Question

The bar graph shows the average beak depth (distance from the top of the beak to the bottom) of a population of finches. The data were collected in 1976 and in 1978, after a drought occurred in 1977 in the area.







Which factor BEST describes the change in this population of finches?

Answer 1

Natural selection (directional selection). The 1977 drought changed available food (fewer, tougher seeds), so finches with deeper beaks survived and reproduced more. Alleles for larger beaks increased in frequency, raising the population’s average beak depth by 1978.