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Evidence for Evolution. Today’s Objective (learning goal) To identify how fossils are used as evidence in changes within a species.

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Presentation on theme: "Evidence for Evolution. Today’s Objective (learning goal) To identify how fossils are used as evidence in changes within a species."— Presentation transcript:

1 Evidence for Evolution


3 Today’s Objective (learning goal) To identify how fossils are used as evidence in changes within a species.

4 Section 14.1 Summary – pages About 95 percent of the species that have existed are extinct—they no longer live on Earth. The oldest rocks that have been found on Earth formed about 3.9 billion years ago. Among other techniques, scientists study fossils to learn about ancient species. Clues to the Past

5 Section 14.1 Summary – pages Fossils are evidence of organisms that lived long ago that are preserved in Earth’s rocks. TYPES OF FOSSILS Fossils TypesFormation Trace fossils Casts Molds Petrified fossils Amber-Preserved or frozen fossils A trace fossil is any indirect evidence left by an animal and may include a footprint, a trail, or a burrow. When minerals in rocks fill a space left by a decayed organism, they make a replica, or cast, of the organism. A mold forms when an organism is buried in sediment and then decays, leaving an empty space. Petrified-minerals sometimes penetrate and replace the hard parts of an organism At times, an entire organism was quickly trapped in ice or tree sap that hardened into amber.

6 Section 14.1 Summary – pages Paleontologists, scientists who study ancient life, are like detectives who use fossils to understand events that happened long ago. They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behavior.

7 Section 14.1 Summary – pages Paleontologists also study fossils to gain knowledge about ancient climate and geography. By studying the condition, position, and location of rocks and fossils, geologists and paleontologists can make deductions about the geography of past environments. For example, if they find a fossil of a plant that resembles a present day plant that can only survive in mild weather, they can infer that the conditions were mild when that plant was living as well.

8 Section 14.1 Summary – pages For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die. Most fossils are found in sedimentary rocks. These rocks form at relatively low temperatures and pressures that may prevent damage to the organism. Fossils are not usually found in other types of rock because of the ways those rocks form. For example, the conditions under which metamorphic rocks form often destroy any fossils that were in the original sedimentary rock.

9 Section 14.1 Summary – pages Few organisms become fossilized because, without burial, bacteria and fungi immediately decompose their dead bodies. Occasionally, however, organisms do become fossils in a process that usually takes many years.

10 Section 14.1 Summary – pages A Protoceratops drinking at a river falls into the water and drowns Sediments from upstream rapidly cover the body, slowing its decomposition. Minerals from the sediments seep into the body. Over time, additional layers of sediment compress the sediments around the body, forming rock. Minerals eventually replace all the body’s bone material. Earth movements or erosion may expose the fossil millions of years after it formed.

11 Section 14.1 Summary – pages Scientists use a variety of methods to determine the age of fossils. One method is a technique called relative dating. If the rock layers have not been disturbed, the layers at the surface must be younger than the deeper layers.

12 Section 14.1 Summary – pages Thus, the fossils in the top layer must also be younger than those in deeper layers. Using this principle, scientists can determine relative age and the order of appearance of the species that are preserved as fossils in the layers.

13 Section 14.1 Summary – pages To find the specific ages of rocks, scientists use radiometric dating techniques utilizing the radioactive isotopes in rocks. Radioactive isotopes are atoms that are unstable and break down, or decay, over time, giving off radiation.

14 Section 14.1 Summary – pages Because every radioactive isotope has a characteristic decay rate, scientists use the rate of decay as a type of clock. The half-life of an isotope is the time it takes for half of the isotope in a sample to decay A radioactive isotope forms a new isotope after it decays.

15 If you can know the amount of an unstable isotope that was in a sample And you know the rate at which that isotope decays And you can measure the amount of that isotope presently in the sample You can figure out how old the sample is

16 14 C is used to date organic samples like wood, hair, shells, and other plant and animal products Atmospheric 14 C is incorporated into organic molecules by plants during photosynthesis Animals that eat the plants get 14 C from the plants they eat Black dots represent carbon, grey dots carbon14

17 Section 14.1 Summary – pages Scientists use carbon-14 to date fossils less than years old. Carbon-14 ( 14 C) is an isotope of carbon, that has 6 protons and 8 neutrons 14 C decays to 14 N at a constant rate Every 5,730 years half the 14 C in a sample will emit a beta particle (electron) and decay to 14 N Thus 5,730 years is called the half life of 14 C

18 For example, if the half-life of 14 C (Carbon 14) is 5,730 years and a sample today has 1, C atoms after 5,730 years C atoms will remain

19 C atoms

20 After 5730 years or 1 half-life C and N atoms

21 After 11,460 yrs or 2 half-lives C and N atoms

22 After 17,190 yrs or 3 half-lives C and N atoms

23 After 22,920 yrs or 4 half-lives C and N atoms

24 After 28,650 yrs or 5 half-lives 8 14 C and N atoms

25 After 34,380 yrs or 6 half-lives 4 14 C and N atoms

26 After 40,110 yrs or 7 half-lives 2 14 C and N atoms

27 Section 14.1 Summary – pages Scientists use potassium-40, a radioactive isotope that decays to argon-40, to date rocks containing potassium bearing minerals. Based on chemical analysis, chemists have determined that potassium-40 decays to half its original amount in 1.3 million years.

28 Section 14.1 Summary – pages Scientists always analyze many samples of a rock using as many methods as possible to obtain consistent values for the rock’s age. Errors can occur if the rock has been heated, causing some of the radioactive isotopes to be lost or gained.

29 Section 14.1 Summary – pages The fossil record indicates that there were several episodes of mass extinction that fall between time divisions. A mass extinction is an event that occurs when many organisms disappear from the fossil record almost at once.

30 Phylogenetics

31 The study of evolutionary relationships among groups of organisms (species, populations), which are discovered through: 1.Molecular sequencing data – DNA sequencing and protein synthesis 2.Morphological data matrices – homologous structures, analogous structures, and embryonic development

32 Molecular Sequencing


34 Homologous Structures Scientists Noticed Animals With Backbones Had Similar Bone Structure – Same Structures Different Function Arms, Wings, Legs, Flippers – Limb Bones Develop In Similar Patterns – Help Scientist Group Animals

35 Homologous Structures

36 Analogous Structure Same function with different structures

37 Homologous Body Structures Not All Serve Important Functions – Vestigial Organs Appendix In Man Legs On Skinks

38 Similarities In Early Development Embryonic Structures Of Different Species Show Significant Similarities



41 Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments that blocks the gene flow among the distinct populations. This allows differentiation of characteristics through genetic drift and natural selection.

42 Convergent evolution is the process by which unrelated or distantly related organisms evolve similar body forms, coloration, organs, and adaptations.

43 Adaptive radiation is the evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life.



46 Puncuated Equilibrium A hypothesis in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis. When significant evolutionary change occurs, the hypothesis proposes that it is generally restricted to rare and geologically rapid events of branching speciation (the evolutionary process by which new biological species arise) called cladogenesis. Cladogenesis is the process by which a species (organisms that breed and produce offspring that are also fertile) splits into two distinct species, rather than one species gradually transforming into another.

47 Morphological Change

48 Evolutionary Time Scales Microevolution : Short time scale events (generation-to- generation) that change the genotypes and phenotypes of populations.



51 The term coevolution is used to describe cases where two (or more) species reciprocally affect each other’s evolution. Coevolution is likely to happen when different species have close ecological interactions with one another. These ecological relationships include: 1. Predator/prey and parasite/host 2. Competitive species 3. Mutualistic species

52 Genetic drift -random fluctuations in the numbers of allele differences in a population *Takes place when the occurrence of alleles, increases and decreases by chance over time. *Typically occurs in small populations, where infrequently occurring alleles face a greater chance of being lost *Will continue until the involved allele is either lost by a population or until it is the only allele present in a population at a particular location *Can cause a new population to be genetically distinct from its original population, which has led to the hypothesis that genetic drift plays a role in the evolution of new species.


54 Gene flow (also known as gene migration) is the transfer of alleles or genes from one population to another. Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene). Immigration may also result in the addition of new genetic variants to the established gene pool of a particular species or population.

55 Mutations - when a DNA gene is damaged or changed in such a way as to alter the genetic message carried by that gene. Mutation causes a high rate of natural selection in a changing environment. Natural Selection the gradual process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the reproductive success of organisms interacting with their environment


57 Stabilizing Selection, extreme varieties from both ends of the frequency distribution are eliminated. The frequency distribution looks exactly as it did in the generation before

58 Directional Selection - individuals at one end of the distribution of beak sizes do especially well, and so the frequency distribution of the trait in the subsequent generation is shifted from where it was in the parental generation

59 Diversifying (disruptive) Selection - both extremes are favored at the expense of intermediate varieties. This is uncommon, but of theoretical interest because it suggests a mechanism for species formation without geographic isolation

60 Evolution By Natural Selection The Struggle for Existence Survival of the Fittest Descent with Modification

61 The Struggle for Existence Malthus’ Influence – High Birth Rates & Limited Resources Would Force Life & Death Competition Each Species Struggles For: – Food – Living Space – Resources

62 Survival of the Fittest Fitness – Ability of an Individual To Survive & Reproduce Adaptation – Inherited Characteristic That Increases an Organisms Chance for Survival

63 Survival of the Fittest Adaptations Can Be: – Physical Speed, Camouflage, Claws, Quills, etc. – Behavioral Solitary, Herds, Packs, Activity, etc.

64 Survival of the Fittest Fitness Is Central To The Process Of Evolution Individuals With Low Fitness – Die – Produce Few Offspring Survival of the Fittest AKA Natural Selection

65 Survival of the Fittest Key Concept Over Time, Natural Selection Results In Changes In The Inherited Characteristics Of A Population. These Changes Increase A Species Fitness In Its Environment

66 Natural Selection Cannot Be Seen Directly It Can Only Be Observed As Changes In A Population Over Many Successive Generations – Radiation – Fossil Record



69 Population Growth Thomas Malthus, 1798 – Economist – Observed Babies Being Born Faster Than People Were Dying Population vs. Food Supply

70 Population Growth Key Concept – Malthus Reasoned That If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone Famine, Pestilence Political Instability, War Death Rate Will Increase To Balance Population & Food Supply

71 Population Growth Darwin Realized Malthus’s Principles Were Visible In Nature. Plants & Animals Produce Far More Offspring Than Can Be Supported. – Most Die – If They Didn’t – Earth Would Be Overrun

72 Natural Variation & 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 (Selective Breeding)

73 Natural Variation & Artificial Selection Natural Variation – Differences Among Individuals Of A Species Artificial Selection – Selective Breeding To Enhance Desired Traits Among Stock or Crops

74 Natural Variation & Artificial Selection Key Concept In Artificial Selection, Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful



77 Evidence of Evolution Key Concept Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. 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

78 Geographic Distribution of Living Species Different Animals On Different Continents But Similar Adaptations To Shared Environments

79 Darwin's Theory 1.Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited 2.Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do Not Reproduce

80 Darwin's Theory 3.Because More Organisms Are Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources 4.Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence

81 Darwin's Theory 5.Individuals Best Suited To Their Environment Survive & Reproduce Successfully – Passing Their Traits To Their Offspring. 6.Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species

82 Darwin's Theory 7.Species Alive Today Have Descended With Modifications From Species That Lived In The Past 8.All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent

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