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Modern Evolutionary Classification Section 17-2 Problems with Traditional Classification • Originally, organisms were grouped according to their physical features. • Biologists now group organisms into categories based on their evolutionary history, not just physical similarities. ≠ How are evolutionary relationships determined? • Structural similarities • Geographical distribution • Biochemistry – Similar DNA and proteins • Chromosome comparison – # and structure of chromosomes • Breeding behavior – Ex. Different calls keep mates from within same group • Embryonic development Phylogeny • What is it? – The evolutionary history of a species • How is it shown? – Using models called phylogenetic trees Cladistics • A system of classification based on phylogeny • It classifies organisms according to the order that they diverged from a common ancestor. Cladistics • Scientists look at ancestral characters, those found in the entire line of descent • They also identify a group’s derived traits (unique inherited characteristics not found in a common ancestor) and use them to construct a branching diagram called a cladogram, a model of the phylogeny of a species. How does a cladogram work? • 2 groups on diverging branches probably share a more recent common ancestor than those groups farther away. • They show a probable evolution of a group of organisms from ancestral groups. The Six Kingdoms of Organisms • • • • • • Archaebacteria Eubacteria Protists Fungi Plants Animals Kingdom Archaebacteria • Prokaryotic – Unicellular – No membrane-bound nuclei • Most live in harsh environments – Swamps, deep-ocean vents, etc. – Mostly no oxygen (anaerobic) Kingdom Eubacteria • • • • • Prokaryotic ~5000 species Very strong cell walls Live in most habitats, except extreme Some causes diseases, most are harmless Kingdom Protista • • • • • Eukaryotic Lacks complex organ systems Lives in moist environments Some unicellular, some multicellular Example: kelp Kingdom Fungi • Eukaryotic • Heterotrophic—absorbs nutrients from organic materials in the environment • Immobile (unmoving) • Unicellular or multicellular • Over 50,000 species Kingdom Plantae • • • • • • Eukaryotic Multicellular Photosynthetic Immobile Cells tissues organs organ systems Over 250,000 species Kingdom Animalia • • • • • Eukaryotic Multicellular Heterotrophic Mobile (move from place to place) Cells tissues organs organ systems
