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Natural Selection • Charles Darwin- English scientist who proposed natural selection and early evolutionary concepts. • Studies began by taking a job as a naturalist on the ship HMS Beagle at the age of 21 • Sailed to S. America and the S. Pacific (Galapagos Islands) • Studied & collected biological specimens at each port stopped at along a 5 yr scientific journey Darwin Cont. • Galapagos Islands- islands near the equator where Darwin made many observations and studies. • These studies led to the idea that species can change over time. (Evolutionary Theory) • Darwin used artificial selection to gain insight into which organisms survive in nature. • Artificial Selection- breeding organisms with specific traits to produce offspring with identical traits. • Darwin identified the process of natural selection from his collections and observations Darwin Cont. • Natural Selection- explains the mechanism for • • • • • change in a population. Concepts of natural selection 1. Organisms produce more offspring than can survive. 2. In a population individuals have variations. 3. Individuals with useful variations are better equipped for survival and pass these variations to their offspring. 4. Over time offspring with these favorable variations make up most of the population and may look different from their ancestors. Darwin Cont. • Darwin went on to publish the first book about evolution called On the Origin of Species by natural Selection in 1859. • Darwin’s theory of evolution by natural selection is accepted by almost all of today’s biologist. • Modern biologist define evolution as any change in the gene pool of a population. • Darwin’s spent a lot of time studying the finches and tortoises of the Galapagos Islands. Finches of the Galapagos Islands Darwin’s Finches Evolution of the Horse Evolutionary Evidence • 1. Structural adaptations- adaptations that a population develop to help them survive in their habitat. • Example: mole rats that live underground in darkness are blind but have large teeth and claws. • Blind-don’t need sight • Large teeth-protection from predators since they have no sight. • Large claws-allows for better digging of tunnels. Evidence Cont. • A. Mimicry- a structural adaptation that lets a species resemble or mimic another. • Example- a harmless species may mimic or adapt its appearance to look like a harmful species. Mimicry • Which of these two organism is the harmful one and which is the harmless? • Sryphid Fly Yellow Jacket Evidence Cont. • B. Camouflage- a type of mimicry where the species blends into their surroundings or environment. • Advantages: • 1. Not easily seen by predators • 2. They survive to reproduce Octopus in its pale form. Mimicry and Camouflage • Katydid mimicing a leaf. Can you see it? • Walking Stick blending into its environment. Can you see it? Mimicry and Camouflage These are the wings of a butterfly. Predators think they are looking at two big eyes and stay away. Mimicry & Camouflage • Are these the same butterfly? • No, the one on the right has a bad taste to predators, the one on the left has a good taste • Predators assume they are the same butterfly and avoid both. • Monarch Viceroy Evidence Cont. • 2. Physiological adaptations- changes in an organism’s metabolic processes. • Examples: bacteria, insects, and weeds. • Many of each of these organism no longer respond to the once harmful penicillin and pesticides. Evidence Cont. • 3. Fossils continue to show evidence of change amongst organisms. • As the fossil record continues to become more complete, the sequence of evolutionary events becomes more clear. Evidence Cont. • 4. Anatomy- the physical makeup of an organism • Examples: • A. homologous structures- structures that show a common evolutionary origin. • Can be similar in arrangement, in function, or both Similar Arrangement Of Bones Evidence Cont. • B. Analogous Structures- no common evolutionary origin is shown but a similar function. Such as wings for flight. Homologous Structures Analogous Structures Evidence Cont. • C. Vestigial Structure- a body structure that has no function in a present-day organism, but probably did to an ancestor. • Examples: • Eyes in the blind mole rats • Wings on flightless birds (Ostrich) • Coccyx, appendix, molars, body hair on males Evidence Cont. • 5. Embryology- the study of early development of organisms • Embryology shows similarities between early development of embryo’s in different organisms. • These similarities suggest a common ancestor. • Example: Embryo’s of fish, reptiles, birds, and mammals all have a tail and gill slits. • We know reptiles, birds and mammals do not have gills. • Why do they have gill slits in the embryo stage? Embryology A B C D Human Embryo? Reptile Embryo? Fish Embryo? Bird Embryo? Embryology Cont. Evidence Cont. • 6. Biochemistry- looks at comparisons of the DNA or RNA from different species to show information about evolutionary relationships. Population Genetics • The study of genes in plants and animals developed into the study of population genetics. • Population genetics contributed to the modification of Darwin’s ideas. • Populations, not individuals evolve. • The gene pool must change within a population over time for evolution to have occurred. • Allelic frequency refers to the percentage of any specific allele in the gene pool. Population Genetics Cont. • Scientist refer to frequency of alleles remaining the same over time as genetic equilibrium. • Genetic equilibrium results in no evolving taking place. • Factors that change genetic equilibrium • 1) mutations- any change in the gene due to environmental or chance. • 2) genetic drift- the alteration of allelic frequencies by chance events in small populations. Genetic Drift • Examples of genetic drift • Amish group in Pennsylvania who have short arms, and extra fingers and toes. • 1 out of 14 in their population • 1 out of 1000 in the U.S. population Gene Flow • 3. Gene Flow- the gain or loss of genes in a gene pool from migrating individuals. • The smaller the gene pool the greater the effect. • Natural Selection Acts On Variations • Types: • 1) Stabilizing Selection- natural selection favors average individuals in a population over those who are too small or too large. To Small- no food • Example: Spiders To Large-easily seen • by predators Types of Natural Selection • 2) Directional Selection- natural selection favors one of the extreme variations and not the average. • Example: Woodpeckers with long beaks over small or average beaks. Can you match the beaks with the appropriate food source? • Whippoorwill • Flying Insects • Red-bellied Woodpecker • Ants • Wood Cock • Worm • Cardinal • Seeds Types of Natural Selection • 3) Disruptive Selection- either extreme of a traits variation favors the organism while the intermediate trait does not. • The intermediate phenotype or trait is usually eliminated. • Example: white, tan, and dark brown limpets • White limpet/light rock Tan limpet Dark limpet/dark rock Evolution of a Species • Species- a group of organisms that look alike and can interbreed to produce fertile offspring. • Speciation refers to the evolution of a new species. • Members of a similar population can no longer interbreed and produce fertile offspring. Causes of Speciation • 1) Geographic Isolation- a physical barrier such as lava from volcanic or sea level changes that breaks a large population into smaller populations. • The smaller populations could not interbreed and might adapt to its environment changing the gene pool. • The gene pools of each population may become so different that they can no longer interbreed resulting in a new species. Geographic Isolation Spotted owl subspecies living in different geographic locations show some genetic and morphological differences. This observation is consistent with the idea that new species form through geographic isolation. Spotted owl subspecies living in different geographic locations show some genetic and morphological differences. This observation is consistent with the idea that new species form through geographic isolation. Causes of Speciation • 2) Reproductive Isolation- occurs when organisms that once could interbreed can no longer mate and produce fertile offspring. • Reasons: • Genetic material of the populations become so different that fertilization can’t occur. • Behavior, such as the seasons they mate. Some may mate in the fall and some may mate in the spring. • Result: These populations would never mate. Causes of Speciation • 3) Change in Chromosome number • Mistakes during mitosis or meiosis may lead to polyploid individuals. • Polyploid- more than the normal set of chromosomes • Occurs frequently in plants. Rate of Speciation • 1) Gradualism- speciation occurs through a gradual change of adaptations. • Example: Camel evolution Rates of Speciation • 2) Punctuated Equilibrium- suggest that speciation occurs quickly or in rapid bursts with long periods of genetic equilibrium. • 10,000 yrs or less • Example: Patterns of Evolution • 1) Adaptive radiation- refers to a ancestral species evolves into many species to a number of diverse habitats. • Example: Darwins Finches, Hawaiian Honeycreepers • Hawaiian Honeycreepers Patterns of Evolution • 2) Divergent Evolution- results when populations adapt to different environments becoming less alike resulting in a new species. • Example: Adaptive radiation • 3) Convergent Evolution- distantly related organisms evolve similar traits. (unrelated species) • Example: Cactus Convergent Evolution • North & South American African Desert • Cactus Cactus • Although unrelated they both developed similarities in response to their similar environments.