Finding Order in DiversityChapter 18Page 446

Why Classify? (Why Organize?)• To study the great diversity of life. • Biologists attempt to organize living things into groups

in a logical manner that have biological meaning.

• The science of organizing and classifying is called TAXONOMY. Each life form is given a universally accepted name. (This avoids confusion caused by regional names.)

• What is the name of this animal?• Mountain lion / puma / cougar / panther• Felis concolor

Classification: A Historical Perspective

1. Aristotle (350 BC) – Noted the need for classification. Distinguished organisms by habitat and means of reproduction [simple and obvious groups]Point – God is orderly and organized and we are created in His image, therefore, it is right for us to be ordered and organized…

2. Carolus Linnaeus (1707-1778) – Father of Taxonomy. Two main contributions…

1. Assigned each organism a two-part Latin name. Binomial NomenclaturePart I – Genus (first letter always capitalized)

Part II – species (first letter always lowercase)

[Canis lupus – gray wolf][Canis familiaris – common dog]

-- usually italicized or underlinedLinnaeus focused on two groups of life – Plants

and Animals – he contributed 11,000 biological names.

2. Grouped organisms into a hierarchy of categories: Kingdom (large and general) Phylum Class Order Family Genus Species (small and specific)Taxon - a group to which organisms are assigned according

to the principles of taxonomy, including species, genus, family, order, class, and phylum

Modern Classification• Biologists now group organisms into categories that

represent lines of descent (phylogeny), not just visible physical characteristics.

• Lines of descent form a family tree diagram called a cladogram. [Cladograms are useful tools that help scientists understand how one lineage branched from another in the course of evolution. A cladogram represents evolutionary relationships among a group of organisms.]

Systems of Classification

• The scientific view of life was simpler in Linnaeus’s time:

1. 1700’s Plants and Animals

2. 1800’s Plants, Animals, and Protists (microbes)

3. R.H. Whittaker (1950’s) – proposed a 5 Kingdom system of classification based on cell type – Eukaryotic vs. Prokaryotic

4.(1990’s) – A Six Kingdom Classification System

4. Carl Woese (most recent – late 1990’s) – Proposed the formation of three domains.