1 C HAPTER 8: E VOLUTION AND N ATURAL S ELECTION Darwins dangerous idea: evolution by natural selection Lectures by Mark Manteuffel, St. Louis Community College ; Clicker Questions by Kristen Curran, University of Wisconsin-Whitewater 2 E VOLUTION IN A CTION We can see evolution occur right before us. 3 C OULD YOU BREED FRUIT FLIES WHO COULD LIVE LONGER THAN 20 HOURS ON AVERAGE ? 4 5 6 When these eggs hatch, do you think the flies in this new generation will live longer than 20 hours without food? 7 A POPULATION OF FRUIT FLIES WAS STARVED UNTIL 80% OF THE FLIES WERE DEAD. T HE REMAINING FLIES WERE FED AND OFFSPRING WERE PRODUCED. 8 9 A FTER 60 GENERATIONS THE AVERAGE STARVATION RESISTANCE OF FRUIT FLIES WAS 160 HOURS 1. They are genetically identical to the original population. 2. They are genetically different from the original population. W HAT HAPPENED ? o Evolution a genetic change in the population (group of organisms of the same species living in the same geographic region). o Natural selection the consequence of certain individual organisms in a population being born with characteristics that enable them to survive better and reproduce more than the offspring of other individuals in the population 10 E XPERIMENTS IN E VOLUTION o Dogs? o Rabbits? 11 E VOLUTION o How does evolution occur? o What types of changes can evolution cause in a population? o Five primary lines of evidence o Evolution by natural selection 12 13 It is indeed remarkable that this theory [evolution] has been progressively accepted by researchers, following a series of discoveries in various fields of knowledge. The convergence, neither sought nor fabricated, of the results of work that was conducted independently is in itself a significant argument in favor of this theory. Pope John Paul II, 1996 N ATURAL C HANGES o The characteristics of individuals in a population can change over time. o We can observe such change in nature and can even cause such change to occur. 14 15 16 17 D ARWIN S J OURNEY TO AN I DEA A job on a round-the-world survey ship allowed Darwin to indulge and advance his love of nature. 18 A JOB ON A ROUND - THE - WORLD SURVEY SHIP ALLOWED D ARWIN TO INDULGE AND ADVANCE HIS LOVE OF NATURE. o Age 16, University of Edinburgh, medical studies o Studied theology at Cambridge University o His real love: study of nature 19 D ARWIN S J OURNEY TO AN I DEA Before Darwin, most people believed that all species had been created separately and were unchanging. 20 21 22 J EAN -B APTISTE L AMARCK o Biologist, early 1800s o Living species might change over time. o If we need to jump higher we will learn to jump higher. 23 C HARLES L YELL & J AMES H UTTON o Geologist o 1830 book Principles of Geology o Geological forces had shaped the earth and were continuing to do so. o Gradual but constant change o Darwin had this book with him on the Beagle 24 E MERGING B ELIEFS o People used to think that the earth was 6,000 years old and that species were unchanging. o In the 18th and 19th centuries, scientists began to change their beliefs. o These changes helped shape Darwins thinking. 25 26 D ARWIN S J OURNEY TO AN I DEA Observing geographic similarities and differences among fossils and living plants and animals, Darwin developed a theory of evolution. 27 28 T WO IMPORTANT AND UNEXPECTED PATTERNS : 1. T RAITS EXHIBITED BY SPECIES 29 2. S IMILARITY BETWEEN THE FOSSILS OF EXTINCT SPECIES AND THE LIVING SPECIES IN THAT SAME AREA o Glyptodonts and armadillos 30 D ARWIN S F OSSILS 31 The slides were made by slicing and polishing the fossils into translucent sheets and then placing them between two glass plates so they could be studied under a microscope. D ARWIN S F OSSILS 32 D ARWIN S F OSSILS 33 These images were made available by the Royal Holloway, University of London on Jan. 17, and were collected by Charles Darwin during the course of his famous "Voyage of the Beagle." (University of London, Kevin D'Souza Ho,AP Photo/Royal Holloway) T HOMAS M ALTHUS o Economist o Essay on the Principle of Population o - populations can grow much faster than the food supply. We will eat ourselves out of existence in the foreseeable future. o Darwin realized that favorable variations are preserved 34 T HE B OOK THAT W OULD R OCK THE W ORLD o 1842 first draft o 14 years in a drawer 35 D ARWIN S D ISCOVERIES o Fossils resembled but were not identical to the living organisms in the same area. o Finch species on the Galapagos Islands differed in small but significant ways. 36 D ARWIN S J OURNEY TO AN I DEA In 1858, Darwin published his thoughts on natural selection after decades of percolating and procrastinating 37 38 39 H ISTORICAL P ROGRESS o After putting off publishing his thoughts on natural selection for more than 15 years, Darwin did so only after Alfred Russel Wallace independently came up with the same idea. o They published a joint presentation on their ideas in 1858 and Darwin published a much more detailed treatment in The Origin of Species in 1859, sparking wide debate and discussion of natural selection. 40 41 THE OBSERVATIONS D ARWIN MADE DURING HIS TRIP ON THE HMS B EAGLE ? 1. The earth is shaped by gradual forces. (Lyell) 2. The earth is older than 6,000 years. (Buffon) 3. Populations could grow beyond the ability of the environment to support them. (Malthus) Malthus thesis was that the population of England would soon reach a point that was impossible to feed with the islands resources. 42 F OUR MECHANISMS CAN GIVE RISE TO EVOLUTION. 43 Evolution occurs when the allele frequencies in a population change. 44 45 W ITNESSING E VOLUTION o Alter the population Increase the white phenotype through breeding. o As the generations go by o - Higher proportion of white tigers o Evolution = change on allele frequencies of the population 46 I NDIVIDUALS DO NOT EVOLVE. o Populations evolve get better with the resources they have o Allele frequencies dark colored moths on dark tree trunks 47 4 A GENTS OF E VOLUTIONARY C HANGE 1. Mutation Genetic drift Migration Natural selection Evolution is genetic change in a population. F OUR MECHANISMS CAN GIVE RISE TO EVOLUTION Mutationa direct change in the DNA of an individualis the ultimate source of all genetic variation. 49 M UTATION o An alteration of the base-pair sequence of an individuals DNA o When this alteration occurs in a gene, the change in the DNA sequence may change the allele. 50 51 52 W HAT CAUSES MUTATIONS ? o The process of cells dividing can go awry. o Environmental phenomena o mutagens o Mutations are random o Beneficial? o Detrimental? 53 T ANNING BEDS BOMBARD THE BODY WITH ULTRAVIOLET RADIATION. Can they cause mutations? 54 M OBILE PHONES RELEASE RADIATION. Can they cause brain tumors? 55 M UTATION IS THE ULTIMATE SOURCE OF GENETIC VARIATION IN A POPULATION. 56 N EARLY ALL MUTATIONS REDUCE AN ORGANISM S FITNESS. 57 M UTATION o An alteration of the base-pair sequence in an individuals DNA. o Evolution if it changes an allele the individual carries. F OUR MECHANISMS CAN GIVE RISE TO EVOLUTION Genetic drift is a random change in allele frequencies in a population. 59 60 GENETIC DRIFT IS NOT NATURAL SELECTION : The change in allele frequencies does not influence reproductive success. 61 T HE IMPACT OF GENETIC DRIFT IS MUCH GREATER IN SMALL POPULATIONS THAN IN LARGE POPULATIONS. 62 F IXATION o Genetic drift can lead to fixation for one allele for a gene in a population. o If this happens, there is no more variability in the population for this gene. o Genetic drift reduces the genetic variation in a population. 63 EVOLUTION OF POPULATIONS THE FOUNDER EFFECT POPULATION BOTTLENECKS 64 F OUNDER E FFECT 65 A MISH PEOPLE ARE MORE LIKELY TO HAVE EXTRA FINGERS AND TOES 66 P OPULATION B OTTLENECKS R ETURN OF THE M ICHIGAN S ANDHILL C RANES 67 68 G ENETIC D RIFT o A random change in allele frequencies within a population, o A significant agent of evolutionary change primarily in small populations. F OUR MECHANISMS CAN GIVE RISE TO EVOLUTION Migration into or out of a population may change allele frequencies. 70 Migration, also called gene flow, is the movement of some individuals of a species from one population to another. 71 M IGRATION o Migration, or gene flow, leads to a change in allele frequencies in a population as individuals move into or out of the population. F OUR MECHANISMS CAN GIVE RISE TO EVOLUTION Natural Selection random changes in a population produce an individual better suited to its environment 73 N ATURAL S ELECTION 1. There must be variation for the particular trait within a population. 2. That variation must be inheritable. 3. Individuals with one version of the trait must produce more offspring than those with a different version of the trait. 74 75 C ONDITION 1: V ARIATION FOR A T RAIT o Variation is all around us. o Variation is the raw material on which evolution feeds. 76 C ONDITION 2: H ERITABILITY We call the transmission of traits from parents to their children through genetic information inheritance or heritability. 77 C ONDITION 3: D IFFERENTIAL R EPRODUCTIVE S UCCESS 1. There are more organisms born than can survive. 2. Organisms are continually struggling for existence. 3. Some organisms are more likely to win this struggle and survive and reproduce. 78 D IFFERENTIAL R EPRODUCTIVE S UCCESS - The runt of the litter, less chance of survival. 79 80 M OST AGRICULTURAL PESTS EVOLVE RESISTANCE TO PESTICIDES. How does this happen? 81 82 RABBITS HAVE EVOLVED DUE TO INTERACTIONS WITH PREDATORS 1. Speed 2. Coat color 83 T HROUGH NATURAL SELECTION, POPULATIONS OF ORGANISMS CAN BECOME ADAPTED TO THEIR ENVIRONMENT. 84 Traits causing individuals to have more offspring than others become more prevalent. 85 S URVIVAL OF THE F ITTEST o Reproductive success o Fitness 86 F RUIT F LY E XAMPLE o One fly carries the genes for a version of a trait that allows it to survive a long time without food. o The other fly has the genes for a different version of the trait that allows it to survive only a short while without food. o Which fly has the greater fitness? 87 T HERE ARE THREE IMPORTANT ELEMENTS TO AN ORGANISM S FITNESS : 1. An individuals fitness is measured relative to other genotypes or phenotypes in the population. 88 T HERE ARE THREE IMPORTANT ELEMENTS TO AN ORGANISM S FITNESS : 2. Fitness depends on the specific environment in which the organism lives. 89 T HERE ARE THREE IMPORTANT ELEMENTS TO AN ORGANISM S FITNESS : 3. Fitness depends on an organisms reproductive success compared to other organisms in the population. 90 "S URVIVAL OF THE FITTEST " IS A MISNOMER. T HROUGH NATURAL SELECTION, POPULATIONS OF ORGANISMS CAN BECOME ADAPTED TO THEIR ENVIRONMENT. 91 Organisms in a population can become better matched to their environment through natural selection. 92 93 A DAPTATION TO E NVIRONMENT T HROUGH NATURAL SELECTION, POPULATIONS OF ORGANISMS CAN BECOME ADAPTED TO THEIR ENVIRONMENT. 94 Natural selection does not lead to perfect organisms. 95 96 Evolution in general, and natural selection specifically, do not guide organisms toward better-ness or perfection. If the environment changes, the alleles causing the traits favored by natural selection may change, too. 97 F ACTORS THAT P REVENT P OPULATIONS FROM P ROGRESSING I NEVITABLY TOWARD P ERFECTION 1. Environments 2. Variation 3. Multiple different alleles for a trait, T HROUGH NATURAL SELECTION, POPULATIONS OF ORGANISMS CAN BECOME ADAPTED TO THEIR ENVIRONMENT. 98 Artificial selection is just a special case of natural selection. 99 A RTIFICIAL S ELECTION o Animal breeders and farmers o Determined by humans and not nature, T HROUGH NATURAL SELECTION, POPULATIONS OF ORGANISMS CAN BECOME ADAPTED TO THEIR ENVIRONMENT. 100 Natural selection can change the traits seen in a population in several ways. 101 102 D IRECTIONAL S ELECTION Individuals with one extreme from the range of variation in the population have higher fitness. 103 T URKEYS ON POULTRY FARMS HAVE SUCH LARGE BREAST MUSCLES THAT THEY CAN T GET CLOSE ENOUGH TO EACH OTHER TO MATE. 104 105 S TABILIZING S ELECTION Individuals with intermediate phenotypes are most fit. 106 IS MEDICAL TECHNOLOGY UNDOING THE WORK OF NATURAL SELECTION IN OPTIMIZING THE NUMBER OF BABIES WITH NORMAL BIRTH WEIGHTS ? 107 D ISRUPTIVE S ELECTION Individuals with extreme phenotypes experience the highest fitness, and those with intermediate phenotypes have the lowest. 108 N ATURAL SELECTION CAN CHANGE POPULATIONS IN SEVERAL WAYS : 1. Directional selection, 2. Stabilizing selection, 3. Disruptive selection, 109 M OST MAMMALS DO NOT DRINK MILK AFTER THEY ARE WEANED BECAUSE THEY LOSE THE ABILITY TO DIGEST LACTOSE. T HIS IS TRUE FOR ABOUT 60% OF PEOPLE. B UT MOST PEOPLE OF NORTHERN E UROPEAN DESCENT CAN DRINK MILK ( AREAS WHERE DAIRY FARMING IS HISTORICALLY PREVALENT ). W HAT TYPE OF EVOLUTION WOULD THIS EXEMPLIFY ? 1. Directed selection 2. Stabilizing selection 3. Disruptive selection T HROUGH NATURAL SELECTION, POPULATIONS OF ORGANISMS CAN BECOME ADAPTED TO THEIR ENVIRONMENT. 110 Natural selection can cause the evolution of complex traits and behaviors. 111 112 H OW CAN A WING EVOLVE IF 1% OF A WING DOESN T HELP AN ORGANISM FLY OR GLIDE AT ALL ? 113 O FTEN, STRUCTURES APPEAR BECAUSE THEY SERVE SOME OTHER PURPOSE. F UNCTIONAL S HIFTS 114 115 A DAPTING TO THE E NVIRONMENT o Natural selection can change allele frequencies for genes involving roundabout unrelated paths. o A trait that has been selected for one function is modified at a later time to serve a completely different function. 116 T HE E VIDENCE FOR THE O CCURRENCE OF E VOLUTION IS OVERWHELMING The fossil record documents the process of natural selection. 118 119 120 R ADIOMETRIC DATING 121 122 T HE E VIDENCE FOR THE O CCURRENCE OF E VOLUTION IS OVERWHELMING Geographic patterns of species distributions reflect their evolutionary histories. 124 125 126 B IOGEOGRAPHY T HE E VIDENCE FOR THE O CCURRENCE OF E VOLUTION IS OVERWHELMING Comparative anatomy and embryology reveal common evolutionary origins. 128 129 C HICK EMBRYOS AND HUMAN EMBRYOS BOTH HAVE GILLS BECAUSE 130 H OMOLOGOUS S TRUCTURES 131 O NTOGENY RECAPITULATES PHYLOGENY Why are we all born with one? - Gills - appendixes 132 V ESTIGIAL S TRUCTURES 133 C ONVERGENT E VOLUTION Analogous structures all developed from different original structures. 134 W E C ANNOT H IDE W HERE W E C AME F ROM o Similarities in how organisms look and develop shows their common evolutionary origins. T HE E VIDENCE FOR THE O CCURRENCE OF E VOLUTION IS OVERWHELMING Molecular biology reveals that common genetic sequences link all life forms. The genetic code provides our fourth line of evidence that evolution occurs. 136 DNA S IMILARITIES AND D IFFERENCES o Related vs. unrelated individuals o The more distantly you and another individual are related, the more your DNA differs. 137 DNA S IMILARITY BETWEEN T WO S PECIES o Compare their DNA sequences for individual genes. o In Rhesus monkeys, 138 amino acids are the same as those found in human hemoglobin. 138 R ECENCY OF C OMMON A NCESTRY o Estimates of evolutionary relatedness made from: o Comparative Anatomy o Embryology o The Fossil Record o Molecular Clocks T HE E VIDENCE FOR THE O CCURRENCE OF E VOLUTION IS OVERWHELMING Laboratory and field experiments enable us to watch evolution in progress. A fifth line of evidence for the occurrence of evolution comes from multi-generation experiments and observations. 140 C HANGES IN THE F REQUENCY OF THE V ARIOUS A LLELES 141 142 F IVE PRIMARY LINES OF EVIDENCE : 1. The fossil record 2. Biogeography 3. Comparative anatomy and embryology 4. Molecular biology 5. Laboratory and field experiments 143