Natural History and the Apocalypse

"It is only by becoming sensible of our natural disadvantages that we shall be roused to exertion, and prompted to seek out opportunities of discovering the operations now in progress, such as do not present themselves readily to view."

“We are in the midst of a seismic shift in thinking about the nature of ourselves and the world we live in. It is no hyperbole to describe the magnitude of the shift as an intellectual revolution.”

“A window seat in the stratosphere certainly provides a better place from which to contemplate the world than most philosophers ever had.”

Everything we normally think of as ‘world history’ – the beginnings of agriculture, the building of cities, the invention of writing and mathematics, the rise and fall of civilizations, the scientific and industrial revolutions - has occurred since the end of the last ice age. The next ice age could be very close, could set in with brutal suddenness and would have an apocalyptic impact on the human world. If you thought global warming was the real danger, you don’t know the half of it.[iv]

The last ice age ended around 15,000 years ago. It had lasted for just over 100,000 years. It was preceded by a warm period, known by geologists and climatologists as the Eemian epoch, which had lasted 13,000 years. Before that was the next to last ice age, which had lasted around 100,000 years. Over the past three million years, since the ice ages began, the warm periods have averaged about 10,000 years.[v] We have long since overshot the mark.

In short, just when we thought that global warming was threatening us, it turns out that we are almost certainly dangerously close to the end of the warm period that has been the climatological precondition for the whole of ‘world history’. This has nothing whatsoever to do with human agency and would overwhelm our species with sublime indifference to our religious beliefs, metaphysical speculations and secular ideologies of progress. It may well be more than our sciences can handle – to say nothing of our polities.

It gets better – or worse, depending on whether you’re thinking of the scientific insight or the calamitous implications involved. For the long cycles of ice and warmth, it transpires, have been accompanied by a remarkable phenomenon that neurophysiologist William Calvin described last year as “one of the most shocking scientific realizations of all time.” That “the earth’s climate does great flip-flops every few thousand years and with breathtaking speed.”[vi]

The long cycles appear to be causally related to perturbations in the earth’s orbit around the sun and the tilt of its rotational axis. The flipflops are another matter. They are known among climate scientists as Dansgaard-Oeschger events or D-Os.[vii] They are best illustrated by the most ‘recent’ example. A D-O, known as the Younger Dryas, interrupted the current warm period a few millennia before we invented agriculture.

In Calvin’s words, “12,900 years ago, Europe cooled down to Siberian temperatures within a decade…the rainfall likely dropped by half, and fierce winter storms whipped a lot of dust into the atmosphere. Such conditions lasted for over 1,300 years, whereupon things warmed back up, even more suddenly. The dust settled and the warm rains returned, again within a decade.”[viii] Then ‘world history’ began.

This, it should be emphasized, was not an ice age. It was just a D-O. Such non-linear and drastic climate fluctuations, it turns out, have occurred hundreds of times since the ice ages began. They had, Calvin argues, a rigorous and manifold ‘sculpting’ effect on our species – shaping hominids into canny generalists with a suite of physical attributes and cognitive skills unmatched in the rest of the animal kingdom.[ix]

They did so, however, by decidedly Darwinian means. Through these aeons, the clay of humanity was assuredly shaped by Richard Dawkins’s ‘Blind Watch Maker’ and not by the hand of a loving God.[x] Over the last three million years, our ancestors were again and again compelled to retreat into narrow refugia[xi] as the general hominid population was severely culled by the harsh impact of D-Os and the coming and going of ice ages.

Most of this culling and adaptation afflicted and shaped the many species of hominid that preceded our own, but it eventually produced the hardiest and canniest of hominids – Homo sapiens, as we call ourselves – by about 150,000 years ago. We arose during the ice age before last (before the Eemian), in a world long since populated by other hominids; then colonized the biosphere during the last ice age.[xii]

When it ended, we emerged as the only surviving species of hominid. Homo erectus (a species that had endured for two million years and spread throughout Africa and Eurasia) and Homo Neanderthalensis did not survive the last ice age. A group of scientists at the Godwin Institute of Quaternary Research, Cambridge University, is currently trying to reconstruct the climate fluctuations between 60,000 and 25,000 years ago, in order to ascertain their effect on the demise of the Neanderthals.[xiii]

The climate anomaly that has cradled our rise from nomads and slayers of megafauna[xiv] to city-builders and inventors of weapons of mass destruction has been an unprecedented period of climate stability since the Younger Dryas. Why have things been so stable for about 11,000 years? “No one knows yet”, Calvin tells us. “But we know it’s unusual, and see no reason why it should persist.”[xv]

If you’re temperamentally or theologically inclined to attribute this run of good luck to a benign human “manifest destiny” or to the hand of a loving God, think again. Short of the next ice age, there could be a D-O in the near future, which would cut mean global temperatures by 5 to 10 degrees Celsius, with drastic implications for temperate climate agriculture and all that flows from it. This alone would cause a population crash of unprecedented proportions.[xvi]

What causes D-O events? They seem causally linked to irregularities in the flushing of salt from the North Atlantic. This, at least, is the hypothesis of American geochemist Wallace Broecker, who has been exploring the matter since the mid-1980s.[xvii] There is a conveyor operating in the Atlantic, in which salt sinks to the cold depths of the ocean and is flushed south, with warm water from the tropics (what we call the Gulf Stream) flowing north.[xviii] This is what keeps north western Europe so much warmer than any other region at the same latitude.

If you dilute the salinity of surface water in the North Atlantic, you reduce the precipitation of salt to the lower, colder depths of the ocean. This retards flushing, which, in turn, retards the reverse flow of warm water north, dropping temperatures, which retards evaporation, reinforcing the cycle and sending cool, dry winds crossing the Atlantic to Europe. Such dilution can be caused by a massive discharge of fresh water from the Arctic, Canadian or Greenland icecaps, or excessive precipitation.

A persistent failure of late winter sinking of the ocean surface near Greenland and Iceland is a likely cause of most of the abrupt cooling episodes which have punctuated the long cycles of ice and thaw. In other words, they’ve been the result of adding surplus fresh water to the ocean surface. Broecker’s hypothesis is that this, in turn, triggers a world-wide rearrangement of ocean currents, with a consequent drastic reduction, by around 30%, in evaporation in the tropics. That, in itself, would cool the planet by 5 degrees Celsius.

For the longest time, such D-O events have occurred due to natural contingencies. The irony of global warming is that, for the first time, human agency could bring one about. By melting the Arctic ice cap and increasing precipitation coming off the North American continent into the North Atlantic, global warming could trigger – could already be causing – excessive discharges of fresh water into the North Atlantic. If a D-O event follows, it will not entail a mere climate correction, but a colossal shift which will wreak unprecedented havoc on human civilization.

Can anything be done about this? Well, we might begin by taking more seriously both global warming and the scientific research needed to understand it better.[xix] But there is more to the matter than global warming. If the Broecker hypothesis is correct, the underlying issue is geophysical. It has to do with the ocean currents in the Atlantic. They, geologists have deduced, have a history altogether independent of our species.

The pivotal event in that history was the closure of the ocean gap between North and South America – what William Calvin calls the “Old Panama Canal” – between 4.6 and 3.2 million years ago, as a result of continental drift.[xx] This epochal geological event blocked the easy route for disposing of excess salt from the Atlantic, creating an instability via the salt buildup. The planet’s climate had been slowly cooling for several million years, then the closure of the Old Panama Canal created the Gulf Stream and the salt conveyor.

Evaporative cooling of the Gulf Stream in northern latitudes created excess moisture, which led to the buildup of ice mountains in the north Atlantic region. Thus, quite apart from perturbations in the Earth’s orbital or rotational motion, continental drift itself may have had a major role in the onset of the ice ages from around three million years ago. It also created the mechanism that triggers D-Os.[xxi]

Given this geohistorical understanding, it would seem to be possible for our species to interfere with what Pope Paul VI, in 1968, called “God’s felicitous design”[xxii] and fundamentally alter the conditions that cause D-Os. It would involve building dams to restrict the flow of fresh water into the Atlantic from Canada and Greenland and dramatically widening the Panama Canal to divert the salt flow; altering the ocean currents of three million years.

The problem is that we don’t yet know enough to hazard such terraforming, despite the huge risks in leaving things as they are. Far more research is required, along with sophisticated and redundant computer simulations of climate changes and the environmental implications of the engineering projects in question. We know enough, in other words, to apprehend that our ecological “childhood” could be about to end, but not enough to have any confidence about taking our destiny into our own hands.

Scientific findings of this nature are stunning in their implications, at a number of levels. They confront us with the stark possibility of a global catastrophe on a scale we associate with the extinction of the dinosaurs, or a nuclear winter. They challenge profoundly our hubris as presumptive masters of the biosphere. They make nonsense of pieties about our fate being in the hands of a divine providence. They cast the darkest of shadows over our recent faith in the material “progress” ahead of our civilization.

At the most fundamental level, however, they are a reality check. They challenge us to clarify our priorities at every level from bedtime stories for children to international politics. They underscore what a few seers have been proclaiming since the eighteenth century: that we live in a natural world, not a supernatural one; and that the education we impart to rising generations of our species must be based on a sure grasp of the natural sciences and natural history.

Consider that the immense time frame William Calvin draws us into, in talking of the era of the ice ages, is but the very recent history of the biosphere we have colonized so voraciously. Our common – universal – frame of reference should be the vast geophysical history and cosmology to which these ‘recent’ events are but a coda. Our common and universal sense of ourselves as a species should, in this century, become firmly rooted in an understanding of what we are and how we have become what we are.

Such a common sense would begin with the most basic chronological grasp of the geophysical history of the earth[xxiii], as something altogether truer and more fundamental than any religious creation myth. It would consist of three time parameters. First, the nature and history of life since it emerged in the oceans and around hot vents in the earth 3.8 billion years ago, encompassing the five great mass extinctions between 440 million and 65 million years ago.[xxiv]

Second, the long history of primate evolution, since the extinction of the dinosaurs, 65 million years ago. Third, the awesome history of hominid evolution, from six million years ago through to the explosive coda that we think of as ‘world history’.[xxv] There is no myth on earth as dramatic and powerful as this natural history of the earth we inhabit. Nor, I suggest, is there anything in religious scriptures so sobering or instructive, so awesome and inspiring as the aeons of life on earth.

What we need is an integration of natural history with our common moral and cultural sense of what it is that we are. That is possible, but it is a social and cognitive challenge every bit as daunting in its complexity as the terraforming projects William Calvin ponders as solutions to the D-O phenomenon. It requires a degree of what Harvard biologist Edward O. Wilson calls “fluency across the boundaries” between the humanities and the natural sciences.[xxvi]

Only such fluency, based on an assured curriculum, Wilson has written, “will provide a clear view of the world as it really is, not as it appears through the lens of ideology and religious dogma, or as a myopic response solely to immediate need.”[xxvii] This fluency, grounded in a unity of all knowledge, Wilson calls “consilience”. It has its origins in the first natural scientific speculations, those of Thales of Miletus, for which reason the physicist Gerald Holton has dubbed it “the Ionian Enchantment”.[xxviii]

The vision of consilience is what links the ancient Greeks, the Renaissance and the Enlightenment. It is the highest aspiration of Homo sapiens as a natural being and has been the glory of the species in the few millennia since we created cities and initiated systematic inquiry. It is, Wilson, urges, “the way to renew the crumbling structure of the liberal arts”, which has been undermined in recent decades by abandonment of the ideal of unity, dissolving into “a slurry of minor disciplines and specialized courses.”[xxix]

But far more is at stake than the coherence of the liberal arts. What is at stake is the collective capacity of Homo sapiens to exercise sapience as the climatic golden age that has made our exuberant and violent civilizations possible comes to its end. It could be, of course, as Thomas Homer-Dixon has speculated, that the challenge will be beyond us, because the complexity of the challenges we now face exceeds our collective ingenuity.[xxx]

If we are to rise to the challenge, however, before a D-O or a new ice age (or a new asteroid) overwhelms us, we shall need a global culture both consilient and resilient. The strenuous effort to achieve that would place us in the grand tradition of Leonardo da Vinci and Giordano Bruno, Francis Bacon and Giambattista Vico. It would constitute a global, twenty-first century Renaissance, after the plague years of the twentieth century.

Yet even to evoke such visions is to hope against hope, given the overwhelming natural forces that may confound us. Religious visions and the psychology of revenge quite aside, it could be that our species faces a looming apocalypse about which we can do nothing. A century ago physicists realized that our sun, our superabundant star, would die in the remote future, setting a term to our natural existence. But that was billions of years off. The apocalypse of ice may be imminent, by comparison; merely centuries or even decades away.

That is a stunning thought. There is no cheerful way to confront it. It recalls to my mind an early reflection by Friedrich Nietzsche, dated to 1873, in which he contemplated the future demise of the species: “In some remote corner of the universe, poured out and glittering in innumerable solar systems, there once was a star on which clever animals invented knowledge. That was the haughtiest and most mendacious minute of ‘world history’ – yet only a minute. After nature had drawn a few breaths the star grew cold, and the clever animal had to die.”[xxxi]

Nietzsche was writing just as the physical sciences were beginning to bite deeply into traditional ways of thinking about man and the universe. He was thinking of entropy and the sun and, even in astrophysical terms, he was incorrect to describe the life of the sun as a mere few breaths in nature. It will not die any time soon. But it could, all the same, be cold that brings down civilization and humbles the clever animal who invented knowledge.

And here’s the thing to get. Knowing this is neither haughty nor mendacious. What is haughty is thinking that our climatic golden age was intended for us and that our future is assured. What is mendacious is telling ourselves and our children that all is well or all is in the hands of God, or that business as usual will suffice to see us through the next D-O, or that scientists like Wallace Broecker are just making up all these climate stories.[xxxii]

The natural world is real, it is the only one there is, and it is not designed by Providence for our use and benefit. There have been mass extinctions before. There is no reason at all to believe that we may not be next. How you respond to that proposition will, if you are observing yourself in the conscious manner of a Hamlet[xxxiii], tell you a great deal about what manner of human being you are. Confused or consilient? Resigned or resilient? Think about it, clever animal.

[i] Charles Lyell Principles of Geology, Vol. 1, 1830. Penguin 1997, p. 33.

[ii] Richard Leakey and Roger Lewin The Sixth Extinction: Biodiversity and Its Survival, Weidenfeld & Nicolson, London, 1995, p. 223.

[iii] William H. Calvin A Brain for all Seasons: Human Evolution and Abrupt Climate Change, University of Chicago Press 2002, p. 228. Calvin is affiliate professor of psychiatry and behavioural sciences at the University of Washington School of Medicine in Seattle. The book was Scientific American book of the month and won the Phi Beta Kappa prize for scientific writing. For Calvin’s work more generally, which is voluminous and of the highest order, see his website: http://faculty.washington.edu/wcalvin.

[iv] There is a reason for this. The matter has been seriously underreported by the major media for years. Here is William Calvin’s summation of that aspect of the matter: “The underreporting of abrupt climate change persisted from 1985 to 1998, even in the face of substantial recognition of some of the major players. For example, Wallace S. Broecker – easily the most vigorous of the geoscientists in trying to alert the scientific community, and author of several Scientific American articles – was awarded the US National Medal of Science by President Clinton in 1996 for ‘contributions to understanding chemical changes in the ocean and atmosphere’. (http://www.kva.se/prizes.html). The Danish ice core expert Willi Dansgaard and the British oceanographer Nicholas Shackleton received the Crafoord Prize from the Swedish Academy in 1995…Dansagaard, the Swiss climatologist Hans Oeschger and the French climatologist Claude Lorius received the $150,000 Tyler Prize in 1996.

Yet, despite all this recognition and all those news stories in Science and Nature, the bistable climate story itself (sudden warmings flipping to sudden coolings) was seldom reported in the popular press. It was conflated with other rapid climate changes (volcanoes, ice shelves breaking up) lacking bistable states, or it was simply lost in a greenhouse story. It would be interesting for some student of the media to sort out the underlying reasons why such a major story was ignored.” Ibid. p. 337.

[v] Richard B. Alley The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change and the Human Future, Princeton University Press, 2000. Alley wrote, “Over the last million years, the pattern recorded in cores of Greenland ice has occurred over and over: a long stagger into an ice age, a few millennia of stability, repeat. The current stable interval is among the longest in the record. Nature is thus likely to end our friendly climate, perhaps quite soon – the Little Ice Age may have been the first unsteady step down that path.” (p. 4)

[vi] William H. Calvin, op. cit. p. 3.

[vii] Named by Wallace Broecker after the Danish climatologist Willi Dansgaard and the Swiss geophysicist Hans Oeschger, who pioneered the research into the phenomenon in the early 1980s. See Willi Dansgaard et al ‘Evidence for General Instability of Past Climate From a 250 kyr Ice Core’, Nature, Vol. 364, 1993, pp. 218-19. See also Thomas Levenson Ice Times, Harper & Row, 1989 and Thomas Stocker’s obituary for Hans Oeschger, at http://www.climate.unibe.ch-/oeschger/obituary.html.

[viii] William H. Calvin, op. cit. p. 232.

[ix] The literature on human origins has taken giant strides in recent years. See, inter alia, Ian Tattersall and Jeffrey Schwartz Extinct Humans, Westview Press, 2000; Frans de Waal (ed) Tree of Origin: What Primate Behaviour Can Tell Us About Human Evolution, Harvard University 2001; William H. Calvin and Derek Bickerton Lingua ex Machina: Reconciling Darwin and Chomsky with the Human Brain, MIT Press, 2000. For a beautifully presented digest of some of the best recent research, see the newly published Special Edition of Scientific American ‘New Look At Human Evolution’, in newsagencies until late August 2003.

[x] Richard Dawkins does not, of course, actually believe that a blind deity is responsible for overseeing evolution. The term, which is the title of his book The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design, (Norton, New York, 1986), simply means that the classical argument from design, famously articulated by William Paley in the seventeenth century, which saw in the natural world the sort of evidence of a designing deity as a discovery of a watch would imply the existence of a watchmaker; is a misinference. The actual nature of the universe is such as to suggest no designer, because if one existed we would have to infer from his handiwork that he was blind. David Hume anticipated this critique of Paley’s argument in his eighteenth century Dialogues Concerning Natural Religion, in which it was pointed out that, even if the basic premise was granted (that an artifact points to there being an artificer), the actual evidence around us would lead us to infer not the omniscient, omnipotent and benevolent (loving) God of the Christians, but either an infant deity who had flubbed the job; a superannuated deity, whose powers were failing him; or a team of deities who had failed to coordinate their plans and handiwork sufficiently.

[xi] Refugia are “regions that, in the midst of major population downsizings, still provide the essential elements of the species’ niche for small sub-populations. Shorelines and mountain tops are often refugia locales, with a little bit more climate change resulting in the extinction of the sub-population. Europe has many fewer plant species than one might expect because so many were, in effect, pushed into the Mediterranean during an ice age.” (Calvin op. cit. p. 310).

[xii] This is, actually, the chief theme of William Calvin’s book. It is the great virtue of his argument that he seeks a climatological explanation for the emergence by natural selection and not by design of the specific and distinctive attributes of our kind. As he remarks: “That ‘something’ which made abrupt climate changes different for our ancestors than for the other omnivores isn’t really a settled scientific question. But it may well have to do with the tools that our ancestors invented: the action-at-a-distance of projectile predation, the sharp tools needed for food preparation and the ‘debt tools’ of altruism. Other things built upon them, such as the wonderful tool-kit that we call our vocabulary, such as our abilities to speculate about the future and engage in beyond-the-apes levels of social manipulation. But the basics are exactly what might make a big difference in subpopulation survival during the fragmenting population crashes – and they are things that the other omnivores haven’t also invented.” ibid. p. 165.

[xiii] The project is explained on the Institute’s website: http://www.esc.cam.ac.uk/oistage3/.

[xiv] One of the most dramatic findings of recent years has been the apparent link between the arrival of Homo sapiens in Oceania and the Americas and the extinction of the Pleistocene megafauna – the giant mammals and marsupials of the last ice age. The impact was most severe in Australia, where the great beasts all died out at the end of the last ice age, some 15,000 years ago. Since our species did not arrive in Madagascar or New Zealand until about 1,000 years ago, the impact there was delayed. But once we landed on those islands, the megafauna populations collapsed precipitously. See Leakey and Lewin, op. cit., pp. 171-94, especially the table on p. 187. The key to these extinctions is that human beings had developed their hunting skills for tens of thousands of years in Africa and Eurasia, before they colonized Oceania and the Americas. The megafauna of those regions, however, had had no time at all to become wary of the canny and ruthless hominid predators and suffered disproportionately in consequence.

[xv] William H. Calvin op. cit. p. 224.

[xvi] There are certain historical catastrophes that come to mind, chief among them the devastation and deurbanisation wrought throughout the Levantine coastlands at the end of the Bronze Age, circa 1250 BCE; the devastation inflicted on both Roman Europe and Han China by Hunnish barbarians between the third and sixth centuries CE; the death toll inflicted by the bubonic plague in the fourteenth century CE; and the wholesale depopulation of the Americas by disease and violence in the sixteenth and seventeenth centuries CE. Concerning the last of these, Fernand Braudel remarked that they consisted of a “colossal biological slump…quite incommensurate with the Black Death”, which killed about a third of the European population. The Structures of Everyday Life: The Limits of the Possible, Collins, 1985, pp. 35-38. None of these, however, was on a global scale and none altered the underlying physical conditions that make human flourishing possible.

[xvii] See, in particular, Wallace S. Broecker and George H. Denton ‘What Drives Glacial Cycles?’, Scientific American, Vol. 262, No.1, January 1990, pp. 48-56; Wallace S. Broecker ‘The Great Ocean Conveyor’, Oceanography, Vol. 4, 1991, pp. 79-89; Wallace S. Broecker ‘Massive Iceberg Discharges as Triggers for Global Climate Change’, Nature, No. 372, 1994, pp. 421-24; and Wallace S. Broecker ‘Abrupt Climate Change: Causal Constraints Provided by the Palaeoclimate Record’, Earth-Science Reviews, Vol. 51, August 2000, pp. 137-54. “The climate record kept in ice and in sediment”, wrote Broecker in 1997, “reveals that since the invention of agriculture some 8,000 years ago, climate has remained remarkably stable. By contrast, during the preceding 100,000 years, climate underwent frequent, very large, and often extremely abrupt shifts. Furthermore, these shifts occurred in lockstep across the globe. They seem to be telling us that earth’s climate system has several distinct and quite different modes of operation and that it can jump from one of these modes to another in a matter of a decade or two. So far, we know of only one element of the climate system which has multiple modes of operation: the oceans’ thermohaline circulation. Numerous model simulations reveal that this [‘conveyor’] circulation is quite sensitive to the fresh water budget in the high-latitude regions where deep waters form.”

[xviii] This process is known by oceanographers as thermohaline circulation, “the circulation path determined by temperature and salt – downwellings due to surface water density created by low temperature and high salinity. Because dense water tends to eventually sink through less dense underlying layers, it contributes a vertical aspect to ocean currents. The sinking waters do not always mix with the underlying layers. Sometimes they slide down a continental slope to the ocean bottom (the most dense bottom waters are formed this way near Antarctica). Or they may become so dense from evaporative cooling (and evaporative augmentation of salt near the surface) that they plunge through the underlying layers. More organized thermohaline circulation occurs in giant whirlpools at some places in the Greenland Sea, 10-15 km across, slowly conveying surface waters to the ocean floor in a hard-to-see column.” (Calvin op. cit. p. 311).

[xix] I am compressing and paraphrasing Calvin here. The original passage reads: “We are near the end of a warm period in any event; ice ages return even without human influences on climate. The last warm period abruptly terminated 13,000 years after the abrupt warming that initiated it 130,000 years ago, and we’ve already gone 15,000 years from a similar warm-up starting point. But we may be able to do something to delay an abrupt cooling. Do something? This tends to stagger the imagination, immediately conjuring up visions of terraforming on a science fiction scale…Surprisingly, it may prove possible to prevent flip-flops in the climate [by building dams to restrict the flow of fresh water into the Atlantic from Canada and Greenland and widening the Panama Canal to divert the salt flow]…But relying on such simple fixes presumes that you know what you’re doing…It would be especially nice to see another dozen major groups of scientists doing climate simulations, discovering the intervention mistakes as quickly as possible and learning from them.” Op. cit., pp. 275-77

[xx] C. H. Haug and R. Tiedemann ‘Effect of the Formation of the Isthmus of Panama on Atlantic Thermohaline Circulation’, Nature, No. 393, 18 June 1998, pp. 673-76; Neil D. Opdike ‘Mammalian Migration and Climate Over the last Seven Million Years’, in Elisabeth S. Vrba, George H. Denton, Timothy C, Partridge and Lloyd H. Burckle Palaeoclimate and Evolution, with Emphasis on Human Origins, Yale University Press, 1995, pp. 109-114. See also Mark A. Cane and Peter Molnar ‘Closing of the Indonesian Seaway as a Precursor to East African Aridification Around 3-4 million Years Ago’, Nature, No. 411, 10 May 2001, pp. 157-62, for an argument that the northward movement of the island of New Guinea had a similar effect, by constricting circulation between the Indian and Pacific Oceans.

[xxi] William H. Calvin op. cit. pp. 249-50.

[xxii] Pope Paul VI was referring to the reproductive cycle, in his famous encyclical Humanae Vitae, but the analogy between the biological and the geophysical seems to me to be…felicitous.

[xxiii] There is an interesting debate, of course, about how common intelligent life is in the universe. See Amir Aczel Probability 1: Why There Must Be Intelligent Life in the Universe, Little Brown & Co., Boston 1998; and Peter D. Ward and Donald Brownlee Rare Earth: Why Complex Life Is Uncommon in the Universe, Copernicus, Springer-Verlag, New York, 2000.

[xxiv] The five great mass extinctions were the end-Ordovician (440 million years ago), the Late Devonian (365 million years ago), the end Permian (225 million years ago), the end Triassic (210 million years ago) and the end Cretaceous (65 million years ago). Of these, the end-Ordovician was the most sweeping, because 70% of all phyla of living beings vanished, never to be revived. The end Permian was the most lethal, however, because an estimated 90% of all extant species became extinct at that time, for reasons we have still not been able to reconstruct. For this reason, the Third Extinction has been dubbed “the Great Dying”. See Vincent Courtillot Evolutionary Catastrophes: The Science of Mass Extinction, Cambridge University Press, p/b 2002, 173 pp. In the ancient world, saurian and other extinct megafauna remains were occasionally found, but the ancients lacked a scientific theory as to what they were and interpreted them in vague terms as the remains of monsters, which, in a sense, of course, they were. See Adrienne Mayor The First Fossil Hunters: Paleontology in Greek and Roman Times, Princeton University Press, 2000.

[xxv] For a careful examination of the most explosive part of ‘world history’ – the twentieth century – see John McNeill Something New Under the Sun: An Environmental History of the Twentieth Century, Allen Lane, Penguin, 2000, 421 pp.

[xxvi] Remarkably, in the 332 pages of his book, published in 1998, Wilson makes no mention of D-Os, or of Wallace Broecker and his investigations. In his final chapter, he dwells at some length on the danger of global warming, but seems entirely unaware of the danger of it causing a D-O, or of the recursion of the ice ages. It is sobering to consider that even so immensely well informed a natural scientist and general scholar, as recently as the late 1990s, should have been unaware of this whole line of inquiry and its implications. It is, therefore, doubly ironical that he should quote, of all literary characters, Hotspur, from Shakespeare’s Henry IV, in expressing his optimism that humanity will cope successfully with the environmental challenges it now faces: “I tell you, my lord fool, out of this nettle, danger, we pluck this flower, safety.” Edward O. Wilson Consilience: Unity of Knowledge (1998), p. 289.

[xxvii] Ibid, p. 13.

[xxviii] Ibid. p. 4. Ionian, of course, because Miletus was one of the coastal cities of Ionia, on the Aegean coast of modern Turkey, which was very much part of the Greek world, although incorporated into the Persian Empire in the sixth century BCE.

[xxix] Ibid pp. 12-13.

[xxx] Thomas Homer-Dixon The Ingenuity Gap: How Can We Solve The Problems of the Future?, Vintage, Random House, 2001, 480 pp.

[xxxi] Walter Kaufmann (ed and trans) The Portable Nietzsche, Penguin 1982, p. 42.

[xxxii] “At the moment, we are an ignorant species, flummoxed by the puzzles of who we are, where we came from and what we are for”, wrote Lewis Thomas, in 1979. “It is a gamble to bet on science for moving ahead, but it is, in my view, the only game in town.” Late Night Thoughts in Listening to Mahler’s Ninth Symphony, Viking 1983, p. 15.

[xxxiii] In referring to Hamlet here, I have in mind not simply his famous soliloquies, in which he reflects on the beauty of the world and man as “the paragon of animals” (Act II, Sc.2, ll. 304-320) and ponders whether to commit suicide (Act III, Sc. 1, ll. 56-86), but Harold Bloom’s description of Hamlet as the paragon of intelligent, self-conscious human beings, in Shakespeare: The Invention of the Human, Riverhead Books, 1998. He goes so far as to state, “There are many signs that global self-consciousness increasingly identifies with Hamlet, Asia and Africa included.” (p. 420) For Hamlet is, he argues, the most fully realized, the most fully articulated fictive character in human literature. So much so, that he is, in Bloom’s opinion, a more fully articulated human being than virtually any real person: “Hamlet now seems no more fictive than Montaigne; four centuries have established both as authentic personalities; rather in the same way that Falstaff appears to be as historical a reality as Rabelais”.

Hamlet was the summit of Shakespeare’s art and Shakespeare himself the greatest writer of all time. “Hamlet’s linguistic skepticism co-exists with a span and control of language greater even than Falstaff’s, because its range is the widest we have ever encountered in a single work. It is always a shock to be reminded that Shakespeare used more than 21,000 separate words, while Racine used fewer than 2,000. Doubtless, some German scholar has counted up just how many of the 21,000 words Hamlet had in his vocabulary, but we scarcely need to know the sum. The play is Shakespeare’s longest because Hamlet speaks so much of it, and I frequently wish it even longer, so that Hamlet could have spoken on even more matters than he already covers.” (p. 423). The ideal of human self-awareness, in other words, is embodied, for Bloom, and for much of global culture, in the mind of Hamlet, Prince of Denmark, and our freedom as human beings is enhanced when we enlarge our own imaginations by seeing the world through Hamlet’s eyes. “Hamlet’s freedom”, he writes, “can be defined as the freedom to infer, and we learn this intellectual liberty by attending to Hamlet.” (p. 419, emphasis in the original).