BIOL 108 Chp 8 - Evolution and Natural Selection

Chapter 8 Evolution and Natural SelectionBIOL 108 Rob Swatski Asst Prof BiologyIntro to Bio Sci HACC-York

Learning Goals Be able to Be able to explain how Be able to describe and Be able to populations of explain how Be able to explain the explain organisms can the evidence explain four Darwin’s adapt to their for theevolution in mechanisms journey to an environment occurrence of action. that can give idea. through evolution is rise to natural overwhelming. evolution. selection. 2

Evolution in Action8.1 We can see evolution occur right before us. Could you breed fruit flies who could live longer than 20 hours on average? 4

When these eggs hatch, do you thinkthe flies in this new generation will live longer than 20 hours without food? 6

What Happened? NaturalEvolution Selection The consequence of A genetic change in certain individual organisms in a population the population being born with characteristics that enable them to survive better and reproduce more than the offspring of other individuals in the population 8

DoesEvolution Occur? The answer is an unambiguous YES We can watch it happen in the labwhenever we want. 9

Evolution What types of How does changes canevolution occur? evolution cause in a population?Five primary lines Evolution by of evidence natural selection 10

Take-Home Message 8.1 The characteristics of individuals in a population can change over time. We can observe such change in nature and can even cause such change to occur. 11

Darwin’s Journey to an Idea 8.2 Before Darwin, most people believed that all species had been created separately and14 were unchanging.

Jean-BaptisteLamarck Early 1800s: Species evolvethrough the use & disuse of body parts Characteristics acquired duringlife are inheritedUnsupported by evidence 16

Lamarck’s Hypothesis 17

Aren’t you gladLamarck was wrong? 19

Charles LyellPrinciples of Geology (1830) 20

Charles Lyell Early 1800s geologist: Principles ofGeology (1830)Geological forceshad shaped the earth and werecontinuing to do so. Gradual but constant change 21

Uniformitarianism “The mechanisms of change are constant over time” 22

Take-Home Message 8.2People used to think We can observe such that the earth was change in nature and6,000 years old and can even cause such that species were change to occur. unchanging. These changes helped shape Darwin’s thinking. 23

8.3 Darwin’s Research Darwin always had a deep interest in science & nature Was a student of medicine & theology at Cambridge 5-year voyage on the Beagle after graduation 24

Don’t Listen to Your Parents “You care for nothing but shooting, dogs, and rat-catching. You will be a disgrace to yourself and your family.”25 - DR. ROBERT DARWIN

Voyage ofthe Beagle Collected specimens of South American plants & animals Observed adaptations to many diverse environments Became interested in the geographic distribution of species after a stop at the Galápagos Islands 26

Take-Home Message 8.3 After initially training in medicine and theology, Charles Darwin studied the natural world on a‘round-the-world voyage. 28

8.4 Observing geographic similarities and differences among fossils and living plants and animals, Darwin developed a theory of evolution. 29

Two important and unexpected patterns: 1. Traits exhibited by species 30

2. Similarity between the fossils of extinctspecies and the living species in that same area 31

ThomasMalthus An economist who had a major influence on DarwinMalthus wrote about the potential forhuman population to increase faster than food supplies & other resources 33

Take-Home Message 8.4 Darwin noted unexpected Fossils resembled but were patterns among fossils he not identical to the livingfound and living organisms organisms in the same he observed while on the area. voyage of the Beagle. Finch species on the These observations helpedGalapagos Islands differed him to develop his theory in small but significant of how species might ways. change over time. 35

If you had an idea that was going to outrage society… would you keep36 it to yourself?

AlfredRussellWallace37

8.5 In 1858, Darwinpublished histhoughts on naturalselection afterdecades ofpercolating andprocrastinating.38

Take-Home Message 8.5 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. 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. 41

8.6 Evolution occurs when the allele frequencies in a population change. 43

Witnessing Evolution As the Alter the generations go Evolution = population by… Increase the Change in the Higher proportion white phenotype allele frequencies of white tigers through breeding of a population44

Individuals do not evolve. Populations evolve. 45

NaturalSelection An efficient mechanism of evolution… … and a powerful force in adapting populations totheir environment Evolution andnatural selectionare not the same thing. 46

Agents of Evolutionary Change 2. 4. 1. 3. Genetic NaturalMutation Migration drift selection 47

Take-Home Message 8.6 Evolution is a change in allele frequencies within a population. It can occur by four different mechanisms: mutation, genetic drift, migration, and natural selection. 48

8.7 Mutation—a direct change in the DNA of an individual—is the ultimate source of all genetic variation. 49

Mutation An alteration of the base-pair sequence of an individual’s DNA When this alteration occurs in a gene… …the change in the DNA sequence may change the allele. 50

Causes ofMutations The process of cells dividing can go awry Environmental phenomena: mutagens Mutations are random 53

Mutation is the ultimate source ofgenetic variation in a population. 54

Nearly all mutations reduce an organism’s fitness. RandomlySuppose that select one Is the change you have letter in the more likely written a paper and to make your ten-page change it to paper better paper. another or worse? letter 55

Take-Home Message 8.7Mutation is an alteration of This constitutes evolution ifthe base-pair sequence in it changes an allele the an individual’s DNA. individual carries. Mutation is the only wayMutations can be caused by that new alleles can be high-energy sources or created within a population, chemicals in the and so generates theenvironment and also can variation on which natural appear spontaneously. selection can act. 56

8.8 Genetic drift is a random change in allele frequencies in a population. 57

The important factor that distinguishes genetic drift from natural selection:The change in allele frequencies is not related to the alleles’ influence on reproductive success. 59

The impact of genetic drift is muchgreater in small populations than in large populations. 60

Fixation Genetic drift can lead to fixation for one allele for a gene in a population. If this happens, there is no more variability in the population for this gene. Genetic drift reduces the genetic variation in a population. 61

Two special cases of genetic drift, the founder effect and population bottlenecks, are important in the evolution of populations. 62

Founder Effect A small number ofindividuals may leave a population… …and become thefounding members of a new, isolated population. The founders may have different allele frequencies than the original “source”population, particularly ifthey are a small sample. 63

Take-Home Message 8.8 Genetic drift is a random change in allele frequencies within a population, unrelated to the alleles’ influence on reproductive success. Genetic drift is a significant agent of evolutionary change primarily in small populations. 66

8.9 Migration into or out of a population may change allele frequencies. Migration (gene flow) is the movement of some individuals of a species from one population to67 another.

Take-Home Message 8.9 Migration, or gene flow, leads to a change in allelefrequencies in a populationas individuals move into or out of the population. 68

8.10 When three simple conditions are satisfied, evolution by natural selection occurs. 3. Individuals with one version1. There must be of the trait mustvariation for the 2. That variation produce more particular trait must be offspring than within a inheritable. those with a population. different version of the trait. 69

Condition 1: Variation for a TraitVariation is all around us and is the raw material on which evolution feeds. 71

Condition 2: HeritabilityWe call the transmission of traits from parents to their children through genetic information inheritance or heritability. 72

Condition 3: Differential Reproductive Success 3. Some 1. There are 2. Organisms organisms more are are more organisms continually likely to winborn than can struggling for this struggle survive. existence. & survive and reproduce. 73

Differential Reproductive SuccessFrom all the variation existing in a population, individuals with traits most suited to reproduction in their environment generally leave more offspring than individuals with other traits. 74

Take-Home Message 8.10 Natural selection is a mechanism of evolution that occurs when there is heritable variation for a trait, and individuals with one version of the trait have greater reproductive success than individuals with a different version of the trait. It can also be thought of as the elimination of alleles from a population that reduce the reproductive rate of individuals carrying them relative to the reproductive rate of individuals who do not carry the alleles. 77

Through natural selection, populations of organisms can become adapted to their environment. 79

8.11 Traits causing individuals tohave more offspring than others become more prevalent. 80

“Survival ofthe Fittest” Reproductive success Fitness A measure of the relative amount of reproduction of an individual with a particular phenotype, as compared with the reproductive output of individuals with alternative phenotypes 81

Fruit Fly Example The other fly has One fly carries the genes for a the genes for a different versionversion of a trait Which fly has of the trait thatthat allows it to the greater allows it to survive a long fitness? survive only a time without short while food. without food. 82

The alleles carried by an individual with high fitness will increase their marketshare in a population over time and the population will evolve. 83

3 important elements to an organism’s fitness: 3. Fitness1. An individual’s depends on an 2. Fitness fitness is organism’s depends on the measured reproductive specificrelative to other success environment in genotypes or compared to which the phenotypes in other organisms organism lives. the population. in the population. 84

Take-Home Message 8.11 Fitness is a measure of the relative amount of reproduction of an individual with a particular phenotype, as compared with the reproductive output of individuals with alternative phenotypes. An individual’s fitness can vary, depending on the environment in which the individual lives. 86

8.12 Organisms in a population can become better matched to their environment through natural selection. 87

Take-Home Message 8.12 Adaptation—the process bywhich organisms become better matched to their environment and the specific features that make an organism more fit— occurs as a result of natural selection. 88

8.13 Natural selection does not lead to perfect organisms. 89

Founder Effect Evolution in general, and natural selection specifically, do notguide organisms toward “better-ness” or perfection. If the environment changes, the alleles causing the traits favored by naturalselection may change, too.Why doesn’t naturalselection lead to the productionof perfect organisms? 90

Factors that Prevent Populations fromProgressing Inevitably toward Perfection 3. There may be multiple 2. Variation is different alleles 1. needed as the for a trait, each Environments raw material of causing anchange quickly. selection. individual to have the same fitness. 91

Take-Home Message 8.13Natural selection does 1. Environments cannot lead to organisms change more quickly perfectly adapted to than natural selection their environment can adapt organisms to because: them. 3. There is not always a2. All possible alleles single optimumare not produced by adaptation for an mutation. environment. 92

8.14 Artificial selection is just aspecial case of natural selection. 93

Take-Home Message 8.14 Animal breeders and farmers utilize natural selection when they modify their animals and crops because the three conditions for natural selection are satisfied. Because the differential reproductive success is determined by humans and not nature, this type of natural selection is also called artificial selection. 94

8.15 Naturalselection canchange the traitsseen in apopulation inseveral ways. 95

Directional SelectionIndividuals with one extreme from the range ofvariation in the population have higher fitness. 96

Stabilizing SelectionIndividuals with intermediate phenotypes are most fit. 97

Disruptive SelectionIndividuals with extreme phenotypes experience the highest fitness, and those with intermediate phenotypes have the lowest. 98

Take-Home Message 8.15 1. Directional selection, in Natural selection can which the average value for change populations in the trait increases or several ways: decreases 2. Stabilizing selection, in 3. Disruptive selection, inwhich the average value of a which individuals with trait remains the same extreme phenotypes have while extreme versions of the highest fitnessthe trait are selected against 99

8.16 Natural selection can cause theevolution of complex traits and behaviors. 100

Often, structuresappear because they serve some other purpose. Functional Shifts 103

Take-Home Message 8.16 Natural selection can change allele frequencies for genes involving complex physiological processes and behaviors. This sometimes involves a trait that has been selected for one function being modified at a later time to serve a completely different function. 104

It is indeed remarkable that this theory [evolution] hasbeen 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 independentlyis in itself a significant argument in favor of this theory. —Pope John Paul II, 1996 106

Five primary lines of evidence: 3. 5. Laboratory1. The fossil 2. Comparative 4. Molecular & field record Biogeography anatomy & biology experiments embryology 107

8.17 The fossil recorddocuments the processof natural selection. 108

Take-Home Message 8.17 Radiometric dating confirms that the earth is very old and makes it possible to determine the age of fossils. Analysis of fossil remains enables biologists to reconstruct what organisms looked like long ago, learn how organisms were related to each other, and understand how groups of organisms evolved over time. 112

8-18. Geographic patterns of species’distributions reflect their evolutionary histories. 113

HistoryMatters Who arrived first? Are numerousdifferent habitats available? 114

Take-Home Message 8.18 Studying where populations of species live can help us tounderstand evolutionaryhistories of populations. 116

8.19 Comparative anatomy and embryology reveal common evolutionary origins. 117

Homologous Structures 118

VestigialStructures119

ConvergentEvolutionAnalogousstructures alldeveloped fromdifferent originalstructures. 120

Take-Home Message 8.19 Similarities in how organisms look and develop shows theircommon evolutionary origins. 121

8.20 Molecular biology reveals thatcommon genetic sequences link all life forms. The genetic code provides our fourth line of evidence that evolution occurs. 122

DNA Similaritiesand Differences Related vs. unrelated individuals The more distantly you and another individual are related… …the more your DNA differs. 123

DNA Similaritybetween Two Species Compare their DNA sequences for individual genes. In Rhesus monkeys, 138 amino acids are the same as those found in human hemoglobin. 124

Recency of Common Ancestry Estimates of evolutionary relatedness are made from: Comparative anatomy, embryology, & the fossil record “Molecular clocks” 125

Take-Home Message 8.20 All living organisms are share the same genetic code. The degree of similarity in the DNA of different species can reveal how closely related they are and the amount of time that has passed since they last shared a common ancestor. 126

8.21 Laboratory and field experimentsenable us to watch evolution in progress. A fifth line of evidence for the occurrence of evolution comes from multigeneration experiments and observations. 127

Changes in theFrequencyof the VariousAlleles 128

Take-Home Message 8.21Carefully designed lab experiments andobservations of naturalpopulations allow us to watch and measure evolution as it occurs. 131

BIOL 108 Chp 8 - Evolution and Natural Selection

by Rob Swatski on Feb 25, 2012

Accessibility

Categories

Tags

Upload Details

Usage Rights

1 Embed 10

Statistics

BIOL 108 Chp 8 - Evolution and Natural Selection — Presentation Transcript