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Evolution notes #1

Evolution notes #1






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    Evolution notes #1 Evolution notes #1 Presentation Transcript

    • Development ofEvolutionaryThought
    • Isn’t evolution “just” atheory?•Scientific theories are explanationsthat are based on lines of evidence,enable valid predictions, and havebeen tested in many ways.
    • Evolve – change overtime
    • What is Evolution? Evolution- a change in the genetic composition of a population over time.
    • Paleontology & Evolution Older layers of sedimentary rock (the layers on the bottom) contain fossil species very dissimilar from modern life. Each layer (stratum) is characterized by a unique group of fossil species. As you move upward through the layers, you find species more and more similar to modern life.
    • James Hutton - 1795 A Scottish geologist proposed that it was possible to explain the various landforms by looking at mechanisms currently operating in the world Proposed that the earth was much more than a few thousand years old
    • Jean Baptiste Lamarck Theory of evolution in 1809 mechanism: – use and disuse - the idea that the parts used the most grow stronger; the parts that don’t get used deteriorate – inheritance of acquired characteristics - the modifications that an organism acquires during its lifetime can be passed along to its offspring recognized adaptation to environment as a primary product of evolution
    • Charles Darwin (1809-1882) Father of modernevolutionary theory Born in England HMS Beagle Galapagos Islands
    • What is an adaptation? An inherited characteristic that increases an organism’s ability to survive and reproduce in its specific environment.
    • Darwin’s Observations Darwin noticed that every bird on the Galapagos Islands was a modified finch. The only differences in the birds were their beaks and what they ate. These finches looked very similar to one type on South American continent, but none of these were found in S.A.“How did one species change into a different species?”
    • The Galapagos Finches
    • He wrote On The Origin ofSpecies (1859) after 20years of study.
    • Darwin’s Four Postulates Individuals within a population vary in their traits. Some of these traits are heritable. More offspring are produced than can survive because of limited resources. Individuals with advantageous traits will survive and reproduce.
    • What is natural selection?  Natural selection - a population of organisms can change over generations if individuals having certain heritable traits leave more offspring than others  Natural selection is the mechanism by which evolution is proposed to occur
    • What is “artificialselection”? Nature provides the variation among different organisms, and humans select variations that they find useful. Example: breeding cows, horses, hogs Darwin used this to help support his case for natural selection.
    • Descent withmodification the history of life is like a tree, with multiple branching and re-branching from a common trunk all the way to the tips of the youngest twigs most branches of evolution are dead ends; about 99% of all species that have ever lived are extinct
    • Figure 22.7 Descent with modification
    • Survival of the Fittest• Another name for Darwin’s theory of natural selection. •Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it.
    • Mechanisms ofEvolution
    • Natural Selection &Survival of the Fittest(already discussed with Darwin)
    • Modern Ideas Darwin + Mendel’s work and the work of others, have lead to modern ideas about evolution.Another mechanism of evolution is Genetic Drift (random changes in genes) which occurs through natural selection.
    • Modern Ideas Speciation – formation of new species is due to gradual genetic changes, and that large scale evolution is the result of a lot of small scale evolution. Microevolution – process responsible for the variations that exist within a species, or a change in the allele frequency.
    • Modern Ideas Macroevolution – evolution that occurs between species. Examples: the separation of a species to form two distinct species or the development of a new species from many small changes within an existing species
    • Gene Flow The change in occurrence of genes in a population. This occurs when an individual leaves a population (emigration) or new individual joins a population (immigration).
    • Genetic Drift Random changes in the occurrence of genes through chance events. Can occur when a few individuals of a population break off from the original group and start their own population (founder effect). Large number of population is killed due to disease, starvation, natural disaster, etc. (bottle necking)
    • Punctuated Equilibrium Darwin felt that biological change was slow and steady as indicated in the fossil record. Modern scientists see that this pattern does not always hold. (Darwin’s finches) The term punctuated equilibrium is used to describe a pattern of long, stable periods interrupted by brief periods of more rapid change. This is still controversial today.
    • Evidence ofEvolution
    • Fossil Evidence Fossils provided a detailed record of evolution. Fossils formed in different layers of rock were evidence of gradual change over time.
    • Homologous BodyStructures Structures in different species that may perform different functions but are similar because of their common ancestry Vestigial organs - structures of no apparent function to an organism; leftover from ancestry; ex - snakes have leg & pelvis bones
    • Figure 22.14 Homologous structures: anatomical signs of descent withmodification
    • More homology… Molecular homology - similarity in DNA sequence between an ancestor and its progeny Embryological homology - similarities only apparent in embryological development – ex: all vertebrate embryos have “pharyngeal pouches” which later become gills or Eustachian tubes
    • Patterns ofEvolution
    • Adaptive Radiation When a single species or a small group of species has evolved into several different forms that live in different ways. Example: Darwin’s finches (more than a dozen evolved from a single species)
    • ConvergentEvolution Explains how unrelated species can develop similar characteristics Porpoise (mammal) & Shark (fish) Unrelated animals, but share similar characteristics to suit their environment
    • Analogous structures Show similarity in structure based on adaptation for the same function, not common descent.
    • Divergent Evolution Suggests that many species develop from a common ancestor Penguins (wings for swimming) & vultures (wings for flying) Both are birds, diverged from a common ancestor
    • Co-evolution When two or more organisms in an ecosystem evolve in response to each other. Example: Flowers and their pollinators
    • Camouflage – an animallooks like its environment. http://rainforests.mongabay.com/0306.htm
    • Mimicry- when animals havecoloring and markings tolook like another animal
    • Warm Up!1. What is the difference between “evidence” of evolution and “mechanisms” of evolution?2. What is biological fitness?3. Explain in your own words the term “natural selection”