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5.4.1 Define Evolution

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5.4.1 Define Evolution

Evolution the process of cumulative change in the

heritable characteristics of a population. ‘heritable’ –

changes must be passed on genetically from one generation to the next

Implies that evolution doesn’t happen overnight ‘cumulative’

one change isn’t enough to have major impact on the species

‘population’ changes do not affect just one individual

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5.4.2 Outline Evidence for Evolution

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5.4.2 Outline Evidence for Evolution

Evidence for Evolution provided by:

1. Fossil Record

2. Selective Breeding of Domesticated Animals

3. Homologous Structures

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Fossil Record

Life 500 million years ago was very different from life today

Although planet Earth has had extensive oceans throughout, fish fossils have only been found in rocks 500 million years old or younger (less than 15% the history of life)

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Fossil Record cont’d

Although most of the top predators today are mammals (orca whales, lions, tigers & bears oh my!) ….

… none of them existed at the time of dinosaurs or before!

Most living organisms today have no identical form in the fossil record.

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Fossil record, conclusion

1 possible conclusion drawn from observing fossils is that :

Life on Earth is continually changing.

Most of the changes have been over huge

timescales (hundreds of thousands or millions of years)!!!

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Selective Breeding of Domesticated Animals (a.k.a. Artificial Selection) Selective breeding gives a good record of

recent changes in heritable characteristics Selective Breeding:

Choose males and females with most desirable genetic characteristics

Breed them to get offspring with those specific characteristics

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Selective Breeding cont’d

After selective breeding from dozens to hundreds of generations…

.. certain varieties of animals have unique combinations of characteristics that didn’t exist before.

This demonstrates that evolution is happening due to an accumulation of small changes over time.

Note: Artificial selection (selective breeding) is NOT the same as what happens in nature.

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Homologous Structures

Anatomy = Structure (Form) of the body Physiology = Function of the body

Homologous anatomical structures similar in form and function, yet found in seemingly dissimilar species

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Homologous Structures cont’d

Comparative anatomists noticed that different species have similar structures used for different functions (e.g. the pentadactyl limb of terrestrial

vertebrates).

These are called homologous structures

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The pentadactyl limb

Lizard © Chereka Keaton

Human

Frog

Bat© 2008 Paul Billiet ODWS

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Homologous Structures cont’d

Five-fingered (pentadactyl) limb found in animals such as humans, whales, and bats.

‘penta’ = five ‘dactyl’ = fingers

Although the shape and number of bones may vary, the general format is the same, even though the functions of the limbs may be very different

Homologous structures provide evidence that such organisms have common ancestors

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5.4.3 Populations tend to produce more offspring than the

environment can support

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Mechanism for Evolution

Natural Selection as the mechanism for evolution

Natural Selection accomplished by: Overproduction of offspring Presence of natural variation

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5.4.3 AHH!! TOO MANY BABIES!!Not enough well-fare for them all!!! Animals & plants produce far more offspring

than could ever survive. Plants often produce thousands more seeds

than necessary to propagate the species Fish and turtles lay thousands of eggs but only

a few survive to adulthood

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5.4.4 The consequence of potential overproduction of offspring is a struggle for survival

Too many offspring, not enough resources! Supply and demand

High demand for water, space, nutrients, sunlight, but limited supply.

Consequence? Competition for resources to stay alive.

“Ah Ah Ah Ah Stayin’ Alive, Stayin’ Alive!”

The STRUGGLE FOR SURVIVAL Ex: Struggling to survive the IB Programme…

<Sigh.>

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5.4.5 The members of a species show variation

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Example of No Variation within a species:

Organisms like bacteria reproduce by making a copy of their genetic info and then splitting into two.

Result: 2nd generation identical to the 1st Future generations identical or show very

little change Little chance for DNA modification

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5.4.5 The members of a species show variation (cont’d) Variation is closely related to how successful

an organism is Fish with slightly different shaped mouth may

feed better from coral reef than other fish unable to access

Plants producing different shaped flower may better attract insects for pollination

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Causes of variety

Mutations in DNA Sexual Reproduction promotes variation in

species

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5.4.6 Explain how sexual reproduction promotes variation in a species 2 ways genes are mixed in sexual

reproduction 1st – Meiosis (covered in Topic 4) 2nd – Fertilization (Topic 11)

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5.4.7 Explain how natural selection leads to evolution

Greater survival and reproductive success of individuals with favorable heritable variations (a.k.a. Natural Selection)

can LEAD to …

… change in the characteristics of a population (a.k.a. Evolution)

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Natural selection Evolution

Step 1: Overproduction of offspring Natural variation of offspring due to genetic

differences (body size, pigmentation, resistance to disease)

Useful variations allow individual better chance of survival (hiding from predators, fleeing danger, finding food)

Harmful variations make survival difficult (wrong camouflage, heavy bones for birds, having such a large body size when not enough food to survive)

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Natural selection Evolution

Step 2a: Individuals with genetic characteristics that are POORLY adapted for environment

Tend to be LESS successful at accessing resources

And thus have LESS chance of surviving to maturity

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Natural selection Evolution

Step 2b: Individuals with genetic characteristics that are WELL-adapted for environment

Tend to be MORE successful at accessing resources And thus have BETTER chance of surviving to

maturity Since they survive to adulthood, these successful

organisms have a better chance to reproduce and pass on their genetic characteristics to the next generation.

Over many generations, accumulation of changes in the heritable characteristics of a population results in evolution. THE GENE POOL HAS CHANGED!

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5.4.8 Explain 2 examples of evolution in response to environmental change

One example MUST be Antibiotic Resistance to Bacteria

Other examples could include: The changes in size and shape of the beaks of

Galapagos finches Pesticide resistance Industrial melanism Heavy-metal tolerance in plants

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Antibiotic Resistance in Bacteria

Biotic = Living Antibiotics: medications that kill or inhibit the

growth of bacteria Given to patients suffering from bacterial

infections Overuse of antibiotics can lead to the

production of resistant strains of bacteria

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Disclaimer: The following scenario is fictitious. Any similarity in names or the scenario to real events is purely coincidental.

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Antibiotics Resistance scenario

1. Yo’nique gets sick from bacterial infection (tuberculosis).

2. Dr. Wahoo gives her antibiotic to kill bacteria

3. Yo’nique gets “better” because most of the bacteria are destroyed. Awww yee-uah!

4. But WAIT!!! By a modification of its genetic makeup, one little bacterium is resistant to the antibiotic! OH NO!!!

5. The bacterium is not killed by the antibiotic! It later multiplies in the Yo’nique’s body to make her icky sicky again!!

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Antibiotics Resistance scenario (cont’d)

6. Yo’nique goes back to the hospital, and the same incompetent Dr. Wahoo gives her the SAME antibiotic!

7. Well, because the new strain of bacteria is resistant to that same antibiotic, she doesn’t get any better.

8. So Yo’nique has to go back to the hospital, and Dr. Wahoo realizes his mistake. Hoping Yo’nique won’t realize it too and sue, he prescribes a different antibiotic.

9. Yo’nique doesn’t get better and unfortunately dies of a upper respiratory infection. Sniff.

10. Dr. Wahoo is sued for malpractice by Yo’nique’s family; he loses his license, and is now asking if you want to supersize your fries and coke with your Big Mac meal. Such a shame.

Rest In Peace Yo’nique. Yo’nique, you one in a million.You mah gurl!

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Pesticide Resistance Scenario Pesticides: chemicals that kill animals that are regarded as

pests. 1. Pesticides applied to the field and kills the majority of the mice

that were eating Farmer Billy Joe Bob’s crops.2. Due to natural variations, a few mice are slightly different and

unaffected by the poison.3. Resistant mice survive and reproduce, making a new

population of “mighty mice” – some or all of the members possess the genetic resistance.

4. Seeing more mice eating his crops, Billy Joe Bob puts out more poison. This time fewer mice die.

5. To kill the resistant “mighty mice”, a new pesticide must be used. But Farmer Billy Joe Bob doesn’t realize this, and instead the mighty mice become superheroes and fight crime.

6. Mighty Mice chillax with Hamtaro, Teenage Mutant Ninja Turtles, Thundercats, and Picachu.

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Question 1:

(a) Explain briefly Darwin’s theory of evolution. (4 marks)

(b) Outline two modern examples where evolution can be observed. (2 marks)

(c) State two ways in which the remains of past living organisms have been preserved. (2 marks)

(Total 8 marks)

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(a) Explain briefly Darwin’s theory of evolution. parents produce more offspring than survive; there is competition among members of a species for

survival / struggle for existence;

species show variation;certain variations will give a selective advantage / survival of fittest;

depending on the environment;these variations will be passed on to the next generation;

leading to change in allele frequency;4 max

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(b) Outline two modern examples where evolution can be observed. change of beak shape in Galapagos finches; resistance to pesticides / antibiotics; bird predation on moths; (allow, though some evidence refutes this)

heavy metal tolerance in plants; melanism in ladybirds (ladybugs)

2 max

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(c) State two ways in which the remains of past living organisms have been preserved

fossils; prints / moulds; preserved in amber / tar / peat / petrification; frozen in ice

2 max

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Question 2:

Explain the evidence for evolution provided by the pentadactyl limb. (2 marks)

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Q2: Explain the evidence for evolution provided by the pentadactyl limb.

vertebrates (nearly all) have pentadactyl limbs / homologous structures;

the structure in all is very similar (in spite of different uses);

likely to have evolved from a common ancestor;

2 max