Effects of Natural Selection on Finch Beak Size

This activity guides the analysis of a published scientific figure from a study that investigated evolutionary changes in seed-eating finches after a drought.

In 1976, seeds on the Galápagos island of Daphne Major were diverse and plentiful. A drought in 1977, however, reduced seed availability. The figure in this study shows the distribution of beak depths (measures of beak size) for the island’s medium ground finches. White bars represent the distribution for the initial population in 1976, and black bars represent the distribution for the finches that survived the drought in 1977. The carets on the x-axis indicate the mean beak depths for each group. The “Educator Materials” document includes a captioned figure, background information, graph interpretation, and discussion questions. The “Student Handout” includes a captioned figure and background information. The “Finch Presentation” PowerPoint provides an alternative approach for guiding students through a discussion of the figure.