14

Interpreting natural selection and evolutionHomework 2Worksheet B1.7c is designed for students working at a higher level and contains questions on natural selection and evolution.Stretch Ask students to do the

‘extra challenge’ question on the sheet.

Natural selection and evolutionHomework 1Worksheet B1.7b contains simple questions on natural selection and evolution.Support Before photocopying,

put the number 1 in the last box in the question 2 question stem (for question 2b) and remove the word ‘adaptation’ from the choices in question 1a.

Future evolutionPlenary 2 AfL Lit

Tell students that scientists think that the ice caps are melting and that polar bears hunt seals on this ice in the Arctic. Ask students to work in groups to sketch what they think a polar bear might evolve into, over 20 000 years, due to this change. All students in a group should be able to explain the reasoning behind their creature’s characteristics. They could add labels to their drawings to explain the evolutions.

Darwin’s postcardPlenary 1 AfLAsk students to write a postcard from Darwin to a friend who is not a scientist, explaining his thoughts on evolution. Get students to ‘send’ their postcards to their friends, who then peer-assess the information on the cards in terms of the clarity of the explanation.

LamarckExplaining 2Lamarck was of the opinion that organisms adapted to their surroundings, often by movements of their ‘internal fluids’ that enabled certain body parts to swell. This in turn could allow the organism to be better adapted to a certain environment (e.g. a giraffe with a longer neck, a wading bird with longer legs). This was not really a new idea, but one that Lamarck publicised.Stretch Lamarck’s theory only covered

characteristics that were the result of an organism’s own actions (not the actions of external factors).Support Ask students how Lamarck

would have explained how giraffes got their long necks.

Evolution of Caribbean lizardsExploring 2Students use Worksheet B1.7a presents evidence for speciation in Anolis lizards. Check students’ answers for questions 1 and 3 before they proceed further. If necessary, create discussion that will lead to the two most likely answers (see answer sheet).The DNA evidence for question 5 can be found on AT document Anolis lizards of the Caribbean.Stretch Give students AT document

Grouping Caribbean Anolis lizards and ask them to answer the question at the end.

Student Book spread B1.7Explaining 1A point to bring out in this lesson is that natural selection is the process by which organisms with better adaptations to a habitat are more likely to survive and reproduce.Stretch Ask students to come up

with wording for the subheading for Darwin’s theory if he were to have written his book today.Support Demonstrate survival of the

fittest using a small tray filled with red and yellow counters. Explain that a new bird arrives in the area, who eats yellow counters but not red. Remove the yellow counters and demonstrate that there is now space in the box for more red counters, when they reproduce.

Spreading diseasesStarter 2Ask students whether, if one person in the class gets a cold, everyone will. Elicit the idea that not everyone gets ill (although with some colds more people get them than with others). Challenge students to explain why not everyone gets the cold and introduce the idea that this is partly due to our inherited variation – some people are naturally immune to some colds/diseases. Ask what would happen if a ‘killer cold’ came along.

Changing advantagesStarter 1Quickly sketch a normal distribution curve on the board and tell students that it shows variation in neck length in a population of giraffes. Ask students to explain what the shape of the curve means. Then ask students to suggest why there are more giraffes with the middle neck length and very few with either very short or very long necks. Try to elicit the idea that conditions in the environment might make it easier for mid-length giraffes to survive.

Natural selection game (AT)Exploring 2 Prac

Students play a game to illustrate natural selection using coloured pasta. Full details are given on Teacher and technician practical sheet B1.7.Stretch Show students the pasta and

ask them to design their own games to show natural selection.Support Students use the AT

spreadsheet Pasta insect results to record their results. The spreadsheet will automatically turn their results into a pie chart.

Specification coverage

1.12 Demonstrate an understanding of Darwin’s theory of evolution by natural selection including: a) variation – most populations of organisms contain individuals which vary slightly from one to another, b) over-production – most organisms produce more young than will survive to adulthood, c) struggle for existence – because populations do not generally increase rapidly in size there must therefore be considerable competition for survival between the organisms, d) survival – those with advantageous characteristics are more like to survive this struggle, e) advantageous characteristics inherited – only these better adapted organisms will be able to reproduce successfully and may pass on the advantageous characteristics to their offspring, f) gradual change – over a period of time the population will lose most of the poorly adapted individuals. The population will gradually become better adapted to its environment

1.17 Demonstrate an understanding of how speciation can give rise to the appearance of new species as a result of geographic isolation

1.18 Explain how new evidence from DNA research and the emergence of resistant organisms support Darwin’s theory

2 The interpretation of data, using creative thought, to provide evidence for testing ideas and developing theories

The tasks in this lesson also provide opportunities to cover 3, 7,

10 and 11

B1.1: Classification, variation and inheritance

This lesson introduces the idea of adaptation and how the survival of organisms most well adapted to their environments can lead to changes in species over time – Darwin’s theory of evolution by natural selection.

EvolutionB1.7

© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.

B1.7a Evolution of Caribbean lizards

You do not need to remember the details on this sheet for your exam but you could be asked to apply your knowledge to unfamiliar situations.

The Caribbean islands are a large and mixed group of different pieces of land. Some were created by underwater volcanoes and some are formed from large coral reefs. Most have never been joined to each other or to the mainland, and many are over 100 kilometres from the nearest island. The region is well known for its tropical storms, including hurricanes.

The map shows the main Caribbean islands. Note the distance between the islands, as shown by the scale. The numbers show how many species of Anolis lizards live on each island. There are about 138 species of Anolis lizards in total and many are endemic, meaning they are only found on one island. The theory is that endemic species must have evolved in that place.

Scientists have grouped the species into habitat groups based on the habitat they are found in, such as the crown (top) of trees, on tree trunks, on the ground or a combination of two or more of these habitats. Habitat group Where found (C = Cuba, H = Hispaniola,

J = Jamaica, PR = Puerto Rico) crown C, H, J, PR trunk–crown C, H, J, PR trunk C, H twig C, H, J, PR grass–bush C, H, PR trunk–ground C, H, J, PR

1 Suggest how the Caribbean islands came to be populated by Anolis lizards. Explain your suggestion.

2 Use the theory of evolution by natural selection to explain how individuals in different habitats can evolve into separate species.

One hypothesis for how the different Caribbean Anolis species evolved is that one original species reached an island from the mainland. On that island different species evolved in the different habitats. Then individuals from each of the new species reached other islands, and evolved into further new species of the same habitat group (e.g. a 'twig' species on one island only evolved into twig species on other islands). Another hypothesis is that only one species from each island managed to travel to another island. Then on each island, the one species evolved into the different species in every habitat.

3 Sketch diagrams for each hypothesis to show how they explain the range of species in each of the habitat groups on the Caribbean islands today.

4 In 1998, Jonathan Losos led a group of scientists who took DNA samples from 55 species of Caribbean Anolis lizards, in order to work out the relationships between the species. Use your hypotheses to make predictions about what the DNA evidence would show about the similarity of species between islands.

5 Ask your teacher for the results of the DNA evidence and compare it with your predictions to see which hypothesis is more likely. Use this hypothesis to write a web-page article that explains, either in text or diagrams, how the Caribbean islands became populated with Anolis lizards.

N

Cuba55

Jamaica7

Bahamas1–4

Hispaniola40

PuertoRico11

LesserAntilles

1–2

200 km

mainland(many

species)

38

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© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.

B1.7b Natural selection and evolution

You do not need to remember the details on this sheet for your exam but you could be asked to apply your knowledge to unfamiliar situations.

1 Peppered moths can either be speckled or black. Some scientists captured 488 black moths and 496 speckled ones. They placed a small white paint dot on the underneath of each one and let them go in an unpolluted forest. A couple of months later they recaptured moths in the same area. Of the ones with dots on, they found 34 black ones and 62 speckled ones.

a Suggest one reason why not all the moths with dots on were recaptured.

b Which type of moth seemed to survive better in the forest?

c Why do you think this type of moth survived better in the forest?

d Why was the paint put on the underneath of the moth and not the top?

2 The sentences below describe how modern hedgehogs might have evolved.

a Number the sentences in the order in which you think they occurred.

The predator avoided eating the mammals with the stiffer hair and ate more of the ones with softer hair. So, the mammals with softer hair died out.

A new predator entered the area in which the mammal lived.

Over thousands of years, the mammals with the stiffest hairs were the most likely to survive and gradually this became a species of mammals with spines.

By chance some of the mammals had stiffer hair than others, which made it more difficult for the predator to eat them.

Several million years ago a species of mammal had long, thick hair.

b What process is occurring in the top sentence? Circle one process.

environmental variation natural selection evolution adaptation

c What is the process of forming new species called? Circle one process.

variation Darwinism natural selection speciation

Name Class Date

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© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.

B1.7c Interpreting natural selection and evolution

You do not need to remember the details on this sheet for your exam but you could be asked to apply your knowledge to unfamiliar situations.

1 Some scientists were studying the variation of shells in a species of snail called Cepaea hortensis. The snails were greeny-yellow in colour, but some had swirled stripes on them. The table shows some of the data the scientists collected.

Where the snails were found Tops of reeds Dead leaves on ground around

the bases of the reed stems Shell type Unstriped Striped Unstriped Striped Number found 70 30 38 36

a How many snails in total were found near the tops of the reed plants?

b Work out the percentage of snails found near the tops of reed plants that had stripes.

c Work out the percentage of snails found on the ground that had stripes.

d How does your answer to part c compare with your answer to part b?

e Suggest why the snails with stripes are more common in that area.

2 Woolly mammoths evolved from a mammal called Palaeomastodon. Describe how the mammoths may have evolved such a hairy coat.

Extra challenge

3 Dog whelks are snail-like animals that live on rocks in the sea. Scientists collected some from two areas. The results are shown below:

Where the whelks were found Cable Bay Menai Bridge

Measurement Height (cm) Width (cm) Height (cm) Width (cm) Mean size 2.39 1.71 3.28 1.96

The beach at Cable Bay is very exposed and huge waves crash across the rocks. Suggest why the shells of the whelks found at Cable Bay are different to those at the Menai Bridge.

Palaeomastodon woolly mammoth

40

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1515

40 41

Learning utcomes

1.12Demonstrate an understanding of Darwin’s theory of evolution by natural selection including a variation b over-production c struggle for existence d survival e advantageous characteristics inherited f gradual change

1.17Demonstrate an understanding of how speciation occurs as a result of geographic isolation

1.18Explain how new evidence from DNA research and the emergence of resistant organisms support Darwin’s theory

2 Describe the importance of creative thought in the development of hypotheses and themes.

How many genes does your body contain?

1 a Why is there competition between individuals in a population?b What effect will competition have on the population?

2 Explain what is meant by ‘survival of the fittest’.

3 Explain how a species may become extinct.

4 Why was Darwin’s theory of evolution better than earlier theories?

5 Explain how warfarin resistance evolved in rat populations.

6 State one difference between the mockingbirds in Figures C and D.

7 Ground finches have large, powerful beaks to crush seeds. A closely related species has a narrow beak for probing in small holes for insect larvae. Suggest how this species could have evolved from the seed-eating species.

Watch Out!

There are different theories of evolution, not just Darwin’s, so refer to Darwin’s theory of evolution by natural selection.

Skills spotlightIn 1798, an economist called Thomas Malthus wrote an essay in which he stated that children would die of starvation if people had too many children. This helped to give Darwin an idea. How do you think Darwin was inspired by this essay to make his breakthrough about evolution?

C ��Española�Island�mockingbird D ��Santiago�Island�mockingbird

Organisms generally produce far more offspring than the environment can support. Most will die before they reach adulthood because there are not enough resources (e.g. food and space) for them all.

The offspring will show variation in their characteristics. Some variations will be better adapted to the environment than others. The limited resources will cause competition between individuals. Individuals that happen to have variations that are better adapted will be more likely to survive and others will die. We call this ‘survival of the fittest’ or natural selection. Individuals that survive may breed and so may pass their variations on to their offspring.

Evolution by natural selectionEvolution means ‘a gradual change over time’. In the early 1800s, some scientists realised that species can change over time, but theories of why this happened didn’t explain all the facts. Charles Darwin (1809–1882) drew together several ideas to produce a new theory that was better at explaining the facts.

Darwin knew that there was competition between individuals. He also knew that pigeon breeders selected birds with certain characteristics to breed, which meant that those characteristics were inherited by the offspring. Darwin realised that if the environment changes, then different variations may be better suited to the new conditions. Individuals with those variations will be more likely to survive and pass their characteristics on to offspring. So the range of variation in characteristics of the population will gradually change over generations, which is evolution. If the environment changes too rapidly, and no individuals have adaptations that help them survive, they will all die out and the species may become extinct.

M ost crocodiles live in or near water, but there are crocodiles that survive in the Sahara Desert. They survive

without food for the many months when it is too hot and dry, staying below ground in a kind of hibernation. When the rains eventually arrive they come to the surface to hunt.

WhatisDarwin’stheoryofevolution?

A

Darwin published his theory in his book On the Origin of Species by Means of Natural Selection in 1859. Some scientists didn’t like the theory because it didn’t support what they believed. The theory was discussed and challenged at scientific conferences by scientists studying similar areas of science.

New evidence for Darwin’s theoryOne of the problems with Darwin’s theory when he published it was that there was little evidence for it. Evolution takes time to observe.

Warfarin is a chemical that was used to poison rats in the 1940s and 1950s. When it was first used most rats that ate it died within a few days. But within 10 years, most rats were resistant to warfarin and not affected by it. As a result of variation, there had always been a few rats that were resistant, but at the start nobody realised this. As the poison killed the non-resistant rats, the only ones left to breed were resistant. Scientists are also finding new evidence for Darwin’s theory from the genetic information in different species. Darwin could infer relationships between species from the observable characteristics but now we are able to confirm this using genetic evidence.

EvolutionB1.7

SpeciationDarwin started thinking about evolution after noticing differences between mockingbirds from different Galapagos Islands. He realised they were all very closely related, but each island had its own species. His theory helped him explain this observation. Darwin guessed that originally individuals from one species of mockingbird had reached the islands from South America. The environmental conditions varied between islands, so on each island different adaptations would have been more successful. So each island population evolved in a different way. Over time, the individuals on each island became so different that they couldn’t interbreed with birds from another island. They had become new species, a process called speciation.

Topic B1.1: Classification, variation and inheritance

wetter

Conditions

drier

Members ofthe populationvary in theirability to copewith the conditions

1. In these conditions most of theorganisms are likely to survive

Num

ber

s o

f the

org

anis

mth

at a

re b

est

adap

ted

to

diff

eren

t co

nditi

ons

2. If the conditions get drier, a much smaller number of the organisms are likely to survive. These organisms are known as the ‘fittest’

B ��If�conditions�change,�the�range�of�variation�favoured�by�natural�selection�could�change.�

Answers StudentBook

1 a Not enough resources (e.g. food or

space) for all individuals to survive.

b Limits the size of the population,

because individuals without enough

resources die.

2 Only the individuals that can compete

best for resources will survive.

3 If changes in environmental conditions are

so great that no individuals can survive,

all will die out. If all the environments

where this species live change too

much, the species will go extinct.

4 Because it explained more facts and

observations than earlier theories.

5 Some individuals in the population were

naturally resistant to the poison, other

rats were not resistant. Only rats that were

resistant to the poison survived when they

ate it, the rest died. Resistant rats survived

to breed. Their offspring inherited warfarin

resistance, so the population quickly

evolved to become resistant to this poison.

6 One of: Española Island mockingbird

has darker legs, longer beak, sharper-

pointed beak, more curved beak,

distinct ring of white around its eyes.

7 A good answer will contain the

following points:

• on an island with few seeds (but many

insects)

• some finches had narrower beaks and

were able to reach more insects

• these finches survived more often than

the ones with larger beaks

• the finches with narrower beaks

reproduced more often

• this meant that gradually, the birds got

narrower and narrower beaks,

Skills spotlight

Darwin wondered if Malthus’ idea could be

applied to all living things, not just humans.

ActiveTeach

• AT Darwin’s dangerous idea[BBC Active video]Darwin’s theory of natural selection

• AT Creating new life?[BBC Active video]The possibility of creating new cells

• AT Competition from invasive species[video]Invasive species in Norfolk

• AT Evolution by natural selection[diagram]Figure B – diagram labelling activity

• AT Darwin finch key[word document]Drawings of some of Darwin’s finches

• AT Pasta insect results[spreadsheet]Students fill investigation results

• AT Anolis lizards of the Caribbean(word document)Information on Anolis lizards

• AT Grouping Caribbean Anolis lizards(word document)Details on grouping Anolis lizards

Key terms

competitionevolutionextinctnatural selection

resistantspeciationsurvival of the

fittest