Final answer:
The shift in beak size among Galápagos finches in 1977 is an example of evolution by natural selection, with a drought favoring finches with larger beaks able to crack open larger seeds. This natural selection resulted in larger beak sizes in the next generation of finches.
Step-by-step explanation:
The large shift in beak size among Galápagos finches observed around 1977 can be explained by the principles of evolution by natural selection. Peter and Rosemary Grant, researchers who studied these finches, found that during a drought period, the availability of seeds changed. Larger seeds that only birds with larger beaks could crack open were more available, while smaller seeds were scarce.
Therefore, finches with smaller beaks could not survive as well as those with larger beaks. As a result, many small-beaked birds died, whereas large-beaked birds survived and reproduced. This led to an increased average beak size in the population within just two years, illustrating a rapid instance of evolution by natural selection.
Evolution of Beak Sizes in Galápagos Finches
Darwin's finches, or Galápagos finches, exhibit a variety of beak shapes adapted to different food sources on the islands. This diversity enables them to exploit distinct ecological niches.
When environmental conditions alter, such as during the drought the Grants observed, the food availability influences which finches survive based on their beak characteristics.
The surviving finches' traits are then passed down to subsequent generations, leading to a change in the population's traits over time. This adaptive process was one of the key observations that contributed to Darwin's theory of natural selection.