Transcript natural selection

Evolution
http://www.pbs.org/wgbh/evolution/educator
s/teachstuds/svideos.html
• Is evolution just a theory?
• Why is it so controversial?
• Fossils indicated that living
things have changed.
• Several scientists had ideas
to explain how.
Mechanisms of Evolution – Before Darwin
1) Lamarck
• Lamarck’s Theory of Inheritance of
Acquired Characteristics
– Organisms could change themselves in life
– Organisms gain traits they need
– Pass on these changes to offspring
EX: giraffe necks grow longer
because they stretch to reach
the leaves higher up.
Theory ultimately discarded
Lamarck
• Think about it...
-Can you make yourself any height you
want?
-If you lose an arm, will all your kids have
one less arm?
-If you are born with a birthmark, will all your
kids have it to?
2) Thomas Malthus
• Darwin was influenced by Thomas
Malthus
• He wrote:
“Populations grow as much as the
environment allows”
• So who is Darwin??????
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_2.html
3) Charles Darwin
• English scientist
• Developed his theory of “natural selection”
in the mid 1800’s
• Was a naturalist on the HMS Beagle
(traveled around the world, mostly the
southern hemisphere) for 5 years.
Voyage of the HMS Beagle
Competition
• Wallace in America
• Both naturalists came up with the idea
independently of the other
– Both published their findings in 1858
• “Logically, some organisms would be able
to survive better than others”
– Therefore, they would pass on their traits to
their offspring
Darwin’s Finches
• Good example of how evolution occurs
• Each Galapagos Island has its own unique
species of finch
• Each finch had a head and body well-adapted for
life on that island
• The finches were different species, but looked
similar
•Darwin realized that the finches
had a common ancestor
•He proposed that originally a few
seed-eating finches had flown to
the islands from mainland. Over
millions of years, the finches
adapted to the foods available on
each island – and evolved into
separate species.
In conclusion……
• NATURE had
selected which
finches were best fit
for that type of
environment.
Then Darwin made 2 deductions:
1. Since most offspring don’t survive, all
organisms must have to struggle for
survival. (Others are eaten, or die of
disease.)
2. The ones who survive and reproduce
will pass on their genes.
How Does Evolution Work ??
Natural Selection
Nature selects (NATURAL SELECTION)
those that are best adapted to survive.
“Survival of the Fittest”
Any adaptive advantage (a favorable trait)
that an organism has
is passed to offspring.
4 Keys to Natural Selection
1. All organisms produce more offspring
than can survive.
2. Some organisms in a species survive
and reproduce better than others.
3. Organisms in a species show wide
variation.
4. Variations are inherited and passed
on to the next generation.
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Mutations play big a role in
natural selection by creating
VARIATION.
Example:
The Rabbit Tale Maybe once upon a
time all rabbits had short
ears and managed OK.
Then one day a mutant with big ears
was born.
She was always the first to dive for cover.
Pretty soon, she had babies; some inherited
her big ears.
They all dived for cover as fast as their mom
– faster than the short earred rabbits.
Eventually, only the big earred rabbits are
left.
Example of evolution through
natural selection
Cockroaches
Over the centuries, as man and
cockroaches have shared homes,
cockroaches have become smaller and
flatter – easier access to hiding places.
(Large, fat ones more easily stomped.)
Another example - antibiotic
resistance by natural selection
• Someone gets sick
• Give them antibiotics
• 99% of the bacteria are killed; only the
antibiotic resistant mutants survive
• They thrive and flourish, person gets sick
again
• Bacteria cannot be killed by antibiotics
Artificial Selection
• Breeding for certain
traits
• Environment is very
easy – all organisms
survive
• Breeder for (selects)
the trait he or she
Wants in offspring
Ex – color, size
Review
• http://youtu.be/0SCjhI86grU
Evidence of Evolution
A.Fossils
B.Similarity of embryos
C.Homologous and analogous structure
D.Vestigial structures
E.Similarities in macromolecules
• http://www.pbs.org/wgbh/evolution/educat
ors/teachstuds/svideos.html
A)Fossils – tell us that organisms
that once lived on Earth are not
here any more.
• Fossils found closer to the surface are
YOUNGER than the fossils found below
• Fossils found in the same layer, indicate
that they existed at the same time
B) Embryos of all vertebrates
are similar – common ancestor
C) Homologous Structures – similar
structures with similar functions.
Suggest a common ancestor.
C) Analogous Structures
Structures in unrelated organisms that carry
out same functions.
Exs: -Lungs in mammals
and gills in fish
-Wings of insects and
wings of birds
D) Vestigial Structures
• Reduced or nonfunctional structures
• Examples: appendix, wisdom teeth, human tail
bone
• Interpretation: the vestigial structure was
functional in some ancestor of the modern
organism
• Snakes have pelvic bones; they are known to be
the descendants of four-legged reptiles.
• Vestigial features.The skeleton of a baleen
whale, a representative of the group of
mammals that contains the largest living
species, contains pelvic bones. These bones
resemble those of other mammals, but are only
weakly developed in the whale and have no
apparent function.
Appendix in human
E) Similarities in MacromoleculesProteins
• MORE differences in amino acid sequences of
distantly related species, LESS differences between
species that are more closely related.
Nucleic Acids (what is a nucleic acid???)
• MORE differences in DNA sequences b/t distant
relatives, LESS differences between species that are
more closely related.
DNA sequences
Animal
Human
Gorilla
Chimpanzee
Orangutan
Three pattern types of evolution
• 1) Coevolution
• 2) Convergent Evolution
• 3) Divergent Evolution
Coevolution
• When two species are in close association
and evolve together. Also when a species
evolves as a result of evolution in another
species.
• These organisms may depend exclusively
on each other & be highly specialized!
Convergent Evolution
• When un-related species becomes more
similar over time.
An example is a Dolphin (mammal) and
fish.
Divergent Evolution
• When related species become more
different over time.
• An example is breeding dogs
Divergent evolution is the result of:
1)artificial selection
2) adaptive radiation – where many species
evolve from one species
Label what type of evolution is
occuring
Convergent or Divergent??
Question: Convergent or
Divergent Evolution? Why?
Dolphins and Penguins
Answer: Convergent Evolution
Dolphins are mammals
Penguins are birds
Both have developed flippers to swim,
stream like bodies, blubber to keep warm in
water
Genetic Equilibrium
• Genetic Equilibrium is a balance of alleles
within a population
****Genetic equilibrium does not exist *****
Five Reasons Why Genetic Equilibrium
does not exist
1) Migration
2) Mutations
3) Genetic Drift
4) Non- Random Mating
5) Natural Selection
• 1) Migration – the movement into or out of
a population
- Immigration – the movement INTO a
population
- Emigration – the movement OUT a
population
- The genes will move also!
2) Mutations – the alteration in alleles, or genetic
information
- New traits will form, while harmful traits will
eventually be eliminated
- Creates VARIATION
3) Genetic Drift - Changes in a population that are
caused by change or random events.
EX: large volcano, fire, flood, disease
More effect on a small population more than large
population.
4) Non-random mating – leads to less
“selection” and all alleles would have an
equal chance of being passed on.
5) Natural Selection – where the fittest will
survive. The bad traits will be eliminated
from the population due to natural
selection.
Tempo of Evolution
• Gradualism is a process of evolution in which
the formation of new species occurs gradually
• Punctuated Equilibrium is a process in which
the formation of new species occurs rapidly
between periods of little or no change.
• Formation of new species is called Speciation
Types of Selections
Natural Selection can alter gene
(trait) frequencies of a
population in three ways:
1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
1) Stabilizing Selection
• Most common form
• Nature favors the average trait
• Selection against the two extremes
Ex. Babies born with
low and high
birthweights have a
lower chance for
survivial than
average
Low
Average
High
2) Directional Selection
• Nature favors one extreme
Ex. Peppered moth
-Dark Moth survived on
dark sooty background.
-When pollution became
lighter, nature favored
light colored moth.
Light
Medium
Dark
3) Disruptive Selection
• Nature favors both extremes
• Splits population into 2 groups
Ex. Galapagos
Finches
• Small Birds,
Small Seeds
• Large Birds,
Large Seeds.
Small
Average
Large
• Average Bird
must compete
with both