For the first time ever, scientists have observed one species rapidly turning into another in a population of birds in the Galapagos, off the coast of Ecuador.
On the small island of Daphne Mayor, scientists have discovered the progress of speciation in a group of finches which helped British scientist Charles Darwin identify the process of evolution by natural selection.
Back in 1981, Peter and Rosemary Grant, a British couple who are evolutionary biologists at Princeton University, noticed the arrival of a male, non-native species – the large cactus finch, G. conirostris – to the island.
They then observed the male mating with a female of a local species – medium ground finch, G. fortis – which produced fertile chicks. The couple's near-30 offspring are still being observed by the scientists.
"It is an extreme case of something that we are beginning to notice in general over the years: that evolution, in general, can happen very quickly," Roger Butlin, an expert in speciation who was not involved in the study, told the BBC.
Scientists had long believed two different species could not produce fertile offspring capable of being recognized as a new species. However, it has now been established that members of different species can, in fact, do precisely that.
"We no longer debate what defines a species because it is a futile discussion," said Butlin. Instead, observing the finches is of particular interest, given the role of hybridization in creating new species.
In order to verify the new population was genetically distinct from the island's native finches, the Grants collaborated with fellow scientist Leif Andersson at the University of Uppsala in Sweden, who analyzed the population's genetics.
"One would have expected that the hybrid would begin to reproduce with one of the other species on the island until eventually disappearing... but to our surprise we have confirmed that they are a closed reproductive group," Andersson told the BBC.
The researchers have discovered that, after just two generations, complete reproductive isolation of the native species has occurred.
"What we are saying is that this group of birds behaves like a different species: if a taxonomist came to this island and knew nothing of its history, they would say that there are four species here," said Andersson.