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Transcript
Macroevolution “Large-scale changes in living things, and the production of dramatically new forms of life…” 1. 2. 3. 4. 5. 6. 7. Mass extinctions Adaptive radiation Convergent evolution Divergent evolution Coevolution Gradualism Punctuated equilibrium Mass Extinctions ► More than 99% of all species that ever lived are now extinct 5 mass extinction events in Earth’s history ► Wipes out whole ecological systems (Ex: dinosaurs extinct during K/T event) ► Burgess Shale (many extinct organisms that were VERY different from modern organisms) Adaptive Radiation Remember Darwin’s Finches? ► What was Darwin’s theory about how they came to have different beak sizes? ► Adaptive Radiation… Adaptive Radiation Darwin proposed that all the finches evolved from a single ancestral species ► Each island had a different physical environment, and unique plant species were dominant on each one ► Different plants produced seeds of different sizes, some large, some small ► Over time, the finches best-adapted for the available food on each island produced the most offspring, and became the dominant type in each location ► Due to the distance between the islands, the finches became isolated and no longer bred easily with finches on other islands, leading to distinct species, each with a unique beak size (Speciation) ► This evolutionary process is called Adaptive Radiation ► Convergent Evolution Unrelated organisms, sometimes on different continents, appear to resemble one another quite closely, because of similarities in their NICHE... Convergent Evolution Because their selection pressures are similar, unrelated organisms on different continents often display similar adaptations Divergent Evolution ► Isolated populations of a species evolve independently ► Example: black bear and polar bear: related but different fur color 7 Coevolution Two organisms evolve together as a result of their interdependence (symbiosis) Ex: The Star Orchid has a long spur containing a supply of nectar in its tip. The Giant Hawk Moth has an equally long proboscis that enables it to feed on the nectar, and pollinate the flower. Neither species can survive w/o the other! Gradualism Slow, steady changes in the size and shape of bones… Punctuated Equilibrium Some families display an evolutionary pattern of long, stable periods interrupted by brief periods of more rapid change. Theories of Change ► Has evolution happened very slowly and gradually, with organisms always changing slightly from generation to generation? (this was Darwin’s view…) ► Or is evolution characterized by long periods without change, followed by explosions of diversity (ex. The Burgess Shale)? ► The answer is………BOTH! Evolution of Birds Based on Fossil Evidence Gradualism vs. Punctuated Equilibrium Does evolution affect individuals, populations, or gene pools? Population Genetics The study of genetic traits and changes in populations. Population Genetics 1. Gene pool The combined genetic information of all the members of a particular population. Population Genetics 2. Allele frequency Is the number of times that an allele occurs in a gene pool compared with the number of times other alleles occur (ex. beans and bunnies lab). Population Genetics 3. Genetic equilibrium Allele frequencies remain constant. this even possible in a changing environment?...... ► Is Population Genetics 4. Hardy-Weinberg principle Allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. Population Genetics 5 Conditions to maintain genetic equilibrium 1. Random mating 2. Population must be very large 3. No immigration/emigration 4. No mutations 5. No natural selection! Therefore, if the gene frequency of a population changes then it must have “evolved”! Population Genetics 5. Genetic drift Random and rapid changes in allele frequencies that often occur in small populations No obvious “selection pressures”, just random changes that can occur rapidly when there is in-breeding in a closed population What does the future hold for OUR species…?