This is an interesting example of natural selection that also fueled Darwin's thought. Essentially, we have that in this habitat, there are predominantly two forms of food for finches, the one requiring a big beak (such as large nuts) and the other requiring a shorter and thinner beak. The members of the population with intermediate beaks could eat with difficulty from both sources of food; but finches that had a little thinner or a little bigger beak could get easily access to more food from one source and had an advantage in that they were specializing. This meant that they were fitter to reproduce and pass on this variation to their progeny than the birds with intermediate beaks; this would finally lead to two different populations, one with big beaks and one with smaller beaks, just as Darwin (and Hendry) observed.