The Forest Unseen by David George Haskell


Read: January 2019

How Strongly I recommend it: 10/10

Go to the Amazon page for details and reviews.

1995 Pulitzer Prize winner for general non-fiction. Over a 40 year period, evolutionary biologists Peter and Rosemary Grant studied Darwin’s finches in the Galapagos, surprising even themselves by how quickly they were able to observe evolution in action. The power of Darwin’s theory of evolution has since been demonstrated many times, but Peter and Rosemary Grant were the first to do so successfully. A great book about one of the most exciting studies of animals in the wild and evolution in general.

The text below is taken both from my personal notes and also the author’s writing (exported as kindle highlights).


In 2004, researchers identified gene BMP4, one of the key genes that sculpts and resculpts the finches’ beaks under the pressure of natural selection. BMP4 is also the same gene that helps to shape the human face.

Peter and Rosemary Grant are recipients of The Kyoto Prize, awarded to “those who have contributed significantly to the scientific, cultural, and spiritual betterment of mankind.”


“If I have seen further it is by standing upon the shoulders of Giants.” Isaac Newton

The volcanoes of the Galápagos are Darwin’s shoulders. “Origin of all my views,” he called them. Origin of Origin of the Species.

The Grants do what Darwin could not. Return to the Galápagos year after year. The Grants see what Darwin did not imagine could be seen.

This work becomes one of the most valuable animal studies ever conducted. Zoologists and evolutionists regard it as a classic.

To study the evolution of life through many generations you need an isolated population. If you detect a change in the wingspan of a bird, the teeth of a bear, the fins of a fish, or the mandibles of an ant, you want to be able to explain why the change occurred. You want to know the action to which the change is a reaction. For this you need something in nature approximating the simplicity and isolation of a laboratory. Islands are ideal for this purpose, because it is hard for your subjects to leave them, and it is hard for outside influences to invade.

(Note that one new species did “invade”, mated, and their offspring may soon be named a new species. See Weiner's 2014 New York Times essay, In Darwin's Footstseps. GEOSPIZA STRENUIROSTRIS if named.)

If a castle describes the impossibility of assault… then Daphne Major suggests the near impossibility of life, and the near impossibility of its study by human beings. Yet both have triumphed.


It takes only 1 hr to walk the circumference of Daphne Major.

Whether or not we choose to watch, evolution is shaping us all.

Two species of Darwin’s finches use tools. They pick up a twig, a cactus spine, or a leafstalk, and they trim it into shape with their beaks. Then they poke it into the bark of dead branches and pry out grubs.

One finch eats green leaves, which birds are not supposed to do.

Another, the vampire finch, found chiefly on the rough, remote, cliff-walled islands of Wolf and Darwin, perches on the backs of boobies, pecks at their wings and tails, draws their blood, and drinks it. Vampires also smash boobies’ eggs against rocks and drink the yolk. They even drink the blood of their own dead.

There is a vegetarian species that knows how to strip the bark off twigs into long curling ribbons like Geppetto’s shavings, to get at the cambium and phloem.

There are also species that perch on the backs of iguanas and rid them of ticks. The iguana invites a finch to perch by assuming a posture that makes it look like a cat that wants to be petted.

“The birds are Strangers to Man and think him as innocent as their countrymen the huge Tortoises,” Darwin writes in his diary. “Little birds, within 3 or four feet, quietly hopped about the Bushes and were not frightened by stones being thrown at them. Mr King killed one with his hat.”

That is the way Darwin’s finches enter Darwin’s diary. And for the next five weeks he hardly mentions them. He has too many other adventures to write about.

He finds whole herds of giant tortoises, and rides on the back of one. He picks up one of the iguanas (“imps of darkness”) and throws it into the water, over and over; over and over, it swims straight back to him.

Darwin was not yet an evolutionist: When the vice-governor of the islands told Darwin that the tortoises varied from island to island, Darwin ignored him.

“I did not for some time pay sufficient attention to this statement and I had already partially mingled together the collections from two of the islands. I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted.…” (Darwin)

Linnaeus, divided life on earth into categories. (“God created,” they said; “Linnaeus arranged.”) Today the major headings are kingdom, phylum, class, order, family, genus, and species.

No eureka moment while sailing, no deep falling in love with the galapaglos. More of a peicing together over years with the help of Lyell and John Gould.

Darwin said what others were afraid to say. Ideas of evolution already existed. French naturalist Lamarck. Darwin’s grandfather Erasmus. One of Darwin’s teachers, Robert E. Grant.

“(Did the Finches reach) Galápagos from the coast of South America and then diverged from their ancestors, generation by generation? What if there were no limits to their divergence? What if they had diverged first into varieties, and then gone right on diverging into species, new species, each marooned on its own island? “—If there is the slightest foundation for these remarks,” Darwin wrote, “the zoology of Archipelagoes—will be well worth examining; for such facts undermine the stability of Species.” Then, in a scribble that foreshadowed two decades of agonized caution, Darwin inserted a word: “would undermine the stability of Species.” - Charles Darwin

That was the fabulous moment—not out on the islands but indoors in a cluttered office in London. (JW)

“Hence, both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this earth.” -Charles Darwin

Breeders coined the term natural selection.

Since breeders called the art of choosing “selection,” they called any changes in a breed that did not take place because of their conscious efforts—all of the casual, frustrating, and inexplicable changes in their flocks and herds behind their backs—“natural selection.”

“I had meant to have sent you a line on Sunday, but quite forgot it myself. —Indeed we are all sick & miserable, & I hardly care even for Pigeons, so you may guess what a condition I am in!” -Darwin

To mate, a barnacle sticks a long penis out of its crater and thrusts it down the crater of a neighbor. Since every barnacle in the colony is both male and female, this is not as chancy as it sounds. (!)

Charles Darwin wrote to Captain FitzRoy: “for the last half-month daily hard at work in dissecting a little animal about the size of a pin’s head…and I could spend another month, and daily see more beautiful structure.”

Which specimens were the true species? Where should he draw the line?

“After describing a set of forms as distinct species, tearing up my MS., and making them one species, tearing that up and making them separate, and then making them one again (which has happened to me), I have gnashed my teeth, cursed species, and asked what sin I had committed to be so punished.” (Darwin’s friends knew just how he felt. The botanist Joseph Hooker wrote Darwin across the top of one letter, “I quite understand and sympathize with your Barnacles, they must be just like Ferns!”)

Smith has found that the beaks of song sparrows on Mandarte are all nearly the same length. It is rare to find a beak that is even 10 percent away from the mean. The probability of finding a sparrow that deviant is about four in ten thousand. But in the Galápagos, the Finch Unit has discovered, the probability of finding a cactus finch with a beak 10 percent from the mean is much better than four in a thousand. It is four in a hundred. One of the Grants’ world records in this respect is the depth of the upper mandible of the medium ground finch on Daphne Major. Here, the probability of finding a 10 percent deviation is one in three. That is one of the most variable characters ever measured in a bird. And Darwin’s finches are extraordinarily variable not only in the depth, length, and width of each mandible, and in the relative lengths of the upper and lower mandibles, but also in their wingspans, their body weights, and the lengths of their legs.

Each beak is a hand with a single permanent gesture. It is a general-purpose tool that can serve only a limited number of purposes. Woodpeckers have chisels. Egrets have spears. Darters have swords. Herons and bitterns have tongs. Hawks, falcons, and eagles have hooks. Curlews have pincers.

“To look at the bills of these birds in the hand, we would conjecture wholly different diets,” wrote the biologist and explorer William Beebe, who sailed out to Daphne Major through clouds of yellow butterflies in the wet season of 1923.

The Grant team, like Beebe, Lack, and all the rest, had visited the birds in the wet season. But the dry season might be the time to watch life squeeze Darwin’s finches.

Hybrid swarms and meaningless variation - like the coats of stray mutts and cats? No. Need to go back in the dry season.

If two finch species with rather similar beaks do share an island, their beaks are more divergent in their measurements on that island than they are elsewhere. That is, the longer beak is longer than average, and the shorter beak is shorter than average, almost as if they were consciously trying to get out of each other’s niches. Likewise with barnacles: one species takes the high tide line and another takes the low tide line.

Such experiments seemed to show that no two species eating the identical foods in identical ways can coexist peaceably in the same test tubes, on the same rocks, or on the same islands without one species driving the other to extinction.

Whenever species with very similar beaks try to colonize the same island, Lack decided, they are thrown into competition. The struggle grows so bitter that one or the other species of finch is driven to extinction. But occasionally two like-beaked species evolve enough local differences that the intensity of their competition is reduced. Then both species survive.

To crack a grass seed, which is a speck about the size of a poppy seed, takes very little force, less than 10 newtons. A big cactus seed, the size of a peppercorn, takes more than 50 newtons. Cracking the toughest seeds in the Galápagos requires a force of 250 newtons, which is enough force to lift more than a thousand cactus finches into the air. (!)

There are only 24 Seed Types on Daphne Major.

In most parts of the world, one might find two hundred species of plants in a single spadeful of earth. It would be impossible to find out exactly what a flock of birds is getting in its beaks. But on Daphne Major the finch watchers could get almost a God’s-eye view of their flocks, which never went anywhere and never migrated for the winter. And of course when the watchers unrolled their mist nets, adds Ratcliffe, “every bird you caught was a finch.”

Evolution discloses a meaning in death, although the meaning is like some of the berries that Darwin tasted in the Galápagos, “acid & austere.” There is a special providence in the fall of a sparrow. Even drought bears fruit. Even death is a seed.


Crossing a female horse and a male donkey will never change the gene pools of horses and donkeys by even a single gene, because all mules are sterile. Crossing a male horse and a female donkey will not change their lines much either, because hinnies are small, and less useful around the farm; so farmers seldom let them breed, though not all hinnies are sterile.

Darwin’s followers are always thrilled when they can confirm what Darwin saw, and they are even more thrilled when they can see what Darwin missed. Probably no other major branch of science today is so haunted, dominated, and driven by the thoughts of one man.

Why are there so many different kinds of animals? Or plants?

What Darwin realized is that two varieties living side by side are thrown into competition—competition “in a very large sense,” like the contest the Grants are now watching among ground finches on Daphne Major. Individuals in each of two neighboring varieties will usually find themselves going after the same thing as their neighbors, precisely by virtue of their similarities, like two big-beaked ground finches hunting for the same Tribulus seed.

In the struggle for existence one variety or species must often squeeze another.

The lucky individual that finds a different seed, or nook, or niche, will fly up and out from beneath the Sisyphean rock of competition. Divergence.

Natural selection will have led in effect to another adaptation—the mutual adaptation of two neighbors to the pressures of each other’s existence. And the result of this sort of adaptation would be forks in the road, partings of the ways, new branches on the tree of life: the pattern now known as an adaptive radiation.

Competition among slightly divergent forms everywhere on the planet leads continually to new branches, radiating outward in all directions like a compass rose or the arms of a medieval sun. Darwin called this his principle of divergence..

If the island has only one niche for them, then either the line of the sharp beaks or the line of the small beaks is driven to extinction: one species outcompetes the other. The technical term for this outcome of a battle between two groups of living things is competitive exclusion. But if the island is tall enough to offer one species a new niche, a path out of the race, that species can evolve its way out of the competition. Then it changes in character. The beak bends, melts, morphs, changes shape, through evolution by natural selection, until that lineage of birds is freed from the dreadful war. The technical term for this outcome is character displacement.

“It takes just fourteen generations to turn a Drosophila subobscura from a courtly dancer to a blind, tapping rapist,” notes the student of evolution James Shreeve. “How perishable are our essences! No doubt Aristotle would find all this fiddling around with the edges between things to be very dark stuff indeed.”

One fly likes the lights on, one fly likes the lights off, but every once in a while a pair of them gets together anyway.

Whenever the adaptive landscape heaves and flings about, like a sea under heavy winds, the hybrids among Darwin’s finches will be favored. They will intermingle their genes. But when the landscape returns to the pattern it held before the storm, the birds will settle back to their old peaks, and the sharing of genes will slow again.

On Birds. “No other class of organisms of comparable size is known so comprehensively.”

The total number of bird species in the world is almost 10,000. Almost 1,000 of them, the Grants write, “are known to have bred in nature with another species and produced hybrid offspring…roughly one out of every ten species.”

The flowers we enjoy so much in the plant kingdom are really sperm throwers and sperm catchers. “As we delight in the strange and exotic beauty of orchid flowers,” writes a British biologist, “it is salutary to reflect that we are, in essence, looking at their genitalia.”

So as the plants’ pollen is swept from one plant to another by winds and insects, hybridization is not only inevitable but also desirable, because so many myriads of seeds will fall and sprout in adaptive landscapes that are different from those of their parents. Here natural selection favors great genetic variability, and hybridization is one way to generate it fast.

To the Grants, the whole tree of life now looks different from a year ago. The set of young twigs and shoots they study seems to be growing together in some seasons, apart in others. The same forces that created these lines are moving them toward fusion and then back toward fission. The Grants are looking at a pattern that was once dismissed as insignificant in the tree of life. The pattern is known as reticulate evolution, from the Latin reticulum, diminutive for net. The finches’ lines are not so much lines or branches at all. They are more like twiggy thickets, full of little networks and delicate webbings. This sort of reticulate evolution doesn’t bind lineages together forever; eventually they part ways or fuse.

“Maybe we should all be grateful that Mother Nature is a bit slovenly when it comes to reproduction, for this may ultimately permit the unfolding of the bountiful diversity of life on Earth.” - Evolutionist, Robert Holt

“All is flux,” said the Greek philosopher Heraclitus; “everything flows.” The forms and instincts of living things, the invisible borders among them, and the very coasts and landscapes they inhabit are all more fluid and in more flux than even Heraclitus could have imagined.

The birds are alive and breathing, but they are unfinished; in the Galápagos the sculptor is still at work, measurably and demonstrably.

In a blink of evolutionary time, all of Darwin’s finches could run together and congeal, and the sculptor’s art would be lost.

This same tension between fission and fusion runs through all the kingdoms of animals and plants.

In the Hawaiian Islands, the lineage of a single finch has radiated into more than forty species, with forty beaks, including seed crushers, bug catchers, nectar sippers.

The history of these adaptive radiations is the history of life.

Part III

A Galápagos finch has about one hundred thousand genes, roughly the same number as a human being. The genes are spelled out in a total of about one billion letters, an average of ten thousand letters to a gene. The story is big but the alphabet is small: there are only four letters, named for the four chemical compounds that, as Watson and Crick discovered, make the treads in every spiral staircase of DNA, rather like the leaden letters in a printing press. Their chemical names are guanine, adenine, thymine, and cytosine: G, A, T, and C.

Around the world almost one hundred species of birds are known to have gone extinct since the seventeenth century, together with more than eighty subspecies; more than nine out of ten of these lost species and subspecies lived on islands.

A pesticide applies selection pressure as surely as a drought or flood. The poison selects against traits that make a species vulnerable to it, because the individuals that are most vulnerable are the ones that die first. The poison selects for any trait that makes the species less vulnerable, because the least vulnerable are the ones that survive longest and leave the most offspring. In this way the invention of pesticides in the twentieth century has driven waves of evolution in insects all over the planet. Heliothis is only one case in hundreds.

In 1967, a distinguished entomologist announced in Scientific American the discovery of a “resistance-proof” family of insecticides. The poisons were variants of some of the insects’ hormones. How could insects escape their own hormones? Yet within five years, flies had evolved one-hundred-fold resistance. “This seemed to surprise people,” says Taylor. “It would not have surprised an evolutionary biologist. But it surprised pesticide sprayers and the manufacturers of chemical compounds endlessly.”

“It always seems amazing to me that evolutionists pay so little attention to this kind of thing,” says Taylor. “And that cotton growers are having to deal with these pests in the very states whose legislatures are so hostile to the theory of evolution. Because it is evolution itself they are struggling against in their fields each season. These people are trying to ban the teaching of evolution while their own cotton crops are failing because of evolution. How can you be a Creationist farmer any more?”

In Arkansas in May 1987 only about 6 percent of the moths survived a certain fixed dose of the poison. But by that September, several moth generations later, 61 percent survived that same dose. The same rapid evolution has been observed in cotton fields in Louisiana, Oklahoma, Texas, and Mississippi.

(A single wipe of toilet paper comes away with as many as two trillion individuals of the Bacteroides species, twenty billion individual enterobacteria, and dozens of other species that have never been named by science.)

I took erythromycin. Within a few days, we were both dominated by resistant bacteria. Not only was tetracycline resistance coming up, but also streptomycin, kanamycin, carbenicillin—our bacteria were going from almost nothing to multiple resistance in an amazingly short amount of time.

A human body with AIDS is like an entire Galápagos archipelago: it harbors an increasingly diverse group of viruses after the first one has invaded it. The first virus particle to invade evolves into a swarm of variant strains.

A simple corollary to Darwinian law. Wherever we aim at a species point-blank, for whatever reason, we drive its evolution, often in the opposite direction from what we ourselves desire. The law holds, whatever our reason for shooting at a species, and whether the species is submicroscopic or gigantic.

Before human beings had heaped up a mountain of pesticides in the 1940s, when we were still in the foothills of this evolutionary adventure, farmers in the United States were losing about 7 percent of their crops to insects. During the blitz of the 1970s and 1980s the insects did not lose any ground. Instead they nearly doubled their share, to 13 percent. “Indeed,” note the ecologists Robert May and Andrew Dobson, “the fraction of all crops lost to pests in the United States today has changed little from that in medieval Europe, where it was said that of every three grains grown, one was lost to pests…leaving one for next year’s seed and one to eat.”

Global warming is of special interest here because in these islands the round of the seasons is driven by ocean currents.

A warming of even half a degree centigrade can cause a change in global circulation patterns, and make trade winds and ocean currents veer away on new tracks. Because they depend on winds and currents for their very seasons, the Galápagos Islands are particularly vulnerable to changes like these.

The Grants’ argument about the fission or fusion of Darwin’s finches, for instance, depends on the islands’ climate staying more or less as they have seen it in the last twenty years. That is, when they project the fate of Darwin’s finches, Rosemary and Peter have always assumed there will be no net change in the seasonal cycle of the archipelago. They have assumed that the pendulum of ocean currents will go on swinging annually but erratically between wet seasons and dry seasons. But this is no longer a safe assumption, the Grants write: “Global warming alters the argument.”

Our own tenure has been brief, and on average the term of a species is brief—a few million years. A species that can survive only by causing upheaval around it is in constant danger of extinction, like a tribe that lives for battle.

The rapid accumulation of change is not always progress, and forward motion is not always an advance.

The Book of Life is still being written. The end of the story is not predestined.