CHAPTER 25 NOTES EVOLUTION BY NATURAL SELECTION Darwin s Origin of Species challenged the idea of special creation which said o All species are independent unrelated o Life on earth is about 6000 years old o Species are immutable incapable of change 25 1 The Evolution of Evolutionary Thought Plato claimed every organism was an example of a perfect essence created by God and were unchanging o Typological thinking species are unchanging types and variations within species are Aristotle ordered organisms into a linear scheme called the great chain of being the scale of nature by unimportant or misleading increasing size and capacity o Species are fixed types o Some species are higher more complex better than others e g humans at top Georges Buffon suggests that Earth is much older than previously believed Charles Lyell suggests that geological forces shaped earth and continue to do so may also explain species Jean Baptiste de Lamarck proposed the idea of evolution species are not static but change through time characteristics can be heritable o Claimed simple organisms originate through spontaneous generation and then evolve by moving up the great chain of being over time o Progressive evolution always producing larger more complex species Population individuals of the same species that are living in the same area at the same time Alfred Russell Wallace was a naturalist described ideas for natural selection to Darwin pushed Darwin to publish Darwin claims that variation among individuals in a population was the key to understanding the nature of species population thinking o This theory of evolution overturned the idea that species are static and unchanging proposing a mechanism that could account for change over time 25 2 The pattern of evolution Have species changed and are they related Descent with modification species that lived in the past are the ancestors of the species existing today species change through time Darwin species may change over time by natural selection Fossil any trace of an organism that lived in the past shells tracks excrements o Fossil record all fossils that have been found on earth and described in scientific literature o Extant species species living today Sedimentary rocks form from sand or mud and other materials deposited at locations such as beaches or river mouths known to form in layers o Scientists used similarities in rocks and fossils to create a geologic time scale a sequence of named intervals called eons eras and periods that represent the major events in Earth history Indicated that Earth was much much older than 6000 years 4 6 billion years Radiometric dating Earliest signs of life appeared in rocks that formed 3 4 3 8 billion years ago based on o Observed decay rates of unstable radioactive parent atoms to more stable daughter atoms o The ratio of parent to daughter atoms present in newly formed rocks o The ratio of parent to daughter atoms in a particular rock sample Baron Georges Cuvier publishes detailed analysis of extinct species species that no longer exist o Over 99 of all species that have ever lived are now extinct o Documented fossils and showed that extinction occurs Law of succession extinct species in the fossil record were succeeded in the same region by similar species o Transitional feature a trait in a fossil species that is intermediate between those of ancestral and derived species Supports hypothesis that an ancestral lungfish like species moved from sea to land If traits observed in more recent species evolved from traits in more ancient species then transitional forms are expected to occur in the appropriate time sequence o Vestigial trait a reduced or incompletely developed feature that has no function or reduced function but is clearly similar to functioning organs or structures in closely related species Examples Pseudogenes reduced wings in ostriches and kiwis reduced tail coccyx appendix reduced eyes in moles Evidence that characteristics of species have changed over time Darwin studied Galapagos Island mockingbirds and noticed distinct species with differences in coloration and beak size and shape suggests descended from same common ancestor o Phylogenic tree a branching diagram that describes the ancestor descendant relationships among species o Similar species are found in the same geographic area o Clade contains all species that come from the same common ancestor Homology a similarity that exists in species because they inherited the trait from a common ancestor o Traits are homologous if they are derived evolutionarily or developmentally from the same source structure e g the bony structure of the bat and bird wing o Genetic homology occurs in DNA nucleotide sequences RNA nucleotide sequences or amino acid sequences o Developmental homology recognized in embryos e g gill pouches tails o Structural homology similarity in adult morphology form e g common structural plan observed in the limbs of vertebrates o Genetic homologies cause the developmental homologies observed in embryos which then lead to the structural homologies recognized in adults o Evidence Mouse gene homologous to fruit fly eyeless gene inserted into fruit fly embryos and stimulated expression of the foreign gene in locations that normally grow appendages observed eyes on the legs and antennae o Insect wings and bird wings are NOT HOMOLOGOUS Analogy traits are analogous if they have similar function but are derived evolutionarily or developmentally from different source structures e g the wing of a bat and bird Internal consistency the observations that data from independent sources agree in supporting predictions made by a theory o E g evolution of whales and dolphins cetaceans fossil record shows cetacean species with either land mammal features or aquatic mammals or both o Data from many different sources are much more consistent with evolution than special creation 25 3 The process of evolution How does natural selection work Darwin crossbred pigeons and observed how characteristics were passed onto offspring o Used artificial selection to manipulate the composition of the population Thomas Robert Malthus s book An Essay on the Principle of Population suggested that since many more individuals are born than can survive a struggle for existence occurs o Inspires Darwin s theory of natural selection On the Origin of Species Darwin s four postulates o The individual organisms that make up a population vary in the traits they possess such
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