While the Grants were on the Galápagos, a drought occurred. As a result, fewer seeds were available for finches to eat. Birds with smaller beaks could crack open and eat only the smaller seeds. Birds with bigger beaks could crack and eat seeds of all sizes. As a result, many of the small-beaked birds died in the drought. Birds with bigger beaks survived and reproduced (see Figure below ). Within 2 years, the average beak size in the finch population increased. Evolution by natural selection had occurred.
During a particularly bad infestation of caterpillars Mark sprayed his orchards with pesticide. That year most of the caterpillars died. The next year the pesticide also seemed to be effective but as the years passed more and more caterpillars seemed to be surviving until Mark had no choice but to find a new and stronger pesticide.
After several years were most of the caterpillars susceptibal or immune to the pesticide? ?