Biology 11–12 · Year 11

Natural selection by predation: coloured rice with a one-locus selection model

Module 3: Biological Diversity (Theory of Evolution by Natural Selection)

Practical, model not builtLow risk

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The idea

When a predator finds one colour more easily than another, the proportion of the harder-to-see colour rises generation by generation; the same logic in allele terms gives a predictable change in frequency.

What you need

Horticultural vermiculite dyed with food colouring, one tub per group
Long-grain rice dyed in two colours, 50 grains of each per tub to start, plus a stock for replacement
Forceps; Petri dish; stop clock; results table or spreadsheet (the source provides one)

How to do it

Mix 50 grains of each colour into the vermiculite so that one colour matches the background and the other contrasts.
For 1 minute pick out as many grains as you can with the forceps (this is predation); count the grains removed by colour.
Calculate the survivors of each colour, then top the tub back up to 100 grains by adding equal numbers of each colour (this is reproduction).
Mix and repeat for at least five generations, recording the percentage of each colour at the start of each round.
Plot percentage of the camouflaged colour against generation.
Swap the vermiculite colour and repeat to show that which colour is favoured depends on the environment.

What you should see

The camouflaged colour rises across generations because fewer of it are taken each round; its percentage climbs round by round, and swapping the background reverses the trend. In the allele-frequency model with fitnesses 1, 1 and 0.8 for the three genotypes and a starting frequency of 0.5, the favoured allele reaches 0.526 after one generation, 0.697 after ten and 0.902 after fifty (computed). The learner knows it worked when the plotted proportion climbs steadily rather than fluctuating without direction.

What changes

What you change: background colour (which grain colour is camouflaged)
What you measure: percentage of each grain colour after each generation
What you keep the same: picking time
starting numbers
tub and vermiculite depth
same picker

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Individuals adapt during their lives to match the background; the population changes because some survive and reproduce more.
Natural selection makes a trait appear when it is needed; it acts on variation already present.
The fittest are the strongest or fastest; here fitness is being hard to see.

Safety card

Low riskLearners carry it out

Hazards

Vermiculite dust

Controls

Keep the vermiculite damp; do not blow on it

Note

No hazardous chemicals; RiskAssess (https://www.riskassess.com.au/).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO11-10 BIO11/12-1 BIO11/12-2 BIO11/12-7
Biology 11–12 Syllabus (2025), Year 11 focus area Evolution and ecosystems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-03
Biology 11–12 Syllabus (2025), Year 11 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11WS-01 BI-11WS-02 BI-11WS-07
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities