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Transcript
Evolution Chapter 15 1 Evolution “Nothing in biology makes sense EXCEPT in the light of evolution.” Theodosius Dobzhansky Charles Darwin in later years2 15-1 Darwin’s Theory of Natural Selection 3 Early Ideas On Earth’s Organisms • Aristotle believed species were fixed creations arranged by their complexity • Idea lasted 2000 years 4 Contributor’s to Darwin’s thinking included: : • Charles Lyell –geologic processes still changing Earth – (Principles of Geology book) • Georges Cuvier – species extinction (Catastrophism) • Thomas Malthus – struggle for existence (resources) 5 Contributor’s to Darwin’s thinking included: : • James Hutton - Gradualism • John Baptiste Lamarck – developed idea of change over time. Inheritance of Acquired Characteristics and Law of Use and Disuse • Alfred Russel Wallace – organisms evolved from common ancestors 6 Lamarck’s Theory of Evolution • Law of Use and Disuse • If a body part were used, it got stronger • If body part was NOT used, it dissappeared 7 8 Lamarck’s Theory of Evolution • Inheritance Of Acquired Traits – Traits Acquired During Ones Lifetime Would Be Passed To Offspring Clipped ears of dogs could be passed to offspring! 9 Lamarck’s Mistakes • Lamarck Did NOT Know how traits were inherited (Traits are passed through genes) • Genes Are NOT Changed By Activities In Life • Change Through Mutation Occurs Before An Organism Is Born 10 Charles Darwin the Naturalist 11 Voyage of the Beagle Charles Darwin • Born Feb. 12, 1809 • Joined Crew of HMS Beagle, 1831 • Naturalist • 5 Year Voyage around world • Avid Collector of Flora & Fauna • Astounded By Variety of Life 12 Darwin’s Voyage of Discovery A reconstruction of the HMS Beagle sailing off Patagonia. 13 Darwin Left England in 1831 Darwin returned 5 years later in 1836 14 The Galapagos Islands • Small Group of Islands 1000 km West of South America • Similar Climates • Animals On Islands Unique • Tortoises • Iguanas • Finches • Mockingbirds 15 The Galapagos Islands • Volcanic islands off the coast of South America • Island species varied from mainland species & from island-to-island species 16 17 The Galapagos Islands • Finches on the islands resembled a mainland finch • More types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects…) • Finches had different types of beaks adapted to their type of food gathering • Mockingbirds had different traits suited for their niche! 18 19 Darwin’s Observations • Patterns of Diversity were shown • Unique Adaptations in organisms • Species Not Evenly Distributed • Australia, Kangaroos, but No Rabbits • S. America, Llamas 20 Darwin’s Observations • Both Living Organisms & Fossils collected • Fossils included: •Trilobites •Giant Ground Sloth of South America This species NO longer existed. What had happened to them? 21 Definition • Evolution is the slow, gradual change in a population of organisms over time 22 Darwin’s Observations • Left unchecked, the number of organisms of each species will increase exponentially, generation to generation • In nature, populations tend to remain stable in size • Environmental resources are limited 23 Darwin’s Conclusion • Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals • Only a fraction of offspring survive each generation • Survival of the Fittest 24 Darwin’s Observations • Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike. • Much of this variation between individuals is inheritable. 25 Darwin’s Conclusion • Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals • Called Natural Selection 26 Darwin’s Theory of Evolution •The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection) •New species evolve 27 Natural Variation and Artificial Selection • Abandoned The Idea That Species Were Perfect & Unchanging • Observed Significant Variation in All Species Observed • Observed Farmers Use Variation To Improve Crops & Livestock • Called Selective Breeding 28 Natural Variation and Artificial Selection • Natural Variation – Differences Among Individuals Of A Species • Artificial Selection – Selective Breeding To Enhance Desired Traits Among Stock or Crops 29 30 Natural Selection • 4 Principles of Natural Selection: • 1. Variation • 2. Heritability • 3. Overproduction • 4. Reproductive Advantage . 31 Natural Selection Concepts • The Struggle for Existence (compete for food, mates, space, water, etc.) • Survival of the Fittest (able to survive and reproduce) • Descent with Modification (new species arise from common ancestor replacing less fit species) 32 Survival of the Fittest • Fitness – Ability of an Individual To Survive & Reproduce • Adaptations Can Be: – Physical • Speed, Camouflage, Claws, Quills, etc. – Behavioral • Solitary, Herds, Packs, Activity, etc. 33 Natural Selection • Cannot Be Seen Directly • It Can Only Be Observed As Changes In A Population Over Many Successive Generations – Radiation – Fossil Record 34 Evidence for Evolution – Evolution Observed Selection against small guppies results in an increase in 35 average size Descent With Modification • Takes Place Over Long Periods of Time • Natural Selection Can Be Observed As Changes In – Body Structures – Ecological Niches – Habitats 36 Descent With Modification • Species Today Look Different From Their Ancestors • Each Living Species Has – Descended – With Changes – From Other Species – Over Time 37 Descent With Modification 38 Descent With Modification • Implies – All Living Organisms Are Related – Single Tree of Life • DNA, Body Structures, Energy Sources • Common Descent – All Species, Living & Extinct, Were Derived From Common Ancestors 39 Theory of Evolution Today Supporting Evidence 15-2 40 Evidence of Evolution Key Concept Evidence For This Process Could Be Found In: – The Fossil Record – The Geographical Distribution of Living Species – Homologous Structures of Living Organisms – Similarities In Early Development 41 Fossil Record • Earth is Billions of Years Old • Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time • Derived Traits – newly evolved features • Ancestral Traits – old features 42 Evidence for Evolution – The Fossil Record 43 Geographic Distribution of Living Species • Different Animals On Different Continents But Similar Adaptations To Shared Environments 44 Homologous Body Structures • Scientists Noticed Animals With Backbones (Vertebrates) Had Similar Bone Structure • May Differ In Form or Function • Limb Bones Develop In Similar Patterns • Arms, Wings, Legs, Flippers 45 Homologous Body Structures 46 Homologous Structures 47 Vestigial Body Structures • Not All Serve Important Functions – Vestigial Organs • Appendix In Man • Legs On Skinks or Leg Bones on Snakes 48 Analogous Structures • Used the same but was not made the same way. • Bird wings versus insect wings 49 Similarities In Early Development • Embryonic Structures Of Different Species Show Significant Similarities • Embryo – early stages of vertebrate development 50 Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development 51 Chicken Turtle Rat 52 Human Fetus – 5 weeks 53 Similarities in DNA Sequence 54 Adaptations • Camouflage • Mimicry • Antimicrobial Resistance 55 Evolutionary Time Scales Macroevolution: Long time scale events that create and destroy species. 56 Evolutionary Time Scales Microevolution: Short time scale events (generationto-generation) that change the genotypes and phenotypes of populations 57 Shaping Evolutionary Theory 15-3 • Population Genetics – Hardy-Weinberg Principle – genetic equilibrium (constant frequencies over time) – p + q = 1 – allele frequency – p2 + 2pq + q2 = 1 – genotypic frequency – Table 15.3 (page 432) 58 Mechanisms of Evolution • • • • • • • Genetic Drift Founder Effect Bottleneck Gene Flow Nonrandom Mating Mutation Natural Selection 59 Genetic Drift • In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. That, in a nutshell, is genetic drift. It happens to ALL populations—there’s no avoiding the vagaries of chance. 60 Founder Effect • A founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have: – reduced genetic variation from the original population. – a non-random sample of the genes in the original population. – Example, the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events. 61 The elephant seal population was • Population bottlenecks occur when a bottlenecked due to population’s size is reduced for at least hunting in the 1890s. one generation. Because genetic drift Bottleneck acts more quickly to reduce genetic variation in small populations, undergoing a bottleneck can reduce a population’s genetic variation by a lot, even if the bottleneck doesn’t last for very many generations. This is illustrated by the bags of marbles shown above, where, in generation 2, an unusually small draw creates a bottleneck. 62 Gene Flow • Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population. 63 Nonrandom Mating • Sexual Selection – individuals choose mates based on certain traits. 64 Mutation • A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population. 65 Natural Selection • There is variation in traits. • There is differential reproduction. • There is heredity. • One trait tends to become more common. 66 Types of Selection • 3 types of Natural Selection: – Stabilizing - average – Directional – one extreme – Disruptive – both extremes 67 Reproductive Isolation • Prezygotic – – – – – Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametes die • Postzygotic – – – – Zygote dies Hybrids sterile Hybrids inviability Low hybrid fitness 68 Speciation • Allopatric – due to geographic isolation. Isolation might occur because of great distance or a physical barrier, such as a desert or river • Sympatric - Merely exploiting a new niche may automatically reduce gene flow with individuals exploiting the other niche. This may occasionally happen when, for example, herbivorous insects try out a new host plant. 69 Patterns of Evolution • Divergent Evolution – Adaptive radiation • Coevolution – Predator/prey and parasite/host – Competitive species – Mutualistic species • Convergent Evolution – Analogous features – Bird and bat wings 70