Evolution - Natural selection experiments - Science - Year 10

Teacher Content Information

Natural selection is the process where an environmental factor acts on a population and results in some organisms having more offspring than others. Darwin concluded that natural selection will only occur where there is variation (natural differences) in a population. These natural differences can now be explained through genetics - however at the time when Darwin reached his conclusions about natural selection genetics was unknown.

Biologists call the environmental factor that acts on the population the 'selective agent' and the effect of natural selection on the population is known as 'selective pressure'. The selective agent may be a natural occurring factor such as predation, bacterial infection, competition, temperature, fire, water, or soil nutrients.

Some selective agents act by killing individuals and the individuals who succumb to these selective agents are referred to as 'poorly adapted' or 'less fit'. In other cases, natural selection occurs through what Darwin called 'sexual selection'. This happens when, for example, a female bird is attracted to a male bird with more brightly coloured plumage than other male birds. These males will produce more offspring and their features will be passed onto the next generation.

Teacher instructions

Work through this resource material in the following sequence:

10 minutes - Tune in: Definitions
30 minutes - Find out: Classifying scenarios
20 minutes - Take action: Create an infographic

Tune in: Definitions

Step 1.

Read the Natural selection factsheet.

Step 2.

Discuss:

What does 'natural selection' mean?
Who is responsible for the term?
What are some examples of natural selection?
What is a selective agent?

Find out: Classifying scenarios

Step 1. Watch:

From the Big Bang to Me (https://www.youtube.com/watch?v=nYkdDniQJyw)

Step 2.

Discuss the image of the range of birds.

Prompt student thinking by asking:

What do you notice about these birds? What is the difference between them? Their beaks are all of different lengths and shapes.
Are they the same bird? You might think they're all different, but all of these birds are finches.
So why do they look different? This is the key question. Come up with some hypotheses of why the same bird might have different beaks.

It has something to do with survival, evolution and natural selection.

Instead of just giving you the answer, we're going to do an experiment to find out (although there are some answers below too).

Take action: Courtroom report

Step 1.

Set up six distinct stations around the classroom. You might need to rearrange some tables.Place each collection of 'food' (marbles, pipe cleaners, toothpicks, paper clips, beans, and paper squares) on their own station.Each station should also contain one of each type of 'beak': one pair of scissors, one pair of tweezers, one teaspoon, one clothes peg, one fork, and one knife.

Step 2.

Split students into groups of six. If there are more than six students in a group, that's fine, the group will just have to share in the experimenting.

Step 3.

Explain to students that they are going to rotate around each station.The goal of the experiment is to find which 'beak' is best at picking up which 'food' by measuring how many of each type of food each beak can pick up in one minute.

Step 4.

Before we begin, let's make some hypotheses. Take students to the first station with the marbles. Show them the six different implements on the table. Which 'beak' do students think will be best for picking up the marbles: the scissors, the tweezers, the teaspoon, the clothes peg, the fork, or the knife? Direct students to write their hypotheses in the space indicated in the record table on the Student Worksheet.

Step 5.

Repeat this at all of the remaining stations.

Step 6.

Now assign one group of students to each of the six stations. Each student in each group picks a unique 'beak', which they can select now.

Step 7.

Instruct students to spread the cup of 'food' across their table. Be careful with the marbles - they're likely to roll away!

Step 8.

Put 60 seconds on the clock. When the timer starts, students have to pick up as many pieces of 'food' as they can and return it to the cup. Students should keep track of how many they're able to pick up within the minute. Stop when the timer hits zero.

Step 9.

In the spaces provided, students record how many pieces of food they were able to pick up with their beak.For example, a student at the marbles station may have been able to pick up three marbles using the scissors. Someone else in their group may have been able to pick up ten marbles using the fork. A student in another group may also have used the fork, but was collecting toothpicks instead. It's important to fill in the right section for both the 'beak' and the 'food' type students were using.

Step 10.

Students fill in the rest of their table using the results from the other members of the group.

Step 11.

Groups rotate around the other stations of food. They might like to swap 'beaks', or they might stick with the same instrument.

Step 12.

Once all groups have tried picking up all types of food, they can analyse their results. Fill in the final column of the table about which beak was 'best' for each type of food, based on which beak picked up the most pieces.

Reflection

Compare your results as a class. Prompt discussion by asking:

Were results consistent across the whole class? That is, did everyone choose the same beak as best for the same type of food? Or do some groups disagree on the best beak? This is quite an important scientific question, especially in our role as claims testers. Results should be the same across the whole class, but there are a number of reasons why they might not be. It could be that Jason has pretty shaky hands and wasn't able to pick up any piece of food with the scissors, even when it was the best break for the job.
Were there any beaks that were able to pick up more than one food well? Can you explain why?
Which beaks collected the least amount of food? Can you explain why? Some beaks are just a bit more generalised, making them kind of good at everything. Some beaks are highly specialised, making them extremely good at one thing in particular, and not much good at much else.
Which beak would you prefer to evolve? Why? Guide students towards an understanding of this experiment demonstrating natural selection and evolution. A useful beak is able to eat different types of food, which means it can eat more food, which means it will survive by not going hungry, which means it is likely to have babies with even more of the same beak. Bad beak = no food = not surviving.
What has this got to do with finches? Darwin saw exactly the same experiment playing out in real life. He saw many different finches each with a beak specialised at being great for picking up a certain type of food found in their natural habitat, increasing their chances of survival.

After the discussion, students can answer these questions on the Student Worksheet.

Natural Selection Experiments

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