Adaptation and Change over time
– Recognise that living things can change over many generations.
– Identify how animals and plants are adapted to suit their environment in different ways, and how the pressure to adapt may lead to evolution.
– Understand the importance of variation within a population of animals.
– Organisms within a species are similar but not identical; and offspring are similar but not identical to their parents.
– The similarity occurs because most characteristics are genetically inherited from parents.
– Some characteristics can be new, and arrive through mutations (which occurs by chance). Mutations can be positive, negative or neutral. In other words, can improve, reduce or have no effect on an organism’s fitness (survival and reproduction).
– An adaptation is a characteristic that has become common in a population because it provides improved success under the given environmental conditions.
– Adaptations can be a behaviour, anatomical, or chemical feature.
3) Natural Selection
– Offspring who inherit a certain characteristic that makes the organism more fit, are more likely to survive and reproduce in certain environments than offspring that don’t.
– The favouring of a certain characteristic naturally by the environment is what is known as Natural selection.
– The “fit” characteristic that helps an organism to survive in a certain environment will be more common in the next generation than characteristics that are less “fit”.
– Once the characteristic shifts from being rare to common in a population it is said to have “evolved”, ie “changed over time”.
4) The evolution of the peppered moth is a good example of change over time, and of adaptation emphasising the importance of variation:
The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon. However, because of widespread pollution during the Industrial revolution in England, many of the lichens died out, and the trees that peppered moths rested on became blackened by soot, causing most of the light-coloured moths to die off from predation. At the same time, the dark-coloured moths flourished because of their ability to hide on the darkened trees. If there was no variation in colour, dark moths could not have evolved.
Starter (15 minutes)
Aim: to set up the experiments for the main task. No key learning points are introduced in either of these starters but they are necessary to create a back drop for the main task to be completed.
Important note: if the option one starter is chosen then option one main task should be used and if the option two starter is chosen then option two main task should be used.
Each pair of students should have a piece of A3 white paper, 50 white, and 50 black circles (use the circles on the Circles Worksheet. Checkers or counter pieces might also be useful, as long as they are flat and unadorned). One child in the pair turns around and closes their eyes, whilst the other person in the pair places 20 white and 20 black circles on the piece of white paper. The child that closed their eyes turns around, and using a pair of tweezers they should pick up as many of the circles as possible in 20 seconds. The circles that have not been picked up should be kept, and their number doubled for the next round. The circles that were picked up should be discarded. The process should be repeated, with the children exchanging tasks. The child with their eyes open should shuffle the remaining circles and place them randomly on the paper, before the second round of picking starts. After the second round, the children should count up how many white circles in comparison to black circles remain on the piece of paper. Which value is higher?
***Another fun way to do the same experiment is to have bags of Smarties or M&M candies in two colours, and have the class trying to pick red or green candies from a bag full of brown ones (reds should be more easily seen)***
Split the class into pairs and explain that each pair must design 10 moths (use the moth outline worksheet so that all moths are the same). Explain that you are focusing on the characteristic of camouflage, so they should think about the colour of their moths. Explain that their moths are going to be placed into a habitat (define habitat) and then a predator is going to come and try to eat as many moths as possible. Also explain that their moths can take whatever form they would like i.e. they can be all the same, all different, some the same, some different. Give them 10 minutes to discuss their plan and to draw their moths. This activity can be done in pairs.
Main Body (30 minutes)
Aim: to introduce the idea of adaptation, natural selection and evolution. To make sure students have an understanding that variation is important to prevent animals becoming extinct.
Ask the children what environmental situation they think they may be simulating when they are picking the counters ? Try to prompt them to tell you that they are a predator (a bird) eating it’s pray (an insect).
Then, discussed what happen over time. The children should find that on average, the number of white circles left on the piece of paper is higher than the number of black circles. If this is not the case then make sure the children understand that in nature this is what would be found, and that their experiment may produce incorrect results due to experimental errors (such as the fact that the circles are all slightly raised so they can all be seen, or the children may favour one colour or the other).
Discuss why you would expect to see more white circles than black circles left on the paper. Prompt the children to talk about how the white circles are camouflaged in their habitat (at this point define habitat) and therefore are better able to” survive”. Explain how they are adapted (at this point define adaptation) to their habitat as they have characteristics which help them to survive i.e. camouflage. Then explain how animals that are better adapted to their habitat are more likely to survive than those animals not adapted. Therefore, if you start with a population of animals with a variety of characteristics, over time that population will change, so that the animals that are adapted to the habitat become more common than those that are not. Hence, we get natural selection (at this point define natural selection) of those animals most suited to their habitat causing the population to change over time i.e. evolve (at this point define evolution).
Once you have covered the main points in the discussion the children should repeat the experiment. However you should swap the colour of the background sheet to black to imitate a change in environmental conditions and thus the habitat. Explain how the habitat has suddenly changed due to pollution in the area. Thus, now the trees have changed colour but the circles are the same as before. Each pair should have 30 white circles that represent the circles that were well adapted to the old habitat and 5 black circles which represent the fact that there is always a little bit of variation in a population caused by random mutations (define mutations at this point).
Get the children to write down their predictions – what do they think will happen this time?
Carry out the experiment discarding the circles that are picked off and doubling the circles that are left on the sheet of paper. Once you have repeated the experiment three times count the number of circles left on the piece of paper and determine whether the children’s predictions were correct. The children should find that now there are more black circles left on the piece of paper than white circles.
A clear discussion is needed to reiterate the points learned in the lesson and explain why this has happened. It is crucial that even if the experiments have not gone to plan children understand the key concepts that the experiments should have shown. Teachers should explain that there are many reasons why an experiment might not go to plan as discussed previously. Discuss how the black circles have a characteristic that helps them to survive in this environment i.e. camouflage and so are therefore adapted to the environment. Therefore the black circles are selected for through natural selection and the population evolves to contain more black circles than white circles. Reiterate how as they saw in their experiment an environment can change. This environmental change can cause different characteristics to become advantageous and so different circles may become better adapted to the new habitat and therefore be selected for by natural selection and hence increase in number. As a result there is a change in the population over time. It is important that the children understand it is important to have variation (i.e. the presence of both black and white coloured circles) amongst a type of animal in order to deal with the changes in the environment otherwise one type of animal may totally disappear, like the dinosaurs, this is called extinction (at this point define extinction). It is also very important to reiterate that natural selection takes place over a number of generations and the time depends on the generation time of the animal. Hence an animal with a short generation time (insect) will evolve quickly in comparison to an animal with a long generation time (elephant).
This can then be linked to the real life evolution of the peppered moth by showing the first minute of this video on the peppered moth: https://www.youtube.com/watch?v=yuUi2E3t3UY
Once the children have coloured their moths, present each table with a background you have prepared earlier, it may be stripy, dark, light etc. Each pair on the table must place their moths onto the background. Ask the children to predict as a group what they think is going to happen? Which moths will be eaten and which will survive? Next choose a person from each group who is going to be the predator. This person should then go to another group and act as the predator in the game picking up as many moths, using a pair of tweezers, as possible in 10 seconds. The game should be repeated three times, for each repeat the predators change groups. At the end of each round the moths that are picked up are discarded whilst the moths that are left double in number (the children will have to make new moths if their moth’s survive, they should be identical to the moths that have survived). After three repeats the group should discuss what has happened, were their predictions right?
Discuss why you would expect to see certain moths left on the paper. Prompt the children to talk about how certain moths are better camouflaged in their habitat and therefore are better able to survive. Explain how they are adapted (at this point define adaptation) to their habitat as they have characteristics which help them to survive i.e. camouflage. Then, explain how animals that are better adapted to their habitat are more likely to survive than those animals that are not adapted. Therefore, if you start with a population of animals with a variety of characteristics over time that population will change so that the animals that are adapted to the habitat become more common than those that are not. Hence we get natural selection (at this point define natural selection) of those animals most suited to their habitat causing the population to change over time i.e. evolve (at this point define evolution).
Now complete exactly the same experiment but swap the backgrounds around so that each group has a different background. Explain how this can happen in the natural world as often environments can change for example due to climate warming, which would favour different characteristics. Again ask the children to predict what will happen next. When they have repeated the game three times discuss the findings. Which animals survived? Why do the class think that was? Did the same moths survive as last time? Also discuss which pairs tactics worked best throughout the game? Was it better to have all the same moths or a variety of different moths? The class should find that different moths survived in comparison to the last time, since the environment changed and therefore the moths that previously had beneficial characteristics where no longer adapted to the new habitat. The moths that survived would have been those best camouflaged and thus adapted to the new background. The class should find it is better to have a variety of moths rather than the same moths. As with a variety of moths it is more likely that some of them will survive a change in environment. In contrast if all of them are the same then a certain change in the environment could kill the whole population of moths.
This can then be linked to the real life evolution of the peppered moth by showing the first minute of this video on the peppered moth: https://www.youtube.com/watch?v=yuUi2E3t3UY
Plenary (10 minutes)
Aim: to reiterate the idea of natural selection and evolution, using verbal discussion
A clear discussion is needed to reiterate the points learned in the lesson. It is crucial that even if the experiments have not gone to plan children understand the key concepts that the experiments should have shown. If this is the case then make sure the children understand that in nature this is what would be found, and that their experiment may produce incorrect results due to experimental errors (such as the fact that the moths are all slightly raised so they can all be seen, or the children may favour one moth or the other).
The discussion should cover the following key points:
– First, that animals with advantageous characteristics which improve survival chances are better adapted to a habitat. They therefore exist in higher numbers than those that are not so well adapted. This process occurs through natural selection which selects for characteristics which help an organism survive in a habitat.
– Environments can change. Once an environment changes different characteristics may become advantageous. Thus, different animals may be more adapted to the new habitat, and therefore be selected for by natural selection, increasing in number. As a result there is a change in the population over time.
– It is important to have variation amongst a type of animal in order to cope with environment changes. Otherwise, one type of animal may totally disappear, like the dinosaurs. This is called extinction (at this point define extinction). It is also very important to reiterate that natural selection takes place over a number of generations and the time depends on the generation time of the animal. Hence an animal with a short generation time (insect) will evolve quickly in comparison to an animal with a long generation time (elephant).
Aim: to reiterate the idea of natural selection and evolution, using another example.
1) Gather 50 coins, 50 paper clips, and 50 counters along with a fork, a spoon and a knife.
2) Split the class into three groups. Set up each group with 10 coins, 10 paper clips and 10 counters which make up the population of animals on the carpet (i.e. the prey), give three children per group on of the spoon, knife and fork which make up three different types of predator.
3) The three predators then have 10 seconds to scoop up as many of the animals as possible and put them into a plastic cup.
4) Once the 10 seconds is up any predator that has less than 10 prey dies and is out of the game and any predator with more than 15 prey reproduces and therefore another child with the same implement is introduced into the game (ie now you have two children with a spoon each).
5) At the same time the prey that are still on the table double in number (use the extra coins/paper clips/counters to replenish the surviving animals) and those in the cups are discarded.
6) Repeat this process three times. Every time you repeat the game make sure the predators change (ie give the knives, forks and spoons to a different child in the group).
7) Once the game is over discuss what has happened to both the prey and predators. Discuss how natural selection has taken place and how the population has evolved. Touch on which characteristics are beneficial and therefore selected for in the prey for example being flat and round might make them harder for the predator to pick up. Also discuss which characteristics are beneficial and therefore selected for in the predators for example having a round cupped surface to scoop up the prey.
Provide the children with the link to these two computer games to have a go at home:
– This is a really good game which shows the importance of variation within a type of animal: http://www.sciencechannel.com/games-and-interactives/charles-darwin-game.htm
– This is a fantastic peppered moth game that brings together the ideas outlined in the moth lesson. Click on the Birds Eye View of Natural Selection and then skip through the info to get to the game: http://www.techapps.net/interactives/pepperMoths.swf
Lesson Assessment / Final Questions
1) Natural selection is the change in a population over time. True or false
2) Natural selection happens over many generations. True or false
3) If trees in a forest were black what colour moth would you expect to see? White or black
4) It is important to have variation within a population of animals. True or false
5) The animals we see today are different to the animals seen in the past due to natural selection. True of False
Answers: 1) True 2) True 3) Black 4) True 5) True
– This is a fantastic practical experiment that could be undertaken if time is available http://www.nuffieldfoundation.org/print/3218
– This is a good video showing a great practical lesson on natural selection. Good for helping teacher understanding and to give ideas for interactive lessons: http://www.theguardian.com/science/teacher-blog/2013/feb/01/masterclass-teaching-evolution