Darwin’s finches are some of the most visible and recognizable symbols of evolution in the world today. Biology textbooks feature them prominently, and the National Academy of Sciences has enshrined them in the entrance of their headquarters in Washington, DC. Surely the finches that Darwin collected on the Galápagos islands were a central feature of his evolutionary theory, right?
It was only in 1845, in the second edition ofThe Voyage of the Beagle, that Darwin included a tantalizing sentence about the Galápagos finches:
Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.3
However insightful this statement may have been, Darwin never published anything else about the Galápagos finches for the rest of his life. Nor did he publicly present these birds as direct evidence for this theory of evolution.4
If these finches were so important to Darwin’s evolutionary theory, why did he remain silent about them? One of his comments in The Voyage of the Beagle provides us with a clue:
Unfortunately most of the specimens of the finch tribe were mingled together; but I have strong reasons to suspect that some of the species of the subgroup Geospiza are confined to separate islands.5
When Darwin was exploring the Galápagos himself in 1835, he had not formulated his theory of evolution yet, and thus he did know what data would be necessary to make definitive conclusions about finch evolution. In particular, he did not keep careful track of which of his specimens came from which islands. Moreover, as was customary among naturalists at that time, Darwin only collected a small number specimens—he brought home only 31 finches and 64 total birds from the Galápagos.6
Though Darwin sensed that these birds were truly special, he lacked sufficient evidence to reach any specific conclusions about their evolutionary origins. It would be up to the rest of the scientific community to carry out the necessary empirical research. Subsequent expeditions in 1868, 1891, 1897, and 1905 brought back thousands of Galápagos finch specimens, but instead of unlocking the mysteries of evolutionary theory, the Galápagos finches became a great enigma.7
A century after Darwin's voyage, scientists still struggled to explain the staggering variety of finches on this tiny, remote archipelago. By the mid-1930’s, British Museum ornithologist Percy Lowe argued that the finches presented a "biological problem of first class importance", and he told the British Association for the Advancement of Science that the finches displayed a "bewildering diversity, intergradation, and distribution."8 Who would be up to the challenge of making sense of such tremendous biological complexity?
David Lack had an exceptionally keen eye for bird-watching, and he possessed a passion to match it. By age 15, he had already observed 100 distinct species of birds, and before entering college, authored his first scientific paper. At Cambridge University in the early 1930’s, Lack was disappointed to find that his zoology professors taught “nothing about evolution, ecology, behavior or genetics, and of course nothing about birds.”9 In fact, at that time, there were only two professional ornithologists in all of Britain!
Thus David Lack took it upon himself to create his own learning opportunities. As an undergraduate, he became the president of the Cambridge Ornithological Club, traveled to Greenland for a bird-watching expedition, and cultivated a relationship with the prominent biologist Julian Huxley (grandson of Thomas Henry Huxley). Huxley was an inspiring mentor and encouraged Lack to expand his research further by studying tropical birds.10 Following this advice, Lack embarked on a research trip to Tanzania in the summer of 1934. But his greatest adventure was yet to come.
In 1937, Lack became fascinated by the scientific mysteries surrounding the Galápagos finches. But in order to study their behavior, Lack would need to travel to remote islands halfway around the world. How could he possibly get there? Once again, Julian Huxley was tremendously supportive and raised funds from two prominent scientific societies to pay for his expedition. After a long delay, David Lack and five companions finally set off on their journey.
Instead of residing in comfortable quarters aboard a royal naval ship, Lack’s group subsisted on a shoestring budget, traveled on commercial steamers, and stayed with local settlers. Their experience was definitely not a romantic tale of imperial expedition:
The Galápagos are interesting, but scarcely a residential paradise. The biological peculiarities are offset by an enervating climate, monotonous scenery, dense thorn scrub, cactus spines, loose sharp lava, food deficiencies, water shortage, black rats, fleas, jiggers, ants, mosquitoes, scorpions, Ecuadorian Indians of doubtful honesty, and dejected, disillusioned European settlers.11
Whereas Charles Darwin spent only nineteen days on the shores of the Galápagos, Lack and his crew conducted more than five months of meticulous and exhausting study in the harsh climate. At that time, even the finches themselves provided little solace. Lack wrote,
Darwin’s finches are dull to look at, not only in their orderly ranks in museum trays, but also when they hop about the ground or perch in the trees of the Galápagos, making dull unmusical noises. Only the variety of their beaks and the number of their species excite attention.12
Despite his personal discomforts (or perhaps because of them), Lack did see something on the Galápagos that no one had ever seen before—natural selection at work among its finches through interspecies competition.13
When the birds’ breeding season ended in 1939, Lack was ready to return to his home in England. But the captive finches that he had brought with him fared so badly on the voyage home that he detoured to San Francisco and put them in the care of the California Academy of Sciences. Turning this mishap into an opportunity, Lack stayed there for five additional months to study the Academy’s enormous collection of Galápagos finch specimens.14
To complete his systematic research, Lack then travelled across the United States to study the Galápagos finch collection housed at the American Museum in New York.15 Altogether, Lack examined more than 8000 specimens and specifically measured the length, width, and depth of all their beaks.16
Lack’s final obstacle was in getting his research published. Though he completed his academic manuscript “The Galápagos Finches—A Study in Variation” in 1940, paper shortages during World War II delayed its publication by the California Academy of Sciences until 1945. Were he only interested in making an original contribution to science, Lack could have stopped here and congratulated himself on a job well-done. However, his motivation sprung from a deeper source:
I did not watch birds primarily for scientific reasons but for sheer enjoyment, and from the age of 15 onward returned day after day in a glow of excitement after seeing a new bird or a new habit.17
Lack’s joyful fascination with the Galápagos finches inspired him to continue developing his conclusions long after returning from his expedition. While waiting for his academic paper to be published, he began writing a book that would enable students and the general public to share his excitement about these remarkable birds and the evolutionary processes that shaped them.
First published in 1947, Lack’s book became tremendously influential. Before this time, biology textbooks had never even mentioned the Galápagos finches. But after David Lack’s study, the finches became a primary example of evolution by natural selection, specifically adaptive radiation. Not only did textbooks fully rely on Lack’s findings, they also followed his lead in calling them “Darwin’s finches”, the title of Lack’s famous book.18
What was it about these birds that made them such a prominent symbol of evolution? As Darwin himself pointed out, the numerous Galápagos finch populations each have distinctive beaks, and he speculated that they could have evolved from an ancestral species that came to the islands. But a complete picture of finch evolution would have to wait another hundred years, when David Lack arrived.
During his five months on the Galápagos, including both the rainy and dry seasons, Lack observed that these beak differences enable the finches to subsist on different kinds of food:
The beak differences between most of the genera and subgenera of Darwin's finches are clearly correlated with differences in feeding methods. This is well borne out by the heavy, finch-like beak of the seed-eating Geospiza, the long beak of the flower-probing Cactornis, the somewhat parrot-like beak of the leaf, bud, and fruit-eating Platyspiza, the woodpecker-like beak of the woodboring Catcospiza, and the warbler-like beaks of the insect-eating certhidea and Pinaroloxias.19
But it is also fascinating to consider how these birds got to be so different in the first place. How did a finch come to have a beak like a “parrot”, “woodpecker”, or “warbler”? The answer lies in the distinct characteristics of the Galápagos. Because the islands are so remote, no actual parrots, woodpeckers, or warblers ever settled on it. In the absence of these species, the Galápagos finches were able to adopt feeding habits and forms that they would never have taken on a large continent full of other birds competing for food. The isolation of these islands offered just the right conditions for us to see living examples of adaptive radiation.21
Considering the immense popularity of the Galápagos finches, it is quite surprising to learn that Charles Darwin himself had so little to say about them. In fact, it was actually David Lack, one century later, who conducted the critical research that immortalized the finches in biology textbooks and popular lore. By naming his landmark book Darwin’s Finches,22 Lack paid homage to the man whose voyage on the HMS Beagle helped transform the study of natural history. But at the same time, Lack also obscured the fact that evolutionary biology is an enterprise conducted by a large community of brilliant scholars, not just the product of one man’s efforts.
This tendency to immortalize “great men of science” has also led many people to refer to modern evolutionary theory as Darwinism, despite the fact that it has substantially changed and developed over the past 150 years. It is important to give credit where credit is due, and if that’s the case, we should seriously reconsider how we refer to the Galapagos finches. Evolutionary biologist Dolph Schluter, who studied the finches several decades after David Lack, had this to say: "I find Lack's intuition really stunning given how little information he had. He's my hero actually… They should be called Lack's finches."23