesClass – contains related ordersPhylum – (pl. phyla) or division (bacteria and

plants) contains related classesKingdom - the taxon composed of related

phyla or divisionsDomain – the broadest of taxa.

ACTIVITY: Classify a giant panda, Ailuropoda melanoleuca, completely from domain to species level by referring to Figure 17.4.

The Taxonomic Categories (cont.)

Eukarya, Animalia, Chordata, Mammalia, Carnivora, Ursidae, Ailuropoda, melanoleuca

Answer to Activity:

Determining Species – the definition of species has “evolved” over the years.Typological Species ConceptBiological Species ConceptPhylogenetic Species Concept

Phylogeny – the evolutionary history of a species.Shows evidence of a pattern of ancestry and

descent.

Section 17.2 - Modern Classification

To classify a species, scientists often construct patterns of descent, or phylogenies, by using characters.

Characters – inherited features that vary among species. Characters can be:Morphological - similarity in anatomy

Example – Darwin’s FinchesBiochemical (Molecular) - similarity of nucleic

acids (DNA) and amino acids (proteins)Developmental - similarity in developmental

patternsBehavioral – similarity in vocalization or mating

behaviors

Characters

The evolutionary history of a species or group of related species.

Organizes organisms based on their history and relation to one another.

A phylogenetic tree (or evolutionary tree) is a graphical hypothesis of the proposed phylogeny.A phylogenetic tree is often called a

cladogram.A cladogram is a branching diagram that

represents the evolutionary history of a species.

Cladistics – a method that classifies organisms according to the order that they diverged from a common ancestor.

Phylogeny

Cladogram (Phylogenetic Tree)

Clade

Node