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After Cambridge, Charles was recommended
for a surveying trip on the HMS Beagle.
Darwin sailed around the world on the
Beagle for 5 years, working as a naturalist.
Darwin made many
observations and
collected evidence
on his voyage that
led to his theory
about the way life
changes.
At the time Darwin made
his trip, the majority of
people believed the Earth
and all of its forms of life
had been created only a
few thousand years in
the past.
People also believed that the Earth had not
changed during those few thousand years.
People also believed in fixity of species; in other
words, species never changed.
The first dinosaur to be described
scientifically was Megalosaurus
by William Buckland in 1824.
After careful
observation and
study of new
scientific
discoveries,
Darwin began to
think otherwise.
The Father of Geology
Darwin was influenced
by geologist James
Hutton’s writings that
described geologic
forces he thought had
changed and were still
changing the earth.
Hutton proposed that
the Earth had to be
much more than a few
thousand years old.
Darwin was also
influenced by
geologist Charles
Lyell who wrote
Principia Geologica.
Lyell’s book proposed
that tremendous
geologic processes
had shaped the Earth
such as seen in
volcanoes active in
the present.
On the voyage,
Darwin noticed
that everywhere he
went, the animals
and plants differed
vastly.
Patterns in the species
suggested that the
species had changed
over time and had given
rise to new and different
species.
Many of Darwin’s
conclusions were
based on
observations of
wildlife in the
Galapagos Islands.
The Galapagos
Islands lie 500 miles
west of Ecuador in
the Pacific Ocean,
directly on the
equator.
“Galapagos” means turtle.
Darwin noticed on
these islands,
there were several
types of finches.
What it must have been
like to be Darwin…
In particular,
Darwin observed
something odd
about the
finches: they all
looked like a
bird he had seen
on the South
American
continent.
Darwin wondered if the birds and other
animals had been created to match their
environment, why didn’t these birds look like
the birds of the African continent, since the
environments of both the Galapagos and
Africa were similar.
Darwin guessed that
some of the birds
from South America
migrated to the
Galapagos.
Once on the islands,
the birds must have
changed over the
years.
large ground
finch
woodpecker
finch
cactus finch
This would explain the numerous species of
birds present.
Darwin concluded:
Each species has descended, with changes,
from other species over time.
Darwin called this…
Descent With Modifications
or
(change in species over time)
Darwin based his theory
on his own observations
and the writings of
Thomas Malthus.
Malthus was a British
social scientist who
proposed theories on
factors controlling
population growth:
People have more children than are
able to survive.
There are built-in population checks:
disease, famine, and war.
Darwin extended these
principles to biology, which
helped him form his theory of…
…or Survival of the Fittest.
Natural selection was the
mechanism by which
Darwin proposed that
evolution took place.
Darwin published his
theory in the book
Five basic components of
EQ: How do adaptations
relate to natural selection?
1. All species have genetic variation.
Every species is different,
even within itself.
Variation is caused by
mutations and meiosis.
2. Organisms produce more offspring than
the amount that actually survive.
The female green sea turtle lays a clutch of about
110 eggs. She may lay several clutches.
It is likely that less than 1%
of the hatchlings will ever
reach sexual maturity.
3. Since more organisms are produced than
can survive, there is competition (struggle for
existence).
Competition exists WITHIN and AMONG species.
Within and Among Species for
food
water
shelter
space
And Within a Species for
mates
The constant struggle for survival is affected by
short-term natural disasters. (drought, fires,
floods, snowstorms, hurricanes, and tornadoes)
The constant struggle for survival
is also affected by long-term
changes in the environment. (ice
ages, biome shifts, etc)
4. Survival of the fittest Some organisms
are more suited to their environment as a
result of variations in the species.
Fitness: the ability of an individual to survive
and reproduce in its specific environment.
Fitness is a result of adaptations.
Individuals that are fit to their environment
survive and leave more offspring than those
who aren’t.
He who spreads the most genes wins!
1st
5. Descent with modification: Living species
today are descended with modifications from
common ancestral species that lived in the
past.
Characteristics of fit individuals
increase in a population over time.
Over time, genes for less favored
characteristics will be eliminated
from the gene pool.
Example: giraffes and their
increasingly longer necks.
Natural Selection: Survival of the Fittest
An adaptation is any inherited characteristic
(a genetic variation) that can increase an
organism’s chance of survival.
organism
does
a. An
the variation
exists
first.not
change
because of need or desire to
b. the
environment
survive.
The changes.
organism either
already
has
the
variation
that
c. a variation may give an advantage to
enables
it to survive
or it dies.
survive
environmental
change.
Artificial Selection
• Nature provided the variation but humans
selected those variations that they found useful
(selective breeding)
• Ex: wild strawberry vs. domesticated
strawberry, domestic dogs