Download Darwin and Natural Selection 2014

Darwin’s Observations and
Theory of Evolution
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.
Remember, Evolution Is
• Cumulative change in
heritable characteristics of
a population
• Change in genetic
frequencies over time
• Change with inheritance
From http://evolution.berkeley.edu/evosite/evo101/IIntro.shtml
The Galapagos Islands
• Volcanic islands off the
coast of South America,
500 miles west of Ecuador
in the Pacific Ocean,
directly on the equator
• Island species varied
from mainland species &
from island-to-island
species
• Each island had long or
short neck tortoises
The Galapagos Islands
• Finches on the islands
resembled a mainland finch
• More types of finches
appeared on the islands
where the available food was
different (seeds, nuts, berries,
insects…)
• Finches had different types
of beaks adapted to their
type of food gathering
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’s Observations
• Patterns of Diversity
were shown
• Unique Adaptations
in organisms
• Species Not Evenly
Distributed
• Australia,
Kangaroos, but No
Rabbits
• S. America, Llamas
Darwin’s Observations
• Patterns in the species
suggested that the
species had changed
over time and had given
rise to new and
different species.
• Both Living Organisms
& Fossils collected
• Fossils included:
•Trilobites
•Giant Ground Sloth
of South America
This species NO longer
existed.
What had happened to
them?
Darwin concluded:
Each species has descended, with changes,
from other species over time.
Darwin called this…
Descent With Modifications
or
the slow, gradual change in
a species population over
time
Common Descent with Modification
• Darwin proposed
that organisms
descended from
common ancestors
• Idea that organisms
change with time,
diverging from a
common form
• Caused evolution of
new species
Descent With Modification
• Takes Place Over Long Periods of
Time
• Natural Selection Can Be Observed As
Changes In
– Body Structures
– Ecological Niches
– Habitats
Descent With Modification
• Species Today Look Different From
Their Ancestors
• Each Living Species Has
– Descended
– With Changes
– From Other Species
– Over Time
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
Natural Selection
• Driving force for
evolution
• During the struggle
for resources,
strongest survive &
reproduce
• Idea that at least some
of the differences
between individuals,
which impact their
survival and fertility,
are inheritable
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
The result?
• Organisms with favorable traits are more
fit, thus they leave behind more offspring
than those who are less fit.
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.
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.
The result?
• These favorable traits persist in the population
and will become more frequent.
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, or dies out.
In sum…
• Differential reproductive success
leads to change in favorable traits
among generations
In sum…
• Natural selection occurs as a result
of interactions between the
environment and the genetic
variability demonstrated in living
organisms.
• It is the result of differential
reproductive success.
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