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Transcript
Evolution In the 18th century, people became more mobile • • Why are the different animals and plants in different geographic areas? How do we explain this diversity? As fossils were discovered: why don’t these organisms exist anymore and why do the things living today look totally different from these fossils? Until mid 19th century: Each species was individually created and has remained unchanged over time Lamarck • • Organisms acquire characteristics and pass them on WRONG!!! Lamarck proposed: Each species is a unique individual creation but changes over time (c) Descent with modification Darwin and Wallace: Species descend from a common ancestor 1 Influences on Charles Darwin Lyell - Earth is older than previously thought - Small changes over time have produced the geology that we see today Malthus. - Populations grow resources limit growth. Darwin and the theory of evolution • • Descent with modification leads to evolution of new species The process of natural selection explains how The Voyage of HMS Beagle Credit. Dr. R. Rothman Figure 22.7 Descent with modification The Hawaiian Silversword Alliance 2 Darwin’s observations of natural populations: • Evolution: How Does Evolution Really Work? • • • • Overproduction of offspring. Variation within populations exists and is inherited from the parents Struggle for resources and thus survival. Differential survival and reproduction. Natural Selection - Adaptation • Individuals have different fitness. Fitness is the ability to survive and reproduce offspring Artificial Selection Adaptations Source: http://www.orchids.mu/Species/Angraecum/Angraecum_sesquipedale.htm Evolution = process of change over time • How do fossils form? Evidence comes from a variety of sources 1) fossils 2) biogeography 3) anatomical similarities - Homology - Convergent evolution 5) Molecular data 3 Figure 25.1 A gallery of fossils Figure 15.04 Homology and Convergent Evolution Biogeography • Biogeography is the study of the geographic distribution of organisms Organisms of the Galapagos are more similar to those of mainland South America rather than other tropical islands. Related species are found in distant geographic areas. Figure 25.4 The history of continental drift Key: C = Cassowary; E = Emu; e = Elephant Bird; K = Kiwi; m = Moa; O = Ostrich; R = Rhea. • Continental Drift explains some species distributions 4 Molecular Evidence Microevolution and Macroevolution • Microevolution – changes within species • Macroevolution – how species evolve How does Microevolution happen? • Mutations: Chromosomal Changes It occurs at the population level Mutations Migration Genetic Drift • • • • Genetic drift Migration • • • Deletion Translocation Inversion Insertions The frequency of alleles increases or decreases due to random chance (can also be due to selective forces like habitat loss or mass overhunting) Grass in the foreground is growing on mine tailings The same species is growing in the background 5 Bottleneck Effect Macroevolution is due to isolation • • • Geographic Isolation Reproductive Isolation • Macroevolution • Ecological Isolation factors such as climate or soils may play a role in isolation Dutchman Breeches Reproductive Isolation Geographic isolation Ecological isolation Eastern redbud – east of Mississippi • Western Redbud – California, Utah, Nevada and Arizone Role of Hybridization in Evolution • Hybrids may be significant or important in evolutionary change, depending on how the characteristics of the parents were combined. Introgression - Backcrossing between hybrid and parent. Polyploidy - New cell wall fails to develop between two daughter cells. Sterility - Chromosomes do not pair up correctly. Squirrel Corn 6 Apomixis • Sterile Hybrids may reproduce asexually. Apomixis includes the development and production of seeds without fertilization. - May be highly successful. Dandelions and Wild Blackberries Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display Figure 15.10 7