After 40 years of research on Darwin’s finches, Peter and Rosemary Grant have written their valediction

Peter and Rosemary Grant sit in a cave on Daphne Major Island in 2004. The cave generally was used for cooking; here, Peter is shown measuring the beak of a finch.
Peter and Rosemary Grant sit in a cave on Daphne Major Island in 2004. The cave generally was used for cooking; here, Peter is shown measuring the beak of a finch.
Lukas Keller/University of Zurich

Peter and Rosemary Grant are members of a very small scientific tribe: people who have seen evolution happen right before their eyes.

For the Grants, evolution isn’t a theoretical abstraction. It’s gritty and real and immediate and stunningly fast. To witness evolution, they needed cameras, measuring instruments, computer databases, and advanced laboratory techniques for genetic analysis. Most of all, they needed to be there in person ­— in the field, on the ground, enduring baking days and sweltering nights, cooking in a cave, sleeping in tents, and somehow sustaining themselves on a tiny island in the Galápagos that any reasonable person would declare to  be uninhabitable.

The island is a steep-sided volcanic extrusion named Daphne Major. It is so inaccessible that it has no beach, no landing area, just wave-chewed vertical edges plunging into water so deep it might as well be bottomless. Visitors don’t land on the island so much as they leap to it, jumping from a small boat onto a tiny ledge.

In the Galápagos, the Grants studied Charles Darwin’s finches for 40 years. That was not the original plan when they first visited in 1973: They thought they’d be at it for two. Now the research is done — a monumental achievement, and the subject of a valedictory book, 40 Years of Evolution, published this month by Princeton University Press.

The story of Peter and Rosemary Grant is an unusually satisfying tale. Obviously there’s the scientific success: They’re legendary in their field. In their office in Eno Hall they have a blown-up photograph of the two of them receiving the Kyoto Prize — often regarded as the Japanese equivalent of the Nobel — for their lifetime achievements in basic science. They also have achieved renown among the general public, thanks to the Pulitzer Prize-winning 1994 book The Beak of the Finch by Jonathan Weiner.

The Grants have now been married 52 years. They’re both 77 years old. In a practical sense, their work is done. “We feel with the book we’ve written, we’re closing a chapter on our field research,” Peter Grant says. “If we go back at all, it’ll be for short periods, doing interesting things.”

And yet they can’t truly be finished with their research, because evolution never screeches to a halt, or reaches a final, optimizing moment. Evolution isn’t progressive, linear, deterministic, and destination-driven. Evolution never retires.

“We never reached an identifiable point of diminishing returns, or experienced a sense of completion,” the Grants write near the end of their book. “[O]ne conclusion we draw after 40 years is the same as the conclusion we drew after 20 years: Long-term studies in ecology and evolution should be pursued in an open-ended way because for many of them there is no logical end point. Darwin’s finches have much more to teach us.”

The Grants are almost comically warm and fuzzy, and still in great running condition, save a couple of dents in their fenders. They’ve been at Princeton since 1985 and live a couple of miles from campus, not far from Lake Carnegie.

Their relationship reflects the biological principle of fusion: They have not merely adapted to one another, but have merged to a point in which there is little sense in writing about one without immediately discussing the other. They are deferential to one another, never interrupting, and often looking at one another to see if the other wants to go first.

When I ask what Darwin didn’t know when he visited the Galápagos in 1835, they answer in unison: “Genetics.”

Once, when Peter was out of town giving a talk and Rosemary was in Princeton, they independently had the idea of writing a paper discussing the effects of natural selection on a certain plant on the Galápagos island of Española. When Peter returned, he said, “Here’s my paper.” She said: “Well, here’s mine.” They decided to give both papers to their graduate students. One student said, “Both papers are rubbish.” The Grants put their heads together and came up with one paper that was vastly better than the two originals.

She’s from the Lake District in England and attended the University of Edinburgh; he’s from London and attended Cambridge. They met at the University of British Columbia in Vancouver in 1960, where Rosemary was lecturing in embryology, cytology, and genetics, and Peter — still a graduate student in zoology — was her teaching assistant. They married in early 1962. After stints at McGill University and the University of Michigan, the Grants arrived at Princeton in 1985. Among other things, both taught upper-level undergraduate courses in ecology and evolutionary biology, along with a course for first-year graduate students on new developments in ecology, evolution, genetics, and conservation.

“I don’t think we’ve ever competed with each other,” Rosemary says. “We come at things very differently. But it’s always had a synergistic effect.”

It helps to have a sense of humor, she adds.

Rosemary: “We’re not polite to each other.”

Peter: “I’m polite to you!”

The island of Daphne Major is essentially pristine, unaffected by human influence, and largely free of the invasive species commonly found on settled islands. It is young: It rose from the sea only about 15,000 years ago. Daphne is, in effect, a field laboratory.

And Darwin’s finches are ideal subjects for field research in evolutionary biology. They are tame, and thus easily captured for closer study and measurement (“Beak depth was measured with calipers in the plane of the anterior nares at right angles to the commissure, the line at which upper and lower mandibles meet,” the Grants wrote). There are either 13 or 14 species of “Darwin’s finches” — two populations of a warbler finch don’t mix and have genetic differences but look very similar, hence the ambiguity. The finches of the Galápagos represent a relatively recent evolutionary event, descending from a common ancestor that came from the mainland two million to three million years ago.

The Grants did their fieldwork as a family; their daughters, Nicola and Thalia, grew up as part of the scientific team. The girls were 8 and 6 when they first went to the islands. They were homeschooled by their mother during the hottest part of the day, and in cooler hours would do their own research. Each could bring only a single small bag for the entire months-long camping trip. At night they’d listen to music on a Walkman cassette player. Nicola, the older daughter, remembers reading the Lord of the Rings trilogy and War and Peace. They had a violin, and serenaded the blue-footed boobies. They befriended the cub of a sea lion.

“Quite simply, it was magical,” says Nicola. The Galápagos Islands “are like what the Celts call ‘thin places’ — places where the veil between heaven and earth is frayed. ... I don’t remember ever being bored. We spent our days exploring whatever island we were on, swimming, inventing games, reading; and the older we got, the more we helped our parents with their research work.”

Thalia: “There is always a moment in every child’s life when they suddenly seem to wake up to the world, and for me it was in Galápagos at age 6. It feels like I was born there. For better and worse Galápagos has shaped my whole life, and every direction I have taken.” She became a scientist, writer, and artist, the co-author of a book about Darwin and Galápagos.

Conditions were harsh. An early explorer, the bishop of Panama, wrote after a 1535 visit to the volcanic archipelago, “It looked as though God had caused it to rain stones.” In his novel Galápagos,Kurt Vonnegut wrote of the Spanish explorers: “They did not claim the islands for Spain, any more than they would have claimed hell for Spain.”

Charles Darwin visited in 1835 during the long voyage of the Beagle. He collected specimens of birds, to which he initially paid minimal attention. When he returned to London, zoologist John Gould informed Darwin that his bird collection included a host of new species of finches. Darwin wrote in his diary: “The most curious fact is the perfect gradation in the size of the beaks of the different species ofGeospiza ... Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might fancy that, from an original paucity of birds in this archipelago, one species has been taken and modified for different ends.” In reading these lines, we see the theory of evolution in gestation.

In 1981, a new bird — the Big Bird — arrived on Daphne; one is shown at top. Though still immature, it had a beak that was larger and blunter than a typical medium ground finch, shown above. A prolonged drought opened room in the ecosystem for a new,
In 1981, a new bird — the Big Bird — arrived on Daphne; one is shown at top. Though still immature, it had a beak that was larger and blunter than a typical medium ground finch, shown above. A prolonged drought opened room in the ecosystem for a new, hybrid Big Bird lineage, but the Grants still don’t know whether it will survive or lose its distinctiveness.
P.R. Grant and B.R. Grant

In the middle part of the 20th century, the biologist David Lack visited the Galápagos and stuck around only for a matter of months. Evidently he did not care for the place, as he wrote in Darwin’s Finches in 1947: “The biological peculiarities are offset by an enervating climate, monotonous scenery, dense thorn scrub, cactus spines, loose sharp lava, food deficiencies, water shortages, black rats, fleas, jiggers, ants, mosquitoes, scorpions, Ecuadorean Indians of doubtful honesty, and dejected, disillusioned European settlers.”

Daphne Major is pretty much dead center in the archipelago, between the large islands of Santa Cruz and Santiago. Its total surface area is less than half a square kilometer.

I assumed the Grants had made allowances for the harshness of the environment by jumping into a boat now and again for a quick trip to civilization to take in a movie or enjoy a fine meal with a glass of wine poured from the napkined wrist of a sommelier. But no. There were no daily departures. There wasn’t a boat at all. Without elaborate preparations, they could not leave. They had to bring all their supplies, including water, for months at a time. Still, the Grants loved what they were doing. Peter remembers that one time when he got off the island of Genovesa (another site for long-term fieldwork) he was asked, repeatedly, if he was grateful that he finally could take a hot shower. He said he’d prefer to finish his fieldwork. People persisted: Surely he was happy to be in civilized society! After protesting a few times, the scientist decided to play along. Sure, great to be back, he’d say — not meaning it at all.

The climate ranged from awful to brutal. There were prolonged droughts and prolonged, soaking, miserable rainy seasons. They would have to do much of their work early in the morning, before the heat became unbearable, the lava rock heating up under the equatorial sun. Weiner writes in The Beak of the Finch, “On many days the little island feels like the solar face of Mercury.”

The Galápagos Islands are in the line of fire when the Pacific surface warms up in an El Niño year and spawns daily, endless rainfall. During the wet years, the Grants struggled to dry out, even briefly.

This oscillation of misery would prove essential to the scientific process, for the climatic extremes were, the Grants discovered, winnowers of the weak and major drivers of natural selection.

In what should have been the rainy season of early 1977, only 24 millimeters of rain fell. The Grants watched nature brutalize the two main finch species on Daphne, the cactus finch (Geospiza scandens) and the medium ground finch (Geospiza fortis). Most of the birds died.

The finches feed on different things — some feed on cacti, some will suck the blood of other animals — and their beaks have evolved to different sizes and shapes for this purpose. The Grants focused much of their research on the medium ground finches, which had short beaks adapted for eating small seeds. During the drought, the small seeds grew scarce, and the ground finches had to find alternative food sources. The only survivors were the medium ground finches with larger beaks capable of breaking larger seeds.

Beak size is heritable, and the ensuing Geospiza fortis generations had measurably larger beaks. This was natural selection (from the killer drought) and evolution (from the passing of the genes for larger beak size) in action, witnessed over just two years.

Then came the opposite extreme: Endless rains in 1982–83. The desiccated island suddenly was lush, and entangled by vines that grew several inches a day. The medium ground finches with smaller beaks proved more efficient at feeding on the superabundance of seeds and fruits. Now the average beak size for fortis nudged downward.

The drought of 1977 and the deluge of 1983 gave the Grants and their collaborators stunning insights into evolution in action and generated scientific papers that became iconic in the field of evolutionary biology. Hopi Hoekstra, an evolutionary biologist at Harvard and a huge fan of the Grants, says, “Anyone who has spent time ‘in the field’ knows that nothing goes as planned. Everything that can go wrong eventually will. But here is one of Peter and Rosemary’s greatest gifts: They can take an obstacle and make it into an opportunity. For example, the Grants can turn a major drought or an El Niño event into a beautiful experiment, and in turn gather some of the most celebrated data and results in evolutionary biology!”


We all know how evolution works — or we think we know. Here’s what I would have told you (before interviewing the Grants) about the origin of new species: It involves “natural selection.” There are ecological niches. There’s competition. There’s genetic mutation. Life is hard and nasty and at some point you have the “survival of the fittest.” Is that good enough? No? OK. Time is a key factor: Lots and lots of time will allow evolution to happen. It’s like the secret ingredient, the sugar, in the recipe. With enough time your original species will turn into two species, including one that has horns or a tusk or dorsal spines or some kind of scary frill on the back of the head like a triceratops.

The truth is more complicated than that.

Evolution isn’t linear. There are always many species in the mix, and they are co-evolving, competing, innovating, reproducing, dying, sometimes even going extinct. You have variations within species. There is simultaneous divergence and convergence. There are contrary winds. There are genetic drifts and back-currents. There is hybridization. There are invasive species and a changing competitive landscape. Evolutionary change when viewed in the fossil record looks slow only because the oscillations — the herky-jerky improvisations — are hard to discern, and just the longer-term trends are readily preserved.

Over their seasons on Daphne, the Grants even witnessed the appearance of what some would call a new species. The Grants refer to it, more cautiously, as a “lineage.”

Here’s what happened: In 1981, at a point in their research when they literally knew every finch on the island, a new bird arrived — a large one, 28 grams. The interloper, labeled 5110 (every bird gets a number), likely came from Santa Cruz, a large island visible from Daphne. It looked a lot like a fortis,but also like a scandens. Genetic analysis showed 5110 to be a cross between a fortis and a fortis-scandens hybrid. They called it “the Big Bird.”

The Big Bird had a unique song and, when mature, shiny black plumage that was different from the indigenous Daphne birds. It also was extremely “fit” in the Darwinian sense — and promiscuous, surviving another 13 years and mating with six females, producing 18 offspring. It mated with severalfortis-fortis-scandens hybrids, then with fortis females, and began a new line of Big Birds that sang the song of the original immigrant.

The Grants noticed more changes during a prolonged drought in 2003 and 2004, but these were different than the changes seen in the 1977 drought. This time, when seeds became rare, the larger members of the fortis species were outcompeted for the large seeds by another, bigger species, the large ground finch, Geospiza magnirostris. Meanwhile, the smaller fortis birds that fed on small seeds and needed less nourishment had a better chance of surviving. This was natural selection at work: The fortis population became smaller for generations to come.

The shrinking of fortis opened up room in the ecosystem for the new, hybrid, Big Bird lineage, which began thriving after the drought ended and the island greened up again. “An unresolved question is how long we should wait to see if the lineage will lose its distinctness by breeding with another species, or become extinct through fitness problems with inbreeding,” Peter Grant says. “We are reluctant to name the lineage as a new species when it has been in existence for only a few generations and may be short-lived.”

Scientists previously had reported seeing the processes of natural selection among bacteria, honeycreepers, cichlid fish, and fruit flies. As Peter Grant puts it, “Until we began, it was well understood that agricultural pests and bacteria could evolve rapidly, but I doubt that many people thought that about big, vertebrate animals.”

The Grants believe that hybridization is an important force in the rise of new species, and think this applies, too, to human evolution. For a long time, for example, paleontologists believed that Neanderthals and “modern homo sapiens” did not interbreed when they came into contact in prehistoric times, but recent research indicates that about 20 percent of Neanderthal genes have been preserved in our species. “It’s almost been a hobbyhorse of ours,” Peter says. “We were saying, ‘I bet there has been gene exchange between the lineages of homo sapiens throughout their evolution.’”

The Grants’ new book is targeted at both lay readers and scientists familiar with their work, and broadly discusses their findings about natural selection, hybridization, population variation (why do some populations of birds vary more dramatically in beak size?), the potential vanishing of a species through interbreeding, and, of course, the potential origin of a new species — the Big Bird lineage. They also touch on global warming and its possible effect on Darwin’s finches. Most of all, the book is an affirmation of the importance of long-term fieldwork as a way of capturing the true dynamism of evolution.

“Perhaps the biggest contribution of the Grants’ work is simply the realization not only that evolution can be studied in real-time, but that evolution doesn’t read the textbooks,” observes Jonathan Losos, a Harvard evolutionary biologist.

I ask the Grants what Darwin might say about their work.

Rosemary: “I hope he would be very happy.”

Peter: “He’d say, ‘Just tell me about this inheritance business.’ Then we’d explain to him about genetics. And then he’d say, ‘Why stop at 40?’ And then I would say, ‘Do you realize we are four years older than you were when you died?’” 

Joel Achenbach ’82 is a staff writer at The Washington Post.