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Evidence for Evolution

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Presentation on theme: "Evidence for Evolution"— 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 369-379
Clues to the Past 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. Section 14.1 Summary – pages

5 Section 14.1 Summary – pages 369-379
Fossils are evidence of organisms that lived long ago that are preserved in Earth’s rocks. TYPES OF FOSSILS Fossils Types Formation A trace fossil is any indirect evidence Trace fossils left by an animal and may include a footprint, a trail, or a burrow. When minerals in rocks fill a space Casts left by a decayed organism, they make a replica, or cast, of the organism. A mold forms when an organism is Molds buried in sediment and then decays, leaving an empty space. Petrified fossils Petrified-minerals sometimes penetrate and replace the hard parts of an organism Amber-Preserved or At times, an entire organism was quickly trapped in ice or tree sap that frozen fossils hardened into amber. Section 14.1 Summary – pages

6 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

7 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

8 Section 14.1 Summary – pages 369-379
For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die. 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. Most fossils are found in sedimentary rocks These rocks form at relatively low temperatures and pressures that may prevent damage to the organism. Section 14.1 Summary – pages

9 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

10 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

11 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

12 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

13 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

14 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

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

17 Section 14.1 Summary – pages 369-379
Scientists use carbon-14 to date fossils less than years old. Carbon-14 (14C) is an isotope of carbon, that has 6 protons and 8 neutrons 14C decays to 14N at a constant rate Every 5,730 years half the 14C in a sample will emit a beta particle (electron) and decay to 14N Thus 5,730 years is called the half life of 14C Section 14.1 Summary – pages

18 For example, if the half-life of 14C (Carbon 14) is 5,730 years
and a sample today has 1,000 14C atoms after 5,730 years C atoms will remain

19 256 14C atoms

20 After 5730 years or 1 half-life 128 14C and 128 14N atoms

21 After 11,460 yrs or 2 half-lives 64 14C and 192 14N atoms

22 After 17,190 yrs or 3 half-lives 32 14C and 224 14N atoms

23 After 22,920 yrs or 4 half-lives 16 14C and 240 14N atoms

24 After 28,650 yrs or 5 half-lives 8 14C and 248 14N atoms

25 After 34,380 yrs or 6 half-lives 4 14C and 252 14N atoms

26 After 40,110 yrs or 7 half-lives 2 14C and 254 14N atoms

27 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

28 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

29 Section 14.1 Summary – pages 369-379
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. Section 14.1 Summary – pages

30 Phylogenetics

31 Phylogenetics The study of evolutionary relationships among groups of organisms (species, populations), which are discovered through: Molecular sequencing data – DNA sequencing and protein synthesis 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
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 Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do Not Reproduce

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

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

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

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