Since then the medium ground finch, a long-time Daphne resident, has evolved to have a smaller beak—apparently as a result of direct competition with the larger bird for food.

Evolutionary theory had previously suggested that competition between two similar species can drive the animals to evolve in different directions.

But until now the effect had never been observed in action in the wild.
…
Jonathan Losos is an evolutionary ecologist at Harvard University in Boston, Massachusetts, who was not involved with the Grants’ work.

“This study will be an instant textbook classic,” he said.