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UNIT 8—EVOLUTION & CLASSIFICATION Chapters 16 – 18 16.1: Darwin’s Observations Evolution—the process of change over time Theory of biological evolution developed by Darwin Darwin sailed on the HMS Beagle Darwin’s observations: Different, unrelated species found in different habitats around the world (ex: flightless birds) Different but related species found in different habitats in an area (ex: Galápagos turtles) Fossils of extinct species were similar to living species 16.2: Ideas from Darwin’s Observations Variations can be passed from parents to offspring Artificial selection— selective breeding of plants & animals to produce desirable traits Ex: dog breeding, corn & grain crops 16.3: Darwin’s Theory Adaptation—any inheritable characteristic that increases an organism’s ability to survive & reproduce Ex: body parts, camouflage/mimicry, functions Fitness—how well an organism can survive & reproduce in its environment “Survival of the fittest” Natural selection—organisms that are most suited to their environment survive & reproduce Comparing Anatomy Homologous structures—structures shared by related species; may have been inherited from common ancestor Ex: front limb of reptile, horse, bird Analogous structures—structures that share a common function but not structure Ex: dragonfly & bird wing Vestigial structures— structures that have lost original function Ex: legs in whales, appendix in humans 17.2: Change in Populations Natural selection can lead to changes in allele frequencies, causing changes in phenotype frequencies Frequency of phenotypes forms a bell curve Most common trait forms peak of bell curve Less common traits form edges of bell curve Directional selection—shift in phenotypes to one end of bell curve Stabilizing selection—phenotypes at center of curve are better fit to survive Disruptive selection—phenotypes at ends of curve have higher fitness Allele frequencies do not change in populations that are not evolving Population is at genetic equilibrium Allele frequencies should remain constant unless changes in genetic equilibrium occur: Nonrandom mating (choosing a mate) Small population size Immigration/emigration Mutations 17.3: Speciation Isolating Mechanisms Speciation—formation of new species Reproductive isolation—members of a population stop breeding with each other, causing a split in population Two separate species can evolve Behavioral isolation—caused by changes in behavior Geographical isolation—caused by separation by mountains, rivers, etc. Temporal isolation—caused by differences in reproduction times Adaptive Radiation & Convergent Evolution Adaptive radiation—single (or small group of) species evolve into different forms Convergent evolution—unrelated organisms in similar environments independently evolve similar characteristics 18.1: Classification Systems Assigning Scientific Names Scientific names must refer to one species Everyone must use the scientific name Name usually in Latin or Greek (ex: Felis concolor) Common names can be confusing (ex: cougar, puma, catamount, panther) Dichotomous keys are used for identifying organisms Linnaeus came up with a system of binomial nomenclature—each species given a two-part scientific name Consists of genus & species Genus = similar species (ex: Felis); species = unique to the species (ex: concolor) Similar organisms grouped into taxa (cats, birds, mammals, bacteria, etc.) Linnaean Classification System Organisms grouped into seven taxa: Kingdom Phylum Class Order Family Genus Species Cladograms Evolutionary classification examines traits to determine when organisms branched of from common ancestor Cladogram—diagram that shows evolutionary lines branching from common ancestor Shows relatedness of species Species splitting to two new ones is the branch point of cladogram Bottom of cladogram is ancestral species 18.2: Six Kingdoms Changing Ideas About Kingdoms Linnaeus classified organisms into 2 kingdoms: Animalia & Plantae Organisms later classified into 5 kingdoms Microorganisms classified as Protista, bacteria as Monera, yeasts/mold/mushrooms as Fungi 1990s split Monera into two kingdoms: Archaebacteria & Eubacteria Tree of All Life Kingdoms Archaebacteria & Eubacteria— unicellular & prokaryotic Kingdom Protista—unicellular & eukaryotic Kingdom Fungi—multicellular, eukaryotic, cell walls contain chitin, decomposers Kingdom Plantae—multicellular, eukaryotic, cell walls contain cellulose, photosynthetic Kingdom Animalia—multicellular, eukaryotic, heterotrophic