It was the fourth consecutive and worst year of drought in the islands. Conditions were desperate. Few seeds remained in the soil, and those that did tended to be the toughest and hardest to crack. Imagine you are a common ground finch, Geospiza fortis, and you are about to undergo natural selection. Because of the drought, plants have stopped producing seeds, and the seeds in the soil are rapidly getting eaten up.
Finches use their bills as seed crackers.
Because physical properties and the laws of physics apply to living as well as to nonliving things, we can explore some physical properties of finch bills by substituting models for the bills. Although there are no pecans on the Galapagos Islands, they will be used to model, or stand in for, the large tough seeds that were the only seed species actually available during the drought of 1977. Student Exploration 1. Your bill strength Take a number from a hat or a box or a shoe. Each of you has your own bill force, but you will find it easier to do the cracking if you work in groups.