Natural Selection and Camouflage

There are many varieties of the classic natural selection activity.  I've done a couple of them in the classroom, and the kids have fun while actually gaining a deeper understanding of how adaptation can increase survival.  I really think the hands-on approach helps the concept "click" where textbook examples may be less effective.  After doing the activity, students were better able to predict population adaptation and growth patterns when given other examples from nature.

The activity I have done with middle school, high school, and college students involves using beans of two (or three) different colors (i.e., green, red, black) to represent the "prey species" and three different utensils as "predator species."  Students were grouped into threes and each is given a different utensil (i.e., fork, spoon, knife).  Equal numbers of each color of bean were thrown on the ground in a defined area.  I used a hula hoop to define the "feeding range" of the predator.  You can choose different backgrounds, for example, the first go-round you may use a grassy area so that the green beans blend in.  Then you could switch to asphalt for another run, then compare the two to see which "prey species" survived best in each "habitat."  When I did this activity, I allowed the students to "feed" for 1-minute intervals, then recorded the numbers they caught each round.  

With middle school kids, we did one round, took data, then went inside to calculate the next generation based on a set reproductive rate.  More specifically, we subtracted the number we caught of each color from the total starting number, then multiplied the "survivors" times two to calculate the next generation.  We then formed a conclusion based on the data of which species was best adapted to the environment.  Then we compared the effectiveness of each "predator species," and calculated their survival rate based on a set threshold.  For example, if the species caught a minimum of 10 beans, it would have 3 babies.  If it caught a minimum of 20 beans, it would have 5 babies.  Then we determined which predator was most adapted to the environment.

With high school kids, we did several rounds, and after each round we calculated the number "survivors" and added beans to double their population.  For example, if we started with 20 green beans and they caught 15, we would add 5 more green beans.  Then we repeated the 1-minute feeding interval.  We did this for 3 or 4 generations, then graphed the population growth data.  Then students formed a conclusion based on the graph of which prey species was most successful.

I found another activity geared toward younger children that is more active, called "Birds and Worms" from the Project Learning Tree website, http://www.plt.org/educational-nature-activities-for-families.  This involves using different colored items (such as beans, yarn, pasta) spread onto a grassy or forested area.  The students form two teams and have a relay race to see which team can gather worms the fastest.  Then graph the data to see which color they found the most.  Then, repeat in a different background.  A discussion can follow about how camouflage helps species to survive.