1. NATURAL SELECTION Topic 5.2 IB Biology Miss Werba
The diversity of life has evolved and continues to evolve by natural selection.
Topic 5.2
IB Biology
Miss Werba

2. TOPIC 5 – EVOLUTION & BIODIVERSITY
5.1
EVIDENCE FOR EVOLUTION
5.2
NATURAL SELECTION
4.3
CLASSIFICATION & BIODIVERSITY
4.4
CLADISTICS
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3. THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 A.1 A.2 Statement Guidance
Natural selection can only occur if there is variation among members of the same species.
U.2
Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
U.3
Adaptations are characteristics that make an individual suited to its environment and way of life.
U.4
Species tend to produce more offspring than the environment can support.
U.5
Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
U.6
Individuals that reproduce pass on characteristics to their offspring
U.7
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.
A.1
Changes in beaks of finches on Daphne Major.
A.2
Evolution of antibiotic resistance in bacteria.
NOS
2.1
Use theories to explain natural phenomena—the theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria.
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4. EVOLUTION
5.1 - U.1
The cumulative change in the heritable characteristics of a population.
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5. NATURAL SELECTION
U.4
Populations tend to produce more offspring than the environment can support
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6. Attracting, fertilising
NATURAL SELECTION
U.5
Populations tend to produce more offspring than the environment can support This causes a struggle for survival.
Disease
Avoiding, tolerating
Competition for food
Finding, catching
Competition for space
Shelter, nesting sites
Predation
Catching, avoiding
Competition for mates
Attracting, fertilising
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7. There is VARIATION between members of a species.
NATURAL SELECTION
U.1
There is VARIATION between members of a species.
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8. NATURAL SELECTION
U.2
There is variation between members of a species. Resulting from…
Random mutation
Sexual reproduction
DNA replication
Viral infection
Meiosis
Random fertilisation
Crossing over & recombination in Prophase I
Random assortment of chromosomes in Metaphase I
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9. ADAPTATIONS
U.3
Adaptations are characteristics that make an individual suited to its environment and way of life.
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10. ADAPTATIONS Variations that give an advantage are selected for:
U.3
U.7
Variations that give an advantage are selected for:
The individual which can compete best in the struggle for survival will survive long enough to reproduce – and pass on the trait.
Frequency of these genes will increase and over time, the population will evolve.
Variations that give a disadvantage are selected against:
The individual is less suited to the environment, making it more difficult for them to survive. The individual is less likely to pass on the trait.
Frequency of these genes will decrease.
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11. NATURAL SELECTION Overproduction of offspring OR environmental change
Variation exists in a population
Struggle for survival (due to selection pressures)
Advantageous variations are selected for
Survive to reproduce and pass on genes
Gene frequency increases and adaptation becomes more common in population
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12. REMINDER:
U.6
Only changes in the heritable characteristics of a population can be passed on.
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13. EXAMPLES OF EVOLUTION
5.1 – A.1
A.2
Some species have a short generation time and rapid evolutionary changes can be directly observed.
Most species have a longer generation time and the evolutionary changes are gradual – so there is only indirect evidence for evolution.
Examples of evolution:
Melanism in the peppered moth
Antibiotic resistant bacteria
Darwin’s Finches
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14. ANTIBIOTIC RESISTANCE
NOS.2.1
Use theories to explain natural phenomena
The theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria.
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15. ANTIBIOTIC RESISTANT BACTERIA
Most individuals in a bacterial colony are genetically identical.
Mutations give rise to variations.
Some of these variations will result in resistance to certain antibiotics.
The resistant strain will survive.
Resistance genes are passed on and the resistant population grows.
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16. ANTIBIOTIC RESISTANT BACTERIA
eg. Staphyloccoccus aureus bacteria (Golden Staph) is usually treated with methycillin.
There is now a methycillin-resistant strain of Golden Staph (MRSA).
This is could cause big problems in the future, as bacteria could become resistant to multiple antibiotics.
Could create a colony of “super bugs”!
Worried? Go study pharmacology and research new antibiotics!!!!!
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17. DARWIN’S FINCHES
A.1
The Galapagos Islands are a group of 14 volcanic islands, off the coast of Ecuador.
Darwin visited the islands in 1835 on HMS Beagle.
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18. DARWIN’S FINCHES
A.1
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19. DARWIN’S FINCHES
A.1
The finches evolved from a single population of finches on the mainland.
Darwin believed that they might have been blown off course to their new habitats by a storm.
Each habitat had different selection pressures, so over time (millions of years!), the finches adapted to suit their own islands.
They eventually became separate species.
This is adaptive radiation.
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20. DARWIN’S FINCHES
A.1
Daphne Major
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21. DARWIN’S FINCHES
A.1
The Island of Daphne Major is a small, isolated island susceptible to climate changes.
There are two species of finches that have been studies for years on this island:
large ground finch
medium ground finch – original species on the island
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22. DARWIN’S FINCHES Large ground finch:
Beak is large, ideal for larger seeds.
A drought ( La Niña event) resulted in a shortage of smaller sized seeds
Consequence was a decrease in the number of finches
The mean beak size of surviving finches was high.
The mean beak size of successive generations remained high.
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23. DARWIN’S FINCHES Medium ground finch:
Beak is short and thick, ideal for small and medium seeds.
Heavy and frequent rains (1983 El Niño event) resulted in an abundance of smaller sized seeds
Consequence was a decrease in the mean beak size of successive generations.
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24. NATURAL SELECTION
Q1. Charles Darwin and Alfred Wallace proposed a theory of evolution in the late 1850s.
One observation made by Darwin that helped formulate the theory was
the environment remaining constant during the lifetime of an organism.
individual organisms losing a trait that was not in use.
individual organisms evolving in their own lifetime.
inherited variation existing within a population.
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25. NATURAL SELECTION
Q2.
Since the introduction of the poisonous cane toad to Australia in 1935, there has been an increase in the ratio of body length to head size in two species of snakes, the Red-bellied Black Snake and the Green Tree Snake.
A smaller headed snake cannot consume a large prey item, and so cannot swallow a large cane toad that has sufficient toxin to kill the snake.
The rapid evolution of body dimensions in the Red-bellied Black Snake and the Green Tree Snake most likely came about because
cane toad toxin reduced the head size of the snakes.
even small cane toads contain enough toxin to kill a long-bodied snake.
smaller headed snakes are better at catching cane toads than large headed snakes.
larger headed snakes were killed by the levels of toxin ingested when they ate a large cane toad.
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26. NATURAL SELECTION
Q3. Explain how natural selection can lead to evolution using antibiotic resistance in bacteria as an example. [9]
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