Stnd: 8a
C-Notes: Natural Selection
2/26/2014
(The Mechanism of Evolution)
Objective:
SWBAT identify how
variations of traits play a
role in how Natural
Selection determines the
survival of organisms.
Who was Charles
Darwin?
Father of
Evolution
• Proposed a way HOW evolution works
• He traveled on a British Ship, called HMS
Beagle for 5 years to the Galapagos Islands
(1831) and collected a lot of evidence of the
natural world (animals and their diversity).
• He studied Finches (birds) on their many
different beak shapes and sizes.
• Wrote a book “The Origin of Species”
biblauragraphy.files.wordpress.com
VOYAGE OF THE HMS BEAGLE

Invited to travel around the world


1831-1836 (22 years old!)
makes many observations of nature
 main
mission of the Beagle was to
chart South American coastline
Robert Fitzroy
HMS Beagle
mun.ca
VOYAGE OF THE HMS BEAGLE

Stopped in Galapagos Islands

500 miles off coast of Ecuador
www.frontierdiving.com
Field Research on Galapagos Islands…
GoogleEarth: Isla Floreana, Ecuador
3 min video
http://video.nationalgeographic.com/video/player/places/parks-and-natureplaces/coasts-and-islands/ecuador_galapagos.html
Galapagos Research Home Video
www.thesecondevolution.com
DARWIN FOUND…CLUES IN THE FOSSILS
blogs.technet.com
Darwin found:
Evidence that creatures
have changed over time
foxnews.com
Present day Armadillos
Darwin asked:
Ancient Armadillos
weighing 200 lbs!
Why should extinct
armadillos & modern
armadillos be found on the
same continent?
Darwin found:
Different shells on tortoises on different islands
Darwin asked:
scrapetv.com
Is there a relationship
between the environment &
what an animal
looks like?
DARWIN’S FINCHES
blogs.discovermagazine.com
Why would the
finches have
developed different
beaks?
 variations


differences in beaks in the original flock
adaptations to foods available on islands
 natural

selection for most fit
over many generations, the finches were
selected for specific beaks & behaviors
 offspring
inherit successful
traits

accumulation of winning traits:
both beaks & behaviors
 separate
www.pigeon.psy.tufts.edu
in beaks
into different species
HAWAIIAN FINCHES
Like Darwin’s
Galapagoes finches…
Evolution of different
beaks based on
different foods they eat.
www.fnal.gov
Common ancestral finch
ncse.com
EARLIER IDEAS ON EVOLUTION

LaMarck

evolution by acquired traits
creatures developed traits
during their lifetime
 give those traits to their
offspring


fundivision.net
example

in reaching higher
leaves giraffes stretch their
necks & give the acquired
longer neck to offspring
 NOT
ACCEPTED as valid
wildlife-pictures-online.com..
DARWIN’S VIEW OF EVOLUTION

Darwin
giraffes that already
have long necks
survive better
 leave more offspring
who inherit their long
necks

variation
selection
& survival
reproduction &
inheritance of more
fit traits
What is Artificial
Selection?
(Selective
Breeding)
people have chosen
variations in animals
and plants to
emphasize and
produced plants and
animals that are
beneficial to humans
• Adaptations are traits that
enhance the survival and
reproductive success.
• All species have genetic
variation
What is Natural
Selection?
– traits that help individuals
survive
•
•
•
•
www.solarnavigator.net
farm3.static.flickr.com
survive predators
survive disease
compete for food
compete for territory
– traits that help individuals
reproduce
flickr.com
www.alaskan
adventuretou
rs.com
• attracting a mate
• compete for nesting sites
• successfully raise young
mesh.biology.
Adaptations
3.bp.blogspot.com
What are the Main
Points of Darwin’s
Theory on Natural
Selection?
1. Over production.
Most organisms produce
more offspring than can
survive.
2. Competition.
Organisms compete for
food and resources.
3. Variation.
There is variation among
individuals of a species.
4. Adaptation.
Individuals with traits best
suited to the environment
will survive.
Survival & Reproduction of the Fittest
How does that work?
Variation
Over-Production & Competition
Adaptation
Natural Selection
Nature selects the ones that “fit” the environment
better … survive & reproduce
Why is
Evolution by
Natural
Selection so
strongly
associated
with Darwin?
He developed the Theory of Evolution by Natural
Selection “Survival of the Fittest”
• He believed that all Variation exist first ….then
Evolution
–
Individual organisms differ genetically; their
variations are passed on and inherited through
their genes
How does
Variation
play a role
in Natural
Selection?
www.dailyyonder.com
Genetic Variation is a key to Natural Selection
1. Populations are a mix of different individuals
2. This variation is caused by recombining genes
during meiosis
3. Variation is the result of ….
– Sexual reproduction: how certain genes are passed
on due to meiosis. (Meiosis- Crossing over)
– Mutations: random changes in a DNA sequence that
could have a positive, negative or no effect on an
organism’s fitness.
– Migration: new individuals join a population and
bring in new genes. (genes can move into or out of a
population by migration)
www.wideworldofhorses.com
www2.beverlyajackson.com
Survival & Reproduction of the fittest
msnbcmedia.msn.com
firemice.wordpress.com
strongest…
not
not the
the
biggest…
fastest…
bravest…
…IT
IS the
FITTEST!
www.arktimes.com
pixdaus.com
www.uwyo.edu
Adaptations
the traits that help an organism FIT the
environment better to
survive & reproduce
Evolution explains Unity & Diversity
• Only evolution explains both
– unity of life
• similarities between all living things
– diversity of life
• wide variety of different creatures on Earth
valeofglamorgan.gov.uk
Unity of Life on Earth
Diversity of Life on Earth
CELLS
DNA
A little fun with camouflage…
conservationreport.com
Insects are experts at camouflage!
Search for more on the internet!
Bill Nye Evolution: First 24:00 minutes.
http://player.discoveryeducation.com/index.cfm?guidAssetId=AFA8F02E-A881-468E-BA47www.dpughphoto.com
designboom.com
EBDDFB3A6264&blnFromSearch=1&productcode=US
bisbeemedia.com
What are the
types of Natural
Selection?
There are 3 types:
• Directional Selection
• Stabilizing Selection
• Disruptive Selection
• In “directional selection,”
What is
Directional natural selection favors a
characteristic
on
the
Selection?
extreme of the phenotypic
variation.
–directional selection occurs
in response to a change in
the environment that gives a
competitive advantage to a
particular phenotype
Examples of Directional Selection
Bacteria developing resistance to antibiotics
The beak sizes of ground finches on Daphne
Island
Directional Selection
• Imagine that the environment changes and the
supply of small and medium-sized seeds runs low.
Which beak size will be favored?
• Those birds with the larger beak will be able to
survive on the large seeds!
• In “directional selection,” natural selection favors
a characteristic on the extreme of the
phenotypic variation.
• How does this affect variation?
• Variation of beak size shifts in ONE direction.
Directional Selection
Original
distribution of
beak sizes
How
distribution of
beak sizes
change due to
a changing
environment
• In “stabilizing selection,”
What is
Stabilizing natural selection favors
characteristics
near
the
Selection?
middle (average) of the
phenotypic distribution.
–Occurs when the
environment is stable for
long periods
• Example height variation in
humans
Stabilizing Selection
• Imagine that the environment changes and the supply
of small and large-sized seeds runs low. Which beak
size will be favored now?
• Those birds with the medium beak will be able to
survive on the medium seeds!
• In “stabilizing selection,” natural selection favors
characteristics near the middle of the phenotypic
distribution.
• How does this affect variation?
• Variation of beak size shifts in towards the middle,
decreasing genetic variation at the extremes.
Stabilizing Selection
What is
Disruptive
Selection?
• In “disruptive selection,”
natural selection selects
against the average and
favors characteristics at
BOTH extremes of the
phenotypic variation.
–Example: variations in
height in weeds of lawns
and in the wild.
Disruptive Selection
Original
distribution of
beak sizes
How
distribution of
beak sizes
change due to
a changing
environment
African Seed Crackers
Birds feed on two
types of seeds one
large, one small.
Birds with average
size bills can’t eat
either type efficiently
And so aren’t common
in the population
Disruptive Selection
• Imagine that the environment changes and only
the supply of medium-sized seeds runs low. Which
beak size will be favored now?
• Those birds with BOTH the smaller and larger
beak will be able to survive!
• In “disruptive selection,” natural selection favors
characteristics at BOTH extremes of the
phenotypic variation.
• How does this affect variation?
• Variation shifts to favor two subgroups of birds
specialized in eating different sized seeds.
Natural Selection on Polygenic
Traits
Natural Selection in a Nutshell
Differences in phenotype leads to differences
in the success rate of organisms to reproduce.
Those phenotypes which are better suited to
their environment, have more reproductive
success
• Natural Selection acts on phenotype to change the
gene pool
Natural Selection
• all of the genes in a population are referred to as the
population’s gene pool
• Over time, the selection of phenotypes,
changes the frequency with which alleles occur in a
population’s gene pool
- the alleles for advantageous traits become
more common, while alleles for harmful
traits become less common
Evolution as Genetic Change
• Let’s imagine Darwin’s finches on the Galapagos
Islands as an example.
• There is slight variation in beak length among the
finches, ranging from…
-small beaks (for obtaining small seeds)
-medium beaks (for obtaining medium seeds)
-large beaks (for harder, thick-shelled seeds)