Transcript Four_theories

Four Historical Theories of
Organic Change
Cuvier, Buffon, Lamarck, and Darwin
Georges-Louis LeClerk, Compte de
Buffon
1707-1788
Thought an artificial
taxonomy was a waste of
time. Naturalists should
search for a natural
taxonomy, find the order
in nature.
Asked by the King to
catalog the Royal Garden
collection, Buffon
decided to catalog
everything in nature.
Wrote 36 volume Histoire
naturelle, générale et
particulière.
The Moule Intérieur, said Buffon, was caused
by particles inside of an organism.
Horses in Europe remain brown and Move the horses to Africa, and
distinctly horse-like because their the environment rearranges the
particles, especially in the
environment arranges the particles
embryos, which reshapes the
into a horse shape.
animals over generations.
All animals are affected
equally, and over many
generations, the particles
reshape the horses into
zebras.
Georges Cuvier
1769-1832
Supported the “static model” of
species — species do not change
because they cannot survive
changes.
Comparative anatomist: looking
for patterns in structure,
especially among vertebrate
animals.
Set up a natural, nonhierarchical taxonomy of
animals based on the nervous
system.
Jean-Baptiste Pierre Antoine
de Monet de Lamarck 1744-1829
Protegé of Buffon. Interested in natural
classification of living organisms.
Background was in Botany, but later studied
invertebrates.
Primary questions: Where do you draw the
line between species? How do you “rank”
species?
Favored a theory of inheritance of acquired
characteristics.
Lamarck’s “Organic Law of
Development”
Spontaneous Generation creates new,
simple organisms, such as bacteria.
Woo-hoo, guys,
we’re alive!
Lamarck’s “Organic Law of
Development”
Organisms are shaped by their
environment.
Hmm, changes... I need to
get organized here.
Ooh, a nucleus! Problem
solved!
Lamarck’s “Organic Law of
Development”
Change is teleological (goal-directed).
Organisms have an internal drive to
become more complex.
Being an amoeba is the pits.
I can’t wait until we all
Cool! Tissues! Maybe we’ll
become multicellular.
get real organs
soon. and bilateral
Organs
symmetry! Yeah! Can’t wait
until we turn into mammals!
Lamarck’s “Organic Law of
Development”
Use and disuse of parts causes change that is
passed on to the next generation.
Lamarck says it’s
your fault, Stanley,
that Junior’s legs are
so short. If you
weren’t such a couch
potato and had
gotten some
exercise...
I’m not short,
I’m vertically
challenged.
Sure, blame me,
when you’re the
one who hardly
left the barn
before he was
born.
Charles Darwin
1809-1882
Charles attended boarding school as
a boy, where he developed an interest
in Natural History.
Father sent him to study medicine in
Edinburgh. Turned off by barbaric
surgery practices and dull lectures.
Joined Natural History society, read
Buffon, Cuvier, Lamarck, others.
• Darwin left Edinburgh determined not
to be a physician. Attended Cambridge,
thinking he would be a clergyman.
• At Cambridge, he read Herschel
(philosophy of science), Humboldt
(geological distribution of organisms),
Lyell.
• After graduation in 1831, Darwin was
encouraged by friends to apply to be a
captain’s companion and naturalist on
board the Beagle.
• December 27, 1831: Joins Captain
Fitzroy on board the Beagle for a fiveyear journey.
Voyage of the
H.M.S. Beagle
• Official purpose of the voyage was to survey
the South American coast.
• During the voyage, Darwin observed a
volcanic eruption, an earthquake, and noted
geologic features suggesting an ancient earth.
• In South America, found fossils of ancient
sloths, observed living rheas (ostrich-like
birds) and llamas, many other animals not
described by naturalists. Collected huge
numbers of specimens.
The Galapagos
• In September of 1835, the Beagle
reached the Galapagos Islands.
• Fascinated by the giant tortoises.
Brought three back alive.
• Made detailed observations of finches,
mockingbirds. Realized that they
resembled birds on the mainland, yet
were different. Where did they come
from?
• Besides the Galapagos, Darwin observed
organisms on Tahiti and other Pacific
islands. Later developed theories of coral
reef building.
Darwin’s questions
• Why the replacement of species
geographically; that is, why are the species on
islands not exactly the same as those on the
nearby mainland?
• Why the replacement of species in time?
• Where do species come from in the first
place?
• Change in species appears to be the answer
— but how do species change?
Natural Selection
• Darwin rejected the idea that all members of a
population are shaped equally by the
environment and that all change together.
Selection does NOT look like this:
Generation 1
Generation 100
Generation 200
Natural Selection
• Rather, selection begins with variation. Some
variants in a population may be at an
advantage, some at a disadvantage. Those
with a strong advantage are more likely to
have offspring.
• “Fitness” is the ability to survive.
• “Success” is passing one’s traits to the next
generation.
Natural Selection
• Natural Selection looks more like this.
Suppose in a population of horses, black
horses get hotter in the sun and are more
likely to die of heat exhaustion.
Generation 1
Generation 2
Natural Selection
• But suppose global climate changes alter the
local environment. It becomes cooler and
cloudier. Now the black horses have an
advantage because their black coats help
them stay warmer.
Natural Selection
• Notice the difference:
• Buffon and Lamarck would say, “The
horses need to be darker, so they will get
blacker and blacker each generation.”
• Darwin says, “Black horses are better able
survive and reproduce each generation, so
there will be more and more black horses
each generation.”
Darwin’s New Questions
• Darwin noted two difficulties in his original
theory of Natural Selection:
• Where did variation come from in the first
place?
• How did favorable traits get passed on to
the offspring, if traits of each parent are
blended in the offspring (as was commonly
believed at the time)?
In the 20th Century...
• Darwin’s questions led other scientists to
explore heredity, which led to the science of
genetics.
• Genetic research in the 20th century
supported natural selection as a plausible
mechanism, and raised new questions and
new possibilities.