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Descent With Modification: A Darwinian View of Life


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Title: Descent With Modification: A Darwinian View of Life

Descent With Modification A Darwinian View of
  • chapter 22

Darwin Lamarck Lyell Linnaeus Hooke
Vestigial Organs Homologous structures Analogous Structures The Fossil Record Biogeography
Embryological Homologies Molecular Homologies Natural Selection Artificial Selection Inheritance of Acquired Characteristics
Galapagos Islands Uniformitarianism Gradualism Descent with Modification Taxonomy Evolutionary Adaptations
Match Distinguish Cite Evidence
Differentiate Critique Connect Create Who?
What? Where? When? Why? Which? How?
What is evolution?
  • Discuss _at_ your table.
  • Provide examples of the evolutionary process.
  • 1) WHO? Name the organism
  • 2) WHAT? summarize the physical or behavioral
    traits that make it unique (adaptations)
  • 3) WHY? correlate the cause-effect (trait ?
  • 4) How? Hypothesize construct a scenario that
    would have led to the evolution of that trait.

What is evolution?
  • Organismic evolution means changes in
    populations, species, or groups of species.
  • It occurs because
  • 1. Populations vary by the frequency of
    heritable traits that appear from one generation
    to the next.
  • 2. These traits are represented by alleles
    for genes that modify morphology
    (form/structure), physiology, or behavior.
  • 3. There is a struggle for survival and most
    organisms perish. Only those that survive pass
    their genes on.

Evolution is changes in allele frequencies over
  • Discuss what this statement means.

Can individuals Evolve?
  • NO. Individuals can BE different and can survive
    and pass those genes on or be killed and not.
  • For an organism to change itself to suit its
    environment it would need to change the genes
    (DNA) inside every cell of its body.
  • Most importantly, they would need to change the
    DNA in their gametes- so the change could be
    passed on to the next generation.
  • Some individuals are better suited for their
    environment. They leave more offspring. Over
    generations, the genetic composition of a
    population reflects more of their beneficial

Two areas of evolutionary study
  1. Microevolution describes the details of how
    populations of organisms change from generation
    to generation and how new species originate.
    (next chapters focus)
  2. Macroevolution describes patterns of changes in
    groups of related species over broad periods of
    geologic time. The patterns determine phylogeny,
    the evolutionary relationships among species or
    groups of species. (fossil record)

Evolution of insecticide resistance in insect
Microevolution DDT resistance of insects
Phylogenetic trees are diagrams that show
evolutionary relationships between groups of
extinct and extant organisms
Macroevolution Ex. Fossil Record
The historical context of Darwins life and ideas.
Historical Context of Evolutionary Theory
  • Paradigm shift from organism are STATIC for to
    the idea that organisms can CHANGE FORM.
  • Plato (427-347 B.C.) Two worlds real/ideal world
    that is eternal and world of imperfection we
    perceive through senses. Living things were
    created in their perfect, static form by the
  • Aristotle (384-322 B.C.) scale of nature all
    living forms could be arranged on. Each form
    assigned a rung, all rungs were taken.

nonliving beings- lower plants-higher plants
sponges, jellyfish shellfish - insects --
crustacea cephalopoda -- ovipara - whales
ovoviviparous quadrupeds -- humankind. These are
the "steps of nature," or the "hierarchy of
Tree of Life / Bush of Life instead of a ladder
or hierarchy tips of branches
Natural theology
  • A philosophy dedicated to discovering the
    Creators plan by studying nature- the earth and
    its inhabitants.
  • Adapations were evidence that the Creator had
    designed each and every species for a particular
  • Classifying species was a major objective.

Carolus Linnaeus (1707-1778)
  • Specialized in taxonomy- naming and classifying
    the diverse forms of life.
  • Developed binomial nomenclature- a two part
    naming system.
  • Developed a system of grouping similar species
    into a hierarchy of increasingly general
    categories. (species- genus- family)
  • He saw no evolutionary relationships in his

Georges Cuvier (1769-1832)
  • largely developed paleontology- the study of
  • Big idea species go extinct
  • Observed a pattern of many strata separated by
  • Explanation catastrophism
  • Each boundary between strata corresponded to a
    catastrophe (drought, flood,supervolcano)
    destroyed many of the local species.
  • Area repopulated by immigration.

Figure 22.4 Strata of sedimentary rock at the
Grand Canyon
Figure 22.3 Formation of sedimentary rock and
deposition of fossils from different time periods
Trilobite fossils- lived in the seas hundreds of
millions of years ago
ex. 65mya the meteorite impact in the Gulf of
Mexico brought on the extinction of the
Fathers of Modern Geology Hutton Lyell
  • 1795 James Hutton, Scottish geologist
  • Explained Earths geologic features by the
    theory of Gradualism Speciation occurs
    gradually, profound change is the cumulative
    product of slow but continuous processes.
  • Charles Lyell (1797-1875) geologist
  • incorporated gradualism into the theory of
  • Uniformitarianism Geologic processes have not
    changed throughout Earths history (ie. forces
    that build and erode mountains occur at a steady
    rate) thus Earth is much older than previously

Figure 22.4 Strata of sedimentary rock at the
Grand Canyon
Fossil Record Interpretation
  • Gradualism
  • Vs.
  • Punctuated equilibrium

  • Argues that evolution occurs by the gradual
    accumulation of small changes.
  • Individual speciation events or major changes in
    lineages occur over long periods of geologic
  • Fossil evidence provides snapshots of the
    evolutionary process, revealing only major
    changes in groups of organisms.
  • Intermediate stages of evolution not represented
    by fossils is due to the incompleteness of the
    fossil record.

Punctuated Equilibrium
  • Argues that evolutionary history consists of
    geologically long periods of stasis with little
    or no evolution,
  • interrupted, or punctuated by geologically
    short periods of rapid evolution.
  • The fossil record should consist of fossils
    mostly from the extended periods of stasis with
    few if any fossils from the short bursts of

Phylogenetic trees are diagrams that show
evolutionary relationships between groups of
extinct and extant organisms
Macroevolution Ex. Fossil Record
  • Earth must be very old much older than six
    thousand years (it is 4.5 billion years old)
  • Very slow and subtle processes persisting over a
    long period of time can add up to substantial
  • Slow but significant changes in environments
    caused slow but significant changes in species
    over geologic time.

  • By the end of the 18th century several
    naturalists, including Darwins grandfather
    Erasmus Darwin, suggested that life had evolved
    as environments changed.
  • No one had suggested a mechanism.

THEORY 2 parts
  • Evolution, change in species over geologic time,
    does exist.
  • Theory to explain WHY/HOW the mechanism causing
    this change.

The Inheritance of Acquired Characteristics by
  • Jean Baptiste de Lamarck proposed the first
    explanation which was widely accepted for years.
  • Three parts
  • Use and disuse described how body parts of
    organisms can develop with increased usage, while
    unused parts weaken. Correct.
  • Inheritance of acquired characteristics described
    how body features acquired during the lifetime of
    an organism (such as muscle bulk) could be passed
    on to offspring. Incorrect.
  • Natural transformation of species described how
    organisms produced offspring with changes,
    transforming each generation into a slightly
    different form that is more complex. Species did
    not become extinct nor did they split and change
    into two or more species. Incorrect.

The giraffe
  • Short neck.
  • Food scarce.
  • Stretch neck.
  • Eat.
  • Longer neck.
  • Offspring.
  • Repeat.
  • Inheritance of Acquired Characteristics or
  • With a Partner Create a Lamarkian explanation
    for the evolution of one of your creatures.

Descent with Modification via Natural Selection
  • Charles Darwin 1809-1882
  • Med school dropout
  • BA Natural Theology
  • Captain Fitzroy- HMS Beagle
  • Galapagos, islands of relatively recent volcanic
    origin, 900 km west of SA coast.
  • Gathered mountains of evidence
  • Waited 20 years to write and publish a
    groundbreaking book.

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Beaks adapted to specific foods available on
their home islands.
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  • On the Origin of Species
  • By Means of Natural Selection November 24, 1859
  • Darwinss groundbreaking book explained what had
    once seemed a bewildering array
  • of unrelated facts.
  • He focused on
  • Diversity of organisms
  • Similarities differences
  • Geographic distribution
  • Adaptations to surrounding
  • environments

Main Ideas of Natural Selection
  • Overproduction of offspring populations posses
    an enormous reproductive potential.
  • ex. Darwin calculated that two elephants would
    produce a population of 19 million individuals
    after 750 years if all offspring survived to
    reproductive maturity and fostered their normal
    number of offspring.

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  • 2) Members of a population compete for survival.
  • Population sizes remain stable- populations
    generally fluctuate around a constant size.
  • Resources are limited. Resources such as food,
    water, light dont increase as populations grow
  • Eventually, the needs of a growing population
    will exceed the available resources.
  • As a result, individuals must compete for
  • Influenced by Thomas Malthus 1798 essay on
    human population much of human suffering-
    disease, famine, homelessness, and war- was the
    inescapable consequence of the potential for the
    human population to increase faster than food
    supplies and other resources.

  • 3) Genetic variability exists among individuals
    in a population.
  • Most traits reveal considerable variety in their
  • Ex. Musculature, height, fur color, hair color,
    skin color, eye color, etc.

Figure 22.9 A few of the color variations in a
population of Asian lady beetles
  • 4) Some individuals will be better suited for
    their environment. Only the most fit individuals
    survive. survival of the fittest
  • Individuals with traits best adapted for
    survival in the environment are able to
    out-compete other individuals for resources.

  • 5) Individuals with the better adaptations
    survive and leave offspring who inherit the
    traits of their parents.
  • In turn, the best adapted of these offspring
    leave the most offspring.
  • Over time, traits best adapted for survival in
    the environment and the alleles that generate
    them accumulate in the population.
  • Evolution occurs as advantageous traits

Figure 22.10 Camouflage as an example of
evolutionary adaptation
Weedy/ Leafy Sea Dragon
Key Points of Natural Selection
  1. Populations (groups of interbreeding individuals
    belonging to a particular species and sharing a
    common geographic area) are the smallest unit
    that can evolve. Evolution is measurable over
    successive generations.
  2. Natural selection acts only on heritable
    variations/phenotypes. (not acquired ones)
  3. Natural selection is situational as environmental
    factors vary from place to place and from time to
    time. An adaptation in one situation may be
    useless or even detrimental in another situation.

disciplines agree)
  • Paleontology provides fossils that reveal the
    prehistoric existence of extinct species. As a
    result, changes in species and the formation of
    new species can be studied.
  • Fossil deposits are often among sediment layers.
  • Law of superposition states that the deepest
    layer of earth contains the oldest specimens.

  • 2. Biogeography uses geography to describe the
    distribution of species.
  • Has revealed that unrelated species in different
    regions of the world look alike when found in
    similar environments.
  • Provides strong evidence for the role of natural
    selection in evolution.
  • Ex. Wallaby (marsupial) and Rabbit (placental)
  • flying squirrel-sugar glider

  • 3. Embryology is the study of embryos and their
  • Reveals similar stages in development (ontogeny)
    among related species.
  • The similarities help establish evolutionary
    relationships (phylogeny).
  • Ex. Gill slits and tails are found in fish,
    chicken, pig, and human embryos. These species
    are all vertebrates.

Haeckel exaggerated these Sketches. Not as
similar as shown.
Ontogeny recapitulates Phylogeny is not
  • 4. Comparative anatomy describes three kinds of
    structures that contribute to the identification
    of evolutionary relationships among species.
  • Compares external morphology and internal anatomy
  • Ex. Homologous structures are body parts that
    are structurally similar in related species.
    Serve different functions have been modified by
    different natural selection from the common

These homologous structures are anatomical
evidence of descent with modification.
Modified for grasping, walking, Swimming, flight
  • homologous structures reveal common ancestry and
    a pattern of evolution called DIVERGENT EVOLUTION.

  • Ex) Vestigial organs organs with no apparent
    function or purpose imply evolutionary
    relationships to primitive ancestors.
  • May still be around as an evolutionary relic.
  • The structure served a purpose in an ancient
    ancestor but no longer does.
  • Example pelvic girdle, hind leg bones in whales
  • Tail bone in humans.

Figure 22.17 A transitional fossil linking past
and present
  • Ex) Analagous Structures are body parts similar
    in function but not in structure.
  • Not because they have evolved from a common
  • Instead, because they evolved these similar
    adaptations independently because they evolved in
    similar environments with the same selection

For example the finned, streamlined, fat
insulated bodies of Sharks, Penguins,
Porpoises are all adaptations for a life of
swimming in the seas.
Humming bird
Hummingbird Moth
  • 5) Molecular Biology examines the nucleotide and
    amino acid sequences of DNA and proteins from
    different species.
  • Closely related species share higher percentages
    of sequences than distantly related species.
  • All living things share the same genetic code.
  • Favors evolution of different species through
    modification of ancestral genetic information.
  • For example, more than 98 of the nucleotide
    sequences in humans and chimpanzees are identical.

  • The incorporation of genetics into
    evolutionary thinking created a more
    comprehensive view of evolution called
    neo-Darwinism or the modern synthesis.
  • You will study evolution from a genetic point of
    view in the next chapter.

Historical examples that support the theory of
natural selection
  1. Pesticide resistance
  2. Antibiotic resistance
  3. HIV
  4. Industrial Melanism the peppered moth
  5. Sickle Cell Anemia- Malaria

  • Humans make breeding choices among livestock,
    crops, dogs, horses, etc.
  • drive evolution.

Cattle breeders, ancient africa
Wild mustard
Cabbage, broccoli, brussel sprouts, cauliflower
The Origin of Species was truly radical for its
  • Darwin waited more than 20 years to publish.
  • Challenged prevailing scientific views.
  • Shook the deepest roots of Western culture.
  • Contrasted with the conventional paradigm of an
    Earth only a few thousand years old, populated by
    unchanging forms of life which had been
    individually made during a single week by the
    Creator (along w/ entire universe).

The Origin of Species
  • Darwin continued to gather evidence for nearly 20
  • Lyell cautioned Darwin to publish before someone
    beat him to it.
  • 1858 Alfred Wallace developed a theory of natural
    selection and sent it in a letter to Darwin- it
    was presented at a conference that year.
  • Darwin quickly finished Origin of Species and
    published it the following year- 50 years after
    Lamarck published his ideas .
  • Darwins theory that natural selection, or
    survival of the fittest, was the driving force
    of evolution is now called Darwinism.
  • Descent with modification was used instead of the
    word evolution in his book (until the very last

Descent with Modification
  • Unity in life
  • All organisms related through descent from some
    unknown ancestor that lived in the remote past
  • As the descendants of those ancestral organisms
    spilled into various habitats over millions of
    years, they accumulated diverse modification, or
    adaptations, that fit them to specific ways of

Descent With Modification means evolution
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