Chapter 22 Descent with Modification: A Darwinian View of Life

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Chapter 22Descent with Modification
A Darwinian View of Life
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Question?

• How did the diversity of life originate?
• Through the process of Evolution.

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Evolution

• The processes that have transformed life on earth
  from its beginnings to today's diversity.
• Evolution is the most pervasive principle in
  biology.

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Teaching Philosophy on Evolution
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Evolution

• Has itself "evolved" or changed over time.
• Illustrates Science as a Process.

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Pre-Darwinian Views

• 1. Greeks
• 2. Fixed Species
• 3. Catastophism
• 4. Hutton and Lyell
• 5. Lamarck

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Greek Philosophers

• 1. Plato - Organisms are already perfectly
  adapted to their environments.
• 2. Aristotle - Organisms arranged on a scale of
  life from simple to complex.

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Result

• No evolution.
• Life is already perfect and doesnt need to
  change. All the rungs on life's "ladder"
  are already occupied.

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Fixed Species Concept

• The creator had designed each and every species
  for a particular purpose.

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Result

• No evolution.
• Created the viewpoint that all species could be
  identified and named (Taxonomy). A major
  factor in the Linnaeus classification system.

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Catastrophism

• Georges Cuvier (1769-1832).
• Attempted to relate fossils to current life.

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Theory

• Fossils were the remains of species lost due to
  catastrophe.
• No new species originated species could only be
  lost over time.
• Result - No evolution.

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James Hutton

• 1795 - Gradualism
• Profound change is the cumulative product of
  slow, but continuous processes.

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Result

• Changes on the earth were gradual, not
  catastrophic.

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Charles Lyell

• 1797 - 1875.
• Incorporated Huttons gradualism into a theory
  called Uniformitarianism.

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Uniformitarianism

• Geological processes have operated at the same
  rate over the Earths history.

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Result

• The Earth must be VERY old. (much older than 6000
  years of the fixed species concept).
• Idea that slow and subtle processes can cause
  substantial change.

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Jean Baptiste Lamarck

• Published theory in 1809.
• Theory - Life changed from simple to complex over
  time.

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Lamark

• Fossils were the remains of past life forms.
• Evolution did occur.

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Mechanisms

• 1. Use and Disuse -
• Body parts used to survive become larger and
  stronger.
• Body parts not used to survive deteriorate.

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Mechanisms

• 2. Acquired Characteristics
• Modifications acquired by use/disuse were passed
  on to offspring.

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Problem

• No knowledge of genetics.
• Acquired traits are not transmitted offspring.

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Lamarcks Credits

• Did suggest correctly the role of fossils in
  evolution.
• Did suggest that adaptation to the environment is
  a primary product of evolution.

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Charles Darwin

• Father of the modern theory of evolution.
• Theory - Descent with Modification.

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Darwin's Background

• Trained as a Naturalist (after trying religion
  and medicine).

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Voyage of the Beagle
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Result

• Darwin's training and travel opportunities
  allowed him to formulate and support his ideas on
  Natural Selection.

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Galapagos Finches
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Movie Galapagos Islands
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Movie unique animals

• Marine Iquana

• Tortise

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Alfred Wallace - 1858

• Paper on Natural Selection identical to Darwin's
  ideas.

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Result - July 1, 1858

• Dual presentation of the Wallace-Darwin ideas to
  the Linnaean Society of London.

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Darwin - 1859

• Publication of "The Origin of Species

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Comment

• Darwin best remembered for the theory because of
  his overwhelming evidence and because he
  published.

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Darwinian View

• History of life is like a tree with branches over
  time from a common source.
• Current diversity of life is caused by the forks
  from common ancestors.

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Example
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The Origin of Species

• Documented the occurrence of evolution.
• Suggested that the mechanism for evolution was
  Natural Selection.

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The Facts

• Fact 1 - All species reproduce
  themselves exponentially.

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• Fact 2 - Most populations are normally stable in
  size.
• Fact 3 - Natural Resources are limited (finite).

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Inference 1

• The large number of offspring must compete for
  the finite resources.
• Result - Most offspring die.

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More Facts

• Fact 4 - No two individuals in a population are
  exactly alike.
• Fact 5 - Variation is inheritable.

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Inference 2

• Those individuals whose inherited characteristics
  fit them best to their environment survive and
  reproduce.

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Inference 3

• Offspring inherit the favorable characteristics.
  Populations shift over time as the favorable
  characteristics accumulate.

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Nature

• Determines which characteristics are favorable.
• Determines who survives.
• Result - Natural Selection

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Natural Selection in action
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Artificial Selection

• When man determines the characteristics that
  survive and reproduce.
• Result - the various breeds of animals and plants
  weve developed.

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Ex - Mustard Plant

• Original

• Cultivars

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Evolution Success Measured By

• Survival
• Reproduction
• Whoever lives long enough and has kids is the
  winner in evolution.

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Requirements

• In order for Natural Selection to work, you must
  have
• Long periods of time.
• Variations within a population.

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Subtleties of Natural Selection

• 1. Populations are the units of Evolution.
• 2. Only inherited characteristics can evolve.

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Comment

• Acquired characteristics may allow a species to
  evolve "outside" of Natural Selection.
• Ex culture, learning

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Additional Signs

• 1. Biogeography
• 2. Fossils
• 3. Taxonomy
• 4. Comparative Anatomy
• 5. Comparative Embryology
• 6. Molecular Biology

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Biogeography

• The geographical distribution of species.
• Problem
• Species mixtures on islands
• Marsupials in Australia

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Evolution Viewpoint

• Biogeographical patterns reflect descent from the
  ancestors that colonized that area.

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Fossils

• Relics or impressions of organisms from the past.
• Problem
• Show changes over time from simple to complex.
• Many fossils don't have descendants.

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Evolution Viewpoint

• Life has changed over time.
• Many species failed to survive and became extinct.

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Comments

• 1. Fossilization is a rare event.
• 2. Only hard parts fossilize well.
• 3. Problem in finding fossils.
• 4. Interpretation.
• 5. Missing Links.

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Taxonomy

• Science of Classification.

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Main Categories

• Kingdom
• Phylum or Division
• Class
• Order
• Family
• Genus
• Species

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• Problem - Why can life be grouped this way?
• Evolution Viewpoint -Hierarchy reflects the
  branching genealogy of the tree of life.

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Comparative Anatomy Problems

• Mammal forelimbs

• 1. Homologous Structures - Common "building
  plan with divergent functions.

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Comparative Anatomy Problems

• 2. Vestigial Organs - Rudimentary structures of
  marginal, if any, use.

• Whale Legs

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Human Example
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Evolution Viewpoint

• Remodeling of ancestral structures as their
  functions or adaptations changed.

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Comparative Embryology

• Problem - closely related organisms go through
  similar stages in their embryonic development.
• Ex Gill pouches in vertebrates

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Evolution Viewpoint

• Ontogeny is a replay of Phylogeny.
  (Development reflects descent)

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Molecular Biology

• Study of Evolution at the DNA or protein levels.
• Problem - related species have similar DNA
  sequences.

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Evolution Viewpoint

• Related species share a common ancestrial DNA.
  The closer the relationship, the more similar the
  DNA sequences should be.

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Summary

• Darwin's ideas now a "Theory.
• Predictions of a Theory are tested by experiments
  and observations.
• Be familiar with the pre-Darwin views of
  evolution.

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Summary

• Know Darwins facts and inferences.
• Be able to discuss the various evidences of
  Darwinian evolution.