Download Natural Selection

Which lion
is more
fit?
Warm Up
Describe what is happening in the picture above.
How is the population of mice different in figure 3 than in figure 1?
Engage
• What are the advantages of these animals’
camouflage?
• What are their chances of survival in different
environments? Explain.
What is Evolution?
• Evolution means to change over time.
• This is the process by which modern
organisms have descended from ancient
organisms.
Darwin’s Theory of Evolution by
Natural Selection
• Charles Darwin was a
naturalist who observed
many species.
• He is famous for his trips
to the Galapagos Islands,
his observations of the
finches (and other
animals) and the book he
wrote: “On The Origin of
Species”
Darwin’s Theory of Evolution by
Natural Selection
• He collected and studied fossils (preserved
remains of ancient organisms) and
compared them to living animals
• By looking at the
diagram above, on
which island does
vegetation grow close
to the ground?
• On which island does
it grow higher on
trees?
Fitness
• The ability of an organism to
survive and reproduce
• An organism with an adaptation
is more fit to survive in its
environment, and will reproduce.
Its DNA (with the codes for the
adaptation) gets passed on to its
offspring.
• Fit offspring then survive and
reproduce and even more
offspring are “born” that have the
adaptation.
• Over generations, the DNA in the
whole population changes, so that
all the population has the
adaptation that makes the
population fit for its environment.
“Survival of the Fittest”
• Faster, stronger, good hunter,
better camouflaged
Natural Selection=Survival of
the Fittest
1. Variation exists among individuals in a
species.
2. Individuals of species compete for
resources (food and space).
3. Some competition leads to the death of
some individuals while others survive.
4. Individuals that have beneficial variations
are more likely to survive and reproduce.
Variation
Variation exists within
the gene pool of every
population. This
variation is the result
of random gene
mutations and
translation errors.
Nature basically “selects” certain individuals to
be successful and reproduce and over time the
population changes due to this selection.
Types of Selection
Disruptive Selection
• Describes changes in population genetics
in which extreme values for a trait are
favored over medium values.
• The variance of the trait increases and the
population is divided into 2 distinct groups.
Disruptive Selection
When individuals at the upper and lower ends of the
curve have higher fitness than individuals near the
middle, disruptive selection takes place.
Copyright Pearson Prentice Hall
Stabilizing Selection
• Describes changes in population genetics
in which extreme phenotypes for a trait are
not favored over medium values.
• Extreme phenotypes give individuals a
disadvantage.
Stabilizing Selection
When individuals near the center of the curve have
higher fitness than individuals at either end of the
curve, stabilizing selection takes place.
Copyright Pearson Prentice Hall
Directional Selection
When individuals at one end of the curve have higher
fitness than individuals in the middle or at the other
end, directional selection takes place.
Copyright Pearson Prentice Hall
Results of Natural Selection
1. Adaptation-any inherited characteristic
that increases an organisms chances of
survival.
2. Speciation- formation of a new species
3. Extinction- disappearance of a species
from all parts of its geographical range.
• Adaptation – any inherited characteristic
that increases an organism’s chance of
survival. (Remember the source of any
new trait is a mutation.)
• Adaptations make an organism better
suited to the environment. So in the
struggle for survival, organisms with
adaptations suited to the environment will
be more likely to survive and reproduce.
Adaptations
The favorable variations are called
Adaptations. They are key for survival.
These peppered
moths are a good
example of industrial
melanism.
Peppered moth: Evolution in action
Year % dark % light
1848
5
95
1895
98
2
1995
19
81
clean air, light-colored bark
pollution, dark-colored bark
Clean Air Act, light-colored bark
industrial melanism
Adaptations
• This frogfish is perfectly
adapted to its
environment.
• The porcupine has
adapted sharp quills
that make it difficult for
other animals to eat it.
Speciation-creates a new species.
Speciation will occur when the gene pools of two
populations become separated.
Behavioral Isolation:
Two or more populations are
capable of interbreeding, but
won’t because of courtship
rituals.
Temporal Isolation:
Two or more species
reproduce at different
times.
_____________ Isolation
• Ex. meadowlarks using 2
different songs to attract mates
________________ Isolation
• Ex. orchids that pollinates once a
year
Speciation
Geographic Isolation:
Two or more
populations are
separated by
geographical barriers
such as mountains or
rivers.
Extinction
Simply put, those
who are not well
adapted to their
environment do not
survive and
reproduce. This
means they
eventually become
extinct.
The dinosaurs could not
adapt well to the sudden
change in their environment,
so they became extinct.
Extinction!
How bad would it be
to lose the polar bear
forever?
• Global warming has
caused glaciers to melt.
• Polar bears must swim
further distances between
each iceflow.
• As the distances increase,
more polar bears are
drowning.
Survival of the Fittest!?
As the polar bears
lose their habitat,
some are crossing into
grizzly bear territory.
As they try to adapt to
the grizzly bear
habitat, they are also
beginning to breed
with them.
Natural Selection Summary Points
for Reproductive Success
1. Inherited variation – there are genetic
variations (differences) between individuals
of a population
• The more genetic diversity, the more
variations of alleles that are suited for the
environment. The more offspring will
survive and reproduce.
• The population will then continue.
Natural Selection Summary Points
for Reproductive Success
2. Overproduction of offspring – there are
more offspring are produced than can
survive
3. Struggle for existence – there is
competition for survival among the
members of the population
Genetic Variation
(Inherited)
• variation in alleles of genes that
occurs both within and among
populations
Peppered moth
(Example of Genetic Variation)
• Why did the population change?
– early 1800s = pre-industrial England
• low pollution
• lichen on trees = light colored bark
– late 1800s = industrial
• factories = soot coated trees
• killed lichen = dark colored bark
– mid 1900s = pollution controls
• clean air laws
• return of lichen = light colored
bark
• Peppered Moth
– 2 types: dark vs. light
Peppered moth