Observing evolution as it happens
Emily Singer writes in Quanta:
When Rosemary and Peter Grant first set foot on Daphne Major, a tiny island in the Galápagos archipelago, in 1973, they had no idea it would become a second home. The husband and wife team, now emeritus biology professors at Princeton University, were looking for a pristine environment in which to study evolution. They hoped that the various species of finches on the island would provide the perfect means for uncovering the factors that drive the formation of new species.
The diminutive island wasn’t a particularly hospitable place for the Grants to spend their winters. At less than one-hundredth the size of Manhattan, Daphne resembles the tip of a volcano rising from the sea. Visitors must leap off the boat onto the edge of a steep ring of land that surrounds a central crater. The island’s vegetation is sparse. Herbs, cactus bushes and low trees provide food for finches — small, medium and large ground finches, as well as cactus finches — and other birds. The Grants brought with them all the food and water they would need and cooked meals in a shallow cave sheltered by a tarp from the baking sun. They camped on Daphne’s one tiny flat spot, barely larger than a picnic table.
Though lacking in creature comforts, Daphne proved to be a fruitful choice. The Galápagos’ extreme climate — swinging between periods of severe drought and bountiful rain — furnished ample natural selection. Rainfall varied from a meter of rain in 1983 to none in 1985. A severe drought in 1977 killed off many of Daphne’s finches, setting the stage for the Grants’ first major discovery. During the dry spell, large seeds became more plentiful than small ones. Birds with bigger beaks were more successful at cracking the large seeds. As a result, large finches and their offspring triumphed during the drought, triggering a lasting increase in the birds’ average size. The Grants had observed evolution in action.
That striking finding launched a prolific career for the pair. They visited Daphne for several months each year from 1973 to 2012, sometimes bringing their daughters. Over the course of their four-decade tenure, the couple tagged roughly 20,000 birds spanning at least eight generations. (The longest-lived bird on the Grants’ watch survived a whopping 17 years.) They tracked almost every mating and its offspring, creating large, multigenerational pedigrees for different finch species. They took blood samples and recorded the finches’ songs, which allowed them to track genetics and other factors long after the birds themselves died. They have confirmed some of Darwin’s most basic predictions and have earned a variety of prestigious science awards, including the Kyoto Prize in 2009.
Now nearly 80, the couple have slowed their visits to the Galápagos. These days, they are most excited about applying genomic tools to the data they collected. They are collaborating with other scientists to find the genetic variants that drove the changes in beak size and shape that they tracked over the past 40 years.Quanta Magazine spoke with the Grants about their time on Daphne; an edited and condensed version of the conversation follows.
QUANTA MAGAZINE: Why did you decide to go to the Galápagos? What drew you to study finches specifically?
ROSEMARY GRANT: I had more of a genetics background and Peter more of an ecological background. But we were both interested in the same process — how and why species form. We both wanted to choose a population that was variable in a natural environment.
The Galápagos had several things that were very important. The islands are young, and there are lots of populations of finches that occur together and separately on the different islands. The islands were in close to pristine condition, having never been inhabited by humans. We knew that any changes would be natural changes and not the result of human interference.
The climate is extremely dynamic. The archipelago lies astride the equator and is subject to the El Niño–Southern Oscillation phenomenon. There are years with a terrific amount of rainfall, which is very good for finches. But it can also get years of drought, when many birds die. We now know that up to 80 to 90 percent of birds on the small islands die in times of drought. Those extremes would give us the opportunity to measure the climate variations that occurred and the evolutionary responses to those changes.
PETER GRANT: We had three main questions in mind. First, how are new species formed? That’s the Darwinian question of the origin of species. Second, do species compete for food? If they do, what effect does that have on the structure of animal communities? That was a hot topic in the early 1980s. There was very little experimental evidence at the time, so there was plenty of scope for taking a position one way or another. Third, why do some populations exhibit large variation in morphological traits like body size and beak size?
What was it like stepping on the island for the first time? . . .