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Natural Selection and the Evidence for Evolution The theory of evolution is the most fundamental concept in biology. What is the origin of evolution? • Fossil records have been important to science since the 18th century. • Fossils have formed concepts & answers questions • Several ideas have been proposed but only 1 ideas accepted today by scientists. Charles Darwin (1809-1882) • English scientists-founder of modern evolutionary theory • 1831 – naturalists • Collect, study & store specimens while on ship Beagle • Developed theory to explain how evolution occurs HMS Beagle Darwin on HMS Beagle Snoppy discovers Darwin's "Voyage of the Beagle" is not about his trip to mall, but about biological evolution Darwin on the HMS Beagle • He began in 1831 at age 22 when he took a job as a naturalist on the English ship HMS Beagle, which sailed around the world on a five-year scientific journey. • As the ship’s naturalist, Darwin studied and collected biological and fossil specimens at every port along the route • For the next 20 years, Darwin’s work refined his explanations for how species change over time. In the Galapagos • On the Galapagos Islands, Darwin studied many species of animals and plants that are unique to the islands but similar to species elsewhere. • He realized that individuals struggle to compete in changing environmental conditions. Darwin continues his studies How did this help Darwin? • He knew that many species produce large numbers of offspring. • He also knew that such species had not overrun Earth. • Only some individuals survive the competition and produce offspring Galapagos tortoise are the largest On Earth, different from other Tortoises in body size and shape Galapagos finch Is adapted to feed On cacti. Galapagos marine iguanas Eat algae from the ocean Large claws help to cling To slippery rocks Artificial Selection artificial selection is the process of intentional or unintentional modification of a species through human actions which encourage the breeding of certain traits over others Darwin hypothesis that there was a force in nature that worked like artificial selection Natural Selection • Natural selection is a mechanism for change in populations. • It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation. • As a result, each generation consists largely of offspring from parents with these variations that aid survival. • In nature, organisms produce more offspring than can survive • Darwin proposed this idea of natural selection to explain how species change over time Darwin explains natural selection • In any population, individuals have variations. Fishes, for example, may differ in color, size, and speed. Darwin explains natural selection • Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation. Darwin explains natural selection • Over time, offspring with certain variations make up most of the population and may look entirely different from their ancestors. Adaptations for Evolution • According to Darwin’s theory, adaptations in species develop over many generations. Structural adaptations arise over time • Learning about adaptations in mole-rats can help you understand how natural selection has affected them. • The ancestors of today’s common mole-rats probably resembled African rock rats. Structural adaptations arise over time • Some ancestral rats may have avoided predators better than others because of variations such as the size of teeth and claws. Structural adaptations arise over time • Ancestral rats that survived passed their variations to offspring. • After many generations, most of the population’s individuals would have these adaptations. Structural adaptations arise over time • Over time, natural selection produced modern mole-rats. • Their blindness may have evolved because vision had no survival advantage for them. Other structural adaptations • Mimicry is a structural adaptation that enables one species to resemble another species opossum plays possum well This fence lizard has adapted to mimic tree trunk color Caterpillar mimics Bird droppings In one form of mimicry, a harmless species has adaptations that result in a physical resemblance to a harmful species. The tasty Viceroy Butterfly (left), Mimics the bitter tasting Monarch on The Right Caterpillar mimics a viper In both looks & movement Structural adaptations arise over time • In another form of mimicry, two or more harmful species resemble each other. • For example, yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior. Animals use Camouflage • Camouflage allows animals to blend with their surroundings Tartan Hawkfish – blends with Bright gorgonian fans A narrow-headed frog native to Madagascar, blends with the mud & Tree trunks in its environment Fossil Evidence Fossils are important in Evolution Because they provide a record Of early life and history Other Evidence Anatomy Homologous Structures: Similar Analogous Structures: Similar In arrangement, function or in both body parts in function w/ no evolutionary origin Vestigial Structure: A body structure in a present day organism That no longer serves its original purpose, but was useful to An ancestor Section 2 Natural Selection • There are three different types of natural selection that act on variation: • 1. Stabilizing • 2. Directional • 3. Disruptive • Stabilizing selection is a natural selection that favors average individuals in a population. Selection for average size spiders Normal variation Natural selection acts on variations • Directional selection occurs when natural selection favors one of the extreme variations of a trait. Normal variation Selection for longer beaks Natural Selection on Variations • In disruptive selection, individuals with either extreme of a trait’s variation are selected for The Effects Of Natural Selection • Natural selection can significantly alter the genetic equilibrium of a population’s gene pool over time • Significant changes in the gene pool could lead to the evolution of a new species over time Speciation • The evolution of new species, a process called speciation occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment. Geographic Isolation • Geographic isolation occurs whenever a physical barrier divides a population Isolated habitat fragments are similar to islands in the way in which the species living there are effected. Gradualism • Gradualism is the idea that species originate through a gradual change of adaptations Adaptation Radiation Hawaiian honeycreepers When an ancestral species evolves into an array of species to fit a number of diverse habitats, the result is called adaptive radiation 13 Species of Darwins Finches Differences: structures of their beak-adaptation for cactus eaters, seed eaters, insect eaters… Darwin’s finches of the Galapagos Divergent Radiation • Adaptive radiation is a type of divergent evolution, the pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly distinct Diversity in new environments Extinct mamo Amakihi Crested honeycreeper Kauai Niihau Molokai Oahu Maui Lanai Akialoa Kahoolawe Akepa Akiapolaau Possible Akikiki Ancestral Lasan finch Liwi Hawaii Apapane Maui parrotbill Palila Ou Grosbeak finch Diversity in a New Environment • Divergent evolution occurs when populations change as they adapt to different environmental conditions, eventually resulting in new species. Convergent Evolution • A pattern of evolution in which distantly related organisms evolve similar traits is called convergent evolution Migration • Seasonal movements to an area for breeding •Birds Fly south for The winter