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.

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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