Classification of Organisms

3.5 Analyze how classification systems are developed upon speciation. 3.5.1 Explain the historical development and changing nature of classification systems. 3.5.2 Analyze the classification of organisms according to their evolutionary relationships (including dichotomous keys and phylogenetic trees).

Taxonomy Taxonomy is branch of biology that groups and names organisms based on studies of their different characteristics.

Ancient Classification Systems Aristotle- Greek philosopher (384-322 B.C.) Classified organisms as either plants or animals based on physical similarities. Greeks and Romans Created categories called genera to group types of animals and plants. Until mid-1700s Specific types of organisms were named with Latin descriptive words. Problems arose when new organisms were discovered. Groups did not show evolutionary relationships.

Carl Linnaeus’s System Swedish botanist (1707-1778) Developed a system for naming organisms with two words called binomial nomenclature. The first word is the genus in which an organism belongs. The second word is the species name of an organism which describes the organism. Together these two words today are referred to as an organism’s scientific name. Scientific names are in Latin and either in italics or underlined. The first word is written with a capital letter.

Today Scientists today have created a system of classification in which organisms of similar genera are placed into a family. Organisms of similar families are placed into an order. Similar orders are placed in a class. Similar classes are placed into a phylum. Similar phyla are placed into a kingdom, and similar kingdoms are placed in a domain. Students can create mnemonic devices to remember the taxonomic levels. For example, Did King Philip Come Over For Good Soup?

Scientific Classification of Humans 1. Domain- Eukarya 2. Kingdom- Animalia 3. Phylum- Chordata 4. Class- Mammalia 5. Order- Primates 6. Family- Hominidae 7. Genus- Homo 8. Species- sapiens

Domain- Eukarya Consists of all organisms made of one or more cells that have a nucleus as well as other membrane-bound organelles. There are currently 3 domains- Archaea, Bacteria, and Eukarya. Archaea and Bacteria consists of prokaryotic organisms.

Kingdom Animalia Consists of organisms that are multicellular, eukaryotic, lack a cell wall, and are heterotrophic. Other Kingdoms within the Domain Eukarya include Plantae, Fungi, and Protista.

Phylum Chordata All animals in this subgroup have a notochord, pharyngeal slits, and a post-anal tail at some point in development. Other examples of phyla within the Animalia Kingdom include Porifera, Mollusca, Echinodermata, Annelida, Arthropoda, and Nematoda.

Class Mammalia Consists of organisms that produce milk for their young and have hair. Examples of other classes within the Chordata Phylum include Aves, Reptilia, Amphibia, and Osteichthyes

Order Primates Consists of mammals that exhibit high levels of intelligence. Examples of other orders within the Mammalia Class include Carnivora, Artiodactyla, Cetacea, Insectivora, Rodentia, and Monotremata

Family Hominidae Consists of all primates that walk upright.

Genus Homo Consists of all humans including ancestors of modern humans.

Species sapiens Consists of only modern humans. A species is a group of organisms that can successfully breed and produce fertile offspring.

Classification System Change Discovery of new organisms both living and extinct. Formation of new species (speciation). Genomics- finding distinct differences between organisms allowing for the creation of new groups and subgroups.

Cladograms Diagrams showing the evolutionary history of derived traits in a specific group of organisms. In this cladogram example, the numbers represent different types of organisms and the letters represent traits. Organism 1 does not have any of the traits while Organism 5 has all 4 of the traits.

Dichotomous Keys A series of questions or characteristics used for identifying organisms. Some keys are formulated for identifying organisms based on their common names while others on organisms’ scientific names. In this dichotomous key example, organisms are identified based on physical descriptions of their ears. It is essential to start with choices 1a and 1b for each organism or you may get the wrong answer. For example, three of the organisms have ears that are separated.