Peter and Rosemary Grant’s long-running study of Darwin’s finches has revealed evolution to be a more dynamic and unpredictable process than Charles Darwin could ever have imagined.
Communications Manager
Peter and Rosemary Grant are evolutionary biologists and Emeritus Professors at Princeton University. They have been studying Darwin’s finches on the Galapagos islands since 1973, carrying out intensive fieldwork on Genovesa for ten years and on the small island of Daphne Major for 40 years.
To celebrate the publication of a new edition of their landmark study, we invited them to share some insights from their remarkable research.
Charles Darwin believed you could not observe or study evolution because it happens far too slowly. Our study on Daphne Major has shown the opposite. Evolution by natural selection of long-lived birds can be witnessed, measured and interpreted in a matter of years. For example, Darwin’s mechanism of natural selection causes divergence in size when two species compete for a food resource. During a prolonged drought of two-and-a-half years, we witnessed the average beak and body size of the population of the medium ground finch (Geospiza fortis) becoming smaller after its larger members were outcompeted for food by another larger finch species, Geospiza magnirostris.
Charles Darwin believed you could not observe or study evolution because it happens far too slowly. Our study on Daphne Major has shown the opposite.
They alert us to the possibility that evolutionary change is taking place in other plants and animals in Galapagos, unstudied and therefore unrecorded. The Galapagos Archipelago is young, the oldest island less than 5 million years old, and it is dynamic. Not only is it volcanically active and subjected to the El Niño Southern Oscillation, with years of excessive rainfall interspersed by droughts, but over the last million years it has experienced ten glacial cycles that substantially altered the sea level, resulting in islands fusing together and splitting apart as water was either locked up at the poles or released during the interglacials. Thus, populations of plants and animals were alternately brought in contact with each other or split apart.
They show what happens to bird populations in the natural state on uninhabited islands. Their numbers oscillate between highs and lows in population sizes from abundance to scarcity. They also show that species hybridise in nature, leading to a reshuffling of genetic factors that can fuel changes through natural selection when the environment changes.
Darwin’s finches, named after Charles Darwin, are small land birds, 17 species of which are endemic to the Galapagos Islands.
The most conspicuous change has been in the number of people, both visitors and residents. Less conspicuous are the changes brought about by introduced species. For example, the avian vampire fly (Philornis downsi) has now established itself and is responsible for higher mortality in finches and flycatchers. Similarly, introduced yellow paper wasps (Polistes versicolor) feed on caterpillars and deplete the supply of this important food for the finches. Positive changes are the increasingly comprehensive efforts to solve the outstanding conservation problems.
We are sure he would be delighted to discover that evolution by natural selection has been measured in one of the species of finches that today bear his name. He would feel vindicated, and would probably add that he wished he had the genetic knowledge available to us today, and had been able to spend more than five weeks on Galapagos!
We have a range of resources to inspire and educate young people about evolution and the wonders of Galapagos, tailored to different age groups and available in both English and Spanish.
