03 ch22selection2008print
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Evolutionary forces that change populations include natural selection and genetic drift. Natural selection occurs when heritable traits that increase survival and reproduction accumulate in a population over generations, leading to adaptive change. Genetic drift is the change in a population's allele frequencies due to random events rather than environmental selection, resulting in random change. Other evolutionary forces include sexual selection, predation selection, physiological selection, coevolution, and the founder effect from population bottlenecks or new colonies founded by a small group.
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03 ch22selection2008print
- 1. Evolutionary Forces What changes populations? AP Biology 2007-2008
- 2. Forces of evolutionary change __________________________ traits that improve survival or reproduction will accumulate in the population adaptive change ___________________________ frequency of traits can change in a population due to chance events random change AP Biology
- 3. Natural Selection Selection acts on any trait that affects survival or reproduction predation selection physiological selection sexual selection AP Biology
- 4. Predation Selection Predation selection act on both predator & prey behaviors camouflage & mimicry speed defenses (physical & chemical) AP Biology
- 5. Physiological Selection Acting on body functions disease resistance physiology efficiency (using oxygen, food, water) biochemical versatility HOT STUFF! protection from injury Some fish had the variation of producing anti-freeze protein 5.5 mya The Antarctic Ocean freezes over AP Biology
- 6. Physiological selection Dogs pee on trees…Why don’t trees pee on dogs? plant nutrient NH3 animal waste One critter’s trash is another critter’s treasure! AP Biology
- 7. Sexual Selection Acting on reproductive success attractiveness to potential mate fertility of gametes successful rearing of offspring Survival doesn’t matter if you don’t reproduce! QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. AP Biology
- 8. Sexual selection QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. It’s FEMALE CHOICE, baby! AP Biology
- 9. The lion’s mane… Females are attracted to males with larger, dark manes Correlation with higher testosterone levels better nutrition & health more muscle & aggression better sperm count / fertility longer life But imposes a cost to male AP Biology HOT! Is it worth it??
- 10. Sexual selection Acts in all sexually reproducing species the traits that get you mates sexual dimorphism influences both morphology & behavior can act in opposition to natural selection Jacanas Is there a testable hypothesis in there? AP Biology
- 11. Sexual selection Sexual selection acts in all sexually reproducing species ___________________________ it influences both morphology & behavior it acts on both males and females Is there a testable hypothesis in there? AP Biology Jacanas
- 12. Coevolution ___________________________ ___________________________ predator-prey disease & host competitive species mutualism pollinators & flowers AP Biology
- 13. Effects of Selection Changes in the average trait of a population AP Biology
- 14. Genetic Drift ____________________________________ ____________________________________ not adaptation to environmental conditions not selection _____________________ small group splinters off & starts a new colony _____________________ some factor (disaster) reduces population to small number & then population recovers & expands again but from a limited gene pool AP Biology
- 15. Founder effect __________________________________ __________________________________ just by chance some rare alleles may be at high frequency; others may be missing skew the gene pool of new population human populations that started from small group of colonists example: AP Biology colonization of New World albino deer Seneca Army Depot
- 16. Distribution of blood types Distribution of the O type blood allele in native populations of the world reflects original settlement AP Biology
- 17. Distribution of blood types Distribution of the B type blood allele in native populations of the world reflects original migration AP Biology
- 18. Out of Africa Likely migration paths of humans out of Africa 10-20,000ya 10-20,000ya 50,000ya Many patterns of human traits reflect this migration Many AP Biology
- 19. Bottleneck effect ____________________________________ __________________________________ famine, natural disaster, loss of habitat… loss of variation by chance event alleles lost from gene pool not due to fitness narrows the gene pool AP Biology
- 20. Cheetahs All cheetahs share a small number of alleles less than 1% diversity as if all cheetahs are identical twins 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat AP Biology
- 21. Evolution is "so overwhelmingly established that it has become irrational to call it a theory." -- Ernst Mayr What Evolution Is 2001 Professor Emeritus, Evolutionary Biology Harvard University (1904-2005) AP Biology 2007-2008
Editor's Notes
- Even though it’s very hot to have a large mane the benefit of attracting mates and successfully producing & rearing young since you have that large mane outweighs the costs. Females who chose these males were more “successful” (more, healthier young) and therefore had a greater opportunity to pass on the trait of being attracted to longer darker manes to their daughters and the trait of having longer, darker manes to their sons.
- Small founder group, less genetic diversity than Africans All white people around the world are descended from a small group of ancestors 100,000 years ago (Chinese are white people!)
- South & Central American Indians were nearly 100% type O for the ABO blood system. Since nothing in nature seems to strongly select for or against this trait, it is likely that most of these people are descendants of a small band of closely related "founders" who also shared this blood type
- The global frequency patterns of the type B blood allele: Note that it is highest in central Asia and lowest in the Americas and Australia. However, there are relatively high frequency pockets in Africa as well. Overall in the world, B is the rarest ABO blood allele.
- Migration Paths According to the "Out of Africa" theory, modern humans appeared as a single African species nearly 100,000 years ago, then spread throughout the world (K.Wong, Is Out of Africa Going Out the Door?, Scientific American 281(2), August 1999).
- Born in 1904 in Germany, Mayr trained as a medical student but realized he had a greater passion for studying birds and biology. Emigrating to the United States, he became a curator at the American Museum of Natural History, working on bird classification while formulating his key ideas about evolution. In 1942 he published his most important work, Systematics and the Origin of Species . Mayr moved to Harvard University in 1953 and served as director of the school's Museum of Comparative Zoology from 1961 to 1970. Since then, he has published a number of books and chapters and received the prestigious Japan Prize for Biology in 1983. In his landmark 1942 book, Mayr proposed that Darwin's theory of natural selection could explain all of evolution, including why genes evolve at the molecular level. On the stubborn question of how species originate, Mayr proposed that when a population of organisms becomes separated from the main group by time or geography, they eventually evolve different traits and can no longer interbreed. It's this isolation or separation that creates new species, said Mayr. The traits that evolve during the period of isolation are called "isolating mechanisms," and they discourage the two populations from interbreeding. Moreover, Mayr declared that the development of many new species is what leads to evolutionary progress. "Without speciation, there would be no diversification of the organic world, no adaptive radiation, and very little evolutionary progress. The species, then, is the keystone of evolution."