Transcript Evolution
Evolution Evolution • Change over time • Theory that modern organisms descended from ancient organisms due to how they have changed over a long period of time • Charles Darwin is credited for this theory Types of Evolution • Microevolution – changes that occur over a relatively short amount of time – Ex: Peppered moth • Macroevolution – changes that occur over a relatively long amount of time – Ex: Galapagos finches • Megaevolution – theory that every living organism has one common ancestor Peppered Moths Charles Darwin • Traveled to various places around the world (Galapagos Islands, Argentina, Australia) and made observations about the organisms and environments (ecosystems) he saw Galapagos Islands • Had different species of finches and tortoises • The different species of finch evolved from same ancestor • The different species of tortoise evolved from same ancestor Galapagos Finches • Group of finches traveled from mainland (Equador) to Galapagos Islands • Ate mainly one food source • One food source not enough for all finches and their offspring • Different finches adapted to various food sources (insects, nuts, fruit, berries, nectar from flowers, etc.) and migrated to different islands to look for those food sources • Different species of finch have different sized beaks due to the food sources they eat Galapagos Tortoises • Evolved similar to finches • Group of tortoises traveled from mainland to islands • Group eventually separated and went to different islands • New species of tortoises resulted from the subgroups mating within their own groups • Evidence – different species have different shaped shells Darwin’s Observations • Darwin noticed that although some of the places that he visited had similar environments (similar ecosystems) but had different organisms (plants and animals) – Ex: Argentina and Australia • Similar ecosystems (grasslands) • Australia had kangaroos but no rabbits • Argentina had rabbits but no kangaroos • Although Argentina and Australia have similar ecosystems, why are some organisms in one place but not the other? • Darwin’s Evidence for Fossil record Evolution – fossils of ancient organisms resemble present day organisms • Geographic distribution of living organisms – similar but unrelated organisms in similar environments • Homologous structures – Structure of a body part is similar in another organism, but its function may be different • Similarities in development – embryos of many animals are similar – organisms have same embryonic tissues but different mature forms Homologous Structures Similarities in Development Human Embryo Whale Embryo Dog Embryo Cat Embryo Chimpanzee Embryo Natural Selection • Fitness – ability of an organism to survive and reproduce • Survival of the fittest – organisms that are best adapted to their environment and will have the best chance to survive and reproduce – Ex: a fast fox will have a better chance of survival than a slow fox (fast fox should be able to catch more prey than the slow fox) • Adaptations – inherited traits that increase an organisms chance of survival Genes and Variation • In genetic terms, evolution is any change in gene (alleles) frequencies in a population over time • Populations have a gene pool – Gene pool – all the genes (and their alleles) in a population • Relative frequency – how often a gene occurs in a population – Ex: how often the gene for brown fur appears in a population of mice Genes and Variation Cont’d… • Main sources of genetic variation – Mutations – change in DNA sequencing – Gene shuffling – different combinations of genes are produced during gamete (sex cell) formation • Phenotypes for a trait determined by how many genes control the trait – Single gene trait – trait controlled by one gene – Polygenic trait – trait controlled by multiple genes Evolution as Genetic Change • Hardy-Weinberg Principle – allele frequencies in a population stay the same unless one or more factors change the frequencies – For evolution to occur, at least one of these factors MUST NOT happen: • • • • • Random mating Large population size No migrations No mutations No natural selection Speciation • Speciation – formation of a new species • Populations must become reproductively isolated from one another for a new species to evolve – forms of reproductive isolation • behavioral isolation – populations have different reproductive behaviors • geographic isolation – geographic barriers • temporal isolation – populations reproduce at different times Speciation of the Galapagos Finches • Speciation of Galapagos Finches occurred by: – – – – – Founding a new population Geographic isolation Changes in new population’s gene pool Reproductive isolation Ecological competition