Variation and evolution
Learners understanding of evolution and variation is often confused because they tend to refer to individuals rather than populations. Students will, for example, write about individuals needing to develop a particular characteristic in order to survive. It is important therefore in the delivery of this topic to consistently refer to populations.
Students need to appreciate that in any given population of a species there is usually extensive genetic variation. Within this topic area students will need to revisit the idea of mutations. Often students struggle with this concept as they believe mutations to be something bad, whilst obviously this is not the always the case as is demonstrated in natural selection and evolution.
Students need to be able to describe what evidence there is for evolution. This includes an understanding of the work of Darwin and Wallace. Often, through popular science and the media students have come across the term 'survival of the fittest' and have a misconception about the meaning of this, taking it to mean the literal sense when actually the 'fittest' refers to 'best adapted'.
Links and Resources
This resource considers Darwin’s theory of evolution by natural selection and includes a teacher presentation of images, student activities with web links (where they also view these images) and teacher notes, which include the answers to all questions asked on the activity sheet.
The two activities would work well either as individual or as group activities within a classroom environment, so that answers can be discussed as a class with reference to the images and information provided.
This resource contains a good, teacher-delivered presentation that summarises evolution by natural selection. The presentation can be used to round off the topic or as a starter activity during a revision session. It summarises Darwin’s main observations:
• Species produce more offspring than survive to reproduce.
• Population numbers remain more or less constant.
• Members of the same species show variation.
• Certain characteristics are passed from one generation to the next.
These materials look at biodiversity and then the example of Darwin’s finches in the Galapagos.
This activity will help to see how well students have understood the theory of natural selection.
You may wish to focus just on the finches part of the resources. The topic can be introduced with slides 13 to 17 of the presentation. The activity then models the effectiveness of beak size in gathering different food types. Full notes are given with the materials.
Following the activity move onto the question prompts on slide 18. Discuss the answers as a class. Slide 21 then shows students the different finches and their food sources that Darwin observed when he visited the Galapagos.
You can pose the question: How did all these different types of finches develop on these isolated islands. Have students work in groups to see if they can explain using the steps in natural selection.
Discuss progress with each group and provide prompt cards as necessary. Give them one at a time.
This activity really gets to the heart of whether students have understood the concept of natural selection or not. Groups should be given sufficient time to formulate their explanation. Make sure that students realise that variation is random and that selection pressures enable the most favourable to survive and be passed on to the next generation. Many think of it the other way around. That is, because it would be good to have a beak that can pick up particular seeds, then they will be developed to do so.
Conclude with slide 23.
This resource provides all the required materials for a lesson on Peppered moths, as an example of modern evolution.
There is a link to a video on the ARKIVE website which could be watched as a whole class activity, and then working either individually or in groups students could answer the worksheet of questions provided.
This Catalyst article considers the evidence for evolution and the ongoing conflict between scientists and creationists. Central to this discussion is the work of Darwin, which is neatly summarised in this article. Students could be asked to read this article as a homework activity and could summarise the arguments into a table.
Teachers should be aware of the sensitivities around this type of discussion in relation to certain religious beliefs.
For further ideas on how to make effective use of Catalyst articles see: Using Catalyst Magazine: Scientists and How They Work
This resource was aimed at key stage 3 students, but would make for a fun starter activity for GCSE students, perhaps at the beginning or end of this topic.
The resources allows students to explore natural selection using different coloured baits (spaghetti ‘worms’) that are selected and eaten by birds. Uneaten ‘worms’ are counted after predation and the ‘worm’ population is replenished in proportion to those colours which remain. After several cycles of predation and ‘breeding’, the proportions of the colours in the population change, simulating directional selection.
The level of challenge of the resource can be increased as it is possible for students to also test which factors influence the rate at which the two types of prey are selected by the birds. For example:
- What happens when you change the colour of background that the worms are placed on?
- The location of the test area?
- The size of the worms?
The activity could also be used as a data collection activity, with data from different classes being pooled and students asked to present this.
The downloadable interactive Tree of Life video can be used to introduce students to Darwin’s theory of evolution by natural selection. The video illustrates how new species have developed from common ancestors.
Whilst this is the culmination of Darwin’s work, by using this at the start of the topic it helps to set the context of the work to come. You can pose the question, “How do we know this?” Students can then work in groups to discuss the types of evidence they would need to gather to answer this question. How do scientists go about developing a theory of evolution? This is what Darwin did over 150 years ago.
After some time for discussion, collect ideas for the types of evidence or observations that would be needed. Keeping these on a flip chart or board allows them to be revisited as the topic develops. They can be compared with how Darwin worked.