Profile of Peter R. Grant

In 1940, as the Second World War escalated, 4-year-old Peter Grant was evacuated from London to a school in the English countryside on the Surrey–Hampshire border. Far from being traumatized by his sudden relocation, Grant, already a budding naturalist, remembers those years fondly.

Peter Grant.

“Our school was in the middle of fields with access to a little bit of forest,” he recalls. “I was just fascinated by the great big diversity of organisms that live in the outside world.” Safe from the destruction in London, Grant collected butterflies, watched birds, and identified flowers.

This early experience helped shape his career in ecology and evolutionary biology, which has resulted in some remarkable accomplishments. Grant is now an emeritus professor and Class of 1877 Professor of Zoology at Princeton University (Princeton, NJ). He was elected to the National Academy of Sciences in 2007.

Grant and his wife Rosemary, who was elected to the Academy in 2008, received the Kyoto Prize in Japan in December 2009. No strangers to international acclaim, the Grants are also members of the Royal Society of London, the Royal Society of Canada, and have won the Royal Society Darwin Medal, the Darwin-Wallace Medal of the Linnean Society, and the Balzan Foundation Prize.

Grant’s Inaugural Article in the November 16, 2009 issue of PNAS details both the random and deterministic processes that can influence the development of a species (1). Grant and his wife observed the immigration in 1981 of a medium ground finch (Geospiza fortis) to Daphne Major, the small volcanic island in the Galápagos chain that has played host to much of the couple’s research. The lone bird was unusual in many respects; it sang an atypical song, was larger than similar birds, had a pointed, oversized beak, and contained alleles that marked it as a hybrid.

The Grants followed the fate of this finch and its descendents for 28 years. In the fourth generation, a severe drought on Daphne Major reduced the lineage to one male and one female; these two birds then bred with each other. The descendents of this pair in the next two generations mated only with each other.

“We witnessed the origin of reproductive isolation,” Grant explains, “and if Darwin were alive, he would declare the lineage to be a new species.”

From British to Mexican Islands

Grant was born in 1936 in southeast London, no more than 15 km from where Darwin wrote his magnum opus on evolution. When Grant returned to the London area near the end of World War II, he attended Whitgift School in South Croydon, and he credits his biology teachers for stoking his interest in the natural sciences.

In college at the University of Cambridge (Cambridge, UK), Grant continued to study biology. He focused on zoology and botany but developed a side interest in geology. Before graduating, Grant decided to experience life “across the pond.” He flew into Montreal, Canada, and hitchhiked west to Vancouver, where he worked as a parking attendant for a summer.

Grant fell in love with British Columbia’s natural beauty—its snow-capped mountain peaks and its wilderness. At the time, professional options were plentiful in North America. “The scope for exploring the biological world appeared to be so much greater in Canada and the United States than in my crowded little island of Britain,” he recalls.

Grant applied for a doctoral program at the University of British Columbia (Vancouver, BC, Canada), and within days of beginning his Ph.D. in zoology he met Rosemary.

“We were the first English people each of us met shortly after our respective arrivals, and we were married a little more than a year later,” he says.

In graduate school, Grant focused on ecology and evolution and examined the degree to which they are interconnected. “The questions I asked were always ‘why’ questions,” he says. “Why are there a few species of animals here and many more over there? Why do animals and plants have the properties they do? The answers are to be found, in many cases, in natural environments.”

An opportunity arose on Mexico’s Tres Marías islands in the Pacific Ocean for Grant and his wife to conduct field studies. They evaluated the beak sizes of the islands’ terrestrial birds, which preceded but informed their later research on Darwin’s finches.

“Compared with their mainland relatives,” Grant says, “the Tres Marías’ birds had, on average, bigger beaks. The bigger the beak, the greater the range of available food items. There is actually a global propensity toward birds having larger beaks on islands, taking advantage of ecological opportunities there.”

This research supported his then-nascent hypothesis that past competition for food between species played an important role in evolutionary changes (2).

Of Mice and Finches

After obtaining his doctorate, Grant embarked on a postdoctoral year at Yale University (New Haven, CT), where he studied with ecologist G. Evelyn Hutchinson. A fellow University of Cambridge graduate, Academy member, and Kyoto Prize winner, Hutchinson’s research on lakes and the freshwater system in the early 20th century launched the modern field of American limnology.

Grant credits Hutchinson with furthering his intellectual development. “He embodied my ideal values of the academic scholar. From him I learned not to be afraid of creative speculation when it can enlighten.”

Grant returned to Canada in 1965, accepting a tenure track position at McGill University (Montreal, QC, Canada). There, he devised a method to test whether the competition hypothesis worked in the present as it seemed to in the past. He switched from birds to mammals and studied the interactions between grassland voles and woodland mice. His research demonstrated that competition for food and space—and not solely environmental cues—drives the behavior of the rodents (3).

During the following decade, Grant felt that in-depth, biologically informed statistical analyses would be needed to test his hypothesis, and he and his wife began searching for model organisms. At the time, “the Galápagos seemed remote, far away. It is the Mecca for evolutionary biologists, but I never thought I’d ever go there.”

Grant recalls reading British evolutionary biologist David Lack’s Darwin’s Finches (4), and inspiration struck. “At the same time Rosemary and I had discussed the question of why some populations are unusually variable, and once again I remembered from Lack’s work that some of the Darwin’s finch populations were among them.”

In 1973, Grant and his wife embarked on their first trip to the Galápagos Islands. They have returned every year since, often spending months at a time on Daphne Major.

Peter Grant working on Daphne Major.

Competition in the Galápagos

Since their first Galapagos visit, Grant has sought to uncover how 14 species of Geospiza finches arose from a single ancestral species on the South American mainland. A comprehensive answer to this question could serve as a model for understanding the origin of biological diversity in a wide range of organisms, he says.

During their initial trip to the archipelago, Grant and his wife caught, banded, and released numerous finches on many of the Galapagos’s islands. They investigated the relationship between different finch species, their food supplies, and beak sizes to determine how the birds had adapted to exploit their respective environments (5). More than 80% of the finches that they had banded on Daphne Major remained on the half-kilometer-wide island. The results from across the archipelago showed a strong signature of the effects of competition, especially under stressful conditions, Grant explains.

Grant and his wife soon realized that Daphne Major’s small size—the island takes less than an hour to traverse end-to-end by foot—provided a safe, if not ideal, environment for their two children, Nicola and Thalia. “Camping with a family held no special perils,” Grant mentions, “and our daughters accompanied us after our first trip. This continued every year until they became undergraduates.”

When they arrived on the island, Grant and his family first had to carry supplies up its steep, rocky face, and then set up tents and a makeshift kitchen in a shallow cave, he says. “Then, we put nets up to capture birds and conduct our research.” The scientists tagged finches with colored bands, weighed them, and took measurements of beak and body size. Later, they also drew a small amount of blood from the birds for genetic analyses.

Witness to Natural Selection

After 13 years at McGill, Grant and his family moved to Ann Arbor, Michigan when he accepted a professorship at the University of Michigan. He and Rosemary continued their trips to the Galápagos, and in 1976 they started banding nestlings with the help of graduate students Peter Boag, Trevor Price, and Lisle Gibbs.

One of their most significant findings occurred in 1977, when Boag was on Daphne and a severe drought struck the islands. Nearly 85% of Daphne Major’s medium ground finch population starved to death. Survival was not random (6).

During the drought, the seed supply for the finches consisted mainly of hard woody fruits of Tribulus plants. Birds had already depleted the smaller, softer seeds of other plants early in the season. Larger finches with bigger beaks that were capable of cracking Tribulus seeds survived at a higher rate than birds with small beaks.

Using measurements of parents and their offspring, Grant and Boag calculated the heritability of beak and body size and found it to be high (7). The next year when the rains resumed, the offspring of the survivors were large and had big beaks, like their parents. Thus, Grant observed that the medium ground finch population had undergone an evolutionary change (8). He had witnessed evolution by natural selection, only five years after he began research in the Galápagos.

Despite differences in the types of finches and the island’s flora, a parallel study conducted by the Grants on an island northeast of Daphne Major, Genovesa, confirmed the results (9). The researchers concluded that weather patterns directly affected the birds’ food supply and therefore played a major role in the fitness of finches.

Five years later, the Grants observed events that would again change the makeup of the finch community on Daphne Major. First was a prolonged rainy season brought by the El Niño-Southern Oscillation. “It was the strongest such event of the last 400 years—it rained for eight months straight, instead of the usual one or two months,” Grant says.

The constant precipitation transformed the island’s vegetation into a community of small seed-producing plants. When the island experienced another drought two years later, small-beaked members of the medium ground finch population had a slight survival advantage. The El Niño rains had altered the food supply, and smaller-beaked finches could more rapidly devour seeds than birds with larger beaks could—the opposite of what had happened a few years earlier (10).

A different species of bird, the large ground finch (G. magnirostris), colonized Daphne Major at around the same time, although the effects of this subsequent colonization would not be felt for 2 decades. “We just had some amazing luck that year,” Grant says.

In late 2003 and going into 2004, another major drought parched the island. “It was as bad as the 1977 drought—almost the same amount of rain fell,” Grant notes. By then, the large ground finches had established a significant population of approximately 300 birds on Daphne Major. These birds competed with larger-beaked medium ground finches for Tribulus seeds and won the struggle for survival (11).

The population of medium ground finches crashed, with 90% dying of starvation. “The survival advantage shifted strongly to the small-beaked members of the medium ground finch population. Evolution by natural selection had occurred again,” Grant says.

Molecular Evolution

The Grants moved their research from the University of Michigan to Princeton University (Princeton, NJ) in 1985, where they have remained ever since. Their trips to the Galápagos have continued, and a flexible teaching schedule has allowed them to vary the season of their visits.

Since moving to Princeton, the Grants have broadened their approach to studying the evolution of Darwin’s finches. Using statistical methods, they have been able to predict the amount of evolutionary change that should occur from a parental generation of finches to their offspring by leveraging the wealth of data they have collected over the years (8).

Collaborations have also paid off for Grant, especially in examining the molecular genetics of evolution. A phone call from Harvard Medical School’s Clifford Tabin initiated a series of studies that identified some of the genes involved in beak size, shape, and length (12). The group examined a list of genetic factors known to be involved in craniofacial development in mammals and in birds to find potential candidate genes in the finches. They discovered that bone morphogenetic protein-4 (BMP-4), which plays a critical role as a signaling molecule in human embryonic development, directed the width and height of finches’ beaks (13). A different signaling molecule, however, determined beak length. Using microarray techniques, the researchers identified calmodulin, and found that the amount of the calcium-responsive protein also varied in finches, according to beak length. “It was the first time that a role for calmodulin had been seen in craniofacial development,” Grant says (14).

Refueling the Genetic Pool

Recently Grant has taken a look at finch hybrids. Typically, finches choose mates on the basis of song, as well as beak size and shape. Nestlings learn the song of their species from their fathers, and the male nestlings copy it. Female birds of the species seek out mates that sing their father’s song. On occasion, males will incorrectly reproduce their species’ song and attract females of another species. The resulting hybrid animals often exhibit phenotypic characteristics of both of their parents, as detailed in Grant’s Inaugural Article (1).

Grant’s research illustrates the conditions under which these hybrid animals survive. “We see it as fission and fusion. Hybrids, such as between G. fortis and G. scandens finches, can be at an advantage under some conditions and at a disadvantage under others, for ecological reasons and not for genetic ones,” he says.

“I learned not to be afraid of creative speculation when it can enlighten.”

“In fact, the birds exist in a kind of equilibrium state, dying and replenishing at a more-or-less equal rate over the long-term,” Grant explains. “We suspect that this fusion/fission oscillation goes on a lot in biological systems.”

Hybrid finches breed not with each other but with their progenitor G. fortis or G. scandens species. This mating pattern “refuels the genetic pool of potential evolutionary responsiveness of each population,” Grant says. In case of a dramatic environmental change, such as drought or monsoon, species with a diverse set of genes, and thus physical capabilities, will be more likely to survive than those that are cut off from this extra genetic input.

“This introgressive hybridization and exchange of genes we see in Darwin’s finches turns out to be of great general significance for evolutionary biology, from bacteria to plants and mammals.” The Grants’ 2008 book, How and Why Species Multiply. The Radiation of Darwin’s Finches, details the results of their work on the multiplication of finch species over 36 years (15).

Long-Term Luck

Increasingly, Grant has focused on synthesizing the many factors at play in evolution. “The direction we’re heading in is to be able to characterize the evolutionary process in any organism in terms of natural ecological influences on the one hand, and genetic factors on the other. We’re closing a gap in our knowledge of the connection between what goes on inside and outside organisms, and eventually, we’ll have a much deeper understanding of the evolutionary process.”

Though he has shuttled between three continents for most of his adult life, Grant’s research exemplifies the benefits of long-term natural studies in one location. He says that he and his wife “gained important insights about evolution from events occurring [long after] we began going to the Galápagos. ‘Luck comes to the prepared mind,’ it is said, and it also comes to those who persist and are in the right place at the right time.”

“Rosemary and I have had that luck several times over through being privileged to work in a fascinating, fluctuating, environment.”