Unit 6. Evolution & Charles Darwin

I. Evolution & Scientific Creationism

  A. Evolution. A theory that proposes change (micro & macro) in organisms over time.

    1. Charles Darwin- On November 24, 1859, "On the Origin of Species by Means of Natural

      Selection" was published presenting evidence for the evolution of species.

  B. Scientific Creationism- A belief that life was create by an infinite being.

resource: The creation/evolution continuum.  Where do you stand?

Reading: Scientific Method and Scientific Creationism: Evolution vs. Religion

resource: Time line of evolutionary thought

II. Pre-Darwinian views.

  A. Idealism- Plato (427-347 B.C.)

    -philosophy which stated life is an imperfect representation of ideal forms (gods)

    -According to Plato the visible world is simply a copy of a supersensible, intelligible, ideal world, and

     consequently "things" are but an impression stamped on reality by that which is of a higher, spiritual nature.

  B. Scala Naturae- "Scale of Nature". Aristotle (384-322 B.C.)

    1. life exists on a scale of complexity. (like a ladder)

      a. All forms of life fall along a single progression

      b. At bottom of ladder are sponges

      c. In middle are insects and snails

      d. At the very top (surprise!) are humans

    - Life on the scale is fixed and static. No changes in order are allowed (no evolution).

  C. Carolus Linnaeus- (1707-1798)- "Father of taxonomy"

    -sought to classify life according to Aristotle's philosophy

    1. taxonomy- a branch of biology dealing with naming and classifying life

      -Linnaeus used a binomial system (2 named system):  Genus & Species

      -By classifying organisms he was trying to reveal God's plan. Deus creavit, Linneaus disposuit

      -Darwin will use this taxonomic system as a focal point in arguments for evolution

D. Jean Baptiste Lamarck- (1744-1829). Published in 1809 (same year Darwin was born)

    -established early principles associated with evolution by comparing current species to fossils

    1. Use and Disuse- Useful organs are enhanced and non-useful organs are discarded. (Giraffe)

    2. Inheritance of acquired characteristics- Useful traits that are enhanced are passed to offspring

      -natural inheritance- Giraffe

      -man-influenced inheritance- evolution of dogs.

  E. Early Theories on the origins of life

    1. Spontaneous generation- Life arises from non-living substances, abiogenesis

      a. Francesco Redi-(1668) attempted to disproved spontaneous generation. maggots and meat experiment

      b. John Needham- (1749) used meat broth to verify life can arise from organic molecules

      c. Lazzaro Spallazani-(1776) discredited Needham's work based on experimental errors

        -his work wasn't accepted because he didn't address the "vital force"

      d. Louis Pasteur-(1861) discredited Needham's work but was able to include the "vital force"

        -Biogenesis- life arises only from living things.

      e. Alexander Oparin- believed early life arose from primordial seas. Oparin-Haldane theory

      f. Stanley Miller & Harold Urey- synthesis of amino acids from inorganic substances.

       -this addresses the origins of life on earth. Miller's experiment

 Resource: How these scientists addressed spontaneous generation  

    2. Origin of cells

      a. Simple organic molecules- from Miller-Urey experiment

      b. Polymerization- organic molecules can easily polymerize in absence of oxygen

      c. Protocell- lipid-membraned structures that resemble true cells in certain functions

      d. Early cells-must have been autotrophic due to lack of "food". Archaebacteria

          1. chemoautotrophs- use simple organic chemical as a source of energy

            ex. Acidothermophiles- live in highly acid/high temperature environments.

          2. photoautotrophs- use light energy as a source of energy

      e. Endosymbiont theory- prokaryotic cell that engulfed other, smaller cells that survived as a symbiont

PNAS Review: On the origin of cells

review: The origin of life. Very interesting.

III. Charles Darwin ( 1809-)

  In 1831, Darwin was commissioned as a naturalist aboard the H.M.S. Beagle which set forth to

  explore the coasts of South America and the Galopagos Islands. In his journeys he studied the diversity

  of the flora and fauna of specific areas. 

Activity: Darwin's trip. directions & map

  A. Darwin Established 2 Principles

    1. Decent with Modification- Life modifies itself as generations progess

      -analogous to a tree- each branch is a modification of a species

      -most branches lead to dead ends (extinction)

      -99% of all species to have every existed are now extinct.

resource: The Origin of Species. Charles Darwin. Online format

    2. Natural Selection and Adaptation- For every species, differential success in reproduction and

      adaptation of each organism is what drives Decent with Modification.

      a. Darwin states 5 facts to support this theory of Natural Selection which leads to 3 principles of

       Natural Selection

         -Fact 1: All species have potential to reproduce beyond the capabilities of the environment

         -Fact 2: Most populations are stable in size

         -Fact 3: Natural resources are limited

      1. Principle 1: Only a fraction of all offspring survive because of the struggle for limited resources

         -Fact 4: Individuals of a population vary in their characteristics. No 2 organisms are alike

         -Fact 5: Variation between organisms is inherited

      2. Principle 2: Survival depends upon hereditary make-up. Those individuals who adapt to their

          environment the best will have the highest proportion of offspring. "Survival of the fittest".

      3. Principle 3: The unequal ability of survival will lead to gradual changes in the population, with the

          more favorable characteristics accumulating over generations.

resource: Darwin & Natural Selection

resource: Darwin's finches

Images: Darwin's Finches: Types of beaks; Beak changes over time

Paper: Phylogeny of Darwin's finches as revealed by mtDNA sequences. PNAS

IV. Evidence for Evolution

  A. Biogeography- The study of species in a particle area

      - Darwin found species are related closer to neighboring species rather than species of corresponding

        environments.

Resource: Reptiles of the Galapagos  

  B. Fossil Record- shows evidence of fossil succession

    1. Paleobiology- the science of studying living organisms of the past

    2. Fossil- a preserved remnant or impression left by an organism that lived in the past

      a. fossilization- the process by which a fossil is produced

        1. burial- an organism must be buried to avoid bacterial & environmental decomposition

        2. preservation- preserving the organism or impression in the sediment

           a. original preservation- the organism is left "relatively" unchanged. (Mammoths in ice)

           b. altered preservation- process where original composition has been altered.

      b. dating fossils- requires radioactive elements that reside in all living organisms (C-14)

          a. half-life- the amount of time required for 1/2 of a radioactive sample to decay to its stable form

     3. Geologic time scale- A time table of evolutionary significant changes in the earth and life

      a. Precambrian-4,500 to 543 mya: early uni-cellular organisms

      b. Paleozoic era- 543 to 248 mya: rise of the animals

      c. Mesozoic era- 248 to 65 mya: rise of the dinosaurs

      d. Cenozoic era- 65 mya to today: rise of the mammels     

Resource: Geologic Time Machine. UC Berkeley

  C. Taxonomy- The study of comparing and classifying organisms by common characteristics. (ch. 17)

  D. Comparative Anatomy- Anatomical similarities between individuals of separate species exist.

    1. Homologous structures- structures which are similar in appearance and function due to common ancestry

       a. Convergent evolution-process in which organisms not closely related independently acquire some common

           characteristic(s). This usually reflects similar responses to similar environmental conditions.

      ex. forelimbs

    2. Analogous structures- structures which are similar but don't appear to have common ancestry

        ex. wings in insects and birds

    3. Vestigial organs- organs which have little or no use but appear to be a remnant of a useful ancestral organ

        ex. vestigial organs in humans

  E. Comparative Embryology- Similar species go through similar stages in embryonic development

    1. embryo- The early developmental stages of of both plants and animals

  F. Molecular Biology- organisms all share a common DNA structure. Similar organisms share similar DNA

     sequences which inevitably code for similar proteins. 

    1. Universal genetic code

    2. Protein phylogeny- comparing protein structures in different organisms

V. Mechanisms of Evolution

  A. Genetic Variability-

    -organisms of the same population vary due to genetic variability-

    1. Gene pool- the accumulation of genes within a population

    2. Allele frequency- the percentage occurrence of a certain allele within the gene pool

      -the difference in allele frequencies is the basis for variance within a population

    3. Genetic equilibrium- allele frequencies that remain constant from one generation to the next

      -changes in this equilibrium is seen as evolution.

      -natural selection acts by changing the allele frequencies due to organisms adapting to their environment

  B. Speciation- The origin of a new species in nature

    1. Two patterns of evolutionary change

       a. Anagenesis (phyletic evolution)- transformation of unbranched speciation

        b. Cladogenesis- transformation of branched speciation

           - this promotes biological diversity = more species

           -also offers the opportunity for a species to yet remain in existence

Image:: Anagenesis vs. Cladogenesis

Image: Patterns of Evolution in Horses

    2. Modes of Speciation

      a. Divergence- population splits and migrates to new environment

          ex. Galapagos Islands- new organisms migrate there from existing populations

Image: Divergence

      b. Peak Shifts- occurrence where natural selection has influenced survival of certain species and/or

           characteristics. -this causes changes in a population's gene pool

        1. stabilizing selection- natural selection selects organisms that fit an "average"

        2. directional selection- natural selection selects organisms with an extreme phenotype

          -this is seen as a one-way shift.

        3. disruptive selection- natural selection selects organisms away from the average

            -this is a two-way shift

Image: Peak Shifts

      c. Catastrophic changes-

        1. Bottle-neck effect- a natural disaster non-selectively reduces the gene pool to a small sub-set

    3. Rates of Speciation

      a. Gradualism- changes in species is slow and gradual, occurring in small periodic changes in the gene pool

      b. Punctuated Equilibrium- evolution occurs in spurts of relatively rapid change with long periods of non-change.

            - this theory is commonly found in the fossil record.

Image: Gradualism vs Punctuated Equilibrium

    4. Species divergence- separation of organisms that leads to speciation

        a. Pre-zygotic reproductive barriers- factors which prevent certain organisms from breeding

          1. ecological (geographical) isolation- populations that exist in isolated habitats. orioles

          2. temporal isolation- matings that occur at different times of the year/day. Violets

          3. behavioral isolation- no sexual attractiveness between males and females prevent mating. funny.

          4. mechanical isolation- differences in reproductive anatomies prevent copulation

          5. gametic isolation- gametes are not compatible (biochemical and/or chromosomal differences)

        b. Post-zygotic reproductive barriers- factors that hinder zygote development and/or zygote sterility

          1. hybrid invariability- zygotes fail to develop or fail to reach sexual maturity

          2. hybrid sterility- offspring fail to produce functional gametes (e.g. mules from horse + donkey)

          3. hybrid breakdown- offspring can reproduce but next generation are feeble or sterile

    5. Changes in gene pool

      a. Hardy-Weinberg Principle- Allele frequencies within a population remain constant unless acted upon by

         environmental forces.

        1. Five conditions are required for Hardy-Weinberg equilibrium.

          a. The population is very large.

          b. The population is isolated (no migration of individuals, or alleles, into or out of the population).

          c. Mutations do not alter the gene pool.

          d. Mating is random with respect to the genes involved.

          e. All individuals are equal in reproductive success (no natural selection).

       2. Hardy-Weinberg Law-

         a. For any gene, 2 alleles exists: 

           1. Dominant (D)

           2.  Recessive (d)

           3. total alleles for any gene is 100%, so  %D + %d = 100%

         b. For any trait, 3 genotypes exist:

           1. Homozygous Dominant (DD)

           2. Heterozygous (Dd)

           3. Homozygous Recessive (dd)

           4. for any genotype % HomoDom + % Hetero + % HomoRec = 100%

        c. We use p for the ratio of dominant allele and q for the ratio of recessive allele

           1.  p + q = 1

           2. p² + 2pq + q² = 1