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Chapter 15 Evolution 15-1 Darwin’s Theory of Natural Selection 1 Charles Darwin 1809-1882 As a boy liked nature study Flunked out of med school Theology degree from Christ College, Cambridge Became minister Church of England 1831 job as naturalist on HMS Beagle 5 year world voyage to chart coasts 2 Unique Galapagos Islands 1000 km off west coast of South America Unique species animals, similar to S.A. but not exact Unique species animals on each island, similar to S.A. and each other but not exact 3 Darwin’s Finches Especially interesting is the number and variety of these birds Each island had own variety dependent on the food source 4 5 Darwin’s Influenced by: 1. 2. 3. 4. Thomas Malthus: human species grows faster than food supply; competition for food, space, mates, shelter; struggle to survive Pigeon breeding: found individual variation, could breed desirable traits into a population (artificial selection) His 13 children: found individual variation 22 years of study after HMS Beagle to formulate his ideas 6 Natural Selection Is a mechanism for change in a population Groups NOT INDIVIDUALS evolve Occurs when organisms with certain variations survive, reproduce, and pass their variations onto the next generation 7 Theory of Natural Selection (old) A. C. Organisms produce more offspring than can survive Individuals with certain helpful variations survive in their environment, reproduce, and pass helpful variation on to offspring Individuals in a population have variations D. Overtime, individuals with helpful variations make up more and more of the population B. 8 15.1 Darwin’s Theory of Natural Selection Natural Selection (NEW) Individuals in a population show variations. Variations can be inherited. Organisms have more offspring than can survive on available resources. Variations that increase reproductive success will have a greater chance of being passed on. 9 Origin of Species by Means of Natural Selection By Charles Darwin Published in 1859 10 Other’s Ideas on Evolution Alfred Wallace: had same ideas about natural selection as Darwin, but Darwin published first (both presented their ideas in 1858 at a scientific meeting) Genetics has changed ideas about evolution; now we measure frequency of allele in gene pool Gene pool: all the genes of a population 11 Chapter 15 Evolution 15-2 Evidence of Evolution 12 Evolution and Natural Selection Darwin’s theory of natural selection is not synonymous with evolution. It is a means of explaining how evolution works. The theory of evolution states that all organisms on Earth are related; share a common ancestor. 13 Evidence for Evolution 1. 2. 3. 4. 5. 6. Fossils Anatomy Embryology Biochemistry Geographic Distribution Adaptations 14 1. Fossils Record of early life Ancestors of whales were dog sized land animals Record is incomplete 15 2. Anatomy A. Homologous structures: similar arrangement or function or both Evidence that organisms evolved from a common ancestor (Analogous structures: body parts do not have common evolutionary origin but have similar function) 16 Homologous Structures 17 2. Anatomy B. Vestigial structures: body part that has no function today but probably did in ancestor eyes of blind mole rat eyes of blind cave fish wings of flightless birds human appendix, little toe, muscles to move ears… 18 3. Embryology Embryo: earliest stage of growth and development Similarities for all vertebrates Gill slits tail Tail Gill slits Suggest a common ancestor 19 20 4. Biochemistry Comparison of DNA, RNA, and/or proteins Newest RNA evidence is that there are three types (Domains) of organisms Archae Eubacteria Eukarya Prokaryote Prokaryote Eukaryote Archaebacteria Eubacteria Protista Fungi Plants Ancestral Prokaryote Animals 21 5. Geographic Distribution The distribution of plants and animals that Darwin saw first suggested evolution to Darwin. Rabbit Mara 22 5. Geographic Distribution Patterns of migration were critical to Darwin when he was developing his theory. Evolution is intimately linked with climate and geological forces. Biogeography is the branch of science that studies the world distribution of organisms. 23 6. Adaptations A. Any variation that helps an organisms’ chance for survival Structural Adaptations: can take millions of years mimicry: enables one species to resemble another species; harmless look like harmful all harmful look alike 24 6. Adaptations A. Structural Adaptations camouflage: enables species to blend in with surroundings so that they are not easily found by predators 25 6. Adaptations B. Physiological adaptations: takes shorter time Changes in organisms metabolic processes (function) antibiotic resistant bacteria pesticide resistant insects (head lice) herbicide resistant weeds 26 6. Adaptations Not all features of an organisms are necessarily adaptive. Example: helplessness of human babies. Human babies are born at a much earlier stage of development than other mammals. This is probably not an adaptation but a consequence of the larger brains and upright posture of humans. 27 Chapter 15 Evolution 15-3 Shaping Evolutionary Theory 28 Population Genetics and Evolution Darwin knew NOTHING about genes, never read the work of Mendel even though they lived about the same time Darwin: 1809-1882 Mendel: 1822-1884 29 Populations NOT individuals evolve Individuals can’t change their genes, can’t change their genotypes and can’t change their phenotypes or trait Individuals can only respond to their environments as their genes allow 30 Natural Selection acts on Phenotypes If an individual has a phenotype that is poorly suited to their environment, the individual organism may not survive and/or may not reproduce to pass their genes on to the next generation 31 Natural Selection acts on Phenotypes Each member of a population has the genes that characterize the traits of the species All the genes (and alleles) of individuals make up the gene pool of the population Evolution occurs as a population’s genes and their frequencies change over time 32 Allelic Frequency Allelic frequency: % of any specific allele = Number of specific allele Total number of alleles Can change over time or stay the same 33 Hardy-Weinberg Principle Hardy-Weinberg principle states that when allelic frequencies remain constant, a population is in genetic equilibrium. 34 Hardy-Weinberg Principle Equation: and p2 + 2pq + q2 = 1 p+q=1 This equation allows us to determine the equilibrium frequency of each genotype in the population. Homozygous dominant (p2) Heterozygous (2pq) Homozygous recessive (q2) 35 36 Genetic Equilibrium Frequency of alleles stays the same over many generations Not evolving Phenotypes remain the same too 37 Changes in Genetic Equilibrium 1. 2. 3. 4. 5. Mutations Genetic Drift Gene Flow Nonrandom mating Natural Selection 38 1. Mutations Caused by environmental factors like radiation and chemicals Caused by random chance Some mutations are lethal and quickly eliminated Some mutations are helpful (useful) and new allele or gene becomes part of the population’s gene pool 39 2. Genetic Drift Alteration of allelic frequency by chance events Small populations that become isolated by natural events can evolve differently Bottleneck effect: disasters such as earthquakes, floods kill victims unselectively Founder effect: few individuals colonize an isolated area (Darwin’s finches) 40 3. Gene Flow Movement of individuals into or out of a population When individuals immigrate or emigrate their genes go with them Example: westward expansion in the US 41 4. Nonrandom mating Usually organism mate with those in close proximity. (May result in inbreeding). Usually organisms mate with those of the same or similar phenotype. 42 5. Natural Selection Acts on variation Some variations increase or decrease an organism’s chance for survival Variation can be inherited and are controlled by alleles 43 5. Natural Selection Four Types of Natural Selection that act on variation A. B. C. D. Stabilizing Selection Directional Selection Disruptive Selection Sexual Selection 44 Stabilizing Selection Favors average Reduces variation Example: Large spiders easy to see and be eaten while small spiders have a hard time getting food 45 Directional Selection Favors one extreme Can lead to rapid evolution Example: Over time there were more and more darker colored Peppered Moths in the industrial area of England in the 1800’s 46 Disruptive Selection Both extremes are favored Average (mean) disfavored Leads to the evolution of two species Example: Light yellow butterfly overtime becomes either nearly white or orange 47 Sexual Selection Sexual selection operates in populations where males and females differ significantly in appearance. Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival. Example: tail of mail peacocks, while beautiful, makes the organism a greater target for predators. 48 The Evolution of Species Species: group of organisms that look alike and can breed to produce fertile offspring Speciation: process of evolution of new species occurs when members of similar populations no longer interbreed to produce fertile offspring in their natural environment 49 Reproductive Isolation Prezygotic isolation mechanisms make fertilization unlikely. Can’t mate to produce fertile offspring Genetic differences: genetic material too different so no fertilization results Behavioral differences: mate at different times of day or at different season; different “courting” rituals 50 Reproductive Isolation Fertilization is possible between a tiger and a lion but the offspring is sterile. Postzygotic isolation occurs when fertilization has occurred but a hybrid offspring cannot develop or reproduce. Prevents offspring survival or reproduction. 51 Speciation In allopatric speciation a physical barrier divides one population into two or more populations; geographic isolation. 52 Geographic Isolation Islands, lava flows, rock slides, rivers changing course Populations become physically separated Over time each small population adapt differently to environments and have different gene pool When gene pool becomes too different then two species exist 53 Speciation In sympatric speciation a species evolves into a new species without a physical barrier. 54 Patterns of Evolution Divergent Evolution (adaptive radiation): become different Convergent Evolution: become the same Coevolution: the evolution of one species effects the evolution of another species 55 Divergent Evolution Adaptative radiation:: one ancestral species evolves into many species to fit diverse habitats 56 Convergent Evolution Distantly related organisms evolve similar traits Occurs when unrelated species occupy similar environments in different parts of the world African and American cactus 57 58 Coevolution The relationship between two species might be so close that the evolution of one species affects the evolution of the other species. Example: specialized mouth parts 59 Two Theories of Speciation Gradualism: species originate through gradual, slow change Evolution of the horse 60 Two Theories of Speciation Punctuated Equilibrium: speciation relatively quickly (10, 000 years) with long periods of no evolution (genetic equilibrium) High environmental change Evolution of elephants 61