Peter and Rosemary Grant observed a small group of the large ground finches that colonized Daphne Major in the Galápagos Islands. Within a few years, the descendants of the colonists had evolved beaks that were much larger than those in the original source population. What factors did the Grants think influenced this evolution?

1) Founder effect and genetic drift: Small colonizing population did not represent the original gene pool of the source population and was more likely to undergo genetic drift.

2) Natural selection

Explanation:

Evolution of the population of the finches with larger beaks might have occurred due to one of the following mechanisms:

a) Founder effect and genetic drift: Since the size of the colonizing population was small, it did not carry all the genes and their alleles present in the gene pool of the original population. The small population size made it more likely to evolve by any chance event.

b) Natural selection: The availability of different food types in the new habitat led to the natural selection of the larger beaks as the finches with larger beaks might have been able to better exploit the available food resources.