Probably the most daunting task that we face, as partly rational animals with adrenal glands that are too big and prefrontal lobes that are too small, is the contemplation of our own relative weight in the scheme of things. Our place in the cosmos is so unimaginably small that we cannot, with our miserly endowment of cranial matter, contemplate it for long at all. No less difficult is the realization that we may also be quite random as presences on earth. We may have learned about our modest position on the scale, about how to prolong our lives, cure ourselves of disease, learn to respect and profit from other tribes and other animals, and employ rockets and satellites for ease of communication; but then, the awareness that our death is coming and will be succeeded by the death of the species and the heat death of the universe is scant comfort. Still, at least we are not in the position of those humans who died without ever having the chance to tell their story, or who are dying today at this moment after a few bare, squirming minutes of painful and fearful existence.
In 1909, a discovery of immense importance was made in the Canadian Rockies, on the border of British Columbia. It is known as the Burgess shale, and though it is a natural formation and has no magical properties, it is almost like a time machine or a key that enables us to visit the past. The very remote past: this limestone quarry came into existence about 570 million years ago and records what palaeontologists familiarly call «the Cambrian explosion». Just as there have been great «dyings» and extinctions during evolutionary time, so there have been energetic moments when life was suddenly profuse and various again. (An intelligent «designer» might have managed without these chaotic episodes of boom and bust.)
Most of the surviving modern animals have their origins in this grand Cambrian burgeoning, but until 1909 we were unable to view them in anything like their original habitat. Until then, also, we had to rely upon the evidence mainly of bones and shells, whereas the Burgess shale contains much fossilized «soft anatomy», including the contents of digestive systems. It is a sort of Rosetta Stone for the decoding of life forms.
Our own solipsism, often expressed in diagram or cartoon form, usually represents evolution as a kind of ladder or progression, with a fish gasping on the shore in the first frame, hunched and prognathous figures in the succeeding ones, and then, by slow degrees, an erect man in a suit waving his umbrella and shouting «Taxi!» Even those who have observed the «sawtooth» pattern of fluctuation between emergence and destruction, further emergence and still further destruction, and who have already charted the eventual end of the universe, are half agreed that there is a stubborn tendency toward an upward progression. This is no great surprise: inefficient creatures will either die out or be destroyed by more successful ones. But progress does not negate the idea of randomness, and when he came to examine the Burgess shale, the great paleontologist Stephen Jay Gould arrived at the most disquieting and unsettling conclusion of all. He examined the fossils and their development with minute care and realized that if this tree could be replanted or this soup set boiling again, it would very probably not reproduce the same results that we now «know».
It may be worth mentioning that this conclusion was no more welcome to Gould than it is to you or to me: in his youth he had imbibed a version of Marxism and the concept of «progress» was real to him. But he was too scrupulous a scholar to deny the evidence that was so plainly displayed, and while some evolutionary biologists are willing to say that the millimetrical and pitiless process had a «direction» toward our form of intelligent life, Gould subtracted himself from their company. If the numberless evolutions from the Cambrian period could be recorded and «rewound», as it were, and the tape then played again, he established there was no certainty that it would come out the same way. Several branches of the tree (a better analogy would be with small twigs on an extremely dense bush) end up going nowhere, but given another «start» they might have blossomed and flourished, just as some that did blossom and flourish might equally well have withered and died. We all appreciate that our nature and existence is based upon our being vertebrate. The earliest known vertebrate (or «chordate») located in the Burgess shale is a two-inch and rather elegant creature named, after an adjoining mountain and also for its sinuous beauty, Pikaia gracilens. It was originally and wrongly classified as a worm (one must never forget how recent most of our knowledge really is), but in its segments, muscularity, and dorsal-rod flexibility it is a necessary ancestor that yet demands no worship. Millions of other life forms perished before the Cambrian period was over, but this little prototype survived. To quote Gould:
Wind the tape of time back to Burgess times, and let it play again. If Pikaia does not survive in the replay, we are wiped out of future history — all of us, from shark to robin to orangutan. And I don’t think that any handicapper, given Burgess evidence as known today, would have granted very favorable odds for the persistence of Pikaia.
And so, if you wish to ask the question of the ages — why do humans exist? — a major part of the answer, touching those aspects of the issue that science can treat at all, must be: because Pikaia survived the Burgess decimation. This response does not cite a single law of nature; it embodies no statement about predictable evolutionary pathways, no calculation of probabilities based on general rules of anatomy or ecology. The survival of Pikaia was a contingency of «just history». I do not think that any «higher» answer can be given, and I cannot imagine that any resolution could be more fascinating. We are the offspring of history, and must establish our own paths in this most diverse and interesting of conceivable universes — one indifferent to our suffering, and therefore offering us maximum freedom to thrive, or to fail, in our own chosen way.
A way «chosen», one must add, within very strictly defined limits. Here is the cool, authentic voice of a dedicated scientist and humanist. In a dim way, we knew all this already. Chaos theory has familiarized us with the idea of the unscripted butterfly wing-flap that, stirring a tiny zephyr, eventuates in a raging typhoon. Saul Bellow’s Augie March shrewdly observed the fritillary corollary that «if you hold down one thing, you hold down the adjoining». And Gould’s mind-stunning but mind-opening book on the Burgess shale is entitled Wonderful Life, a double entendre with an echo of the best-loved of all American sentimental movies. At the climax of this engaging but abysmal film, Jimmy Stewart wishes he had never been born but is then shown by an angel what the world would be like if his wish had been granted. A middlebrow audience is thus given a vicarious glimpse of a version of Heisenberg’s principle of uncertainty: any attempt to measure something will have the effect of minutely altering that which is being measured. We have only recently established that a cow is closer in family to a whale than to a horse: other wonders certainly await us. If our presence here, in our present form, is indeed random and contingent, then at least we can consciously look forward to the further evolution of our poor brains, and to stupendous advances in medicine and life extension, derived from work on our elementary stem cells and umbilical-cord blood cells.