We are only drifting

Author: István Scheuring

Recommended age: 10-99

Number of players: 10-40

Space needed for the game: classroom, where players can move

Difficulty level: 1

Playing time: 10 minutes

Preparation time: 2 minutes

Accessories: Two cards with different colors, or anything which fits our palm and can be divided into two parts.

Short description: The game shows how different genes can disappear from the population merely because of random effects. We demonstrate that smaller the population, faster the gene loss.

Preparations: Cards or small objects, two different ones for each player.

Course of the game: Every player receives two cards (red and blue, in this example). The game leader asks them to close their eyes. Those who are touched by the game leader hide the blue card in their hands and put the red one away (e.g. in their pocket). Those who are not touched by the game leader, hide the red in their hands and put the blue in their pockets. The game leader touches half of the players, so that there are equal red and blue cards in the hands initially. The players start to move about, and for a sign, they pair up. (If there are an even number of players, then the game leader can participate, too.) If the pair holds different colours, one of the players takes the card of the other player, so she has two cards in her hand. She mixes them behind her back, then she hides one card in one hand and another one in the other hand and shows her hands to the other player. The other player then chooses a hand (and thus a card). Let us assume that she has chosen the blue card. Then both players take their blue cards in their hands, and they put the red card in their pockets. The game continues with moving and choosing a new pair as before. After 2-4 rounds the game leader stops the game and asks the players to close their eyes. Then she asks those who have the blue card in their hand to raise their hands (from that she can calculate the number of players with red cards). Then she records this number on a sheet of paper. If all of the players have the same color in their hands, then the game is over. It is interesting then to show how the number of cards changed in function of time. We can make a figure with these data. It is worth playing the game repeatedly to show that because of the random effects, one time the red cards, other times the blue cards will disappear. The time needed for the disappearance of one of the colors will change from game to game as well. I suggest forming smaller groups from the team and play the game within the groups. Thus players can feel that the smaller the group (population), the shorter the time needed for the disappearance of one of the colors. Instead of red and blue cards we can use cards of different forms (circle and rectangular), or cards with different words or small figures (e.g. rose and tulip).

Biological background: The essence of genetic drift is that if there are two alleles with the same fitness, then these alleles transfer to the next generation with equal probability, but randomly (both colors are chosen with equal probability, in our case). Since the size of the population is finite, the result of the random choice will be that one of the alleles disappear from the population.

References: Wikipedia -- Genetic drift