Transcript Darwin`s Voyage on the Beagle

Darwin’s Voyage on the Beagle 1831-1836
– Darwin was Fitzroy's fourth choice
– Purposes of voyage: Provide maps of South America useful to the British Navy.
Britain viewed South America as a market for its manufactured products and a
source of raw materials.
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Layout of the Beagle. The ship was 90ft long by 24 feet wide. Darwin’s
cabin was only 10ft by 11ft.
Darwin brought: microscope, telescope, compass,
barometer, rain gauge, guns, preserving fluids for
specimens.... and Lyell's Principles of Geology (Vol. 1).
St. Jago in Cape Verde Islands
Due to quarantine restrictions the Beagle cannot stop at
the Canary Islands.
First stop is the Cape Verde islands
St. Jago is a volcanic island with both vegetation and
bare rocks. Darwin sees a horizontal white band on
some rocks 30 feet above sea level. On close
examination Darwin discovers this band is made up of
compressed sea shells and corals.
How had the sea shells got there?
His geological speculations begin (based on Lyell's
work).
Frontispiece of Lyell’s “Principles of Geology
– The temple is that of Jupiter
Serapsis at Pozzouli. The
three columns show evidence
of having been underwater at
some time in the past. The
bottom parts are smooth,
above that is a layer of shells
embedded in stone.
– Conclusion: Temple initially
built by Romans above the
water line had been partly
submerged for a time.
– Lyell was a gradualist. He had
adopted Hutton's ideas of
slow never ending change.
Geological processes still
operating were shaping the
earth, including the slow rise
and fall of land.
South America
Bahia – Darwin entranced
by plants and animals in
jungle.
Fossils – Finds his first
fossils in the southern
pampas, at Punta Alta,
including a jawbone and
tooth characteristic of a
megatherium, a huge
extinct animal with
similarities to the modernday sloth.
Megatherium
Sloth
Darwin reads Lyell's second volume, which focused on how
animals and plants respond to a changing landscape.
Lyell is anti-Lamarck. Lyell believes each species was adapted to
the place in which it came into existence. If the environment
changes too much, the species died out.
Darwin, having seen and touched Megatherium bones accepts
this. Lyell has explanation for extinction of species but not for their
coming into being.
Darwin continues to search out fossils as the Beagle tracks up and
down the coast. Finds megatherium bones together with shells of
creatures that still existed.
Envisions megatheriums living in the not-too distant past as the
coast of South America slowly rose.
Darwin sees a Lyellian world, but has no answer for species
creation.
Geographical Distribution of Species
Rhea a native pampas bird that Darwin was familiar
with.
Darwin hears from locals about a smaller darker rhea
that lives only in the southern part of the pampas.
Darwin finds this smaller rhea in the south, and is told it
is the only kind of rhea in that area.
Two very similar species with separate but overlapping
ranges. Why?
Concepcion Earthquake, Chile, 1835
Severe earthquake caused massive destruction and loss
of life. The earthquake also raised surrounding land by
several feet.
Darwin finds mussel beds now lying above high tide, with
the mussels all dead.
Another confirmation of Lyell's theory.
An example of destructive power of nature rather than a
benevolent nature designed for man's use.
Galapagos Islands/ Mainland Comparisons
Galapagos are dry volcanic islands filled with reptiles,
including giant land tortoises.
Birdlife – Darwin notices three varieties of mockingbirds,
each found on only one island. Similarities to mockingbirds
found on mainland.
Finches were the most common bird – he collects six
types of finches from three islands, but assumes each type
could be found on all the islands. Similarities to mainland
birds.
Tortoises – Local prisoners believed each island had its
own particular kind of tortoise, characterized by slightly
different shell shape. Darwin uninterested as he believes
tortoises originally brought to islands by sailors as food
Galapagos finches
Due to very different beak
size Darwin assumed that
some of the finches were
wrens.
Charles Darwin's
Journal of
Researches
Coral Atolls
Lyell believed coral atolls grew
as a result of slowly rising
underwater volcanoes.
Darwin speculates that land
rising in South America must
mean land falling somewhere
else. Perhaps coral reefs grew
as a result of sinking
volcanoes?
Fitzroy's soundings around an
atoll showed that coral grew on
a underwater mountain
surrounded by very deep water.
Showed coral reef had grown
upward as volcano submerged.
Darwin's geological
speculations bearing fruit.
From The Voyage of the
Beagle
Voyage home
Darwin draws up catalog of his collections and reflects
on what he has found.
His mockingbirds got him thinking:
“When I see these Islands in sight of each other, &
possessed of but a scanty stock of animals, tenanted by
these birds, but slightly differing in structure & filling the
same place in Nature, I must suspect they are only
varieties…If there is the slightest foundation for these
remarks the zoology of the Archipelagoes – will be well
worth examining; for such facts would undermine the
stability of species.”
Did islands have a unique role in making species less
stable? How pliable was nature? How had colonization by
one species from the mainland turned into different
varieties?
Darwin - Back in England
Lyell had used Darwin's fossils of giant extinct sloths,
armadillos and llamas to show that living species were
closely connected to the species that they replace.
More food for Darwin's beginning speculations on
evolution.
John Gould examines Darwin's birds – his wrens and
finches. Gould realizes that they are all finches, differing
in beak shape, and that they are all separate species,
not just varieties. And they have close relatives on the
mainland. Somehow the original finch immigrants on the
Galapagos had changed enough to produce new
species. Darwin realizes the importance of isolation in
creating new species.
Darwin finds his niche in the world, examining what
Lyell couldn't, the origin and stability of species.