UNIT XI EVOLUTION Test Friday 2-24

Transcription

1 Unit 9: Evolution

2 UNIT XI EVOLUTION Test Friday 2-24 THE THEORY OF EVOLUTION The theory of evolution is one of the most fundamental concepts in Biology. Evolution Is defined as changes in a over population of organisms time. The scientist considered to be the founder of modern evolutionary theory is. Charles Darwin

3 A. History of Evolutionary Theory During the 1700s, several scientists began challenging the idea of a world in which changes did not occur. These scientists and their hypotheses were very important to Darwin s work.

4 A. History of Evolutionary Theory 1. Gradualism - Geologists (Hutton & Lyell) first suggested that the planet was much older than previously thought; began to find evidence that changes were slowly, but constantly taking place.

5 A. History of Evolutionary Theory 2. Malthus Published an essay that had a huge impact on Darwin. Proposed that organisms over - reproduce; in other words, reproduce at a rate than resources can supply greater

6 A. History of Evolutionary Theory 3. Lamarck Lamarck was one of the first scientists to propose a mechanism for evolution; that is, the in population a of organisms over. time His major hypotheses included: changes

7 3. Lamarck Cont. Tendency Toward Perfection Stated that organisms were continually changing in order to live. more successfully

8 3. Lamarck Cont. Use and Disuse Changes in size and/or shape of a structure in an organism was a response to use or disuse. Structures used extensively grew bigger and structures used less frequently. got smaller Inheritance of Acquired Traits

9 Acquired Traits

10 B. Charles Darwin ( ) 1. Darwin s History Darwin s data was collected on a 5-year journey around the world on the HMS Beagle. He made observations and collected data throughout the journey. He used this data to propose a hypothesis to explain the diversity he saw.

11 1. Darwin s History Cont. The area that had the greatest impact on Darwin was the Galapagos Islands due to the differences he saw in the same animals living on different islands.

12 Galapagos

13 He began to suspect that populations from the mainland changed after reaching the Galapagos.

14 Upon his return he talked to animal breeders & called what they did to direct breeding to produce offspring with the desired traits, Artificial selection which is the same as what we called selective breeding last unit.

15 2. Darwin s Observations Members of a population often vary greatly in their. traits Traits are inherited from. parents to offspring All species are capable of producing more offspring than environment can support Variations that increase reproductive success will have greater change of being passed on than those that do not increase repro. success

16 3. Darwin s Theories Based on his observations and the hypotheses of other scientists Darwin proposed evolution occurred by a process called Natural Selection: 1. Organisms with favorable traits tend to survive and ; reproduce thereby leaving more descendants than other individuals Fitness = ability to survive and reproduce

17 3. Darwin s Theories 2. This will result in an accumulation of these traits in the population if they are heritable, changing the original make-up genetic of the population Adaptations = traits enriched in a population that increase the fitness of an organisms having them

18 III. THE PRINCIPLES OF EVOLUTIONARY THEORY thorns on a cactus, Examples of adaptations are camouflage, antibiotic resistance in bacteria

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22 4. Darwin s Legacy Did not publish his findings for years Alfred Wallace formed identical hypotheses based on his research. Sent his manuscript to Darwin, and finally Darwin was persuaded to publish his own conclusions Released, Origin of Species still considered one of the greatest scientific works ever written

23 4. Darwin s Legacy Darwin s two major contributions: Darwin popularized (but did not originate) the idea that species evolve over time and share common ancestry This became widely accepted quickly in the scientific community Darwin proposed how this happened with his original theory of natural selection It wasn t widely accepted until the early 20 th century

24 III. EVIDENCE FOR EVOLUTION A. Fossils Fossils are preserved bones and traces of organisms Fossils provide a record of earlier life and evidence that evolution has occurred. Types: Imprints, molds (impressions), casts (filled impression), tracks, hard parts, actual remains.

25 Evidence of Evolution A. Evidence from Fossils 1. Dating Fossils a) Absolute Dating- 1) Radioactive used to find the age of rocks. Uranium-Lead, Potassium-Argon dating b) Relative Dating 1) Sediments are laid down in strata lowest isotopes 2) layers are oldest position 3) A fossil s in undisturbed rock gives its age relative to other fossils.

26 III. EVIDENCE FOR EVOLUTION Fossils can be used to deduce the sequence of changes that occurred in a species or group of organisms over time. Transitional fossils are remains of organisms with characteristics that are intermediate between those of an ancestral and descendent group.

27 Copyright Pearson Prentice Hall

28 III. EVIDENCE FOR EVOLUTION There are two major classes of traits when studying transitional fossils: 1. derived traits- newly evolved features such as feathers, that do not appear in the fossils of common ancestors 2. ancestral traits- more primitive features such as teeth & tails, that do appear in ancestral ones

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30 III. EVIDENCE FOR EVOLUTION B. Biogeography- The geographic distribution of species can be explained by common descent and the limits geography imposes on migration. (common descent = shared ancestors)

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32 III. EVIDENCE FOR EVOLUTION Distantly related species living in different parts of the world with similar environments have similar adaptations Closer inspection shows these species are often more closely related to geographically closer species with different adaptations

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34 III. EVIDENCE FOR EVOLUTION C. Comparative anatomy Scientists use anatomical studies of different organisms for evidence of evolutionary relationships. 1. Homologous structures-for example, appendages that are very similar in structure, but differ in function are known as homologous structures. Examples of homologous structures are. arm of human, flipper of dolphin, wing of bat

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36 III. EVIDENCE FOR EVOLUTION 2. Vestigial Structures - A structure that is reduced in function in a living organism, but may have been used by an ancestor is known as a vestigial structure. A structure may become vestigial when an organism changes in form or behavior. Examples are wings of ostrich. eyes on cave fish, human appendix

37 III. EVIDENCE FOR EVOLUTION 3. Analogous structures- Not all similar features are evidence of common ancestry. Analogous structures ca be used for the same purpose & can be superficially similar in construction but are not inherited from a common ancestor. They show that functionally similar features can evolve independently in similar environments. Ex wings birds vs. insects

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39 III. EVIDENCE FOR EVOLUTION D. Embryology Similarities in the structures of developing embryo of different organisms are considered to be proof of a close evolutionary relationship.

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41 III. EVIDENCE FOR EVOLUTION E. Comparative biochemistry Scientists use DNA studies to determine the evolutionary relationship between organisms. The more similar the DNA (or protein AA sequence), the closer the evolutionary relationship

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43 IV. MECHANISMS FOR EVOLUTION A. Evolution occurs because of natural selection - a mechanism for change that occurs when organisms with favorable characteristics for a particular environment survive and reproduce to pass these characteristics on to. offspring

44 IV. MECHANSIMS FOR EVOLUTION Evolution does not occur in an individual; instead it refers to heritable changes that occur in a population over time. In other words, evolution is a change in allele frequency for any gene in a population.

45 IV. MECHANSIMS FOR EVOLUTION Other mechanisms work with natural selection to produce genetic changes in populations:

46 In jaguars, the mutation is dominant hence black jaguars can produce both black and spotted cubs, but spotted jaguars only produce spotted cubs when bred together. V. MECHANSIMS FOR EVOLUTION Cont. A. Mutation A mutation is a. change in DNA Although mutations are often, harmful sometimes the resulting change in phenotype may be beneficial to an organism under certain conditions.

47 V. MECHANSIMS FOR EVOLUTION Cont. If the change occurs in the, gametes this change will be passed onto the offspring of that organism.

48 V. MECHANSIMS FOR EVOLUTION Cont. A mutation is the ultimate source of new alleles in a species. Without a variety of alleles for genes in population, natural selection has nothing to choose Low variation = low ability of population to adapt

49 V. MECHANSIMS FOR EVOLUTION Cont. gene pool A is a collection of all the alleles for every gene in a population. Large gene pool = high variation. Small gene pool = low variation.

50 V. MECHANSIMS FOR EVOLUTION Cont. Clarifications about common misconceptions: 1. Random mutations alone cannot cause adaptation. Non-random natural selection is required for forming adaptations. 2. Organisms do not try to mutate in response to challenge. Variation must be already present for selection to operate.

51 V. MECHANSIMS FOR EVOLUTION Cont. B. Diploidy Most organisms are diploid, which means. double set of chromosomes This allows for increased genetic variation in a population. Heterozygote Advantage Seen in sickle cell allele and. malaria Recombination Leads to increased genetic variation as a result of crossing over during prophase I of. meiosis

52 V. MECHANSIMS FOR EVOLUTION Cont. C. Gene Flow Gene flow occurs when organisms from one community migrate to another. This introduces new alleles into the gene pool of another population, changing its genetic makeup.

53 V. MECHANSIMS FOR EVOLUTION Cont. D. Genetic Drift This describes a situation in which random change in allele frequency in gene pool is magnified because the population size is very. small Causes of genetic drift include

54 V. MECHANSIMS FOR EVOLUTION Cont. Bottleneck effect large portion of population destroyed in disaster Founder effect segment of population moves to new habitat Simple illustration of founder effect. The original population is on the left with three possible founder populations on the right

55 Add to notes: Genetic drift ultimately results in the loss of alleles from the genepool. Only mutations and gene flow can introduce new alleles and increase diversity

56 IX. MECHANSIMS FOR EVOLUTION Cont. E. Single Gene Traits-Natural selection on single gene traits can lead to changes in allele frequencies and therefore to evolution. EX. Color change in a lizard poplution

57 IX. MECHANSIMS FOR EVOLUTION Cont. F. Selection of Polygenic Traits-Natural selection can affect the distributions of phenotypes in 3 ways: Directional Selection-Individuals at one end of the bell curve have higher fitness than those in the middle or other end. EX: Birds with bigger beaks are selected for over Medium & small beaks.

58 IX. MECHANSIMS FOR EVOLUTION Cont. Stabilizing Selection-Individuals in the middle have the highest fitness causing the curve to narrow. EX: Birth weight, babies in the middle weight range are more likely to survive than smaller or larger babies Disruptive Selection-when individuals at both ends of the curve have the higher fitness. If lasts long enough can cause the curve to split in two and create two distinct phenotypes. EX. Finches beak sizes, large & small beaks are selected for &the medium beak Struggle to survive.

59 IX. MECHANSIMS FOR EVOLUTION Cont.

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61 III. Macroevolution D. As organisms survive and adapt, speciation may occur. Speciation is the formation of new species - a group of similar organisms that breed with one another and produce fertile offspring.. that is, babies that can make babies

62 For speciation to occur population must diverge & then be reproductively isolated. Abert & Kaibab squirrels of the Grand Canyon

63 F. Isolating Mechanisms: allow for the gene pools to become separate so they can form a new. species (No gene flow) Reproductive isolation- as new species evolves, populations become reproductively isolated from each other.

64 Prezygotic- prevents reproduction by making fertilization unlikely because of geographic, ecological, behavioral, temporal or other differences. Ex: Eastern & Western Meadowlark have overlapping ranges & are similar in appearance but use different mating songs & do not interbreed. Ex: Fireflies- similar species but mate at different times of night

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66 Postzygotic- when fertilization has occurred but a hybrid offspring or Cannot develop reproduce; prevents offspring survival or reproduction Ex. Mule, liger

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69 V. Macroevolution G. The failure of an organism to adapt to changes in its environment will ultimately lead to its extinction because of. natural selection

70 V. MACROEVOLUTION A. Extinction-More than % 99 of all species that have ever lived are now, extinct which means the species has died out. Darwin proposed possible reasons with competition for resources & environmental change

71 Fig. 1: Number of assessed taxa in each species group in Volume 1. For each species group, the pie chart shows the absolute number of taxa and that number as a percentage of all taxa (n = 478). By agreement, neobiota are not included in the analysis.

72 V. MACROEVOLUTION Mass extinction has occurred several times, wiping out entire. ecosystems Meteorites, volcanic action, and Tectonic plate movement has been blamed. Mass extinctions clear the way for evolution of other species. EX: Mammals

73 V. MACROEVOLUTION B. Adaptive radiation or divergent evolution - the process where a single species has evolved through natural selection into diverse forms that live in short period of time that live in different ways. Often follows mass extinctions EX: Finches & tortoises of the Galapagos C. Convergent evolution when unrelated species evolve similar traits even though they live in different parts of the world because of similar ecology & climate. EX: Mara of South America & rabbit of England

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75 X. MACROEVOLUTION Co-evolution D. is when a change in one organism leads to a corresponding change in another organism. EX: Orchid/moth bee with other flowers E. Punctuated Equilibrium Equilibrium is another pattern of evolution. Unlike gradualism punctuated equilibrium is characterized with long periods of stability interrupted by brief periods of rapid change. It is controversial but known that evolution does occur at different rates.

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