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Title: Evolution

Puzzle of Life's Diversity
Chapter 15
Darwinian Revolution
  • Darwin became a naturalist on the HMS Beagle in
    1831 and took a 5 year journey around the world.
  • Darwin made many observations and collected
    evidence that led him to his theory of evolution.

  • Darwin collected many plant and animal specimens.
  • He found many fossils of organisms once alive
    that resembled organisms presently living.

Fossils from the San Francisco Bay region.
Mesozoic fossils are all marine, (J) Jurassic
"clams" , (K) a Cretaceous ammonite, and (L) a
Cretaceous ichthyosaur. Land-animal fossils are
all Cenozoic in age, such as (M) part of the
Miocene beaver skull, (N) a Pleistocene
saber-toothed cat, and (O) a Pleistocene mammoth.
Galapagos Islands
  • Darwin observed that the characteristics of many
    animals and plants varied noticeably among the
    different Galapagos Islands.

Dome shaped shell - Isabela Island
Saddle back shell - Hood Island
Darwin observed the similarities and differences
amongst these finches and noticed how their beaks
varied and were suited for the type of food they
Origins of Evolutionary Thought
  • (1785) James Hutton - Earth is shaped by
    geological forces over long periods of time.
  • (1798) Thomas Malthus - more offspring are born
    than survive, limited by food and space.
  • (1809) Jean-Baptiste Lamarck - organisms acquire
    or lose traits by selective use or disuse passing
    on the trait to the next generation.

Lamarcks reasoning for his law of use and disuse
Origins of Evolutionary Thought
  • (1831) Charles Darwin - evidence from voyage
    around the world laid the groundwork for his
    theory of evolution.
  • (1833) Charles Lyell - processes occurring now
    shaped Earths geological features over long
    periods of time.
  • (1858) Alfred Wallace - he also speculated that
    evolution by natural selection occurs. This
    spurred Darwin on to publish his theory.

Origin of Species
  • Darwin proposed that new species originate from
    ancestral forms through the gradual accumulation
    of adaptations over very long periods of time.
  • In his book, Darwin describes descent with
  • Some heritable variations in populations are
    better suited than others and since organisms
    tend to produce more offspring than the
    environment can support, competition for
    resources favors those better suited. These
    individuals reproduce and pass on their traits.
  • Darwin observed artificial selection in which
    nature provided variation and humans selected
    variations they found useful.

Variation leading to Natural Selection
Insect Resistance
Artificial Selection
Darwin proposed this idea.
Descent with Modification
Descent with modification implies a common
ancestor with a single tree of life linking all
living things.
Darwins Theory Explains
Many Observations
  • In humans use of drugs selects for pathogens
    that through chance mutations are resistant to
    the drugs effects.
  • Bacteria and viruses evolve rapidly due to rapid
    rates of mutation and reproductive, posing a
    challenge to our society.

HIV Resistance to 3TC
Evidence of Evolution
  1. Fossil Record
  2. Geographical distribution of living species
  3. Homologous structures
  4. Similarities in embryological development
  5. Comparing DNA

Fossils Chronicle Life on Earth
  • Fossils
  • provide the
  • strongest
  • evidence of
  • evolution.
  • Sedimentary
  • strata reveal
  • the relative
  • ages of fossils.
  • Absolute ages are determined by radiometric

Geographic Distribution of Living Species
  • During his voyage, Darwin observed animals in
    similar environments on different continents that
    had similar anatomy and behavior.

Divergent Evolution
All species of finch on the Galapagos Islands
evolved from a common ancestor from Ecuador.
Differing selective pressures on the each Island
was the driving force for the evolution of beaks.
During the past few decades scientists have
demonstrated that what is now called South
America was part of a large land mass called
Gondwana, which included Australia and Antarctica.
Horses have a complex evolutionary history. The
earliest horses evolved in North America many
lineages arose and died out, and ancestors of
several of these lineages crossed into Asia over
the Bering land bridge and into South America
over the Central America land bridge.
Convergent Evolution
Organisms living in different geographical
locations under similar ecological conditions are
exposed to similar pressures of natural
selection. Evolution of shared traits in
unrelated species is convergent evolution.
  • Regardless of the appearance of organisms, two
    species are closely related when they share
    common ancestry.

Homologous Body Structures
  • Homologous structures have different functions
    but evolved from common ancestries.
  • Forelimbs of all mammals show the same
    arrangement of bones with different functions.

Analogous Structures
Analogous structures have a similar function but
are anatomically different.
Vestigial Organs
  • Humans also have vestigial features, evidence of
    our own evolutionary history. The appendix is
    believed to be a remnant of a larger,
    plant-digesting structure found in our ancestors

Cave-dwelling tetra fish are blind they have
small vestigial eyes that do not work. Why have
them? Biologists have found a possible answer
genetic mutations that hamper eye development
also may increase the number of taste buds. Thus,
mutations that happened to give the fish an
advantage in tasting and smellinga huge benefit
in a dark environmentmight also have
inadvertently, and harmlessly, caused the
degeneration of their eyes.
Pythons and boa constrictors have tiny hind leg
bones buried in muscles toward their tail ends.
These are vestigial. Vestigial legs are a clue
that snakes descended from lizards. Over 100
million years ago, some lizards happened to be
born with smaller legs, which, in certain
environments, helped them move about
unencumbered. As generation after generation
survived and reproduced, this new form flourished.
Comparative Embryology
  • All vertebrate embryos have a tail and pharyngeal
  • This
  • indicates
  • a common
  • ancestor.

  • Genes are not active at the same time.
  • Those that are active during early development
    are less subject to change than genes that are
    active later.
  • This is because mutations occurring early in
    development have a far greater chance of being
    lethal and would not be passed on to future
  • Mutations occurring later in development have
    more limited effects, are less likely to be
    lethal and are more likely to be passed on.
  • Thats why humans and chickens are so different
    at later stages despite similarities as embryos.

Comparing DNA
  • Comparing DNA sequences is the most direct way to
    determine evolutionary relationships.
  • The sequence of nitrogenous bases is more similar
    in closely related species than in species that
    are not as closely related.
  • Scientists can use this information, with
    knowledge of mutation rates, to estimate how long
    its been since 2 species shared a common

Summary of Darwin's Theory
  1. Organisms differ and these differences may be
  2. Organisms produce more offspring than survive.
  3. Organisms compete for limited resources.
  4. Organisms best suited to their environment
    survive and reproduce, passing on these traits.
  5. This process of natural selection causes species
    to change over time.
  6. Species alive today descended with modification
    from a common ancestor uniting all organisms in a
    tree of life.
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