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    Patterns and Process: The Darwinian Revolution

      We live in an ordered universe.
      Therefore, patterns inevitably emerge among our observations.
      Most patterns are the result of some process.

      Patterns comprise

      • regularity
      • order
      • repeatability in sets of observations

      Humans observe and measure their observations of the natural world.
      These observations are empirical data, or facts.

      Humans have a long history of trying to make sense of observed patterns.

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    Supernatural Explanations

    There are about as many creation stories as there are cultures.

    1. Each of these stories is different from the others,
    xx so they can't all be true.

    2. Empirical evidence for supernatural creation is lacking.

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    Plato and Aristotle: An Unchanging World

    About 2500 years ago, these Greek philosophers posited
    that the world was divinely created and unchanging.

    Aristotle devised the scala naturae ("Ladder of Nature"),
    his idea of the creator's hierarchy of being.


(click on pic for a larger view)

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    Intellectual Stirrings in the Renaissance

    In Natural Theology In 1802, William Paley published Natural Theology,
    in which he set out to prove the existence of God as evidenced by
    the beauty and order of Nature.

    This work reflected the prevailing belief that science should be
    dedicated to determining the Grand Plan of the Creator.

    But that century also saw the first stirrings of ideas about
    the natural world that did not involve the supernatural.

    Let's visit a "Who's Who of Evolutionary Thought" (<-- required link)
    in the 18th and 19th centuries.

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    Lamarck: Use it or Lose it

    In 1801, Lamarck presented his Theory of Inheritance of Acquired Characteristics.

    Sentiments interieurs ("inner feeling", Fr) was cited as a driving force of evolution:

      If the environment presents a challenge to an individual,
      the "inner feeling" of the individual will respond by altering
      the morphological traits necessary to meet that challenge.

    Use vs. disuse:

    • Constantly used structures increase in size (hypertrophy) and efficacy.
    • Disused structures decrease in size (atrophy) and become vestigial.

    Acquired characteristics could then be passed on to the individual's offspring.

    Lamarck's theory was one of the first truly testable ideas about how evolution proceeds.

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    NeoLamarckian Ideas?

    Some relatively discoveries could be dubbed neolamarckian.

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An Evolutionary Glossary

organic evolution

the process by which a population undergoes genetic changes from one generation to the next

gene

a unit of inheritance, composed of DNA, that controls a physical trait

alleles

Different versions of the same gene.
Example: Gene encodes ear wax.
Alleles of the ear wax gene can encode wet or dry ear wax.

species

A group of living organisms able to interbreed in nature to produce fertile, viable offspring;
defined by reproductive isolation (<--required link) from other species

population

All members of the same species living in a defined region or area

deme

a local, actively interbreeding subpopulation that shares a distinct gene pool

gene pool

all the genes at all loci in every member of an interbreeding population

evolutionary adaptation

1. the process by which a population evolves to become better suited to its environment

    Used in a sentence: Penguins have undergone evolutionary adaptation to be able to fly underwater.

2. a character/trait that has resulted from the evolutionary process

    Used in a sentence: A penguin's flipperlike wings are an evolutionary adaptation for underwater flight.

speciation

the evolution of distinct, reproductively isolated species from an ancestral species

microevolution

genetic change within a species over generations

macroevolution

the evolution of taxonomic groups, from speciation to the formation of larger taxonomic groups;
large scale evolutionary changes over long periods of time

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Individual organisms do not evolve.

Individual organisms change via short-term adaptations.

Only populations evolve.

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The Darwinian Revolution

    Charles Darwin

    Charles Darwin was an English naturalist.

    He was among the first to propose that all living species
    are descended from a common ancestor.

    Like most scientists of the time, he was initially a creationist.

    But his studies of the natural world led him to a different view
    of how life's diversity originated.

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    The Voyage of the Beagle

    At the age of 22, Charles embarked on the
    H.M.S. Beagle for a five year voyage as
    "unpaid gentleman scholar and naturalist"
    and learned companion for Captain Robert Fitzroy.

    While the Beagle's crew mapped South American coastlines, Darwin went ashore and collected living specimens from every landing locality.

    His explorations on the Galapagos Islands
    inspired the foundations of his theory.

    He returned to England, married his cousin Emma, and began to study and write.

    The works of

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    Artificial Selection

    In addition to reading the works of many scholars,
    Darwin observed and bred domestic animals.

    He noticed that humans could generate animals
    exhibiting desired traits with selective breeding.

    He called this practice artificial selection, and wondered
    whether nature itself might operate on a similar principle,
    "naturally selecting" individuals best suited for survival.

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    I Think...

    Musing over the years, Darwin came to visualize the evolution of life as a spreading tree.

    • The ancestor is represented by the base of the tree.
    • The descendant species are represented as the ends of the branches.

    He termed this gradual change of one species into another
    "descent with modification".

    He believed that this occurred due to a process he called natural selection.

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Darwin's observations led him to profound conclusions.



These inferences can be distilled into four tenets.

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    Overproduction

    Organisms are capable of producing huge numbers of offspring.

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    Heritable Variability

    Those offspring are variable in appearance and function,
    and some of those variations are heritable.

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    Competition

    Environmental resources are limited,
    and those varied offspring must compete for their share.

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    Differential Reproduction

    Survival and reproduction of the varied offspring is not random.

    Those individuals whose inherited characteristics make them
    better able to compete for resources will leave more offspring
    than those not as well adapted.

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    Survival of the Fittest?

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    What is the Smallest Unit that Can Evolve?

    Any trait (= character) expressed by an individual may be

    • adaptive - increases the likelihood of reproductive success
    • maladaptive - decreases the likelihood of reproductive success
    • neutral - does not affect the likelihood of reproductive success

    Consider that overall phenotype is the product of
    multiple gene interactions and environmental influence.

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    The Immortal Gene

    Natural selection results in a shift in relative allele frequencies.

    The end result of natural selection is a population carrying genes (and alleles)
    that make them well-suited to their environment.

    Differential survival (inheritance) of "competing" alleles
    will result in increased frequency of those alleles
    that promote their own propagation by producing (or contributing to)
    adaptive phenotypic traits.

    This is the essence gene-centered evolution described by
    Professor Richard Dawkins in The Selfish Gene
    .

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    The "Selfish" Gene?

    A "selfish" gene is neither selfish nor does it encode
    "selfishness" in the individual expressing it.

    But a "selfish" gene's expression does have evolutionary consequences
    that serve its own implicit "interest" in replication and, if possible, immortality.

    A gene's "best interest" may not coincide with
    what one might (subjectively) consider to be in its host's best interest.

    Can you think of some widespread traits in any species that seem to be crazy bad for the individual expressing them?

    As long as the gene's manifestation causes it to be passed on...mission accomplished.

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Evolutionary Thought in the Age of Enlightenment

Georges-Louis Leclerc, Comte de Buffon (1707-1788)

Buffon was among the first Age of Enlightenment philosophers to suggest that the earth might be older than 6000 years.

An expert in many sciences from astronomy to biology,
his life's work was creation of a Histoire Naturelle,
an encyclopedia of all that was known about the world in his time.

Instead of using conventional Biblical wisdom,
he referred to Newton's ideas about physics.
He proposed such novel, radical ideas as

  • our solar system's planets were formed from solar debris
  • earth started out as a molten rock, devoid of life
  • the earth might be as old as 70,000 years (inconceivable at the time!)
  • life might have been generated spontaneously, chemically, in the primordial oceans
  • even large organisms might have been formed this way (Well, you can't always bat a thousand.)

Evolution via migration
Buffon proposed that, as species migrated from places of origin,
the raw materials available to renew them were different.
This, he said, caused individuals to change in form.
Buffon's idea was the first known suggestion that living things could change over time.

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Jean Baptiste Lamarck (1744-1829)

In 1801, Lamarck presented his
Theory of Inheritance of Acquired Characteristics.

Its main tenet: changes an organism acquired during its lifetime could be passed on to its offspring.

Lamarck said these changes were driven by sentiments interieurs ("inner feelings", Fr): environmental challenges would drive individuals to physically change to meet those challenges.

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Georges Cuvier (1769-1832)

Though his expertise was in natural history and zoology, Cuvier is best known as the "father of paleontology" for his work on fossils and their relationship to the earth where they were found.

He was the first to establish extinction as a fact by demonstrating organismal diversity in deeper sedimentary strata were different from that in more recent strata.

Like most scientists and philosophers of his time,
Cuvier was a staunch creationist.

He proposed that periodic, catastrophic floods (generated by a divine creator) were responsible for the fossil record.

Catastrophism is the theory that sudden, relatively brief, violent events (floods, volcanic eruptions, etc.) are the main forces that shape the surface of the earth.

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By Joseph Wright of Derby - Unknown, Public Domain, Link

Erasmus Darwin

Charles Darwin's grandfather, Erasmus Darwin, a physician, was a proponent of evolution.

As a student, young Charles read his grandfather's writings and was inspired by them.

But it was only after his voyage on the Beagle that Charles Darwin began to incorporate ideas from other sources into his own musings about evolution.

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James Hutton (1726-1797)

Hutton was a Scottish geologist who challenged the catastrophism theory.

He proposed that slow, continuous processes such as erosion had been the major factors forming earth's topography.

He dubbed this theory gradualism.

Some refer to Hutton as the "Father of Modern Geology".

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Sir Charles Lyell (1797-1875)

This Scottish geologist and author of Principles of Geology proposed the theory of uniformitarianism.

This was an expansion of Hutton's Theory of Gradualism.

Lyell contended that not only was earth shaped by slow, continuous processes,
but that these processes had been going on for a very long time and could still be observed.

His work challenged many of Cuvier's ideas, which were the geological "conventional wisdom" of the time.

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(Thomas) Robert Malthus (1766-1834)

Malthus was an English religious scholar.

In his work

An Essay on the Principle of Population

he suggested that much of humanity's suffering (disease, famine, homelessness and war) was the inevitable result of overpopulation: humans reproduce more quickly than their food supply and other resources can support them.

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Charles Robert Darwin (1809-1882)

One of the most influential scientists of all time,
Darwin elucidated his theory of how evolution proceeds
in his then controversial work,
On the Origin of Species by Means of Natural Selection (1859).

On the Origin of Species is arguably the most important
biological work ever written.
Most modern biology is framed in the
context of evolution by means of natural selection.

Evolution by means of natural selection occurs when
individuals expressing heritable adaptive traits
leave a greater proportion of their genes to the next generation
than conspecifics lacking those heritable adaptive traits.

This is the essence of natural selection.

Because of the theological controversy he knew his work would provoke,
Darwin did not publish his ideas for 20 years after he wrote them.

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Alfred Russel Wallace (1823-1913)

Wallace was a British explorer, naturalist, geographer, anthropologist, and biologist.
He is best known as the scientist who almost
"scooped" Charles Darwin.

Wallace independently conceived the idea of natural selection.
He sent a letter outlining his ideas to Darwin
(then an established naturalist), and the contents
--Darwin's own theory in publishable form--sent Darwin into despair.

His friends Charles Lyell and botanist Joseph Hooker
came to the rescue, urging Darwin to present his work
alongside that of Wallace at the Linnaean Society on July 1, 1858.

Lyell and Hooker presented the paper for him,
and history credits priority to Darwin.

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Motoo Kimura (1924-1994)

In 1968, Mtoo Kimura published his
Neutral Theory of Molecular Evolution.

The theory describes how random, neutral DNA mutations
can have profound evolutionary consequences over time.

Kimura proposed that these neutral mutations could spread through populations via genetic drift.

Genetic drift is a random process by which some individuals
--due only to chance--contribute more genes
to the next generation than other individuals.

These "lucky" individuals are genetically overrepresented
in the next generation ONLY because of CHANCE,
not because they had adaptive traits.

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"Survival of the Fittest"

An individual's Darwinian fitness is defined as its reproductive output compared to that of its conspecifics.

Thus, "survival of the fittest" translates as "survival of the most reproductively successful".

Survival is only one aspect of evolutionary fitness.
It may not even be the most important aspect of reproductive success.

Modern biologists avoid using the phrase "survival of the fittest"
to describe Darwin's theory.

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