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15.1 Section Objectives – page 393 Summarize Darwin’s theory of natural selection. Section Objectives: Explain how the structural and physiological adaptations of organisms relate to natural selection. Distinguish among the types of evidence for evolution.
Section 15.1 Summary – pages 393-403 Darwin on HMS Beagle
Section 15.1 Summary – pages 393-403 As the ship’s naturalist, Darwin studied and collected biological and fossil specimens at every port along the route. His studies provided the foundation for his theory of evolution by natural selection. Darwin on HMS Beagle
Section 15.1 Summary – pages 393-403 Darwin explains natural selection Darwin proposed the idea of natural selection to explain how species change over time. In nature, organisms produce more offspring than can survive.
Section 15.1 Summary – pages 393-403 Darwin explains natural selection In any population, individuals have variations. Fishes, for example, may differ in color, size, and speed.
Section 15.1 Summary – pages 393-403 Darwin explains natural selection Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation.
Section 15.1 Summary – pages 393-403 Darwin explains natural selection Over time, offspring with certain variations make up most of the population and may look entirely different from their ancestors.
Section 15.1 Summary – pages 393-403 Adaptations: Evidence for Evolution Recall that an adaptation is any variation that aids an organism’s chances of survival in its environment. Darwin’s theory of evolution explains how adaptations may develop in species.
Section 15.1 Summary – pages 393-403 Structural adaptations arise over time Some other structural adaptations are subtle. Mimicry is a structural adaptation that enables one species to resemble another species.
Section 15.1 Summary – pages 393-403 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. Structural adaptations arise over time
Section 15.1 Summary – pages 393-403 Structural adaptations arise over time Another subtle adaptation is camouflage , an adaptation that enables species to blend with their surroundings. Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.
Section 15.1 Summary – pages 393-403 Physiological adaptations are changes in an organism’s metabolic processes. In addition to species of bacteria, scientists have observed these adaptations in species of insects and weeds that are pests. Physiological adaptations can develop rapidly
Section 15.1 Summary – pages 393-403 Fossils Fossils are an important source of evolutionary evidence because they provide a record of early life and evolutionary history.
Section 15.1 Summary – pages 393-403 Anatomy Structural features with a common evolutionary origin are called homologous structures . Homologous structures can be similar in arrangement, in function, or in both. Whale forelimb Crocodile forelimb Bird wing
Section 15.1 Summary – pages 393-403 Anatomy The body parts of organisms that do not have a common evolutionary origin but are similar in function are called analogous structures . Although analogous structures don’t shed light on evolutionary relationships, they do provide evidence of evolution.
Section 15.1 Summary – pages 393-403 It is the shared features in the young embryos that suggest evolution from a distant, common ancestor. Fish Reptile Bird Mammal Pharyngeal pouches Pharyngeal pouches Tail Tail Embryology
Section 1 Check Question 1 _______ is considered to be the fundamental concept of biology. D. structural adaptation C. artificial selection B. the modern theory of evolution A. genetics The answer is B. CA: Biology/Life Sciences 7a-8g
Section 1 Check Question 2 Breeding organisms with specific traits in order to produce offspring with identical traits is called _______. D. artificial selection C. mutation B. adaptation A. natural selection The answer is D. CA: Biology/Life Sciences 8a
Section 1 Check Question 3 What is the difference between artificial selection and natural selection? Answer Artificial selection is the intentional breeding of organisms with specific traits in order to produce offspring with identical traits. Natural selection occurs when organisms with favorable variations of traits survive in nature, reproduce, and pass these favorable variations to offspring. CA: Biology/Life Sciences 8a
Section 1 Check Question 4 Mimicry and camouflage are NOT examples of _________. D. artificial selection C. evolution B. natural selection A. adaptation The answer is D. CA: Biology/Life Sciences 8a
Section 1 Check Question 5 How does mimicry differ from camouflage? Answer Mimicry is an adaptation that allows one species to resemble another species. Camouflage is an adaptation that allows one species to resemble its surroundings. CA: Biology/Life Sciences 6g
15.2 Section Objectives – page 404 Section Objectives Relate changes in genetic equilibrium to mechanisms of speciation. Summarize the effects of the different types of natural selections on gene pools. Explain the role of natural selection in convergent and divergent evolution.
Section 15.2 Summary– pages 404-413 There are three different types of natural selection that act on variation: stabilizing, directional, and disruptive. Natural selection acts on variations Some variations increase or decrease an organism’s chance of survival in an environment.
Section 15.2 Summary– pages 404-413 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
Section 15.2 Summary– pages 404-413 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
Section 15.2 Summary– pages 404-413 Natural selection acts on variations In disruptive selection , individuals with either extreme of a trait’s variation are selected for. Selection for light limpets Normal variation Selection for dark limpets
Section 15.2 Summary– pages 404-413 Recall that a species is defined as a group of organisms that look alike and can interbreed to produce fertile offspring in nature. The evolution of new species, a process called speciation (spee shee AY shun), occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment. The Evolution of Species
Section 15.2 Summary– pages 404-413 Physical barriers can prevent interbreeding In nature, physical barriers can break large populations into smaller ones. Geographic isolation occurs whenever a physical barrier divides a population. A new species can evolve when a population has been geographically isolated.
Section 15.2 Summary– pages 404-413 The Evolution of Species When geographic isolation divides a population of tree frogs, the individuals no longer mate across populations. Tree frogs are a single population.
Section 15.2 Summary– pages 404-413 The Evolution of Species The formation of a river may divide the frogs into two populations.
Section 15.2 Summary– pages 404-413 The Evolution of Species Over time, the divided populations may become two species that may no longer interbreed, even if reunited.
Section 15.2 Summary– pages 404-413 Patterns of Evolution Biologists have observed different patterns of evolution that occur throughout the world in different natural environments. These patterns support the idea that natural selection is an important agent for evolution.
Section 15.2 Summary– pages 404-413 Diversity in new environments When an ancestral species evolves into an array of species to fit a number of diverse habitats, the result is called adaptive radiation .
Section 15.2 Summary– pages 404-413 Adaptive radiation in both plants and animals has occurred and continues to occur throughout the world and is common on islands. 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
Section 15.2 Summary– pages 404-413 Different species can look alike A pattern of evolution in which distantly related organisms evolve similar traits is called convergent evolution . Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world.
Section 2 Check The fur of an Arctic fox turns white in the winter. Is this an example of natural selection? Why or why not? Question 1 CA: Biology/Life Sciences 7a-8g
Section 2 Check The answer is no . An individual cannot evolve a new phenotype (in this case, changing the color of its fur) within its lifetime in response to its environment. CA: Biology/Life Sciences 7a-8g
Section 2 Check Which type of natural selection does NOT favor the evolution of new species? Question 2 D. directional C. stabilizing B. disruptive A. divergent CA: Biology/Life Sciences 7d, 8b
Section 2 Check The answer is C. Stabilizing selection reduces variation in a population. CA: Biology/Life Sciences 7d, 8b
Section 2 Check Which of the following rarely affects a population’s genetic equilibrium? Question 3 D. disruptive selection C. gene flow B. lethal mutations A. genetic drift CA: Biology/Life Sciences 7c
Section 2 Check The answer is B. Organisms with lethal mutations do not survive. Therefore, organisms with lethal mutations cannot produce enough offspring to affect a population’s genetic equilibrium. CA: Biology/Life Sciences 7c
Section 2 Check Why are the Galapagos Islands rich in unique species of organisms? Question 4 D. The island species have been subjected to stabilizing selection. C. The island species have been subjected to increased gene flow. B. The islands are geographically isolated. A. The islands are an area exhibiting an abnormal number of mutations. CA: Biology/Life Sciences 8d
Section 2 Check The answer is B. Geographic isolation has helped to keep the islands’ species unique. CA: Biology/Life Sciences 8d