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TOPIC 5.2 – NATURAL SELECTION
5.2 – A – Natural Selection & Variation
Understandings
U1: Natural selection can only occur if there is variation among members of the same species.
Key Terms
Natural Selection
IB BIO – 5.2 3
http://clarkscience8.weebly.com/uploads/2/6/3/7/2637711/5525251.gif?952
Natural selection describes how
organisms better adapted to their
environment tend to survive and
produce more offspring.
It can change the traits of a
population over time.
In the example to the left:
• Birds prefer to eat green
beetles
• Green beetles get eaten more
often
• Over time, brown beetles with
thrive and reproduce.
Understandings
U1: Natural selection can only occur if there is variation among members of the same species.
Key Terms
Natural Selection
Variation
IB BIO – 5.2 4
http://scienceillustrated.com.au/blog/wp-content/uploads/2012/05/finches.gif
In order for natural selection to occur, Darwin concluded that there
must be variation amongst the members of a population.
If all members were identical,
then some individuals would
not be favored more than
others.
Genetic variation can result
from several processes:
• Mutation
• Meiosis
• Sexual Reproduction
Understandings
U2: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Key Terms
Mutation
IB BIO – 5.2 5
http://www.yourgenome.org/sites/default/files/illustrations/diagram/dna_mutations_deletion_yourgenome.png
Mutations are changes in an organism’s DNA sequence. New alleles
are created, which can change the traits of a species member.
Understandings
U2: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Key Terms
Mutation
IB BIO – 5.2 6
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Mutation_and_selection_diagram.svg
Mutations are changes in an organism’s DNA sequence. New alleles
are created, which can change the traits of a species member.
Members with favorable traits are more
likely to survive and pass them on
Understandings
U2: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Key Terms
Meiosis
IB BIO – 5.2 7
https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Meiosis_Overview.svg
Meiosis contributes to variation by producing new combinations of
alleles. Because of crossing over and independent orientation, no
two gametes produced are likely to be the same.
Understandings
U2: Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
Key Terms
Sexual Reproduction
IB BIO – 5.2 8During sexual reproduction,
male and female gametes fuse
to form a diploid cell.
As a result of this fusion, the
offspring contains alleles from
two individuals.
This allows mutations from
different members to come
together, creating new
combinations of alleles.
http://projects.cbe.ab.ca/diefenbaker/biology/bio%20website%20final/notes/molecular_genetics/Image37.gif
VID
EO
SIB BIO – 5.2 9• Stated Clearly: What is Natural Selection?
https://www.youtube.com/watch?v=0SCjhI86grU
• MinutePhysics: Evolution vs. Natural Selection
https://www.youtube.com/watch?v=S1t5_iGN0xE
• California Academy of Sciences: Genetic Variation, Gene
Flow and New Species
https://www.youtube.com/watch?v=11iYk0Yrx3g
REVIE
WIB BIO – 5.2 101. Define natural selection.
2. Outline natural selection as the driving force for the
process of evolution.
3. Outline the importance of variation in natural
selection.
4. List three sources of variation.
5.2 – B – Adaptation & Competition
Understandings
U3: Adaptations are characteristics that make an individual suited to its environment and way of life.
Key Terms
Adaptations
IB BIO – 5.2 12
http://www.toonts.com/wp-content/uploads/2015/12/bear1-6.jpg
Adaptations are traits that
make an individual better
suited to its environment or
lifestyle.
There is often a correlation
between structural adaptations
and their functions.
For example, polar bears have:
• White fur for camouflage,
• Large paws for walking in
snow,
• Thick blubber for insulation
Understandings
U3: Adaptations are characteristics that make an individual suited to its environment and way of life.
Key Terms
Adaptations
IB BIO – 5.2 13
http://www.toonts.com/wp-content/uploads/2015/12/bear1-6.jpg
Plants also have many
structural adaptations that
help them thrive in various
environments.
For example:
• Flowers attract pollinators,
which promotes variation
• Wide leaves provide more
surface area for
photosynthesis
• Some plants have a thick
cuticles which allows them
to survive drought
conditions
Understandings
U3: Adaptations are characteristics that make an individual suited to its environment and way of life.
Key Terms
Adaptations
IB BIO – 5.2 14
http://www.toonts.com/wp-content/uploads/2015/12/bear1-6.jpg
Adaptations develop over many generations and can be passed on
from parent to offspring. However, traits that develop or are
obtained in a single lifetime cannot be passed to offspring.
Understandings
U4: Species tend to produce more offspring than the environment can support.
Key Terms
IB BIO – 5.2 15
https://upload.wikimedia.org/wikipedia/commons/5/56/Anemone_Fish_Eggs.jpg
Species vary in the number of offspring they can produce. It is
often related to their size, lifespan and time needed for maturation.
Some species can produce
hundreds of offspring at once
while others only a few in their
lifetime.
Overall, though, there is a
tendency for species to produce
more offspring than the
environment can support.
This results in competition for
survival.
Understandings
U5: Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
Key Terms
Competition
IB BIO – 5.2 16In the struggle for existence,
members of species compete with
each other for:
• Territory
• Mates
• Food
Those better adapted for obtaining
these tend to survive and produce
more offspring.
Those less adapted tend to die off
or produce fewer offspring.
https://upload.wikimedia.org/wikipedia/commons/9/95/Fighting_Flamingos_(6911914548).jpg
Understandings
U6: Individuals that reproduce pass on characteristics to their offspring.
Key Terms
IB BIO – 5.2 17
http://www.toonts.com/wp-content/uploads/2015/12/zebra_in_the_water_images_background.jpg
Species members that reproduce can pass their traits to their
offspring. However, this does not include traits that they obtained
during their lifetime. So, acquired traits are not significant in the
process of evolution.
Understandings
U7: Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
IB BIO – 5.2 18Over time, the frequency of beneficial alleles increases in a
population as the better-adapted members reproduce. As a result,
the characteristics of the population will gradually change.
https://userscontent2.emaze.com/images/fb405ce8-6b20-4dc2-b042-21e3b612005e/f7899f42-a689-4c48-8b1e-2dadd675a567.png
VID
EO
SIB BIO – 5.2 19• BBC Teach: Adaptation in Animals
https://www.youtube.com/watch?v=anRp7FQ9CKY
• SciShow: Starfish Eyes, Octopus Blood and Human
Evolution in Action
https://www.youtube.com/watch?v=pxmmF2bWy9M
• TED-Ed: Myths and Misconceptions about Evolution
https://www.youtube.com/watch?v=mZt1Gn0R22Q
• Dnews: Can We Evolve Without Competition?
https://www.youtube.com/watch?v=jHQcKUJGZSM
REVIE
WIB BIO – 5.2 201. Define adaptation.
2. Outline the role of adaptations in determining
which members of a species reproduce.
3. Describe the effect of natural selection on the
characteristics of a population over time.
5.2 – C – Evolution Examples
Applications
A1: Changes in beaks of finches on Daphne Major.
Key Terms
Daphne Major
IB BIO – 5.2 22Daphne major is a volcanic island
located near the Galapagos
Islands. There has been much
research into the finches that
reside there.
It has been shown that beak
characteristics and diets are closely
related. When one changes, so
does the other.
This is an example of natural
selection occurring in short periods
of time.
https://static01.nyt.com/images/2014/08/05/science/05JPESSA1/05JPESSA1-master1050.jpg
Applications
A1: Changes in beaks of finches on Daphne Major.
Key Terms
Medium Ground Finch
IB BIO – 5.2 23On the island, the medium ground finch, G. fortis, eats small seeds.
In the absence of competition for these seeds, G. fortis members
have smaller body sizes and beaks.
https://coreybradshaw.files.wordpress.com/2011/02/figure1.jpg
Applications
A1: Changes in beaks of finches on Daphne Major.
Key Terms
Medium Ground Finch
IB BIO – 5.2 24In 1977, a drought caused a
shortage of small seeds, forcing
G. fortis to feed on larger ones
instead.
Most of the population died, but
those with larger beaks were
able to feed on the new food
source and survive.
This resulted in a rapid change
of the average beak size in the
population.
https://coreybradshaw.files.wordpress.com/2011/02/figure1.jpg
Applications
A1: Changes in beaks of finches on Daphne Major.
Key Terms
Medium Ground Finch
IB BIO – 5.2 25
http://www.proprofs.com/quiz-school/user_upload/ckeditor/4_3_finch1a.png
In 1982-83, severe El Nino events
caused 8 months of heavy rain. This
increased the supply of small seeds.
G. fortis with smaller beaks
reproduced quickly, bringing down the
average population beak size.
During subsequent dry years, similar
changes in beak size were observed.
Applications
A1: Changes in beaks of finches on Daphne Major.
Key Terms
Medium Ground Finch
IB BIO – 5.2 26This immediate response of beak size to environmental conditions
illustrates the effect of natural selection on populations. There are
very few examples where this can be directly observed.
http://4.bp.blogspot.com/-Eq3KvWytexA/UvhfqzFu8hI/AAAAAAAAAo8/L_4pDRAJ4EY/s1600/large&small+brighter.jpghttp://4.bp.blogspot.com/-Eq3KvWytexA/UvhfqzFu8hI/AAAAAAAAAo8/L_4pDRAJ4EY/s1600/large&small+brighter.jpg
Applications
A2: Evolution of antibiotic resistance in bacteria.
Key Terms
Antibiotics
IB BIO – 5.2 27
https://upload.wikimedia.org/wikipedia/commons/2/20/Antibiotic_sensitvity_and_resistance.JPG
Antibiotics are chemicals that are used to kill or inhibit the growth
of bacteria. They are used to control infection by pathogenic cells.
However, bacteria are able to respond to changes in their
environment and are capable of evolving resistance to antibiotics.
Applications
A2: Evolution of antibiotic resistance in bacteria.
Key Terms
Antibiotics
IB BIO – 5.2 28
https://upload.wikimedia.org/wikipedia/commons/2/20/Antibiotic_sensitvity_and_resistance.JPG
Antibiotics affect bacteria by targeting processes necessary for life.
These targets can include the synthesis of:
DNA Cell Wall Proteins
Applications
A2: Evolution of antibiotic resistance in bacteria.
Key Terms
Antibiotic Resistance
IB BIO – 5.2 29
https://www.thermofisher.com/blog/behindthebench/wp-content/uploads/sites/9/2016/04/Mechanism-of-antibiotic-resistance-1.jpg
Bacteria can develop antibiotic resistance when a naturally
occurring variation enables them to nullify the drug’s effects. Some
possibilities are shown here.
Applications
A2: Evolution of antibiotic resistance in bacteria.
Key Terms
Antibiotic Resistance
IB BIO – 5.2 30
http://www.cdc.gov/media/dpk/2013/images/untreatable/img1.jpg
Developing Resistance
1. Antibiotics can be used to
treat bacterial infections.
2. When the bacteria are
exposed to antibiotics, most
are killed.
However, genetic variation
results in some cells being
naturally resistant.
3. Resistant cells begin to
replicate and take over the
population.
Applications
A2: Evolution of antibiotic resistance in bacteria.
Key Terms
Antibiotic Resistance
IB BIO – 5.2 31Developing Resistance
4. The new bacteria population is resistant to the antiobitic that was
used. In some cases, these cells can also transfer the property to
other bacteria through conjugation.
http://www.reactgroup.org/toolbox/wp-content/uploads/2015/02/natural-selection_140211.png
Applications
A2: Evolution of antibiotic resistance in bacteria.
Key Terms
Antibiotic Resistance
IB BIO – 5.2 32Similarly to the finches in Daphne Major, this rapid change in a
population characteristic illustrates the effect of natural selection.
Changes in the environment result in different adaptations thriving.
http://www.reactgroup.org/toolbox/wp-content/uploads/2015/02/natural-selection_140211.png
VID
EO
SIB BIO – 5.2 33• Natural Selection: Finches of Daphne Major
https://www.youtube.com/watch?v=OOeb7f9NTUo
• Science News: Watch Antibiotic Resistance Evolve
https://www.youtube.com/watch?v=yybsSqcB7mE
• TED-Ed: What Causes Antibiotic Resistance
https://www.youtube.com/watch?v=znnp-Ivj2ek
• Kurzgesagt: The Antibiotic Apocalypse Explained
https://www.youtube.com/watch?v=xZbcwi7SfZE
REVIE
WIB BIO – 5.2 341. Outline the changes of finch beak size on Daphne
Major in response to varying food sources.
2. Outline the development of antiobitic resistance in
bacteria populations.
