Download Chapter 5 Darwin and the Voyage of the Beagle

Charles Darwin
and the Voyage
of the Beagle
Psalm 104:24-30
O LORD, how manifold are your works!
In wisdom you have made them all; the earth is full of your
creatures. Yonder is the sea, great and wide, creeping things
innumerable are there, living things both small and great. There
go the ships, and Leviathan that you formed to sport in it.
These all look to you to give them their food in due season;
when you give to them, they gather it up; when you open your
hand, they are filled with good things.
When you hide your face, they are dismayed; when you take
away their breath, they die and return to their dust.
When you send forth your spirit, they are created; and you
renew the face of the ground.
What was the motivation for a
“new explanation”?
• Discuss with your neighbor and generate
some suggestions for each of the following…
– What was the current, widely held notion of
“origins”?
– What shortcomings did the prevailing idea(s)
have?
Overview
• By the early 19th century, many of the basic concepts
necessary to develop a scientific explanation for the
diversity of life on Earth were in place:
– Ancient Earth (James Hutton millions years old earth)
– Extinction of species as represented in fossils (immutable)
– Similarity (continuity) of species (Ray & Linnaeus)
– No mechanism was available to explain how species could change over time
– Most if not all “ men of science” were convinced that organisms had
descended through inheritance from previously existing organisms.
Words from Dr. Strohmeyer…
• An obvious or veiled argument is often made that religion
(Christianity being the main target and lumped in with all religions
of every type as being the same and thereby mythical) and it’s
accompanying theological/philosophical views were wrong and a
negative influence in various ways.
• Many evolutionists will claim to be scientific and unbiased but in
reality science exists only because there is a “philosophy of
science”—a means for defining what constitutes science. Thus no
one does anything (including science) without a worldview bias.
And for current science the philosophy of life (worldview) is
naturalism and its accompanying subisms.
– So a word of caution, just because a textbook in a course makes certain
claims, doesn’t mean these claims are true. Academic people write
textbooks, often later in career and are largely secular and liberal in their
worldviews. SO BE DISCERNING as you learn! There is truth and there is
untruth. Guard your mind and choose your truth by checking it against
scripture and in prayer!!!
Theodosius Dobzhansky
• “Nothing in biology makes sense except in the
light of evolution”.
• How would you define “theory”?
– Biological evolution is called a theory
because …
– The theory of evolution provides…
Theodosius
Dobzhansky,
ca.1966
3 important questions remained:
1. How were species to be regarded?
2. What natural cause or mechanism could explain
organismal change?
3. What hereditary mechanism could enable new
species to arise?
• Q1 - Could not be resolved by Darwin and others of his day. Why
not?
• Q2 - Darwin provided a theory for organismal change based on
evolutionary biology (dysteleological)—as opposed to various
design (teleological) hypotheses of the day—i.e. William Paley.
• Q3 - was addressed in part in Darwin’s day by Gregor Mendel but his
work remained undiscovered (not understood) for another 40 years.
Fossils
• An essential basis for understanding evolutionary
relationships
• Various views on Fossils
– 16th-17th Centuries– “stones” images of God’s creation, placed
on Earth for man’s admiration and use but formed naturally by
God—body parts displays/models.
– Errors in the plan of nature, causing some species to become
extinct? For them fossils were lusi naturae (“ jokes of nature”).
– Thomas Jefferson and many others proposed that fossil species
were not really extinct, only rare. (not completely wrong—
living fossils are known)
Fossils
• Various views on Fossils (cont.)
– Caused by the Noachian flood described in Genesis.
– Purposely implanted into Earth at the time of creation in order
to test humanity’s faith in religion.
• Contrary arguments proposed the reality of fossils and led to more
naturalistic attempts to understand fossil origins.
– George Cuvier saw that fossils from younger rocks were more
like living organisms than were fossils from older rocks—
stratigraphy.
Fossils
• In Darwin’s day, the fossil record was sporadic, the result of
serendipitous collecting and random finds. While more concerted
efforts have since been made,
• The fossil record is still considered incomplete for a variety of
reasons.
– What reasons do you suggest?
*Decomposition
*Erosion
*Sympatric speciation more rare?!?
*Soft-bodies
*Geological processes
*Many fossils are still buried… (yet to be
discovered)
Stratigraphy
Fossils
• A complete evolutionary progression of fossils from most
ancient to most recent has never been found in a single
locality.
• Nevertheless, fossils provide the hard evidence for
evolution, evidence used by Charles Darwin who first
offered an acceptable explanation for historical changes
among organisms and thereby helped tie all organisms
together by a community of descent: evolution.
Fishapod (Tiktaalik roseae)

Illuminates steps leading to
evolution of tetrapods from
fish—explanation level

Had broad skull, flexible
neck, eyes on top,
interlocking rib cage
suggesting lungs, pectoral
fins resembling primitive
wrist and 5 finger-like
bones—basic fact level

Peek above water and look
for prey—pure speculation
with no real way of knowing
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Defining Species
• Plato – Idealism
– Organisms’ imperfect representations of essence
– A form of teleology/design is the archetypetype
• Aristotle – Great Chain of Being
– Species immutable
– Hierarchical order of imperfect  perfect (also teleological—
ascent towards perfection)
• Leibnitz – gaps in “chain” suggest evolution towards
perfection. Proposed that universe was imperfect and
that it and all in it was evolving towards perfection-major philosophical shift.
• Bonnet – Preformationism—homunculus, teleology
– Unfolding of preconceived plan in embryo into perfect adult
Classification of Species
• Classification schemes of many types made defining and
organizing species a VERY difficult task.
• Mid- to late-1600s, John Ray was the first to carry out a
thorough study of the natural world
– Developed an early classification system
– Modern species concept
• Extended by Carolus Linnaeus (1707-78)
– Binomial nomenclature: genus species
– Still believed in species constancy, dismissing evolutionary
transformation and was ardently idealistic and teleological
• Neither proposed that evolutionary change promotes the
formation of new species
Biological Importance of Species
• Late 1700s, small number of European scientists
suggest life forms are not fixed
• Buffon (1707-1788)
– Life forms change over time
– Defined species by ability to reproduce fertile offspring
– Natural barriers to species possible "reproductive
isolation"
– Variation within a species accepted through a degenrative
mechanism (genetic entropy of a sort)
– Evolutionary transformation still rejected as contrary to
religion
Classification of Species
• Jean-Baptiste de Lamark
(1744-1829)
– Dismissed fixity of species—
recognition of species actually
hindered a theory of evolution
because species seemed to be fixed.
– Proposed branching classification of
animals
– Animals evolved from each other
– Believed living things evolved upward
toward human “perfection”
– Inheritance of acquired
characteristics—somatic inheritance
Species Concepts
• Morphological species (morpho-type)
– Shared similar characters
– Special case: Paleontological species—reproductive isolation
cannot be determined for fossils, thus not a biological species. In
situations in which a set of paleontological species can be
identified as representing a series of ancestral and descendant
populations, paleontological species also may be recognized as
evolutionary species.
• Biological species
– Cross produces viable offspring
– Sexually reproductive species
• Evolutionary species
– Isolation based on multiple character types
Charles Darwin (1809-1882)
Figure 1B & 1C: Charles Darwin
© National Library of Medicine.
• Born to upper middle-class British family
• Age 16, Edinburgh University to study medicine
• Cambridge University with the intention of
becoming a minister of the Church of England
• 1831 set sail on the H.M.S Beagle
– Not as ship’s naturalist but as captain’s companion
Voyage of the Beagle
Voyage of the Beagle (1831-1836)
• Collected specimens in the Brazilian tropics
• Unearthed fossils of extinct species
– Discovered fossil bones in Argentina, such as the 6mhigh giant sloth, Megatherium.
• Explored the Galapagos Archipelago
– Darwin read Lyell's Principles of Geology—promoted
uniformitarianism over catastrophism.
• Struck by distinctive traits of island species
Galapagos Islands
• Small volcanic islands off
western coast of South America.
• Darwin collected many
specimens of finch.
– He later noted that each
island had finches with a
unique beak shape.
• Tortoises and land iguanas too…
Darwin's Finches
– Each island has unique beak shape.
– Variation in beak shape provides
advantages for the food source
available on each island.
– Beak shape modified, but how?
• Natural Selection—what about that Bmp-4 story—
rapid beak change by gene regulation rather than
gradual genetic change.
Darwin’s Influences
• Theory shaped by several different fields of study—it was
in the air at the time academically speaking
–
–
–
–
–
Grandfather (common descent)
Geology—Lyell/Hutton (contemporaries-Lyell friend)
Economics—Malthus
Biology—Lamarck, Buffon and others
Voyage of the Beagle
• General academic atmosphere just prior to and during
Darwin’s time that began to favor natural explanations.
“Would it be too bold to imagine that, in the great length
of time since the earth began to exist, perhaps millions of
ages before the commencement of the history of mankind
would it be too bold to imagine that all warm-blooded
animals have arisen from one living filament, which the
great First Cause endued with animality, with the power of
acquiring new parts, attended with new propensities,
directed by irritations, sensations, volitions and
associations, and thus possessing the faculty of continuing
to improve by its own inherent activity, and of delivering
down these improvements by generation to its posterity,
world without end!”
• Erasmus Darwin (grandfather)
• Uniformitarism hypothesis from geology—
Lyell/Hutton
– Slow recurring geological processes lead to
substantial change (i.e. erosion,) rather than
catastrophic events
– Earth was much older than 6,000 years
– Darwin read Lyell's Principles of Geology
(influnced by Hutton), and used it to study
geological features during the voyage—promoted
uniformitarianism over catastophism.
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• Thomas Malthus, and his essay on economics…
• Aided Darwin in his ideas about how natural
selection worked via competition and selection and
survival of the fittest.
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After the voyage on The Beagle
• Begins to formulate theory of evolution around 1837 and
has much of it worked out by mid 1840s
• Spent several additional years studying barnacles,
perhaps to become an expert in a species. Also studied
many other organisms to a lesser extent.
• 1856, began writing his book
• Why do species change? In seeking an answer over the
next 20 years, Darwin explored a variety of theories.
– One of the most persistent, a theory that later had many
adherents in France and the United States, was most fully
developed by Jean-Baptiste Lamarck. We know it as
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Lamarckian inheritance.
Lamarckian Inheritance
• Where others had looked at fossils and saw species extinction,
Lamarck made the intellectual leap of proposing the continuity of
species by gradual modification through time.
• By the early 19th century, most naturalists accepted the inheritance
of acquired characters, the utility ( adaptedness) of features, and
the concept of some internal force toward change.
• To explain how modifications occurred and the exquisite
relationships ( adaptations) through which organisms exploited their
environments, Lamarck is credited with proposing that
– variations among organisms originate because of the organisms’ response to
the needs of the environment;
– this ability to respond in a particular direction accounts for the adaptation of
new features and their passage to subsequent generations
– Water bird legs, giraffe’s long neck, etc (just-so-stories)
Lamarckian Inheritance
• Lamarckism – adaptations driven by an inner vital force that
helped organism evolve to perfection (simple to complex) by
sensing the needs of the new environment and creating new traits
that could be passed to offspring.
2 (3) Laws
1. Principle of Use and Disuse.
– In every animal that has not passed the limit of its development — like
Linnaeus, Lamarck saw organisms as progressing through some internal
principle — more frequent and continuous use of any organ gradually
strengthens, develops and enlarges that organ and gives it a power
proportional to the length of time it has been so used. The permanent
disuse of any organ imperceptibly weakens and deteriorates it, and
progressively diminishes its functional capacity, until it finally disappears.
Lamarckian Inheritance
2. Inheritance of Acquired Characters
– All of the acquisitions or losses wrought on individuals through the influence
of the environment, and hence through the influence of the predominant
use or permanent disuse of any organ, are passed on by reproduction to the
new individuals that arise, provided that the acquired modifications are
common to both sexes, or at least to the individuals producing the young
3. Some would list the drive toward perfection as a third process
central to Lamarck’s thinking.
• By proposing a materialistic explanation for evolution (inheritance
of acquired characters), an explanation that reflected the close
interactions known to occur between organisms and their
environment, Lamarck fostered a climate of opinion in which
evolution could be understood in the same fashion as any other
natural event.
• Many detractors (i.e. Cuvier) and eventually proven incorrect
Key Concepts
• Darwin explained the relationships between organisms as
the result of common descent from a single ancestor.
• Darwin proposed a theory of evolution by natural
selection (and sexual selection).
• The fossil record, the biogeography, and domestication all
provided evidence for Darwin’s theories.