Survival of the Kisses: Natural selection in chocolates

Survival of the Kisses: Natural selection in chocolates

Learning Objective: 

1. Simulate predator-based natural selection on a population of organisms
2. Contrast natural selection with random change in allele frequencies
3. Acknowledge that even random changes in inherited characters is evolution

Assessment: 

Students respond to questions throughout the activity, followed by a class discussion of important points.

Logistics: 

·       Students come to class having read the section of their textbooks that covers natural selection. In a previous class, they have worked on other activities that should have solidified their understanding of exactly what “evolution” means.

·       Each table is given two bags of Hershey’s Kisses candies, containing 10 each of Plain, Almond, Caramel-filled, and Dark Chocolate (total of 40). One bag is labeled “Random”, and the other is labeled “Choice.”  Students are told that the candies in each bag represent a single population of organisms (NOT four different species), and that the four different varieties represent heritable traits.

·       Each person at the table is instructed to eat one Kiss from each of the two bags every “generation.” Students each pick one candy at random from the “Random” bag, and then from the “Choice” bag select one of two varieties that the table has decided will be their group’s preferred types.

·       Once each person has taken one candy from each bag, the remaining candies of each variety in each bag are tallied and converted into a proportion of the total remaining candies. Populations are then brought back up to 40 by adding the number of candies of each type in a manner that preserves the new proportions. The students are told that this represents the population’s annual reproductive event.

o   E.g., if the fraction of plain kisses remaining in a bag is 6/30, this is a proportion of 0.2. To maintain this proportion in the next generation of 40 individuals, the students need to add 2 plain candies to the bag:    6 + 2 = 8;      8 /40 = 0.2

·       This continues for 5 generations, or until no candies remain to bring populations in all bags back up to 40.

·       Students then plot the proportions of each type of kiss in each generation in Excel. Plots in both bags always show changes in proportions, but in the “Choice” bag students see a drop-off among the two varieties their table chose to focus on.

·       Students are then asked to summarize their results, to explain how the “Choice” bag demonstrates how natural selection operates, and to offer their opinion as to whether evolution also occurred in the “Random” bag.