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Transcript
In the 18th century, people became more mobile ► Why are there different animals and plants in different geographic areas? ► How do we explain this diversity? Evolution ►As Where do species come from? fossils were discovered: ► Why don’t these organisms exist anymore? ► Why do the things living today look totally different from these fossils? Slide 1 Slide 2 Until mid 19th century: Each species was individually created and has remained unchanged over time Different Explanations Fig. 9.01a Slide 4 Slide 3 Lamarck was first to propose how life evolves ► Use Lamarck proposed (1809): Each species is a unique individual creation but changes over time Slide 5 and Disuse: Disuse: Parts of the body that were used became bigger and stronger, those unused disappeared ► Inheritance of acquired characteristics: characteristics: Organisms passed on those modifications developed during the INDIVIDUAL’s lifetime (WRONG) Slide 6 1 The Voyage of HMS Beagle (c) Descent with modification Darwin and Wallace: Species descend from a common ancestor through changes over time Slide 7 Slide 8 Darwin and the theory of evolution ► Descent with modification leads to evolution of new species process of natural selection explains how Credit. Dr. R. Rothman ► The Slide 9 Slide 10 Figure 22.7 Descent with modification Slide 11 Slide 12 2 Darwin’s observations of natural populations ► Evolution: How Does Evolution Really Work? ► Parents often produce more offspring than will replace themselves but OVER TIME populations remain steady in size. ► Offspring are similar to their parents ► Variation within populations exists and is inherited from the parents Slide 13 Darwin’s observations of natural populations ► Resources Slide 14 Natural Selection ► Adaptations are limited ► In a population there is a continuous struggle for existence. Individuals have different fitness. Fitness is the ability to survive and reproduce offspring Slide 15 are the traits of an organism that help it to survive and reproduce in its environment. ► Individuals that are best adapted to their environment will survive to reproduce. Slide 16 Figure 22.11b Artificial selection: diverse vegetables derived from wild mustard Artificial Selection Slide 17 Slide 18 3 Evolution = process of change over time ► Evidence How do fossils form? comes from a variety of sources 1) fossils 2) biogeography 3) anatomical similarities ►Homologous structures structures ►comparative embryology ►Vestigial 5) Molecular data Slide 19 Figure 22.2 Fossils of trilobites, animals that lived in the seas seas hundreds of millions of years ago Slide 20 Figure 25.1 A gallery of fossils Slide 21 Slide 22 Biogeography (a) Velociraptor Tail acts as a counterbalance ► Biogeography is the study of the geographic distribution of organisms (b) Oviraptosaur Oviraptosaur has finer vertebrae and a portion similar to tail feather insertion platform Organisms of the Galapagos are more similar to those of mainland South America rather than other tropical islands. Related species are found in distant geographic areas. (c) Archaeopteryx of modern birds Intermediates in the fossil record (d) Eagle Slide 23 Slide 24 4 Figure 25.4 The history of continental drift Marsupials and Eutherians ► Continental Drift explains some species distributions Slide 25 Key: C = Cassowary; E = Emu; Emu; e = Elephant Bird; K = Kiwi; m = Moa; O = Ostrich; R = Rhea. Slide 26 Comparative embryology ► http://www.pbs.org/wgbh/evolution/educat ors/course/session3/explain_c.html Slide 27 Comparative embryology Slide 28 Homologous structures Slide 29 Slide 30 5 Biochemical/molecular/genetic evidence Vestigial Structures Ribs Ileum Femur Slide 31 Natural Selection in Action Slide 32 Chapter 23: Evolution of Populations Slide 33 Individuals are selected, but populations evolve!!! Slide 34 The Modern Synthesis ► Populations are the units of evolution Selection is the most important mechanism of evolution ► Gradualism explains how large changes occur as the result of small changes over a long period of time ► Natural ► Grass ► The in the foreground is growing on mine tailings same species is growing in the background Slide 35 Slide 36 6 Genetic Variation and Evolution ► Populations = localized group capable of interbreeding and producing fertile offspring ► = basic unit of evolution ► An important consequence AND requirement of evolution is the maintenance of genetic variation (phenotypic variation) within a population. Slide 37 ► GENE POOL – the sum of all alleles found in a population ► The HARDYHARDY-WEINBERG EQUILIBRIUM MODEL provides a model based upon certain assumptions to which real populations can be compared. Slide 38 ► Allele frequencies are maintained over generations ► This maintains genetic variation Slide 39 The Hardy Weinberg Theorem Slide 40 ► Population = 500 plants 320 Red, 160 pink, 20 white ► How ► Describes gene pools that are NOT evolving ► Provides a benchmark for comparison with evolving populations ► Frequencies of alleles will remain constant over time if only Mendelian segregation and recombination are at work. Slide 41 many TOTAL alleles are there for flower color in the population? 1000 ► How many CR and how many CW ? (think individual alleles) 800 CR and 200 CW ► If mating is random, then the genotype frequencies will be at HardyHardy-Weinberg Equilibrium Slide 42 7 HardyHardy- Weinberg Model Assumptions ► No mutations ► All matings are random ► No gene flow ► Populations must be very large ► No natural selection Slide 43 Slide 44 How is the equation applied? Mutation ► By determining and following allele frequencies as they change within a population. ► There are several things that can affect allele frequencies. GENE FLOW GENETIC DRIFT bottleneck effect founder effect MUTATION NONRANDOM MATING ► Rates Slide 45 are low in higher organisms, high in lower organisms ► 1/100,000 genes/generation Slide 46 Gene flow does occur Genetic drift ► The frequency of alleles increases or decreases due to random chance (can also be due to selective forces like habitat loss or mass overhunting) overhunting) Slide 47 Slide 48 8 Bottleneck Effect Founder Effect Slide 49 Slide 50 Genetic Variation Natural Selection is the primary mechanism of adaptive evolution ► Occurs in individuals in populations of all species ► Variation is not always heritable (a) Map butterflies that emerge in spring: orange and brown Slide 51 Variation within populations characters characters ► Polymorphisms Slide 52 Figure 23.9 A, B Variation between populations ► Geographic ► Discrete (b) Map butterflies that emerge in late summer: black and white variation ► Clinal variation ► Quantitative Phenotypic – males vs. females Genetic - height Slide 53 Slide 54 9 Figure 23.12 Modes of selection How does natural selection alter gene frequencies? Slide 55 Slide 56 Figure 23.16x1 Sexual selection and the evolution of male appearance appearance How is genetic variation preserved??? ► Diploidy ► Balancing selection when natural selection maintains stable frequencies of two or more phenotypic forms in a population Heterozygote Advantage Slide 57 Slide 58 Figure 23.16x2 Male peacock WHY SEX? ► It is still not well understood why sexual reproduction continues. Most accepted hypothesis is disease resistance ► http://www.pbs.org/wgbh/evolution/educat ors/course/session2/elaborate_b.html Slide 59 Slide 60 10 Organisms are not perfect ► Evolution is limited by historical constraints ► Adaptations are compromises ► Chance and natural selection interact ► Selection can only act on existing variation Slide 61 11