New York Times

The party is about to begin.

In a week or so, the trumpets will sound, heralding the start of 18 months of non-stop festivities in honor of Charles Darwin. July 1, 2008, is the 150th anniversary of the first announcement of his discovery of natural selection, the main driving force of evolution. Since 2009 is the 200th anniversary of Darwin's birth (Feb. 12), as well as being the 150th anniversary of the publication of his masterpiece, "On the Origin of Species" (Nov. 24), the extravaganza is set to continue until the end of next year. Get ready for Darwin hats, t-shirts, action figures, naturally selected fireworks and evolving chocolates. Oh, and lots of books and speeches.

But hold on. Does he deserve all this? He wasn't, after all, the first person to suggest that evolution happens. For example, his grandfather, Erasmus Darwin, speculated about it towards the end of the 18th century; at the beginning of the 19th, the great French naturalist Jean-Baptiste Lamarck made a strong case for it. Lamarck, however, failed to be generally persuasive because he didn't have a plausible mechanism — he could see that evolution takes place, but he didn't know how. That had to wait until the discovery of natural selection.

Natural selection is what we normally think of as Darwin's big idea. Yet he wasn't the first to discover that, either. At least two others — a doctor called William Wells, and a writer called Patrick Matthew — discovered it years before Darwin did. Wells described it (admittedly briefly) in 1818, when Darwin was just 9; Matthew did so in 1831, the year that Darwin set off on board HMS Beagle for what became a five-year voyage around the world.

It was a few months after returning from this voyage that Darwin first began to consider seriously the possibility of evolution, or the "transmutation of species." At this time he knew nothing of Wells's and Matthew's accounts of natural selection; indeed, both accounts languished in obscurity until after the "Origin" was published. (After the "Origin" appeared, Matthew wrote to a magazine to draw attention to his statements on the subject; he then proceeded to put "Discoverer of the Principle of Natural Selection" on the title pages of his books. This annoyed Darwin.)

By 1858, Darwin had spent more than 20 years studying plants and animals and thinking about evolution. He had filled notebook after notebook with his thoughts on how evolution works; he had, in 1844, written a short manuscript on the subject that was to be published in the event of his untimely death; and he had discussed evolution with a few close friends. But he had published nothing. (He had, however, published books on several other subjects, including an exhaustive study of barnacles, both living and extinct.) Then, in June of that year, Darwin received a package from a young man named Alfred Russel Wallace; in the package, Wallace enclosed a brief manuscript in which he outlined the principle of evolution by natural selection.

What happened next is famous in the history of biology. On July 1, 1858, Wallace's manuscript, as well as a couple of short statements on natural selection by Darwin (a segment of the 1844 manuscript, and part of a letter he'd written in 1857), were read at a meeting of the Linnean Society in London. The meeting had been organized by some of Darwin's scientific friends to establish his priority in the discovery.

Of the material presented that night, the manuscript by Wallace is, in some respects, the more impressive: it is clearer and more accessible. Yet it is Darwin we celebrate; it is Darwin who, like a god in a temple, sits in white marble and presides over the main hall at the Natural History Museum in London. Why?

The reason is the "Origin." Without the publication of the "Origin" the following year, the meeting at the Linnean Society could well have passed unnoticed, the Darwin-Wallace statements going the same way as those by Matthew and Wells. Indeed, the meeting had so little impact at the time that, at the end of the year, the president of the Linnean Society said, "The year which has passed has not, indeed, been marked by any of those striking discoveries which at once revolutionize, so to speak, the department of science on which they bear."

This is one of my all-time favorite quotations (and I am fond of using it) because it shows how, at the time, little significance was attached to the Linnean Society meeting. We see that meeting as important now because of what happened next: it galvanized Darwin into writing and publishing the "Origin."

And the "Origin" changed everything. Before the "Origin," the diversity of life could only be catalogued and described; afterwards, it could be explained and understood. Before the "Origin," species were generally seen as fixed entities, the special creations of a deity; afterwards, they became connected together on a great family tree that stretches back, across billions of years, to the dawn of life. Perhaps most importantly, the "Origin" changed our view of ourselves. It made us as much a part of nature as hummingbirds and bumblebees (or humble-bees, as Darwin called them); we, too, acquired a family tree with a host of remarkable and distinguished ancestors.

The reason the "Origin" was so powerful, compelling and persuasive, the reason Darwin succeeded while his predecessors failed, is that in it he does not just describe how evolution by natural selection works. He presents an enormous body of evidence culled from every field of biology then known. He discusses subjects as diverse as pigeon breeding in Ancient Egypt, the rudimentary eyes of cave fish, the nest-building instincts of honeybees, the evolving size of gooseberries (they've been getting bigger), wingless beetles on the island of Madeira and algae in New Zealand. One moment, he's considering fossil animals like brachiopods (which had hinged shells like clams, but with a different axis of symmetry); the next, he's discussing the accessibility of nectar in clover flowers to different species of bee.

At the same time, he uses every form of evidence at his disposal: he observes, argues, compares, infers and describes the results of experiments he has read about, or in many cases, personally conducted. For example, one of Darwin's observations is that the inhabitants of islands resemble — but differ subtly from — those of the nearest continents. So: birds and bushes on islands off the coast of South America resemble South American birds and bushes; islands near Africa are populated by recognizably African forms.

He argues that the reason for this is that new islands become colonized by beings from the nearest continents, and that the new inhabitants then begin evolving independently. He then asks: can animals and plants from the continents get to new islands, especially those that are far out at sea? To investigate this, he conducts experiments to see how long seeds from different plants can remain immersed in saltwater and still begin to grow. In short, he tests his reasoning over and over again.

He is also, in some respects, surprisingly far-seeing. The "Origin" does not just expound natural selection. It contains a wealth of additional ideas and hypotheses, some of which Darwin went on to elaborate in other books. Among them: sexual selection. This is the idea — and it remained controversial until recently — that males in many species are burdened with showy ornaments like enormous tails because the females of their species have, by repeatedly picking the showiest males as their mates, caused them to evolve them that way.

This is not to say that the "Origin" is flawless, or that Darwin was right in every respect. It isn't, and he wasn't. Nor is the book a definitive account of how evolution works. It wasn't even definitive in his lifetime: he published six editions, revising, sometimes heavily, from one to the next. (In the third edition, which appeared in 1861, he introduced a historical sketch in which he discusses his precursors, including Matthew and Wells.) Yet his knowledge of the natural world is so immense, and the scrutiny to which he subjects his ideas is so thorough and scrupulous, that the "Origin" presents a grand new vision of the world. A vision that, as far as possible given the knowledge available at the time, he worked out in every detail. A vision that changed the world forever.

Let's party!

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NOTES:

The historical events described here can be found in any biography of Darwin; I drew on Janet Browne's — Knopf, in two volumes, "Voyaging" (1995) and "The Power of Place" (2002). The anecdote of Matthew annoying Darwin can be found on page 109 of "The Power of Place"; the quotation from the president of the Linnean Society can be found on page 42 of the same volume.

Many thanks to Dan Haydon, Horace Judson, Gideon Lichfield, Dmitri Petrov, Elizabeth Pisani and, especially, Jonathan Swire, for insights, comments, arguments and suggestions.