I'm crossposting most of Toby Ord's quotations from the page linked above. I left off a few that I didn't like, or that seemed redundant with others by the same author.

If you know of other good quotations on the same theme, add them in the comments! If we get a few comments, I'll send the page to Toby in case he wants to add more examples to his site.

Ord's description of the page: 

From some of the earliest realisations of the possibilities that lie before us, through to a much deeper understanding of the nature and importance of the greatest threats and opportunities facing humanity.

EARLY THOUGHTS ON THE POSSIBILITY OF EXTINCTION

In the 19th century, a number of thinkers began to turn their attention to the possibility (or inevitability) of human extinction.

Within a finite period of time past the earth must have been, and within a finite period of time to come the earth must again be, unfit for the habitation of man as at presently constituted, unless operations have been, or are to be performed which are impossible under the laws to which the known operations going on at the present in the material world are subject.

— Lord Kelvin, 1852

When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled. Judging from the past, we may safely infer that not one living species will transmit its unaltered likeness to a distinct futurity. And of the species now living very few will transmit progeny of any kind to a far distant futurity; for the manner in which all organic beings are grouped, shows that the greater number of species in each genus, and all the species in many genera, have left no descendants, but have become utterly extinct. We can so far take a prophetic glance into futurity as to foretell that it will be the common and widely spread species, belonging to the larger and dominant groups within each class, which will ultimately prevail and procreate new and dominant species. As all the living forms of life are the lineal descendants of those which lived long before the Cambrian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world. Hence, we may look with some confidence to a secure future of great length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.

— Charles Darwin, The Origin of Species, 1859

I firmly believe that before many centuries hence, science will be the master of man. The engines he will have invented will be beyond his strength to control. Some day science may have the existence of mankind in its power, and the human race commit suicide, by blowing up the world.

— Henry Adams, 1862

We refer to the question: What sort of creature man’s next successor in the supremacy of the earth is likely to be. We have often heard this debated; but it appears to us that we are ourselves creating our own successors; we are daily adding to the beauty and delicacy of their physical organisation; we are daily giving them greater power and supplying by all sorts of ingenious contrivances that self-regulating, self-acting power which will be to them what intellect has been to the human race. In the course of ages we shall find ourselves the inferior race. Inferior in power, inferior in that moral quality of self-control, we shall look up to them as the acme of all that the best and wisest man can ever dare to aim at.

— Samuel Butler, ‘Darwin among the machines’, 1863

It is part of the excessive egotism of the human animal that the bare idea of its extinction seems incredible to it. “A world without us!” it says, as a heady young Cephalaspis might have said it in the old Silurian sea. But since the Cephalaspis and the Coccostëus many a fine animal has increased and multiplied upon the earth, lorded it over land or sea without a rival, and passed at last into the night. Surely it is not so unreasonable to ask why man should be an exception to the rule. From the scientific standpoint at least any reason for such exception is hard to find.

…for all we know even now we may be quite unwittingly evolving some new and more terrible plague—a plague that will not take ten or twenty or thirty per cent, as plagues have done in the past, but the entire hundred.

No; man's complacent assumption of the future is too confident. We think, because things have been easy for mankind as a whole for a generation or so, we are going on to perfect comfort and security in the future. We think that we shall always go to work at ten and leave off at four, and have dinner at seven for ever and ever. But these four suggestions, out of a host of others, must surely do a little against this complacency. Even now, for all we can tell, the coming terror may be crouching for its spring and the fall of humanity be at hand. In the case of every other predominant animal the world has ever seen, I repeat, the hour of its complete ascendency has been the eve of its entire overthrow.

— H. G. Wells, ‘The Extinction of Man’, 1894

The atomic bomb had dwarfed the international issues to complete insignificance. When our minds wandered from the preoccupations of our immediate needs, we speculated upon the possibility of stopping the use of these frightful explosives before the world was utterly destroyed. For to us it seemed quite plain that these bombs and the still greater power of destruction of which they were the precursors might quite easily shatter every relationship and institution of mankind... war must end and that the only way to end war was to have but one government for mankind.

— H. G. Wells, The World Set Free, 1913

[regarding a fictional weapon, only loosely related to the actual atomic bomb]

There will come soft rains and the smell of the ground,
And swallows calling with their shimmering sound;
And frogs in the pools singing at night,
And wild plum-trees in tremulous white;
Robins will wear their feathery fire
Whistling their whims on a low fence-wire;
And not one will know of the war, not one
Will care at last when it is done.
Not one would mind, neither bird nor tree
If mankind perished utterly;
And Spring herself, when she woke at dawn,
Would scarcely know that we were gone.

— Sara Teasdale, ‘There Will Come Soft Rains’, 1918

The future will be no primrose path. It will have its own problems. … Whether in the end man will survive his ascensions of power we cannot tell. … But it is only hopeful if mankind can adjust its morality to its powers.

— J. B. S. Haldane, Daedalus; or, Science and the Future, 1923

Mankind has never been in this position before. Without having improved appreciably in virtue or enjoying wiser guidance, it has got into its hands for the first time the tools by which it can unfailingly accomplish its own extermination. That is the point in human destinies to which all the glories and toils of men have at last led them. They would do well to pause and ponder upon their new responsibilities. … Surely if a sense of self-preservation still exists among men, if the will to live resides not merely in individuals or nations but in humanity as a whole, the prevention of the supreme catastrophe ought to be the paramount object of all endeavour.

— Winston Churchill, ‘Shall We All Commit Suicide?’, 1924

In a future which our children may live to see, powers will be in the hands of men altogether different from any by which human nature has been molded. Explosive forces, energy, materials, machinery, will be available upon a scale which can annihilate whole nations. Despotisms and tyrannies will be able to prescribe the lives and even the wishes of their subjects in a manner never known since time began. If to these tremendous and awful powers is added the pitiless sub-human wickedness which we now see embodied in one of the most powerful reigning governments, who shall say that the world itself will not be wrecked, or indeed that it ought not to be wrecked? There are nightmares of the future from which a fortunate collision with some wandering star, reducing the earth to incandescent gas, might be a merciful deliverance.

— Winston Churchill, ‘Fifty Years Hence’, 1931

THE ATOMIC SCIENTISTS

Many of the scientists who developed nuclear weapons felt a heavy responsibility to educate the public about their risks. This included the possibility that a full-scale nuclear war with the current (or future) weapons may spell the end of humanity.

If we focus our attention on the next twenty-five years we may say that development is likely to reach some point intermediate between the first bomb detonated over Hiroshima and processes which once initiated might put an end to all life on earth. Just what intermediate point will be reached within twenty-five years no one can tell.

— Leo Szilard, speech at the Atomic Energy Conference, 21 Sep 1945

It is not even impossible to imagine that the effects of an atomic war fought with greatly perfected weapons and pushed by the utmost determination will endanger the survival of man.

— Edward Teller, ‘How Dangerous Are Atomic Weapons?’, 1947

The extreme danger to mankind inherent in the proposal [to develop thermonuclear weapons] wholly outweighs any military advantage.

— Robert Oppenheimer et al., Report of the General Advisory Committee, 1949 

[Regarding proposed thermonuclear weapons] Such a weapon goes far beyond any military objective and enters the range of very great natural catastrophes. By its very nature it cannot be confined to a military objective but becomes a weapon which in practical effect is almost one of genocide. … The fact that no limits exist to the destructiveness of this weapon makes its very existence and the knowledge of its construction a danger to humanity as a whole. It is necessarily an evil thing considered in any light.

— Enrio Fermi and I. I. Rabi, Report of the General Advisory Committee, 1949

Much has been said of the prospect that man, along with many other forms of life … would disappear as a species. In time, not a long time, that may come to be possible. What is more certain and more immediate is that we would lose much of our human inheritance, much that has made our civilization and our humanity… the threat of the apocalypse will be with us for a long time; the apocalypse may come.

— Robert Oppenheimer, ‘Science and our Times’, 1956

A very large nuclear war would be a calamity of indescribable proportions and absolutely unpredictable consequences, with the uncertainties tending towards the worse … All-out nuclear war would mean the destruction of contemporary civilization, throw man back centuries, cause the deaths of hundreds of millions or billions of people, and, with a certain degree of probability, would cause man to be destroyed as a biological species.

— Andrei Sakharov, ‘The Dangers of Thermonuclear War’, 1983

COLD WAR LEADERS

There are many remarks by Cold War leaders which show that they took seriously the possibility that a full scale nuclear war may be able to destroy humanity entirely.

The Dark Ages may return, the Stone Age may return on the gleaming wings of Science, and what might now shower immeasurable material blessings upon mankind, may even bring about its total destruction. Beware, I say; time may be short.

— Winston Churchill, 1946

Yet the promise of this life is imperiled by the very genius that has made it possible. Nations amass wealth. Labor sweats to create—and turns out devices to level not only mountains but also cities. Science seems ready to confer upon us, as its final gift, the power to erase human life from this planet.

— Eisenhower, Inaugural Address, 1953

I have spent my life in the study of military strength as a deterrent to war, and in the character of military armaments necessary to win a war. The study of the first of these questions is still profitable, but we are rapidly getting to the point that no war can be won. War implies a contest; when you get to the point that contest is no longer involved and the outlook comes close to destruction of the enemy and suicide for ourselves—an outlook that neither side can ignore—then arguments as to the exact amount of available strength as compared to somebody else's are no longer the vital issues. When we get to the point, as we one day will, that both sides know that in any outbreak of general hostilities, regardless of the element of surprise, destruction will be both reciprocal and complete, possibly we will have sense enough to meet at the conference table with the understanding that the era of armaments has ended and the human race must conform its actions to this truth or die.

— Eisenhower, 1956

Unconditional war can no longer lead to unconditional victory. It can no longer serve to settle disputes. It can no longer concern the great powers alone. For a nuclear disaster, spread by winds and waters and fear, could well engulf the great and the small, the rich and the poor, the committed and the uncommitted alike. Mankind must put an end to war—or war will put an end to mankind. … Today, every inhabitant of this planet must contemplate the day when this planet may no longer be habitable. Every man, woman and child lives under a nuclear sword of Damocles, hanging by the slenderest of threads, capable of being cut at any moment by accident, or miscalculation, or by madness. The weapons of war must be abolished before they abolish us.

— John F. Kennedy, speech to the UN general assembly, 1961

Our problems are manmade—therefore, they can be solved by man. And man can be as big as he wants. No problem of human destiny is beyond human beings.

— John F. Kennedy, speech at American University, Washington, 1963

Mankind would be wholly destroyed.

— Leonid Brezhnev, speech to the Polish Sejm, 1974 

In an all-out nuclear war, more destructive power than in all of World War II would be unleashed every second during the long afternoon it would take for all the missiles and bombs to fall. A World War II every second—more people killed in the first few hours than in all the wars of history put together. The survivors, if any, would live in despair amid the poisoned ruins of a civilization that had committed suicide.

— Jimmy Carter, Farewell Address to the Nation, 1981

The Soviet Union holds that nuclear war would be a universal disaster, and that it would probably mean the end of civilization. It may lead to the destruction of all mankind.

— Soviet government booklet, 1981

A great many reputable scientists are telling us that such a war could just end up in no victory for anyone because we would wipe out the earth as we know it. And if you think back to a couple of natural calamities—back in the last century, in the 1800’s, just natural phenomena from earthquakes, or, I mean, volcanoes—we saw the weather so changed that there was snow in July in many temperate countries. And they called it the year in which there was no summer. Now if one volcano can do that, what are we talking about with the whole nuclear exchange, the nuclear winter that scientists have been talking about?

— Ronald Reagan, 1985

Models made by Russian and American scientists showed that a nuclear war would result in a nuclear winter that would be extremely destructive to all life on earth; the knowledge of that was a great stimulus to us.

— Mikhail Gorbachev, 2000

RUSSELL & EINSTEIN

While not actively involved in the design or deployment of nuclear weapons, Bertrand Russell and Albert Einstein shaped the public discussion around the grave risks to humanity during the first decade of the nuclear era.

The prospect for the human race is sombre beyond all precedent. Mankind are faced with a clear-cut alternative: either we shall all perish, or we shall have to acquire some slight degree of common sense. A great deal of new political thinking will be necessary if utter disaster is to be averted.

— Bertrand Russell, ‘The Bomb and Civilisation’, 9 Aug 1945

We do not want to look at this thing simply from the point of view of the next few years; we want to look at it from the point of view of the future of mankind.

— Bertrand Russell, speech in the House of Lords, 28 Nov 1945

Our world faces a crisis as yet unperceived by those possessing power to make great decisions for good or evil. The unleashed power of the atom has changed everything save our modes of thinking and we thus drift toward unparalleled catastrophe. … a new type of thinking is essential if mankind is to survive and move toward higher levels.

— Albert Einstein, 1946

I advocate world government because I am convinced that there is no other possible way of eliminating the most terrible danger in which man has ever found himself. The objective of avoiding total destruction must have priority over any other objective.

— Albert Einstein, ‘A reply to the Soviet scientists’, 1948

As geological time is reckoned, Man has so far existed only for a very short period—a million years at the most. What he has achieved, especially during the last 6,000 years, is something utterly new in the history of the Cosmos, so far at least as we are acquainted with it. For countless ages the sun rose and set, the moon waxed and waned, the stars shone in the night, but it was only with the coming of Man that these things were understood. In the great world of astronomy and in the little world of the atom, Man has unveiled secrets which might have been thought undiscoverable. In art and literature and religion, some men have shown a sublimity of feeling which makes the species worth preserving. Is all this to end in trivial horror because so few are able to think of Man rather than of this or that group of men? Is our race so destitute of wisdom, so incapable of impartial love, so blind even to the simplest dictates of self-preservation, that the last proof of its silly cleverness is to be the extermination of all life on our planet?—for it will be not only men who will perish, but also the animals, whom no one can accuse of Communism or anti-Communism. I cannot believe that this is to be the end. I would have men forget their quarrels for a moment and reflect that, if they will allow themselves to survive, there is every reason to expect the triumphs of the future to exceed immeasurably the triumphs of the past. There lies before us, if we choose, continual progress in happiness, knowledge, and wisdom. Shall we, instead, choose death, because we cannot forget our quarrels? I appeal, as a human being to human beings: remember your humanity, and forget the rest. If you can do so, the way lies open to a new Paradise; if you cannot, nothing lies before you but universal death.

— Bertrand Russell, ‘Man’s Peril’, 1954

The thing to emphasise is that war may well mean the extinction of life on this planet. The Russian and American Governments do not think so. They should have no excuse for continued ignorance on the point. … although the H-bomb at the moment occupies the centre of attention, it does not exhaust the destructive possibilities of science, and it is probable that the dangers of bacteriological warfare may before long become just as great.

— Bertrand Russell, letter to Einstein proposing the Manifesto, 1955

Here, then, is the problem which we present to you, stark and dreadful and inescapable: Shall we put an end to the human race; or shall mankind renounce war?

— Bertrand Russell & Albert Einstein, The Russell-Einstein Manifesto, 1955

SCHELL

With its focus on the moral significance of losing humanity’s entire future, Jonathan Schell’s book The Fate of the Earth marked a turning point in our understanding of existential risk. While focused on nuclear war, it introduced many of the key points that are common to all existential risks.

It is of the essence of the human condition that we are born, live for a while, and then die. Through mishaps of all kinds, we may also suffer untimely death, and in extinction by nuclear arms the number of untimely deaths would reach the limit for any one catastrophe: everyone in the world would die. But although the untimely death of everyone in the world would in itself constitute an unimaginably huge loss, it would bring with it a separate, distinct loss that would be in a sense even huger—the cancellation of all future generations of human beings. …

The distinctness of this second death from the deaths of all the people on earth can be illustrated by picturing two different global catastrophes. In the first, let us suppose that most of the people on earth were killed in a nuclear holocaust but that a few million survived and the earth happened to remain habitable by human beings. In this catastrophe, billions of people would perish, but the species would survive, and perhaps one day would even repopulate the earth in its former numbers. But now let us suppose that a substance was released into the environment which had the effect of sterilizing all the people in the world but otherwise leaving them unharmed. Then, as the existing population died off, the world would empty of people, until no one was left. Not one life would have been shortened by a single day, but the species would die. In extinction by nuclear arms, the death of the species and the death of all the people in the world would happen together, but it is important to make a clear distinction between the two losses; otherwise, the mind, overwhelmed by the thought of the deaths of the billions of living people, might stagger back without realizing that behind this already ungraspable loss there lies the separate loss of the future generations.

  — Jonathan Schell, The Fate of the Earth, 1982

And there is another, even vaster measure of the loss, for stretching ahead from our present are more billions of years of life on earth, all of which can be filled not only with human life but with human civilization. The procession of generations that extends onwards from our present leads far, far beyond the line of our sight, and, compared with these stretches of human time, which exceed the whole history of the earth up to now, our brief civilized moment is almost infinitesimal. Yet we threaten, in the name of our transient aims and fallible convictions, to foreclose it all. If our species does destroy itself, it will be a death in the cradle—a case of infant mortality.

   — Jonathan Schell, The Fate of the Earth, 1982

And if at first we find these future people to be somewhat abstract we have only to remind ourselves that we, too, were once “the future generation,” and that every unborn person will be as vivid and important to himself as each of us is to himself. We gain the right perspective on extinction not by trying to peer into the inhuman emptiness of a post-human universe but by putting ourselves in the shoes of someone in the future, who, precisely because he has been allowed to be born, can rejoice in the fact of being alive.

  — Jonathan Schell, The Fate of the Earth, 1982

When it comes to judging the consequences of a nuclear holocaust there can be no experimentation, and thus no empirical verification. We cannot run experiments with the earth, because we have only one earth, on which we depend for our survival; we are not in possession of any spare earths that we might blow up in some universal laboratory in order to discover their tolerance of nuclear holocausts.

— Jonathan Schell, The Fate of the Earth, 1982 

With the generation that has never known a world unmenaced by nuclear weapons, a new order of the generations begins. In it, each person alive is called on to assume his share of the responsibility for guaranteeing the existence of all future generations. And out of the new sense of responsibility must come a worldwide program of action for preserving the species. This program would be the guarantee of existence for the unborn and the measure of the honor and the humanity of the living. Its inauguration would mark the foundation of a new common world, which would greatly transcend the old, pre-nuclear common world in importance and in the strength of its ties. Without such a program in place, nothing else that we undertake together can make any practical or moral sense.

  — Jonathan Schell, The Fate of the Earth, 1982

SAGAN

As part of the team of researchers who first discovered the possibility of nuclear winter, Carl Sagan became one of the leading voices regarding the existential risk from nuclear weapons and what it means for the future of humanity. Like Schell, his work was marked by both conceptual clarity and power of expression.

Some have argued that the difference between the deaths of several hundred million people in a nuclear war (as has been thought until recently to be a reasonable upper limit) and the death of every person on Earth (as now seems possible) is only a matter of one order of magnitude. For me, the difference is considerably greater. Restricting our attention only to those who die as a consequence of the war conceals its full impact.

If we are required to calibrate extinction in numerical terms, I would be sure to include the number of people in future generations who would not be born. A nuclear war imperils all of our descendants, for as long as there will be humans. Even if the population remains static, with an average lifetime of the order of 100 years, over a typical time period for the biological evolution of a successful species (roughly ten million years), we are talking about some 500 trillion people yet to come. By this criterion, the stakes are one million times greater for extinction that for the more modest nuclear wars that kill “only” hundreds of millions of people.

There are many other possible measures of the potential loss—including culture and science, the evolutionary history of the planet, and the significance of the lives of all of our ancestors who contributed to the future of their descendants. Extinction is the undoing of the human enterprise.

— Carl Sagan, ‘Nuclear War and Climatic Catastrophe: Some Policy Implications’, 1983

It might be a familiar progression, transpiring on many worlds—a planet, newly formed, placidly revolves around its star; life slowly forms; a kaleidoscopic procession of creatures evolves; intelligence emerges which, at least up to a point, confers enormous survival value; and then technology is invented. It dawns on them that there are such things as laws of Nature, that these laws can be revealed by experiment, and that knowledge of these laws can be made both to save and to take lives, both on unprecedented scales. Science, they recognize, grants immense powers. In a flash, they create world-altering contrivances. Some planetary civilizations see their way through, place limits on what may and what must not be done, and safely pass through the time of perils. Others, not so lucky or so prudent, perish.

— Carl Sagan, Pale Blue Dot, 1994

Many of the dangers we face indeed arise from science and technology—but, more fundamentally, because we have become powerful without becoming commensurately wise. The world-altering powers that technology has delivered into our hands now require a degree of consideration and foresight that has never before been asked of us.

— Carl Sagan, Pale Blue Dot, 1994

I do not imagine that it is precisely we, with our present customs and social conventions, who will be out there. If we continue to accumulate only power and not wisdom, we will surely destroy ourselves. Our very existence in that distant time requires that we will have changed our institutions and ourselves. How can I dare to guess about humans in the far future? It is, I think, only a matter of natural selection. If we become even slightly more violent, shortsighted, ignorant, and selfish than we are now, almost certainly we will have no future.

— Carl Sagan, Pale Blue Dot, 1994

They will gaze up and strain to find the blue dot in their skies. They will love it no less for its obscurity and fragility. They will marvel at how vulnerable the repository of all our potential once was, how perilous our infancy, how humble our beginnings, how many rivers we had to cross before we found our way.

— Carl Sagan, Pale Blue Dot, 1994

RECENT PHILOSOPHY

Philosophical attention to the problem of existential risk has been scarce even to this day, but it has not been restricted to just a couple of figures. Here are some of the more clear or powerful statements on the problem over the last fifty years.

The human intellect has enabled man to change his environment in an unprecedented way—and to annihilate various other species—and even to realize macro effects and the annihilation of his own species. … Our habits of behaviour and thinking, our ideas and moral rules have been formed during very many generations in a very special period of terrestrial history. They do not seem to be predestined for eternity. On the contrary, any future of humanity on a biological time scale will need at least adaption of thinking and acting and in particular of moral habits to the historical transition into the period of macro problems.

— H. J. Groenewold, ‘Modern Science and Social Responsibility’, 1968

Normally, the utilitarian is able to assume that the remote effects of his actions tend rapidly to zero. … It seems plausible that the long-term probable benefits and costs of his alternative actions are likely to be negligible or cancel one another out.

An obviously important case in which, if he were a utilitarian, a person would have to consider effects into the far future, perhaps millions of years, would be that of a statesman who was contemplating engaging in nuclear warfare, if there were some probability, even a small one, that this war might end in the destruction of the entire human race. (Even a war less drastic than this might have important consequences into the fairly far future, say hundreds of years.) Similar long term catastrophic consequences must be envisaged in planning flight to other planets, if there is any probability, even quite a small one, that these planets possess viruses or bacteria, to which terrestrial organisms would have no immunity.

— J. J. C. Smart, Utilitarianism For and Against, 1973

I want to illustrate the relevance of metaphysics to ethics by reference to what is the greatest moral problem that has ever faced the human race: the question of nuclear war. … the threat of nuclear war makes us envisage macro effects (effects on all people and the whole earth): the end of the human race, perhaps also of mammalian life itself, and the end of the prospect of humans evolving into yet higher and more wonderful forms of life. … Those who comfort themselves with the thought that mutual deterrence has kept the peace for thirty years forget the importance of low probabilities in the macro context. Indeed what does it matter, from the perspective of possible millions of years of future evolution, that the final catastrophe should merely be postponed for (say) a couple of hundred years? Postponing is only of great value if it is used as a breathing space in which ways are found to avert the final disaster. And even a small probability that we shall not have this breathing space will yield negative expected utility of macro dimensions.

— J. J. C. Smart, Ethics, Persuasion and Truth, 1984

Suppose we could take a drug which would render us infertile, but make us so happy that we would not mind being childless. Would it be wrong for everyone now alive to take it, ensuring that we would be the last generation? Would it have mattered if the human race had become sterile thousands of years ago? Some people are indifferent to either of these possibilities, and I have no argument to convince them. But other people, including me, think that to end the human race would be about the worst thing it would be possible to do. This is because of a belief in the intrinsic value of there existing in the future at least some people with worth-while lives. And, if we reject any kind of time bias, it is hard to see the case for valuing extra people spread out across future time that would not also place some value on extra people contemporary with us.

— Jonathan Glover, Causing Death and Saving Lives, 1977

The crucial role we fill, as moral beings, is as members of a cross-generational community, a community of beings who look before and after, who interpret the past in light of the present, who see the future as growing out of the past, who see themselves as members of enduring families, nations, cultures, traditions.

— Annette Baier, ‘The Rights of Past and Future Persons’, 1981

I believe that if we destroy mankind, as we now can, this outcome will be much worse than most people think. Compare three outcomes:

(1) Peace.

(2) A nuclear war that kills 99% of the world's existing population. 

(3) A nuclear war that kills 100%.

(2) would be worse than (1), and (3) would be worse than (2). Which is the greater of these two differences? Most people believe that the greater difference is between (1) and (2). I believe that the difference between (2) and (3) is very much greater.

My view is held by two very different groups of people. Both groups would appeal to the same fact. The Earth will remain inhabitable for at least another billion years. Civilization began only a few thousand years ago. If we do not destroy mankind, these few thousand years may be only a tiny fraction of the whole of civilized human history. The difference between (2) and (3) may thus be the difference between this tiny fraction and all of the rest of this history. If we compare this possible history to a day, what has occurred so far is only a fraction of a second.

One of the groups who hold my view are Classical Utilitarians. They would claim, as Sidgwick did, that the destruction of mankind would be by far the greatest of all conceivable crimes. The badness of this crime would lie in the vast reduction of the possible sum of happiness.

Another group would agree, but for very different reasons. These people believe that there is little value in the mere sum of happiness. For these people, what matters are what Sidgwick called the ‘ideal goods’—the Sciences, the Arts, and moral progress, or the continued advance towards a wholly just world-wide community. The destruction of mankind would prevent further achievements of these three kinds. This would be extremely bad because what matters most would be the highest achievements of these kinds, and these highest achievements would come in future centuries.

— Derek Parfit, Reasons and Persons, 1984

The part of our moral theory ... that covers how we affect future generations ... is the most important part of our moral theory, since the next few centuries will be the most important in human history.

— Derek Parfit, Reasons and Persons, 1984

We live during the hinge of history. Given the scientific and technological discoveries of the last two centuries, the world has never changed as fast. We shall soon have even greater powers to transform, not only our surroundings, but ourselves and our successors. If we act wisely in the next few centuries, humanity will survive its most dangerous and decisive period. Our descendants could, if necessary, go elsewhere, spreading through this galaxy.

— Derek Parfit, On What Matters, vol. 2, 2011

What now matters most is how we respond to various risks to the survival of humanity. We are creating some of these risks, and we are discovering how we could respond to these and other risks. If we reduce these risks, and humanity survives the next few centuries, our descendants or successors could end these risks by spreading through this galaxy.

Life can be wonderful as well as terrible, and we shall increasingly have the power to make life good. Since human history may be only just beginning, we can expect that future humans, or supra-humans, may achieve some great goods that we cannot now even imagine. In Nietzsche’s words, there has never been such a new dawn and clear horizon, and such an open sea. 

If we are the only rational beings in the Universe, as some recent evidence suggests, it matters even more whether we shall have descendants or successors during the billions of years in which that would be possible. Some of our successors might live lives and create worlds that, though failing to justify past suffering, would have given us all, including those who suffered most, reasons to be glad that the Universe exists.

— Derek Parfit, On What Matters, vol. 3, 2017

If global warming extinguishes humanity, according to total utilitarianism, that would be an inconceivably bad disaster. The loss would be all the future wellbeing of all the people who would otherwise have lived. … According to total utilitarianism, although the chance of extinction is slight, the harm extinction would do is so enormous that it may well be the dominant consideration when we think about global warming.

— John Broome, Counting the Cost of Global Warming, 1992

I nevertheless feel inclined to say that the probability of the human race avoiding extinction for the next five centuries is encouragingly high, perhaps as high as 70 per cent. Also that if it did so, then it would be likely either to continue onwards for many thousand centuries or else to be replaced by something better.

— John Leslie, The End of the World, 1996

Our approach to existential risks cannot be one of trial-and-error. There is no opportunity to learn from errors. The reactive approach—see what happens, limit damages, and learn from experience—is unworkable. Rather, we must take a proactive approach. This requires foresight to anticipate new types of threats and a willingness to take decisive preventive action and to bear the costs (moral and economic) of such actions.

We cannot necessarily rely on the institutions, moral norms, social attitudes or national security policies that developed from our experience with managing other sorts of risks. Existential risks are a different kind of beast. We might find it hard to take them as seriously as we should simply because we have never yet witnessed such disasters. Our collective fear-response is likely ill calibrated to the magnitude of threat.

— Nick Bostrom, ‘Existential Risks: Analysing Human Extinction
Scenarios and Related Hazards’, 2002

We might also have custodial duties to preserve the inheritance of humanity passed on to us by our ancestors and convey it safely to our descendants. We do not want to be the failing link in the chain of generations, and we ought not to delete or abandon the great epic of human civilisation that humankind has been working on for thousands of years, when it is clear that the narrative is far from having reached a natural terminus.

— Nick Bostrom, ‘Existential Risk Prevention as Global Priority’, 2013

Our present understanding of axiology might well be confused. We may not now know—at least not in concrete detail—what outcomes would count as a big win for humanity; we might not even yet be able to imagine the best ends of our journey. If we are indeed profoundly uncertain about our ultimate aims, then we should recognize that there is a great option value in preserving—and ideally improving—our ability to recognize value and to steer the future accordingly. Ensuring that there will be a future version of humanity with great powers and a propensity to use them wisely is plausibly the best way available to us to increase the probability that the future will contain a lot of value. To do this, we must prevent any existential catastrophe.

— Nick Bostrom, ‘Existential Risk Prevention as Global Priority’, 2013

It may not be absurd hyperbole—indeed, it may not even be an overstatement—to assert that the most crucial location in space and time (apart from the big bang itself) could be here and now. I think the odds are no better than fifty-fifty that our present civilisation on Earth will survive to the end of the present century. Our choices and actions could ensure the perpetual future of life (not just on Earth, but perhaps far beyond it, too). Or in contrast, through malign intent, or through misadventure, twenty-first century technology could jeopardise life's potential, foreclosing its human and posthuman future. What happens here on Earth, in this century, could conceivably make the difference between a near eternity filled with ever more complex and subtle forms of life and one filled with nothing but base matter.

— Martin Rees, Our Final Century, 2003

Most educated people, even if they are fully aware that our emergence took billions of years, somehow think we humans are the culmination of the evolutionary tree. That is not so. Our Sun is less than half way through its life. It is slowly brightening, but Earth will remain habitable for another billion years. However, even in that cosmic perspective—extending far into the future as well as into the past—the twenty-first century may be a defining moment. It is the first in our planet’s history where one species—ours—has Earth’s future in its hands and could jeopardise not only itself but also life’s immense potential.

— Martin Rees, foreword to Global Catastrophic Risks, 2008

Even if we think the prior existence view is more plausible than the total view, we should recognize that we could be mistaken about this and therefore give some value to the life of a possible future—let’s say, for example, 10 per cent of the value we give to the similar life of a presently existing being. The number of human beings who will come into existence only if we can avoid extinction is so huge that even with that relatively low value, reducing the risk of human extinction will often be a highly cost-effective strategy for maximizing utility, as long as we have some understanding of what will reduce that risk.

— Katarzyna de Lazari-Radek & Peter Singer, The Point of View of the Universe, 2014

FURTHER THOUGHTS ON EXISTENTIAL RISK

Miscellaneous quotations related to existential risk.

Smoke rises, the mist is spreading.
Weep, my friends,
and know that by these deeds
we have forever lost our heritage.

— Unknown author, one of the last Aztec poems, 1521

But what might be the Consequences of so near an Appulse; or of a Contact; or, lastly, of a Shock of the Coelestial bodies, (which is by no means impossible to come to pass) I leave to be discuss’d by the Studious of Physical Matters.

― Edmund Halley, Synopsis of the Astronomy of the Comets, 1705

Was there really any chance that an atomic bomb would trigger the explosion of the nitrogen in the atmosphere or of the hydrogen in the ocean? This would be the ultimate catastrophe. Better to accept the slavery of the Nazis than to run a chance of drawing the final curtain on mankind!

Oppenheimer’s team must go ahead with their calculations. Unless they came up with a firm and reliable conclusion that our atomic bombs could not explode the air or the sea, these bombs must never be made.

— Arthur Compton, Atomic Quest, 1956

[recalling a meeting with Oppenheimer in 1942]

Then came a burst of white light that seemed to fill the sky and seemed to last for seconds. I had expected a relatively quick and light flash. The enormity of the light quite stunned me. My instantaneous reaction was that some- thing had gone wrong and that the thermal nuclear transformation of the atmosphere, once discussed as a possibility and jokingly referred to a few minutes earlier, had actually occurred.

— James Conant, diary entry after the Trinity test, 1945

Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty or might continue as a chain reaction. Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star. Occasionally, however, he joked that the scientists in their unworldly urge to lay bare all the secrets under heaven might some day set the globe on fire. But undoubtedly a good deal of time would pass before that came about, Hitler said; he would certainly not live to see it.

— Albert Speer, recalling the German nuclear programme, 1970

Once a machine is designed that is good enough, say at a cost of $100,000,000, it can be put to work designing an even better machine. At this point an "explosion" will clearly occur; all the problems of science and technology will be handed over to machines and it will no longer be necessary for people to work. Whether this will lead to a Utopia or to the extermination of the human race will depend on how the problem is handled by the machines. The important thing will be to give them the aim of serving human beings.

It seems probable that no mechanical brain will be really useful until it is somewhere near to the critical size. If so, there will be only a very short transition period between having no very good machine and having a great many exceedingly good ones. Therefore the work on simulation of artificial intelligence on general-purpose computers is especially important, because it will lengthen the transition period, and give human beings a chance to adapt to the future situation.

— I. J. Good, ‘Speculations on Perceptrons and other Automata’, 1959

The human race’s prospects of survival were considerably better when we were defenceless against tigers than they are today, when we have become defenceless against ourselves.

— Arnold Toynbee, speech to the World Food Congress, 1963

As a scientist I am profoundly concerned about the continued involvement of the United States and other nations in the development of biological warfare. This process puts the very future of human life on earth in serious peril.

— Joshua Lederberg, ‘Biological Warfare and the Extinction of Man’, 1969

We physicians who shepherd human life from birth to death have a moral imperative to resist with all our being the drift toward the brink. The threatened inhabitants on this fragile planet must speak out for those yet unborn, for posterity has no lobby with politicians.

— Bernard Lown, Nobel Peace Prize Acceptance Speech, 1985

There are no catastrophes that loom before us which cannot be avoided; there is nothing that threatens us with imminent destruction in such a fashion that we are helpless to do something about it. If we behave rationally and humanely; if we concentrate coolly on the problems that face all of humanity, rather than emotionally on such nineteenth century matters as national security and local pride; if we recognize that it is not one’s neighbors who are the enemy, but misery, ignorance, and the cold indifference of natural law—then we can solve all the problems that face us. We can deliberately choose to have no catastrophes at all.

— Isaac Asimov, A Choice of Catastrophes, 1979

I don’t think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I’m an optimist. We will reach out to the stars.

— Stephen Hawking, The Daily Telegraph, 2001

ON HUMAN PROGRESS AND CONTINUITY OVER DEEP TIME

Reflections from various times on the greater patterns and trends of human history and the relationships between the generations.

Someone, I tell you, will remember us, 
even in another time.

— Sappho, c. 600 BCE

The search for the truth is in one way hard and in another easy—for it is evident that no one of us can master it fully, nor miss it wholly. Each one of us adds a little to our knowledge of nature, and from all the facts assembled arises a certain grandeur.

— Aristotle, Metaphysics, c. 350 BCE

The time will come when diligent research over long periods will bring to light things which now lie hidden. A single lifetime, even though entirely devoted to the sky, would not be enough for the investigation of so vast a subject ... And so this knowledge will be unfolded only through long successive ages. There will come a time when our descendants will be amazed that we did not know things that are so plain to them … Let us be satisfied with what we have found out, and let our descendants also contribute something to the truth. … Many discoveries are reserved for ages still to come, when memory of us will have been effaced.

— Seneca the Younger, Naturales Quaestiones, 65 CE

My fate is to live among varied and confusing storms. But for you perhaps, if as I hope and wish you will live long after me, there will follow a better age. This sleep of forgetfulness will not last for ever. When the darkness has been dispersed, our descendants can come again in the former pure radiance.

— Petrarch, Africa, 1343

The goal of an encyclopedia is to assemble all the knowledge scattered on the surface of the earth, to demonstrate the general system to the people with whom we live, & to transmit it to the people who will come after us, so that the works of centuries past is not useless to the centuries which follow, that our descendants, by becoming more learned, may become more virtuous & happier, & that we do not die without having merited being part of the human race.

— Diderot, Encyclopédie, 1751–1772

Ages of laborious ascent have been followed by a moment of rapid downfall; and the several climates of the globe have felt the vicissitudes of light and darkness. Yet the experience of four thousand years should enlarge our hopes, and diminish our apprehensions; we cannot determine to what height the human species may aspire… We may therefore acquiesce in the pleasing conclusion that every age of the world has increased, and still increases, the real wealth, the happiness, the knowledge, and perhaps the virtue, of the human race.

— Edward Gibbon, The Decline and Fall of the Roman Empire, 1766–1789

‘If we contrast the rapid progress of this mischievous discovery [gunpowder] with the slow and laborious advances of reason, science, and the arts of peace, a philosopher, according to his temper, will laugh or weep at the folly of mankind. 

— Edward Gibbon, The Decline and Fall of the Roman Empire, 1766–1789

Society is indeed a contract… It is a partnership in all science; a partnership in all art; a partnership in every virtue, and in all perfection.  As the ends of such a partnership cannot be obtained except in many generations, it becomes a partnership not only between those who are living, but between those who are living, those who are dead, and those who are to be born.

— Edmund Burke, ‘Reflections on the Revolution in France’, 1790

The remedies for all our diseases will be discovered long after we are dead; and the world will be made a fit place to live in, after the death of most of those by whose exertions it will have been made so. It is to be hoped that those who live in those days will look back with sympathy to their known and unknown benefactors.

— John Stuart Mill, diary entry for 15 April 1854

How far are we to consider the interests of posterity when they seem to conflict with those of existing human beings? It seems, however, clear that the time at which a man exists cannot affect the value of his happiness from a universal point of view; and that the interests of posterity must concern a Utilitarian as much as those of his contemporaries, except in so far as his actions on posterity—and even the existence of human beings to be affected—must necessarily be regarded as uncertain.

— Sidgwick, The Methods of Ethics, 1874

It is not only with pain that the world is shot—it is shot with promise. Small as our vanity and carnality make us, there has been a day of still smaller things. It is the long ascent of the past that gives the lie to our despair. … It is possible to believe that all the past is but the beginning of a beginning, and that all that is and has been is but the twilight of the dawn. It is possible to believe that all that the human mind has ever accomplished is but the dream before the awakening. … All this world is heavy with the promise of greater things, and a day will come, one day in the unending succession of days, when beings, beings who are now latent in our thoughts and hidden in our loins, shall stand upon this earth as one stands upon a footstool, and shall laugh and reach out their hands amid the stars.’

— H. G. Wells, ‘The Discovery of the Future’, 1902

Looked at on the astronomical time-scale, humanity is at the very beginning of its existence—a new-born babe, with all the unexplored potentialities of baby-hood; and until the last few moments its interest has been centred, absolutely and exclusively, on its cradle and feeding-bottle. It has just become conscious of the vast world existing outside itself and its cradle; it is learning to focus its eyes on distant objects, and its awakening brain is beginning to wonder, in a vague, dreamy way, what they are and what purpose they serve. Its interest in this external world is not much developed yet, so that the main part of its faculties is still engrossed with the cradle and feeding-bottle, but a little corner of its brain is beginning to wonder. 

Taking a very gloomy view of the future of the human race, let us suppose that it can only expect to survive for two thousand million years longer, a period about equal to the past age of the earth. Then, regarded as a being destined to live for three-score years and ten, humanity, although it has been born in a house seventy years old, is itself only three days old. But only in the last few minutes has it become conscious that the whole world does not centre round its cradle and its trappings, and only in the last few ticks of the clock has any adequate conception of the size of the external world dawned upon it. For our clock does not tick seconds, but years; its minutes are the lives of men.’

— James Jeans, Eos, or The Wider Aspects of Cosmogony, 1928

Certain it is that, while men are gathering knowledge and power with ever increasing and measureless speed, their virtues and their wisdom have not shown any notable improvement as the centuries have rolled. 

… We have the spectacle of the powers and weapons of man far outstripping the march of his intelligence; we have the march of his intelligence proceeding far more rapidly than the development of his nobility. We may well find ourselves in presence of “civilization without its mercy”.

It is, therefore, above all things important that the moral philosophy and spiritual conceptions of men and nations should hold their own amid these formidable scientific evolutions. It would be much better to call a halt in material progress and discovery rather than to be mastered by our own apparatus and the forces which it directs. There are secrets too mysterious for man in his present state to know; secrets which, once penetrated, may be fatal to human happiness and glory. But the busy hands of the scientists are already fumbling with the keys of all the chambers hitherto forbidden to mankind. Without an equal growth of mercy, pity, peace and love, science itself may destroy all that makes human life majestic and tolerable.

… Projects undreamed of by past generations will absorb our immediate descendants; forces terrific and devastating will be in their hands; comforts, activities, amenities, pleasures will crowd upon them; but their hearts will ache, their lives will be barren, if they have not a vision above material things. And with the hopes and powers will come dangers out of all proportion to the growth of man’s intellect, or to the strength of his character or institutions.

— Winston Churchill, ‘Fifty Years Hence’, 1931

Each generation exercises power over its successors: and each, in so far as it modifies the environment bequeathed to it and rebels against tradition, resists and limits the power of its predecessors. This modifies the picture which is sometimes painted of a progressive emancipation from tradition and a progressive control of natural processes resulting in a continual increase of human power. In reality, of course, if any one age really attains, by eugenics and scientific education, the power to make its descendants what it pleases, all men who live after it are the patients of that power. They are weaker, not stronger: for though we may have put wonderful machines in their hands we have preordained how they are to use them. And if, as is almost certain, the age which had thus attained maximum power over posterity were also the age most emancipated from tradition, it would be engaged in reducing the power of its predecessors almost as drastically as that of its successors. And we must also remember that, quite apart from this, the later a generation comes—the nearer it lives to that date at which the species becomes extinct—the less power it will have in the forward direction, because its subjects will be so few. There is therefore no question of a power vested in the race as a whole steadily growing as long as the race survives. The last men, far from being the heirs of power, will be of all men most subject to the dead hand of the great planners and conditioners and will themselves exercise least power upon the future.

The real picture is that of one dominant age—let us suppose the hundredth century AD—which resists all previous ages most successfully and dominates all subsequent ages most irresistibly, and thus is the real master of the human species. but then within this master generation (itself an infinitesimal minority of the species) the power will be exercised by a minority smaller still. Man’s conquest of nature, if the dreams of some scientific planners are realized, means the rule of a few hundreds of men over billions upon billions of men. There neither is nor can be any simple increase of power on Man’s side. Each new power won by man is a power over man as well. Each advance leaves him weaker as well as stronger. in every victory, besides being the general who triumphs, he is also the prisoner who follows the triumphal car.’

— C. S. Lewis, The Abolition of Man, 1943

Our progress in the use of science has been great, but our progress in ordering our relations small.

— John F. Kennedy, White House memo, 1962

The very spark that marks us as a species—our thoughts, our imagination, our language, our tool-making, our ability to set ourselves apart from nature and bend it to our will—those very things also give us the capacity for unmatched destruction. … Technological progress without an equivalent progress in human institutions can doom us. The scientific revolution that led to the splitting of an atom requires a moral revolution as well.

— Barack Obama, remarks at the Hiroshima Peace Memorial, 2016

Our galaxy is now in the brief springtime of its life—a springtime made glorious by such brilliant blue-white stars as Vega and Sirius, and, on a more humble scale, our own Sun. Not until all these have flamed through their incandescent youth, in a few fleeting billions of years, will the real history of the universe begin.

It will be a history illuminated only by the reds and infrareds of dully glowing stars that would be almost invisible to our eyes; yet the somber hues of that all-but-eternal universe may be full of color and beauty to whatever strange beings have adapted to it. They will know that before them lie, not the millions of years in which we measure eras of geology, nor the billions of years which span the past lives of the stars, but years to be counted literally in trillions.

They will have time enough, in those endless aeons, to attempt all things, and to gather all knowledge. They will be like gods, because no gods imagined by our minds have ever possessed the powers they will command. But for all that, they may envy us, basking in the bright afterglow of Creation; for we knew the universe when it was young.

— Arthur C. Clarke, Profiles of the Future, 1962

The human mind is used to thinking in terms of decades or perhaps generations, not the hundreds of millions of years that is the time frame for life on Earth. Coming to grips with humanity in this context reveals at once our significance in Earth history, and our insignificance. There is a certainty about the future of humanity that cheats our mind’s comprehension: one day our species will be no more.

— Richard Leakey and Roger Lewin, The Sixth Extinction, 1995

Ecological problems were thought unsolvable because they could not be solved in a year or two. … It turns out that environmental problems are solvable. It's just that it takes focused effort over a decade or three to move toward solutions, and the solutions sometimes take centuries. Environmentalism teaches patience. Patience, I believe, is a core competency of a healthy civilization.

— Stewart Brand, ‘Taking the Long View’, 2000

ON REACHING BEYOND THE EARTH

Thoughts on how we may expand our potential by reaching the planets and stars.

There will certainly be no lack of human pioneers when we have mastered the art of flight. Who would have thought that navigation across the vast ocean is less dangerous and quieter than in the narrow, threatening gulfs of the Adriatic, or the Baltic, or the British straits? Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes. In the meantime, we shall prepare, for the brave sky-travellers, maps of the celestial bodies—I shall do it for the moon, you Galileo, for Jupiter.

— Johannes Kepler, in an open letter to Galileo, 1610

A planet is the cradle of mind, but one cannot live in the cradle forever.

— Konstantin Tsiolkovsky, 1911 

This is the goal: To make available for life every place where life is possible. To make inhabitable all worlds as yet uninhabitable, and all life purposeful.

— Hermann Oberth, Man Into Space, 1957 

Some people become depressed at the scale of the universe, because it makes them feel insignificant. Other people are relieved to feel insignificant, which is even worse. But, in any case, those are mistakes. Feeling insignificant because the universe is large has exactly the same logic as feeling inadequate for not being a cow. Or a herd of cows. The universe is not there to overwhelm us; it is our home, and our resource. The bigger the better.

— David Deutsch, The Beginnings of Infinity, 2011

Like an explosive awaiting a spark, unimaginably numerous environments in the universe are waiting out there, for aeons on end, doing nothing at all or blindly generating evidence and storing it up or pouring it out into space. Almost any of them would, if the right knowledge ever reached it, instantly and irrevocably burst into a radically different type of physical activity: intense knowledge-creation, displaying all the various kinds of complexity, universality and reach that are inherent in the laws of nature, and transforming that environment from what is typical today into what could become typical in the future. If we want to, we could be that spark.

— David Deutsch, The Beginnings of Infinity, 2011

To me, the most inspiring scientific discovery ever is that we’ve dramatically underestimated life’s future potential. Our dreams and aspirations need not be limited to century-long lifespans marred by disease, poverty and confusion. Rather, aided by technology, life has the potential to flourish for billions of years, not merely here in our Solar System, but also throughout a cosmos far more grand and inspiring than our ancestors imagined. Not even the sky is the limit.

  — Max Tegmark, Life 3.0, 2017

ON BECOMING SOMETHING NEW

Reflections on how we may eventually enhance ourselves and what may come after humanity.

When we reflect upon the manifold phases of life and consciousness which have been evolved already, it would be rash to say that no others can be developed, and that animal life is the end of all things. There was a time when fire was the end of all things: another when rocks and water were so.

— Samuel Butler, Erewhon, 1872

The expansion of life over the universe is a beginning, not an end. At the same time as life is extending its habitat quantitatively, it will also be changing and evolving qualitatively into new dimensions of mind and spirit that we cannot imagine. The acquisition of new territory is important, not as an end in itself, but as a means to enable life to experiment with intelligence in a million different forms.

— Freeman Dyson, Disturbing the Universe, 1979

Before the invention of writing, almost every insight was happening for the first time (at least to the knowledge of the small groups of humans involved). When you are at the beginning, everything is new. In our era, almost everything we do in the arts is done with awareness of what has been done before and before. In the early post-human era, things will be new again, because anything that requires greater than human ability has not already been done by Homer or da Vinci or Shakespeare.

— Vernor Vinge, interview, 1997

Homo sapiens, the first truly free species, is about to decommission natural selection, the force that made us. Soon we must look deep within ourselves and decide what we wish to become.

— E. O. Wilson, Consilience: The Unity of Knowledge, 1998

Imagine a world with all the music dried up: what poverty, what loss.  Give your thanks, not to the lyre, but to your ears for the music.  And ask yourself, what other harmonies are there in the air, that you lack the ears to hear?  What vaults of value are you witlessly debarred from, lacking the key sensibility?

— Nick Bostrom, ‘Letter from Utopia’, 2008

Our human experience might be just a small little crumb of what's possible. If you think of all the different modes of being, different kinds of feeling and experiencing, different ways of thinking and relating, it might be that human nature constrains us to a very narrow little corner of the space of possible modes of being. If we think of the space of possible modes of being as a large cathedral, then humanity in its current stage might be like a little cowering infant sitting in the corner of that cathedral having only the most limited sense of what is possible.

— Nick Bostrom, interview in The Atlantic, 2012

With the appearance of humans, just 300,000 years ago, this planet, alone in the cosmos, attained the capacity to know itself ... We are now preparing to hand the gift off knowing on to new forms of intelligent beings. Do not be depressed by this. We have played our part ... perhaps, we can hope that our contribution will not be entirely forgotten as wisdom and understanding spread outwards from the Earth to embrace the cosmos.

— James Lovelock, Novacene, 2019