Transcript Darwin and Natural Selection

Darwin and
Natural Selection
born in Shrewsbury,
England, in 1809
studied medicine at
Edinburgh University
(1825-1827) where the
sight of blood and
surgery without
anesthetics repulsed him
studied to become a
clergyman at Cambridge
University (1827-1831)
After Cambridge,
Charles was
recommended for a
surveying trip on the
HMS Beagle.
He sailed aboard the
Beagle for 5 years,
working as a naturalist.
The Beagle sailed around the world.
This voyage lasted from 1831 to 1836.
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.
James Hutton
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.
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
made these observations
about humans:
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.
Darwin published his ideas in the book
On The Origin of Species by Means of
Natural Selection, or the Preservation of
Favoured Races in the Struggle for Life
Five basic components of
1. All species have genetic variation.
Every species is different,
even within itself.
Look around you…are
you all the same?
2. Organisms produce more offspring than can
survive. Many that survive do not produce
offspring.
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. Decent 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.
variation exists
An the
organism
doesfirst.
not change
because of need or desire to
the environment changes.
survive. The organism either
already
hasmay
thegive
variation
that
a variation
an advantage
toenables
survive environmental
change.
it to survive
or it dies.
Species
• A group of organisms that are closely
related and naturally mate to produce
fertile offspring.
Speciation
• The process by which new species form.
– Separate populations of a single species often
live in different environments
– In each environment, natural selection acts on
populations
– If environments different enough, separate
populations can become dissimilar
Different genes favor survival in different habitats
– As two groups become more different over
time, they may be unable to breed= new
species
Speciation
• What keeps new species separate?
• Reproductive Isolation- two populations
of the same species do not mate with each
other- can be due to…
– Geographic isolation
– Temporal isolation
– Physical differences
– Hybrid sterility
Ex. Garter snakes- some live in water, some are
terrestrial
Ex. Courtship behaviors
Ex. Eastern spotted skunk (late winter) and
western spotted skunk (late summer)
Ex. Differences in blossoms attract different
pollinators
Ex. Gametes of red and purple sea urchins are
unable to fuse
Ex. Hybrid salamanders do not complete
development, those that do develop are frail
Ex. Donkey + horse = mule- sterile
Ex. Even if the first generation of hybrids is viable
and robust, subsequent generations are
weak or sterile- rice
As the environment changes, organisms must
have variations that allow them to survive
(adapt) to those changes or die
If an entire population of
a species cannot adapt,
that species becomes
extinct.
Many scientists
say that the
earth is
currently
experiencing a
mass extinction
crisis.
It is estimated that 1/5 or more of the world’s
species will become extinct if the rainforests
are destroyed.
If we are in a period of mass extinction . . .
What animals will your grandchildren be able
to see in the wild?
Visit the World
Wildlife Fund website
for more information
on endangered
species.
Photos by MartinHarvey
World Wildlife
Fund International