Evolutionary theory is an area where students often come to us with misunderstandings. The ‘bowl of sweets’ analogy is a handy way of providing a memorable concrete model of natural selection. The approach described here is based on an original lesson on natural selection by Carol Tang. I’ve adapted it in ways that make it quicker and more to the point because I’m rarely trying to teach the concepts of natural selection ex nihil and more usually trying to assess how well my students have acquired the relevant ideas earlier in their education and fix things if necessary, so it’s more of an ‘entry check’.
Prepare by putting some sweets in a bowl. There needs to be a variety. I usually include Lindors, Starburst, Skittles and licorice. The licorice is important because most students don’t like it. Whatever you use, check it beforehand to make sure it’s medically (e.g. nuts) and culturally (e.g. kosher/halal) safe for your students. Put an equal number of each type of sweet in the bowl, ensuring the bowl contains a sufficient number so that about half the sweets will be left if every student has one.
This activity assumes either that you know your students have learned about natural selection previously or you have set some advance study on it. At the start of the class, pass the bowl round, inviting the students to take one each. I teach this class near the end of Autumn term so I say it’s because Christmas is coming up. When you want to start discussing evolution, invite the students to gather round while you explain that you put a known number of each type of sweet in the bowl and you’re interested to see what’s left. Tip the bowl out onto a sheet of paper and separate them out, counting how many of each are left (typically for my students, all the Lindors are gone, about half the chews remain and all the licorice is left).
At this point, tell them that the bowl of sweets can be used as an analogy for the process of natural selection and ask them to consider why. From there you can develop a discussion of evolutionary concepts. Questions I generally find useful (obviously, it depends what they come up with) include:
How could the bowl of sweets represent an evolutionary process?
Which is the fittest sweet? (Answer usually Lindor.) What makes you say that? What about if we look at it from the sweet’s point of view?
What do the sweets represent?
What do you (the class) represent?
What are the traits that help a sweet survive in this environment?
In my experience, the analogy of the bowl of sweets provides a useful bridge between the abstract ideas underlying natural selection and the usual exemplifications, most of which seem to involve moths. It’s a rewarding activity as it almost always provides lots of those ‘penny drops’ moments when students suddenly get what it’s all about.
Here is a two lesson sequence on an Edexcel ‘key question of relevance to today’s society’ for biopsychology (zip file of all resources). It’s on the question of whether it’s a good idea to use drugs like Methadone to treat drug addiction. It assumes you’ve set advance reading on the topic. In lesson one the students debate the issue, and in lesson two they plan and write an extended response about it. The lessons are designed to help the students understand what an examiner will be looking for in their responses to this type of question, so teachers of other specifications YMMV.
From what I’ve posted recently you might have got the impression that all I ever teach is choice of statistical test. Believe me, it’s starting to feel that way. Quiz one, quiz two and quiz three are all geared towards the Edexcel specification but could easily be adapted to include a greater range of tests.
I’ve been making quite a lot of use of the quiz/assessment website Socrative.com (free account needed; pay for enhanced features). I’m mainly using it to check comprehension of preparatory reading assignments, particularly for targeting areas where misconceptions are likely to arise (e.g. the difference between privacy and confidentiality when discussing research ethics). Here are some of the quizzes I’ve made recently.