In the 1980s, biologists Peter and Rosemary Grant caught and measured
all the birds from more than 20 generations of finches on the
Galapagos island of Daphne Major. In one of those years, 1977, a
severe drought caused vegetation to wither, and the only remaining
food source was a large, tough seed, which the finches ordinarily
ignored. Were the birds with larger and stronger beaks for opening
these tough seeds more likely to survive that year, and did they tend
to pass this characteristic to their offspring? The data are beak
depths (height of the beak at its base) of 751 finches caught the year
before the drought (1976) and 89 finches captured the year after the
drought (1978).