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Primary Science · Year 6Chapter 6 · Offspring, adaptation and evolution
Year 6 · Chapter 6

Offspring, adaptation and evolution

By the end of this chapter you will be able to

  • Say that offspring are of the same kind as their parents, but are not identical to them
  • Explain that the variation within a species can be measured, and find the mean, range and mode
  • Identify adaptations in animals and plants, and say how each one helps the living thing survive
  • Explain how natural selection can change a population over many generations, which may lead to evolution
  • Use data from a population over several generations to describe a change

You should already know

  • Living things, classification and the groups of animals (Chapter 2 of this book)
  • Fossils, and how living things have changed over time (Chapter 5 of this book)

Where this leads

  • Inheritance and genes in Key Stage 3 and GCSE biology

National Curriculum for England, Key Stage 2 science, Year 6. Content: EV2 recognise that living things produce offspring of the same kind, but offspring normally vary and are not identical to their parents, EV3 identify how animals and plants are adapted to suit their environment in different ways and that adaptation may lead to evolution.

Exercise P  Do you remember?

1
FWhat do we call a place where a living thing lives? Write the word.
2
FWhat do we call an animal that eats only other animals? Write the word.
3
FWhich part of a flowering plant makes seeds? Write the word.
4
FWhat is a group of living things that are alike and can breed together called? Write the word.
5
FWhich group of animals has feathers and lays eggs with hard shells? Write the word.
6.1

Offspring are alike but not identical

Year 6
EV2: living things produce offspring of the same kind, but offspring normally vary and are not identical to their parents
Video lesson: Offspring are alike but not identicalComing soon
Story. Ruby has two rabbits at home, a mother and her baby. “Her babies look like her,” says Ruby. “But they are not exactly the same,” says her uncle. “One has short ears and white fur, and the others do not.”

Offspring are the young of living things. Offspring are of the same kind as their parents: a rabbit has rabbit offspring, and a daisy has daisy offspring.

However, offspring normally vary. This means they are not identical to their parents or to each other. Each offspring may have a mix of features from its parents, so some features are the same and some are different.

Parentlong earsbrown furOffspring 1long earsbrown furOffspring 2short earswhite fur
A parent rabbit with long ears and brown fur, and two offspring: one matches the parent, and one has short ears and white fur. Not to scale.

The table compares the parent and two offspring.

AnimalEarsFur
Parentlong earsbrown fur
Offspring 1long earsbrown fur
Offspring 2short earswhite fur

Key ideas

  • Offspring are of the same kind as their parents.
  • Offspring normally vary, so they are not identical to their parents.
  • Some features may match the parent, and others may be different.
  • Variation is why living things in the same family can look different.
Worked example 6.1.1
Look at the table in section 6.1. Which offspring has the same ears as the parent? Write the name.

Method. Compare the ears in each row.

  1. Read the parent row. The parent has long ears.
    long ears
  2. Read the offspring rows. Offspring 1 also has long ears, but offspring 2 has short ears.
    Offspring 1
  3. Write the answer.
    Offspring 1

Check. Offspring 2 has short ears, which is different from the parent. ✓

Worked example 6.1.2
Is Offspring 2 of the same kind as the parent, even though it has white fur? Write yes or no.

Method. Think about the kind of living thing.

  1. Think about the kind. Offspring 2 is still a rabbit, so it is the same kind of animal.
    rabbit
  2. Decide. It differs in fur and ears, but it is of the same kind, so the answer is yes.
    yes
  3. Write the answer.
    yes

Check. Variation changes features, not the kind of living thing. ✓

Worked example 6.1.3
Do offspring have to be identical to their parents? Write yes or no.

Method. Read the idea of variation.

  1. Read the idea. Offspring normally vary, and they are not identical to their parents.
    not identical
  2. Decide. So offspring do not have to be identical, and the answer is no.
    no
  3. Write the answer.
    no

Check. Variation is normal. ✓

Watch out

Watch out: offspring are of the same kind as their parents, but they are not copies of them. A rabbit baby is always a rabbit, but it can have different features.

Exam tip

Exam tip. When you describe offspring, say that they are the same kind, and that they normally vary from their parents.

Try it (with your teacher, or a grown-up at home). Look at photographs of people in a family with a grown-up, if the family agrees. Notice which features are the same and which are different. Do not share photographs without permission.

Exercise 6A  Offspring are alike but not identical

1
FWhat are the young of living things called? Write the word.
2
FAre offspring usually of the same kind as their parents? Write yes or no.
3
FDo offspring normally vary from their parents? Write yes or no.
4
FLook at the table in section 6.1. What is the colour of the fur of Offspring 2? Write the colour.
5
FWhich two living things in the table have the same ears? Write the two names.
6
FWhich living thing in the table has a different fur colour from its parent? Write the name.
7
PSIs it true that a baby rabbit can have short ears, even when its parents have long ears? Write yes or no.
8
PSAli says that offspring are exact copies of their parents. Is Ali right? Write yes or no.
9
PSA puppy has the same kind of ears as its mother, but a different fur colour. Is the puppy of the same kind as its mother? Write yes or no.
10
PSName one feature that offspring can have that is different from their parents. Write one word.
11
RExplain why a family of rabbits can look alike and still be different. Write one sentence.
12
RExplain why offspring that vary can be helpful to a species. Write one sentence.
13
RChallenge: explain why an offspring that varies from its parents is still a member of the same species. Write one sentence.
6.2

Variation within a species

Year 6
EV2: offspring normally vary and are not identical to their parents; variation can be measured and compared
Video lesson: Variation within a speciesComing soon
Story. Mo and Priya measure six bean seeds from the same pod. “They are all beans, but they are not the same size,” says Mo. “That is variation,” says Priya. “Let’s find the mean and the range, so we can describe it.”

Living things of the same species vary. Seeds from the same plant, animals of the same kind, and people in one family, can differ in size, shape or colour.

Scientists measure variation with three ideas:

051015seed length (mm)10seed 112seed 214seed 312seed 412seed 510seed 6
Bar chart of six bean seed lengths in millimetres: 10, 12, 14, 12, 12 and 10. Seeds from the same pod differ in length.

The table gives the length of each seed.

SeedLength (mm)
Seed 110
Seed 212
Seed 314
Seed 412
Seed 512
Seed 610

Key ideas

  • Variation is the difference between living things of the same species.
  • The range is the highest value minus the lowest value.
  • The mode is the value that occurs most often.
  • The mean is the total divided by the number of seeds.
Worked example 6.2.1
What is the range of the seed lengths in section 6.2? Write the number of millimetres.

Method. Subtract the lowest value from the highest.

  1. Find the highest and lowest. The highest seed is 14 mm and the lowest is 10 mm.
    14 and 10
  2. Subtract. The range is 14 minus 10.
    14 - 10 = 4
  3. Write the answer.
    4 mm

Check. 10 + 4 = 14. ✓

Worked example 6.2.2
What is the mode of the seed lengths? Write the number of millimetres.

Method. Count how often each length occurs.

  1. Count. A length of 12 mm occurs three times, which is more than any other length.
    12 occurs 3 times
  2. Write the mode. So the mode is 12 mm.
    12
  3. Write the answer.
    12 mm

Check. 10 mm occurs twice and 14 mm occurs once. ✓

Worked example 6.2.3
What is the mean of three seeds, 10 mm, 12 mm and 14 mm? Write the number of millimetres.

Method. Add the three lengths, then divide by 3.

  1. Add. The total is 10 + 12 + 14.
    36
  2. Divide. Divide 36 by 3.
    36 divided by 3 is 12
  3. Write the answer.
    12 mm

Check. Three seeds with a mean of 12 mm. ✓

Watch out

Watch out: the range tells you how spread out the values are, not the average. The mean and the mode are different measures.

Exam tip

Exam tip. Give the unit with each answer, and say which measure you found: mean, range or mode.

Try it (with your teacher, or a grown-up at home). Measure the length of ten leaves from the same plant, or ten pieces of the same pasta, with a ruler. Find the range and the mode. Explain why the leaves or pasta are not all the same length.

Exercise 6B  Variation within a species

1
FHow many bean seeds were measured in the table in section 6.2? Write the number.
2
FWhich seed is 14 mm long? Write the name, for example Seed 1.
3
FWhat is the longest length of the seeds? Write the number of millimetres.
4
FWhat is the shortest length of the seeds? Write the number of millimetres.
5
FWhat is the range of the seed lengths? Write the number of millimetres.
6
FWhat is the mode of the seed lengths? Write the number of millimetres.
7
FWhat is the total of the six seed lengths? Write the number of millimetres.
8
FDo seeds from the same pod all have the same length? Write yes or no.
9
PSA seed is 12 mm long, and another is 10 mm. What is the difference between them? Write the number of millimetres.
10
PSMo says the mean of the six seeds is exactly 12 mm. Is Mo right? Write yes or no.
11
PSPriya says the range of 4 mm shows that the seeds vary. Explain why she is right. Write one sentence.
12
RExplain why the mode may be more useful than the mean for finding the most common seed length. Write one sentence.
13
RChallenge: explain why a population with more variation may be better able to survive a change in the environment. Write one sentence.
6.3

Adaptations of animals

Year 6
EV3: identify how animals are adapted to suit their environment in different ways
Video lesson: Adaptations of animalsComing soon
Story. Aisha reads about a camel in a hot desert. “Why has it got a hump?” she asks. Her teacher says, “The hump stores fat, which the camel can use when there is little food. Many animals have features that suit where they live. We call these features adaptations.”

An adaptation is a feature of a living thing that helps it to survive in its environment. The environment is the place where it lives, and all the conditions around it.

Animals are adapted in many different ways. A polar bear has thick fur and a white coat, which keep it warm and help it hide in the snow. An owl has large eyes, which help it to see in low light. A duck has webbed feet, which push water backwards so it can swim.

camel: hump stores fatpolar bear: white furowl: large eyesduck: webbed feeteach feature helps the animal to survive where it lives
Four animals drawn with simple shapes: a camel with a hump, a polar bear with white fur, an owl with large eyes, and a duck with webbed feet. Not to scale.

The table shows each adaptation and how it helps.

Living thingAdaptationHow it helps
Camela hump that stores fat, and wide feet on sandsurvives long periods in deserts with little food
Polar bearthick fur and a white coatkeeps warm, and hides in the snow
Owllarge eyes and soft, fringed featherssees in low light and flies silently to catch prey
Duckwebbed feetpushes water backwards to swim well
Cactusthick stems and spines instead of leavesstores water, and loses little water through its surface

Key ideas

  • An adaptation is a feature that helps a living thing survive in its environment.
  • A camel's hump stores fat, which it can use when food is scarce.
  • A polar bear's white fur helps it hide in snow and keeps it warm.
  • Webbed feet help a duck to swim.
Worked example 6.3.1
Look at the table in section 6.3. What adaptation does a camel have? Write the words.

Method. Find the camel row.

  1. Read the row. The camel has a hump that stores fat.
    hump
  2. Write the words. So the adaptation is a hump that stores fat.
    a hump that stores fat
  3. Write the answer.
    a hump that stores fat

Check. The hump is a store of energy. ✓

Worked example 6.3.2
How does an owl's large eye help it? Write the words.

Method. Read the owl row.

  1. Read the row. Large eyes help the owl see in low light.
    low light
  2. Write the words. So large eyes help it to see in low light.
    see in low light
  3. Write the answer.
    see in low light

Check. The owl hunts at night. ✓

Worked example 6.3.3
Which animal has webbed feet? Write the name.

Method. Find the webbed feet in the table.

  1. Read the table. The duck has webbed feet.
    duck
  2. Write the name. So the animal is a duck.
    duck
  3. Write the answer.
    duck

Check. Webbed feet push the water back. ✓

Watch out

Watch out: an adaptation is a feature that suits the environment. An animal does not choose an adaptation, and the feature is not made by wanting it.

Exam tip

Exam tip. When you describe an adaptation, name the feature, then say how it helps the animal survive in its environment.

Try it (with your teacher, or a grown-up at home). Look at pictures of animals with a grown-up, and choose one adaptation that you think helps it. Explain how it helps the animal in its habitat. Do not touch wild animals.

Exercise 6C  Adaptations of animals

1
FWhich animal in the table has a hump that stores fat? Write the name.
2
FWhich animal has white fur that helps it hide in the snow? Write the name.
3
FWhich animal has large eyes to see in low light? Write the name.
4
FWhat adaptation helps a duck to swim? Write the words.
5
FWhat is the name for a feature of a living thing that helps it survive in its environment? Write the word.
6
FWhat is the name for the place where a living thing lives, and all the conditions around it? Write the word.
7
FWhich adaptation helps a camel to survive when there is little food? Write the words.
8
PSIs a polar bear's white fur an adaptation that helps it hide? Write yes or no.
9
PSName the animal from the table that has the adaptation of webbed feet, and say what the feet help it to do. Write the name.
10
PSAli says the camel grew a hump because it wanted to store fat. Is Ali right? Write yes or no.
11
PSChoose one animal from the table and explain how its adaptation helps it to survive. Write one sentence.
12
RExplain why an owl needs silent flight. Write one sentence.
13
RExplain why a polar bear's thick fur is useful in a cold place. Write one sentence.
14
RChallenge: explain why an animal in a desert might have a feature that stores water or fat. Write one sentence.
6.4

Adaptations of plants

Year 6
EV3: identify how plants are adapted to suit their environment in different ways
Video lesson: Adaptations of plantsComing soon
Story. Sam visits a garden centre. A cactus has sharp spines and a thick green stem. “Why doesn't it have leaves?” he asks. The gardener says, “Its spines and thick stem help it to keep water. That is an adaptation to a dry place.”

Plants are adapted to their environments too. Some plants live where water is scarce, and some live where it is cold, shady or windy.

Plants adapted to dry places are not the same as plants adapted to wet or cold places.

cactus: spines and a stem that stores waterpine: thin needles
A cactus with spines and a thick stem, and a pine branch with thin needles. Not to scale.

Key ideas

  • A cactus has spines and a thick stem that stores water.
  • Spines and needles have a small surface area, so less water is lost.
  • Plants are adapted to the water, light and temperature of their environment.
  • Adaptations of plants are different in different places.
Worked example 6.4.1
What is the adaptation of a cactus that helps it to keep water? Write the words.

Method. Read the cactus description.

  1. Read the description. A cactus has spines instead of leaves and a thick stem that stores water.
    thick stem
  2. Write the words. So the adaptation is a thick stem that stores water.
    a thick stem
  3. Write the answer.
    a thick stem that stores water

Check. Spines also help reduce water loss. ✓

Worked example 6.4.2
Why does a pine tree have thin needles rather than broad leaves? Write one reason.

Method. Think about water loss.

  1. Think about surface. Thin needles have a small surface area.
    small surface
  2. Think about water. So less water is lost from the needles.
    less water
  3. Write the answer.
    to lose less water

Check. Thin needles help the pine survive the cold and dry winter. ✓

Worked example 6.4.3
Which part of a cactus stores water? Write the word.

Method. Read the cactus description.

  1. Read the description. The thick stem stores water, and the spines protect it.
    thick stem
  2. Write the word. So the part that stores water is the stem.
    stem
  3. Write the answer.
    stem

Check. Leaves are not used for storage in a cactus. ✓

Watch out

Watch out: a cactus has spines, which are not leaves, and its stem does the work of storing water. Do not describe the spines as leaves.

Exam tip

Exam tip. Name the plant feature, then say what it helps the plant to do in its environment.

Try it (with your teacher, or a grown-up at home). Look at a plant at home or school, with a grown-up. Feel the leaves, if they are safe to touch, and notice whether they are thick or thin, smooth or hairy. Wash your hands afterwards. Say how one feature could help it in its environment.

Exercise 6D  Adaptations of plants

1
FWhat feature of a cactus has replaced leaves? Write the word.
2
FWhat does the thick stem of a cactus store? Write one word.
3
FWhat shape are the leaves of a pine tree? Write one word.
4
FDo pine needles have a large or small surface area compared with broad leaves? Write large or small.
5
FDoes a cactus have leaves? Write yes or no.
6
FIs a cactus adapted to a dry place? Write yes or no.
7
FWhich plant keeps its needles through the winter: the cactus or the pine? Write the name.
8
PSName the feature that a cactus uses to reduce water loss. Write one word.
9
PSSam says a cactus is adapted to a wet place. Is Sam right? Write yes or no.
10
PSA plant with broad, thin leaves lives in a shady wood. Name one adaptation that helps it: broad leaves to catch light. Write the word for what the leaves catch.
11
RExplain why a cactus with thick stems lives well in a desert. Write one sentence.
12
RExplain why thin needles help a pine tree in a cold, dry winter. Write one sentence.
13
RChallenge: explain why plants that live in very different places have different adaptations. Write one sentence.
6.5

Evolution by natural selection

Year 6
EV3: adaptation may lead to evolution; natural selection changes a population over many generations
Video lesson: Evolution by natural selectionComing soon
Story. In a field, a group of beetles lives on the grass. Some are green and some are brown. Birds eat more of the brown beetles, which are easier to see. “Will the green beetles take over?” asks Tom. “Let’s count them each generation, and find out,” says Mrs Chen.

Evolution is the change in living things over many generations. One way that it happens is natural selection:

  1. living things of a species vary;
  2. some variations help the living thing survive in its environment;
  3. those living things are more likely to survive, reproduce and pass on their features;
  4. over many generations, the population changes.

Adaptation may lead to evolution, because helpful features become more common over time.

variationsurvival of helpful featuresmore offspring with themspecies changes over generationsnatural selection, shown in four steps
Four boxes showing natural selection: variation, survival of helpful features, more offspring with them, and the species changes over generations.

The table shows the percentage of green beetles in each generation of a field population. The rest are brown, and each generation has 100 beetles.

GenerationGreen beetles (%)Brown beetles (%)
Generation 16040
Generation 27030
Generation 38020
Generation 49010
020406080100green beetles (%)gen 1gen 2gen 3gen 460%70%80%90%
Line graph of the percentage of green beetles in four generations: 60%, 70%, 80% and 90%.

Key ideas

  • Evolution is change in living things over many generations.
  • Natural selection: helpful variations help survival, so they become more common.
  • Adaptation may lead to evolution, as helpful features spread through a population.
  • The data shows a change from one generation to the next, not a change in one living thing.
Worked example 6.5.1
Look at the table in section 6.5. What percentage of beetles were green in generation 1? Write the number.

Method. Read the first row.

  1. Read the row. Generation 1 has 60 green beetles out of 100.
    60
  2. Write the number. So the percentage of green beetles is 60.
    60%
  3. Write the answer.
    60%

Check. The brown beetles were 40 out of 100. ✓

Worked example 6.5.2
How many percentage points did the share of green beetles rise from generation 1 to generation 4? Write the number.

Method. Subtract the generation 1 value from the generation 4 value.

  1. Read the values. Generation 4 has 90 per cent green, and generation 1 has 60 per cent.
    90 and 60
  2. Subtract. The rise is 90 minus 60.
    90 - 60 = 30
  3. Write the answer.
    30

Check. 60 + 30 = 90. ✓

Worked example 6.5.3
In generation 3, how many brown beetles were there? Write the number.

Method. Use the total of 100 beetles.

  1. Read the value. Generation 3 has 80 green beetles out of 100.
    80
  2. Subtract from the total. The brown beetles are 100 minus 80.
    100 - 80 = 20
  3. Write the answer.
    20

Check. 80 green plus 20 brown is 100. ✓

Watch out

Watch out: natural selection acts on a whole population over many generations. An individual beetle does not change colour to suit the field.

Exam tip

Exam tip. When you describe evolution, mention variation, survival, reproduction, and many generations.

Try it (with your teacher, or a grown-up at home). Use 20 coloured beads or dried beans: 10 of one colour and 10 of another, scattered on a sheet of paper. Ask a partner to pick up ten beads in five seconds, as a bird would. Keep the ones picked up as "eaten". Repeat for three generations, then count the colours. Which colour survived most?

Exercise 6E  Evolution by natural selection

1
FWhat is the percentage of green beetles in generation 2? Write the number.
2
FHow many brown beetles were in generation 1? Write the number.
3
FIn which generation were the most green beetles? Write the generation number.
4
FBy how many percentage points did the share of green beetles rise from generation 1 to generation 2? Write the number.
5
FIs the share of green beetles rising in each generation? Write yes or no.
6
FWhat is the name of the process in which helpful variations become more common over generations? Write the words.
7
FWhat word describes the change in living things over many generations? Write the word.
8
PSDoes one beetle change its colour during its life to suit the field? Write yes or no.
9
PSIn generation 3, how many green beetles were there? Write the number.
10
PSPriya says natural selection means that the green beetles change colour each year. Is Priya right? Write yes or no.
11
RExplain why a helpful variation is more likely to become common over many generations. Write one sentence.
12
RExplain how the data in section 6.5 could show that natural selection is taking place. Write one sentence.
13
RChallenge: explain why the data shows a population change, and not a single beetle changing. Write one sentence.

Chapter summary

SkillMethod
OffspringOffspring are of the same kind as their parents, but normally vary and are not identical to them.
VariationVariation can be measured with the mean, the range and the mode.
AdaptationsFeatures that suit a living thing to its environment, such as a camel's hump, a polar bear's fur, or a cactus's spines.
Natural selectionHelpful variations help survival and reproduction, so they become more common over many generations.
EvolutionChange in living things over many generations. Adaptation may lead to evolution.

Can you…?

  • I can say that offspring are of the same kind as their parents, but normally vary
  • I can find the range, mode and mean of a set of measurements
  • I can name an adaptation of an animal, and say how it helps it survive
  • I can name an adaptation of a plant, and say how it helps it survive
  • I can describe natural selection in four steps, and explain how a population changes
  • I can use data over several generations to describe a change

Key terms

offspring
the young of living things
variation
differences between living things of the same species
identical
exactly the same
range
the highest value minus the lowest value in a set of results
mode
the value that occurs most often in a set of results
adaptation
a feature of a living thing that helps it survive in its environment
environment
the place where a living thing lives, and all the conditions around it
natural selection
the process in which helpful variations survive and reproduce more, so they become more common
evolution
the change in living things over many generations
generation
one set of offspring in a line of living things

Exercise 6Z  Check-up

1
What are the young of living things called? Write the word.
2
Do offspring normally vary from their parents? Write yes or no.
3
What is the range of the seed lengths in section 6.2? Write the number of millimetres.
4
What is the mode of the seed lengths in section 6.2? Write the number of millimetres.
5
Which animal in section 6.3 has a hump that stores fat? Write the name.
6
What adaptation helps a duck to swim? Write the words.
7
What does the thick stem of a cactus store? Write one word.
8
Using the table in section 6.5, what percentage of beetles were brown in generation 4? Write the number.
9
Name the process that changes a population over many generations, by helpful variations surviving. Write the words.
10
Explain how adaptation may lead to evolution. Write one sentence.

Total 17 marks. Allow about 17 minutes.

Exercise 6X  Practice test questions

1
FOffspring are of the same kind as their parents. Are they always identical to them? Write yes or no.[1 mark]
2
FA bean pod has seeds of lengths 10 mm, 12 mm, 14 mm, 12 mm, 12 mm and 10 mm. Write the range of the lengths, in millimetres.[1 mark]
3
PSUsing the same seed lengths, write the mean length, in millimetres. Add all six lengths, then divide by 6.[2 marks]
4
RA cactus has spines instead of leaves. Explain how the spines help the cactus. Write one sentence.[2 marks]
5
FName the animal that has webbed feet, and say what the feet help it to do. Write one sentence.[2 marks]
6
PSThe percentage of green beetles was 60% in generation 1 and 90% in generation 4. Write the rise in percentage points.[2 marks]
7
RExplain why the green beetles became more common over generations. Write one sentence.[2 marks]
8
FWrite the name of the process in which living things that are better suited to their environment survive and reproduce more. Write the words.[1 mark]
9
RExplain why a plant that lives in a wet place is unlikely to have a thick stem that stores water. Write one sentence.[2 marks]
10
RExplain why an adaptation may lead to evolution over many generations. Write one sentence.[2 marks]
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