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Microevolution

Microevolution. Species exist as a collection of populations (Micro)evolution occurs in populations Basic level of evolution: change in the allele frequency Macroevolution. Agents of Microevolution. Mutations Gene Flow (by migration) Genetic Drift Instability of small populations

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Microevolution

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  1. Microevolution • Species exist as a collection of populations • (Micro)evolution occurs in populations • Basic level of evolution: change in the allele frequency • Macroevolution

  2. Agents of Microevolution • Mutations • Gene Flow (by migration) • Genetic Drift • Instability of small populations • founder effect, bottleneck effect • Non-random mating • sexual selection • Inbreeding • Natural Selection • Modern studies: Darwin’s finches in 1970s, Endler’s guppies, antibiotic resistance in bacteria, insecticide/pesticide resistance

  3. Sexual Selection in Humans Natural selection explains some of the geographic variation in humans: • Sickle-cell anemia is common in African blacks, but not in Swedes • Andean Indians have big chests (larger lungs) and shorter, powerful legs • Eskimos have compact shapes good for heat conservation • Southern Sudanese have slender shapes good for losing heat • North Asians have slit-like eyes for protection against cold (wind), dust, and sun glare off snow/sand On the other hand, some features are difficult to explain via natural selection: • Tasmanians have very dark skin in moderate sunlight conditions (the temperate latitude of Chicago or Vladivostok, and having been there for 10,000 years) • Skin color is only medium in sunny, tropical Southeast Asia • No American Indians have black skin, even in the equatorial areas

  4. Time may not be the best explanation in some cases, as Scandinavians did not live in Scandinavia until 4-5,000 years ago and do have white skin, while American Indians have been in the Amazon for longer time and do not have black skin. Hair color and eye color are even more difficult to explain in terms of natural selection: • Blond hair in Scandinavians (cold and wet) and Australian Aborigines (hot and dry desert) • Blue eyes in Scandinavians, dark eyes in New Guineans - both see well in dim, misty light • Breasts: hemispherical vs. conical • Hairy chests • Penis length • New Guinea: artificial enhancement by brightly colored, up to 2 ft long phallocarps (penis sheaths) Fashion

  5. Art • Unique to humans? • Is it distinctive because it is: • Nonutilitarian • Just for aesthetic pleasure • Transmitted by learning, not genes • Bowerbirds • Music, dance, poetry, fashion, jewelry • Art helps group cohesion • Dangerous behavior (extreme sports, chemical abuse)

  6. Forms of Selection • Disruptive • Stabilizing • Directional • Role of selection for origin of new species

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