Pre IB Biology: Evolution

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  • 1. Evolution
    • A process of change through time.
  • 2. I. Theory of Evolution
    • Suggests that existing forms of life on earth have evolved from earlier forms over long periods of time.
    • Evolution accounts for the differences in structures, function, and behavior among life forms as well as changes that occur in populations over many generations.
  • 3. The Beginning…..
  • 4. Early Earth
    • Geologic Evidence shows that Earth is about 4.6 billion years old.
    • Early on there was so much heat that the Earth molten.
    • The most dense elements settle towards the interior of the Earth making the core the most dense, and the crust the least dense.
    • Earth’s early atmosphere probably consisted of hydrogen cyanide, hydrogen sulfide, carbon monoxide, carbon dioxide, nitrogen and water…
  • 5.
    • Eventually Earth cooled to allow the first rocks to form and eventually (3.8billion yrs.) it cooled to allow water to cool.
    • Thunderstorms riddled the planet, and the ocean was brown due to the presence of iron deposits.
    • So how did the first life form from these conditions?
  • 6. Heterotrophic Hypothesis
    • According to this theory autotrophs developed AFTER the heterotrophs because the original atmosphere lacked CO 2 .
    • The Earth’s atmosphere consisted of N 2 , H 2 , NH 3 and CH 4 .
    • It was not until the development of autotrophs that O 2 became present in the atmosphere.
    • Lightning, UV light and heat created the first organic molecules (which will form the first basic cellular structure)
  • 7.
    • Stanley Miller-Urey Experiment:
    • He wanted to see if the heterotroph hypothesis was valid and could explain the evolution of earth’s atmosphere and environmental conditions.
    • By simulating early atmospheric conditions, Miller was in fact able to convert inorganic molecules, such as CH 4 , NH 3 , H 2 , H 2 0, CO 2 , into amino acids and other organic molecules.
  • 8.  
  • 9. Life’s Origin
    • Miller’s experiment showed that organic molecules could be created but how about cells?
    • Proteinoid Microspheres : these are tiny bubbles formed by organic compounds that can transport water and storing and releasing energy. Perhaps these evolved into cells
    • How DNA and RNA developed is still not yet known for sure…
  • 10.
    • Experiments similar to Miller’s showed that early conditions could form RNA molecules, but how the system of DNA developed and protein synthesis began we are still unsure…
  • 11. Free Oxygen
    • Fossil evidence shows that prokaryotic bacteria existed 3.5 billion years ago and were found in rock-like structures called “ Stromatolites ”
    • These are found in Shark
    • Bay, Australia
    • These bacteria started
    • producing O 2 at great
    • rates as a product of
    • photosynthesis.
    • “ microfossils ”
  • 12. Endosymbiosis
    • About 2 billion yrs ago prokaryotes started to develop internal membrane bound structures, forming ancestral eukaryotes.
    • This theory believes that prokaryotes started entering this new cell and living within it.
    • Some had the ability to use O 2 and transfer into ATP….the first mitochondria…
    • Current studies show that mitochondria and chloroplasts have numerous similarities with bacterial cells…hinted that perhaps one evolved from the other!
  • 13.  
  • 14. II. Evidence of Evolution
    • Observations supporting the theory of organic evolution can be made through the study of:
    • Geologic record,
    • Comparative Cytology,
    • Biochemistry,
    • Anatomy, and Embryology
    http://www.youtube.com/watch?v=DJ-h3j_g-eE
  • 15. Geologic “Fossil” Record
    • Fossils occur in a particular order. Certain fossils appear only in older rocks, and other fossils appear only in more recent rocks.
    • In fact, more than 99 percent of all species that have ever lived on Earth have become extinct , which means the species died out.
    • Meanwhile, over billions of years, ancient unicellular organisms have given rise to the modern bacteria, protists, fungi, plants, and animals that you will study in later units.
  • 16.
    • Earth is between 4.5 to 5 billion years old (determined by radioactive dating of rocks).
    • Fossils - the remains of organisms that no longer exist.
    • Fossils have been preserved in ice, sedimentary rock, amber, and tar.
    • 3. Imprints, casts, and molds of organisms or parts of organisms are frequently found in sedimentary rock.
  • 17.
    • 4. In undisturbed layers (strata) of sedimentary rock, the lower strata contain old fossils while the upper strata contain younger fossils
  • 18. Comparative Anatomy
    • Similarities of basic structures exist between different organisms.
    • Homologous structures are anatomical parts found in different organisms.
    • The presence of such homologous structures suggest that these organisms have evolved from a common ancestor.
  • 19.  
  • 20.
    • Analogous Structures : structures that evolve separately but perform similar functions.
    • Vestigial Organs : organs found within an organism which current species no longer use. perhaps showing ancient similarities b/w common ancestors.
  • 21. Analogous : the wings of different species serve a common purpose but these organisms are not believed to be related through time.
  • 22. Vestigial Organs: Human & Snake
  • 23.  
  • 24. Comparison Embryology
    • Comparison of the early stages of their embryonic development may show similarities that suggest a common ancestor.
  • 25.  
  • 26. Comparative Cytology
    • All living things are made up of cells. Similarities that occur within different cells may be used to show common ancestry.
    • Ex. Presence of certain organelles, ribosomes etc.
  • 27. Comparative Biochemistry
    • All living things contain similar biochemical compounds.
    • Examples would include : structure and function of DNA, RNA, and proteins (including enzymes) are similar in all organisms.
  • 28. III. Theories of Evolution
    • Lamarck’s Theory of
    • Evolution
    • In 1809, the year Darwin was born Lamarck published his theory about how organisms changed over time. He was one of the first to attempt to explain this.
    • Proposed the idea of “ use and disuse ”
  • 29. Lamarck's conception of evolution
  • 30.
    • Organisms ‘acquired’ or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species.
    • He further proposed that organisms’ were constantly trying to achieve a state of perfection, so any variation of a trait that developed must have been beneficial in some way.
    • Are there any flaws in reasoning here?
  • 31. B. Charles Darwin 1809-1882
    • Charles Darwin devised a theory of evolution based on variation and natural selection.
    • Included in hid theory were five main ideas:
    • 1. Overpopulation
    • 2. Competition
    • 3. Survival of the Fittest
    • 4. Reproduction
    • 5. Speciation
  • 32.
    • Darwin stated that organisms were changing gradually through time, and that these changes were important.
    • He used “ artificial selection ” to prove this point. He stated that farmers pick the cow that produces the most milk, or the horse that runs the fastest are the ones used for future breeding.
  • 33. Natural Selection
    • A. Natural selection is the evolutionary process which selects the variation(s) of organisms best suited for a particular environment.
    • B. Natural selection provide a scientific explanation for the fossil record, as well as for the molecular and structural similarities observed among the diverse species of living organisms.
  • 34. 1. Overpopulation
    • Within a population, there are more offspring produced in each generation than can possibly survive.
  • 35. 2. Competition
    • Natural resources; like food, water, and space available to a population is limited.
    • Because there are many organisms with similar nutritional requirements, there must be competition between them for the resources needed to survive.
  • 36. 3. Survival of the Fittest
    • Variations among members of a population make some of them better adapted to the environment than others.
    • It is generally the best-adapted individuals that will survive and reproduce.
    • *The environment is the agent of natural selection determining which species will survive.
  • 37. 4. Reproduction
    • Individuals that survive and then reproduce transmit these variations to their offspring.
    • Darwin called the ability of an individual to survive and reproduce in its specific environment fitness.
  • 38. 5. Speciation
    • As time and generations continue, adaptations are passed on and new species may evolve from a common ancestor.
    • He called this “ Descent with modification ”
  • 39. Setbacks of Darwin’s work
    • Even though Darwin claimed that organisms inherited their traits he had not idea how it happened.
    • Work by scientists, including Watson & Crick explained using the concept of molecular genetics to support his hypotheses.
  • 40. Time Frames of Evolution
    • Two different theories proposed by scientists to address the rate of evolution:
    • 1. Gradualism - proposes that evolutionary change is slow, gradual, and continuous.
    • 2. Punctuated Equilibrium - proposes that species have long periods of stability (several million years) interrupted by geologically brief periods of significant change during which a new species may evolve.
  • 41. Gradualism Punctuated Equilibrium
  • 42. IV. Modern Theories of Evolution
    • The modern theory of evolution includes both Darwin’s ideas of variation and natural selection and the current knowledge of the sources of variations.
    • Sources of Variations
    • Segregation and the recombination of alleles during sexual reproduction.
    • 2. Mutations are random changes in the genes or DNA of sex cells may result in new gene combinations creating variation.
  • 43. B. Variation and Genes
    • Genetic variation is studied in populations (is a group of individuals of the same species that interbreed )
    • Since they interbreed they share a common genetic variety also known as a “ gene pool ”.
    • The relative frequency of an allele is the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur
  • 44.
    • The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction.
    • a. Mutations : any change in a sequence of DNA
    • b. Genetic Shuffling : “crossing over” of genetic information during gamete formation
    • c. Some traits are “ single-gene traits ” while others are “ polygenic traits ” (more than one gene effects the trait)
  • 45.  
  • 46.
    • Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution.
    • Ex: A breed of lizards which are usually brown, give rise to a black lizard. However, the black variation is better camouflaged and so predators miss it. As time goes on the original pop n make decrease in size while the black variation increases.
    Natural Selection and Single Gene Traits
  • 47.
    • When polygenic traits are involved, natural selection is more complex, b/c there is such a wide range of different phenotypes.
    • Natural selection can affect the distributions of phenotypes in any of three ways: directional selection , stabilizing selection , or disruptive selection .
    Natural Selection and Polygenic Traits
  • 48.
    • Directional Selection
    • When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end, directional selection takes place
  • 49.
    • Stabilizing Selection
    • When individuals near the center of the curve have higher fitness than individuals at either end of the curve, stabilizing selection takes place. This situation keeps the center of the curve at its current position, but it narrows the overall graph
  • 50.
    • Disruptive Selection
    • When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle, disruptive selection takes place
    • If the pressure of natural selection is strong enough and lasts long enough, this situation can cause the single curve to split into two. In other words, selection creates two distinct phenotypes
  • 51. Genetic Drift
    • Evolutionary changes doesn’t always occur by natural selection.
    • In small populations, an allele can become more or less common simply by chance.
    • In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance . Over time, a series of chance occurrences of this type can cause an allele to become common in a population.
  • 52.
    • Ex . Genetic Drift can occur when small populations inhabit a new area.
    • These individuals may carry alleles in different relative frequencies than did the larger population from which they came. If so, the population that they found will be genetically different from the parent population
    • This is called the “ Founder Effect ”
    • This sometimes can lead to rare traits to be expressed.
  • 53.  
  • 54. Evolution Versus Genetic Equilibrium
    • To clarify how evolutionary change operates, scientists often find it helpful to determine what happens when no change takes place. So biologists ask: Are there any conditions under which evolution will not occur? Is there any way to recognize when that is the case? The answers to those questions are provided by the Hardy-Weinberg principle , named after two researchers who independently proposed it in 1908.
  • 55. V. The Hardy-Weinberg Principle
    • The Hardy-Weinberg principle states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change.
    • The situation in which allele frequencies remain constant is called genetic equilibrium . If the allele frequencies do not change, the population will not evolve.
  • 56.
    • The Hardy-Weinberg principle states that a sexually reproducing population will have stable allelic frequencies (no genetic change) and therefore will not undergo evolution, given the following five conditions
    • Conditions for non-evolving population :
    • Very large population size
    • No migration
    • No mutations
    • Non-random mating
    • No natural selection
  • 57.
    • Random Mating:
    • - All members of the population must have an equal opportunity to produce offspring.
    • - Random mating ensures that each individual has an equal chance of passing on its alleles to offspring. In natural populations, however, mating is rarely completely random.
    • - Many species, including lions and wolves, select mates based on particular heritable traits, such as size or strength.
    • - Such nonrandom mating means that the genes for those traits are not in equilibrium but are under strong selection pressure.
  • 58.
    • Large Population:
      •   A large population size is also important in maintaining genetic equilibrium.
      • Genetic drift has less effect on large populations than on small ones. That is because the allele frequencies of large populations are less likely to be changed through the process of genetic drift .
  • 59.
    • No Movement Into or Out of the Population (No Migration):
      •   Because individuals may bring new alleles into a population, there must be no movement of individuals into or out of a population.
      • In genetic terms, the population's gene pool must be kept together and kept separate from the gene pools of other populations.
  • 60.
    • No Mutations:
      •   If genes mutate from one form into another, new alleles may be introduced into the population, and allele frequencies will change.
    • No Natural Selection:
      •   All genotypes in the population must have equal probabilities of survival and reproduction. No phenotype can have a selective advantage over another. In other words, there can be no natural selection operating on the population.
  • 61. Ex: If, random mating occurs, then the allele frequency will be the same in the next generation Total Parental Population = 500 Allele Frequency
    • The total number of genes in a population is its gene pool .
    • Let ‘p’ represent the frequency of one gene in the pool and ‘q’ the frequency of its single allele.
  • 62.
    • So, p + q = 1
      • p 2 = the fraction of the population homozygous for p
      • q 2 = the fraction homozygous for q
      • 2pq = the fraction of heterozygotes
  • 63. aa 20 160 320 Frequency of A = 0.8 Frequency of a = 0.2 = p = q p + q = 1 Aa AA
  • 64. If the population is not evolving, given p = 0.8 & q = 0.2, expect AA = Aa = aa = .64 .32 .04
  • 65. VI. The Process of Speciation
    •   Factors such as natural selection and chance events can change the relative frequencies of alleles in a population. But how do these changes lead to the formation of new species, or speciation ?
  • 66.
    • Isolating Mechanisms
    • 1. Reproductive Isolation : When the members of two populations cannot interbreed and produce fertile offspring.
    • 2. Behavioral Isolation : occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior
    Ex: the Eastern and Western Meadowlarks
  • 67.
    • 3. Geographic Isolation : With geographic isolation , two populations are separated by geographic barriers such as rivers, mountains, bodies of water, or even roads
    1 2 3 4 1 2 3 4 1 2 A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat. Later in time, a few individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence. Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island a by genetically different descendants of the ancestral species.
  • 68.
    • 4. Convergent Evolution
    • When different species inhabit similar environments, they sometimes use parts of their bodies to perform similar functions
    • This causes the development of similar features in unrelated animals and “analogous traits” arise
    • Ex. The color and the body shape of killer whales and penguins.
    • However, these organisms can NEVER interbreed!
  • 69.
    • 5. Adaptive Radiation
    • This is when several species form from a single parent species.
    • If a population of the original species, moves and occupies a new niche then eventually they will become different than the original, and so on and so on.
    • Ex: Darwin Finches
  • 70. Darwin’s Finches
  • 71.
    • Peppered moth:
      • two varieties of peppered moth existed, a light colored and a dark colored one
      • as industrialization and coal burning increased, the environment in England where these moths lived became dirtier
      • the dark colored variety of the moth blended into the trees and increased in numbers, while the light colored moth was less adapted and decreased in numbers.
    Modern Example of Natural Selection
  • 72. How many moths do you see?
  • 73. Industrial Melanism in Moths Selection Change in frequency of dark moths Change in allele frequency in gene pool Evolution
  • 74. 1848 2% dark 1898 95% dark
  • 75.
    • Insect resistance to insecticides :
      • Insecticides kill insects not resistant to the insecticide, while insects resistant to the insecticide live to reproduce. The insecticide acts as a selecting agent.
    • Bacterial resistance to antibiotics :
      • Bacteria not resistant to an antibiotic are killed by it, while resistant bacteria live to reproduce. The antibiotic is a selecting agent for these bacteria.
    Other Examples of Natural Selection