Chapter 3, Problem 3Q

Think about how the finch bill data demonstrate Darwin’s postulates.

1. a. What would figure 3.10 have looked like if bill depth was not variable?
2. b. What would figure 3.15 look like if bill depth was variable but the variation was not heritable?
3. c. In figure 3.11, why is the line drawn from 1978 data, alter the drought, higher on the vertical axis than the line drawn front 1976 data, before the drought?

Figure 3.10 Variation In beak depth in medium ground finches This histogram shows the distribution of beak depth in medium ground finches on Daphne Major in 1976. A few birds have shallow beaks; a few birds have deep beaks, most birds have medium beaks. N stands for sample size; the blue triangle along the horizontal axis indicates the mean, or average Redrawn from Boag and Grant (1984b).

Figure 3.11 Heritability of beak depth in Geospiza fortfs This graph shows the relationship between the beak depth of parents and their offspring. Mid parent value is the average of the mother and father; mid offspring value is the average of the offspring. The lines in the graph are statistical best-fit lines. Data for both 1978 and 1976 show a strong relationship between the beak depth of parents and their offspring. Redrawn from Boag (1983).

Figure 3.15 Beak depth in the finches hatched the year before the drought versus the year after the drought The red triangles represent population means Redrawn from Grant and Grant (2003).