Transcript Evolution
Evolution All the changes that have transformed life from its earliest forms to what we see today. Evolution is the result of genetic changes that occur in constantly changing environments. Natural Selection • Populations change in response to their environment. • Acts on phenotype of an organism. (Not genotype) Natural Selection • Determines the differential survival of groups of organisms Phenotype • Observable characteristics (green eyes, brown hair, purple flowers, etc.) Genotype • Genetic makeup of an organism determined by a pair of alleles. Allele • Alternative form of a gene for each variation of a trait. Gene • Unit of hereditary information • Located on a chromosome • Contains DNA Gene Pool • Total genes in a population at any one time Homozygous • Having two identical alleles for a trait Heterozygous • Having two different alleles for a trait Mutation • Change in DNA of a gene or chromosome • Mutations occur constantly in a gene pool Reproductive Isolation • Prevention of mating between formerly interbreeding groups. or • The inability of these groups to produce fertile offspring Geographic Isolation • Physical barrier divides a population • These two groups are not able to mate => may lead to new species Speciation • Formation of a new species Mass Extinction • An episode in which many species suddenly become extinct Punctuated Equilibrium • Evolutionary model • Rapid changes to a species in a short time, followed by periods of little change. Gradualism • Model of evolution involving slow, gradual changes to a species over time. Gradualism vs. Punctuated Equilibrium Bacteria • First form of life on Earth • Evolved 3.5 billion years ago (prokaryotes) • Eukaryotes (complex) formed 1.5 billion yrs ago Multicellular life • Evolved 570 Ma (Cambrian explosion of life!) • Multicellular = more than one cell • Jellyfish-type creatures were first forms • Vertebrates • • • • Have a backbone 1st were jawless fish Amphibians 1st on land Almost all land animals larger than a fist Arthropods • • Have an exoskeleton (Hard outer shell) • First animals on land (scorpion) • Crabs, lobsters, insects, spiders Reptiles • Evolved from amphibians • Diversified into many forms after the Permian mass extinction (250 Ma). • Dinosaurs • • • Evolved from reptiles and dominated the Mesozoic Era • Were wiped out by a large body that impacted Earth 65 million yrs ago Mammals • Were very small during the Mesozioc • Became the dominant life form after the Cretaceous mass extinction (65 Ma) •