Read Shadows of Forgotten Ancestors Online
Authors: Carl Sagan,Ann Druyan
Shadows of Forgotten Ancestors (6 page)
Pangaea was formed about 270 million years ago, during the Permian Period, a trying time for Earth. Worldwide, conditions had been warming. In some places the humidity was very high and great swamps formed, later to be supplanted by vast deserts. About 255 million years ago Pangaea began to shatter—because, it is thought, of the sudden rise of a superplume of molten lava through the Earth’s mantle from its deep seething core. Texas, Florida, and England were then at the equator North and South China, in separate pieces, Indochina and Malaya together, and fragments of what would later be Siberia were all large islands. Ice ages flickered on and off every 2.5 million years, and the level of the seas correspondingly fell and rose.
Towards the end of the Permian Period, the map of the Earth seems to have been violently reworked. Whole oblasts of Siberia were inundated with lava. Pangaea rotated and drifted north, moving mainland Siberia towards its present position, near the North Pole. “Megamonsoons,” torrential seasonal rains on a much larger scale than humans have ever witnessed, drenched and flooded the land. South China slowly crumpled into Asia. Many volcanoes blew their tops together,
belching sulfuric acid into the stratosphere and perhaps playing an important role in cooling the Earth.
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The biological consequences were profound—a worldwide orgy of dying, on land and at sea, the likes of which has never been seen before or since.
The breakup of Pangaea continued. By 100 million years ago South America and Africa, which even today fit together like two pieces of a jigsaw puzzle, were just barely separated by a narrow strait of ocean—receding from one another at about an inch a year. North and South America were then separate continents, with no Isthmus of Panama connecting them. India was a large island headed north away from Madagascar. Greenland and England were connected to Europe. Indonesia, Malaysia, and Japan were part of the mainland of Asia. You might have strolled from Alaska to Siberia. There were great inland seas where none exists today. This time, at a glance from orbit you would have recognized it as the Earth—but with the configuration of land and water strangely altered, as if by a careless, slapdash cartographer. This was the world of the dinosaurs.
Later, the continents drifted further apart, pulled by their underlying plates. Africa and South America continued to recede from one another, opening up the Atlantic. Australia split off from Antarctica. India collided with Asia, raising the Himalayas high. This is the world of the primates.
——
Each of us is a tiny being, permitted to ride on the outermost skin of one of the smaller planets for a few dozen trips around the local star. The great internal engine of plate tectonics is indifferent to life, as are the small changes in the Earth’s orbit and tilt, the variation in the brightness of the Sun, and the impact with the Earth of small worlds on rogue orbits. These processes have no notion of what has been going on over billions of years on our planet’s surface. They do not care.
The longest-lived organisms on Earth endure for about a millionth of the age of our planet. A bacterium lives for one hundred-trillionth of that time. So of course the individual organisms see nothing of the overall pattern—continents, climate, evolution. They barely set foot on the world stage and are promptly snuffed out—yesterday a drop of semen, as the Roman Emperor Marcus Aurelius wrote, tomorrow a
handful of ashes. If the Earth were as old as a person, a typical organism would be born, live, and die in a sliver of a second. We are fleeting, transitional creatures, snowflakes fallen on the hearth fire. That we understand even a little of our origins is one of the great triumphs of human insight and courage.
Who we are and why we are here can be glimpsed only by piecing together something of the full picture—which must encompass aeons of time, millions of species, and a multitude of worlds. In this perspective it is not surprising that we are often a mystery to ourselves, that, despite our manifest pretensions, we are so far from being masters even in our own small house.
ON IMPERMANENCE
The present life of man, O king, seems to me, in comparison of that time which is unknown to us, like to the swift flight of a sparrow through the room wherein you sit at supper in winter, with your commanders and ministers, and a good fire in the midst, whilst the storms of rain and snow prevail abroad; the sparrow, I say, flying in at one door, and immediately out at another, whilst he is within, is safe from the wintry storm; but after a short space of fair weather; he immediately vanishes out of your sight, into the dark winter from which he had emerged. So this life of man appears for a short space, but of what went before, or what is to follow, we are utterly ignorant.
THE VENERABLE BEDE
Ecclesiastical History
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*
You can occasionally see, on the automobile bumper stickers of geology graduate students, the nostalgic plea, “Reunite Gondwanaland” Except in a metaphorical political sense (and it’s not too likely there either) it is the most hopeless of lost causes—on any but a geological time scale But the breakup and separation of continents can go only so far. On a round Earth, what you run away from on one side you will eventually edge into on the other A few hundred million years from now our remote descendants, if any, may witness the reaggregation of a supercontinent Gondwanaland will at last have been reunited
* Although not in consequence of some policy of conscious altruism Any individual that goes along with the stromatolitic arrangement is much more likely to find itself safely on the inside rather than perilously on the outside A communal policy benefits most constituent cells—not entirely risk-free, since those on the outside will be fried, but as if a cost-benefit analysis had been performed for the average cell
“WHAT MAKEST THOU?”Shall the clay say to him that fashioneth it, What makest thou?
Isaiah 45:9
T
he world and everything in it was made for us, as we were made for God:
For the last few thousand years, and especially since the end of the Middle Ages, this proud, self-confident assertion was increasingly common belief, held by Emperor and slave, Pope and parish priest. The Earth was a lavishly decorated stage set, designed by an ingenious if inscrutable Director, who had managed to round up, from only He knew where, a multitudinous supporting cast of toucans and mealy bugs, eels, voles, elms, yaks, and much, much more. He placed them all before us, in their opening night costumes. They were ours to do with as we pleased: drag our burdens, pull our plows, guard our homes, produce milk for our babies, offer up their flesh for our dinner tables, and provide useful instruction—bumblebees, for example, on the virtues not just of hard work, but of hereditary monarchy. Why He thought we needed hundreds of distinct species of ticks and roaches, when one or two would have been more than sufficient, why there are more species of beetles than any other kind of being on Earth, no one could say. No matter; the composite effect of life’s extravagant diversity could only be understood by postulating a Maker, not all of whose reasons we could grasp, who had created the stage, the scenery, and the subsidiary players for our benefit. For thousands of years, virtually everyone, theologian and scientist alike, found this, both emotionally and intellectually, a satisfying account.
The man who wrecked this consensus did so with the utmost reluctance. He was no ideologue bent on kicking in the door of the Establishment, no firebrand. If not for a bit of happenstance he would probably have passed his days as a well-liked Church of England parson in a nineteenth-century rural, picture-postcard village. Instead he ignited a firestorm
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that destroyed more of the old order than any violent political upheaval ever had. Through the astonishingly powerful method of science, this gentleman who was known to find lively
conversation too taxing, somehow became the revolutionary’s revolutionary. For more than a century, the mere mention of his name has been sufficient to unsettle the pious and rouse the bookburners from their fitful slumbers.
——
Charles Darwin was born at Shrewsbury, England, on February 12, 1809, the fifth child of Robert Waring Darwin and Susannah Wedgwood. The Darwin and Wedgwood families were allied through the close friendship of their patriarchs, Erasmus Darwin, the noted author, physician, and inventor, and Josiah Wedgwood, who had risen from poverty to found the Wedgwood pottery dynasty. These two men shared radically progressive views, even going so far as to side with the rebellious colonies in the American Revolution. “He who allows oppression,” Erasmus wrote, “shares the crime.”
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Their club was called The Lunar Society, because it met only during the full moon when the late-night ride home would be well-lit and therefore less dangerous. Among its members were William Small, who had taught Thomas Jefferson science (at the College of William and Mary in Virginia and whom Jefferson singled out as having “probably fixed the destinies” of his life); James Watt, whose steam engines powered the British Empire; the chemist Joseph Priestley, the discoverer of oxygen; and an expert on electricity named Benjamin Franklin.
The poet Samuel Taylor Coleridge thought Erasmus Darwin “the most original-minded man” he had ever known. Erasmus was also making quite a name for himself as a doctor. George III invited him to become his personal physician. (Erasmus declined the honor out of an unwillingness, he said, to leave his happy home in the countryside, but perhaps the champion of American revolutionaries had political reasons as well.) His real fame, though, stemmed from a string of hit encyclopaedic rhyming poems.
Erasmus Darwin’s two-volume work,
The Botanic Garden
, comprising
The Loves of the Plants
, written in 1789, and its eagerly awaited sequel,
The Economy of Vegetation
, were runaway best-sellers. They were so successful that he decided to tackle the animal kingdom next. The result was a 2,500-page tome, this one in prose, entitled
Zoonomia: or, the Laws of Organic Life
. In it he asked this prescient question:
When we revolve in our minds, first the great changes which we see naturally produced in animals after their nativity as in the production of the butterfly from the crawling caterpillar or of the frog from the subnatant tadpole; secondly when we think over the great changes introduced into various animals by artificial cultivation as in horses or in dogs. .; thirdly when we revolve in our minds the great similarity of structure which obtains in all the warm-blooded animals as well as quadrupeds, birds, amphibious animals as in mankind, would it be too bold to imagine that all warm-blooded animals have arisen from one living filament (archetype, primitive form)?
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Erasmus Darwin believed that “There are three great objects of desire, which have changed the forms of many animals by their exertions to gratify them: hunger, security and lust.” Especially lust. The lilting refrain of his last effort,
The Temple of Nature: or, The Origin of Society
,
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was “And hail THE DEITIES OF SEXUAL LOVE.” The capitalization is his. Elsewhere, he observed that the stag had developed horns to fight other males for “the exclusive possession of the female.” There’s no question that he was on to something. But his was a kind of disordered originality, a brilliance that could not be bothered by methodical research. Science exacts a substantial entry fee in effort and tedium in exchange for its insights. Erasmus was unwilling to ante up.
His grandson Charles, who would pay those dues, read
Zoonomia
twice; once when he was eighteen and again a decade later, after he’d been around the world. He took pride in his grandfather’s precocious anticipation of some of the ideas that would make Jean-Baptiste de Lamarck famous twenty years later. However, Charles “was much disappointed” by Erasmus’ failure to investigate, carefully and rigorously, whether there was any truth to his inspired speculations
Lamarck had been a soldier, a self-taught botanist, and the zoologist who had gone on to develop the precursor of the modern natural history museum. When everyone else was thinking in terms of thousands of years, he was contemplating millions. He believed that the idea of the living world walled up into separate compartments called species was an illusion; species are slowly transmogrifying, one into another, he taught, and this would be immediately apparent to us if our lives were not so brief and fleeting.
Lamarck is best known for arguing that an organism could inherit the acquired characteristics of its ancestors. In his most famous example,
the giraffe strains to nibble at the leaves on the higher branches of the tree, and somehow the slightly elongated neck that attends the stretching is passed on to the next generation. Lamarck could not have been knowledgeable of the family history of many generations of giraffes, but he did have relevant data that he chose to ignore: For thousands of years, Jews and Moslems have been ritually circumcising their sons, with no break in continuity, and yet not one case is known of a Jewish or Islamic boy born without a foreskin. Queen bees and drones do no work, and have not for geological ages; yet worker bees whose parents are queens and drones (and never other workers) do not seem to be growing more indolent, generation after generation; instead, they are proverbially industrious.
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Domestic and farm animals have their tails docked, their ears clipped, or their flanks branded for generations, but the newborn show no signs of these mutilations. Chinese women had their feet cruelly bound and deformed for centuries, but infant girls obstinately persisted in being born with normal appendages.
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Despite such counterexamples, Charles would take seriously, for his entire life, the notion of Lamarck and his grandfather Erasmus that acquired characteristics could be inherited.