Most attention has been given to persuading alien observers that we exist at all, rather than sending them messages with substantial content. This task is the same as that faced by my hypothetical Professor Crickson in chapter 1. He rendered the prime numbers into the DNA code, and a parallel policy using radio would be a sensible way to flag our presence to other worlds. Music might seem a better advertisement for our species, and even if the audience lacked ears they might appreciate it in their own way. The famous scientist and writer Lewis Thomas suggested that we broadcast Bach, all of Bach and nothing but Bach, although he feared it might be taken as boasting. But, equally, music might be mistaken, by a sufficiently alien mind, for the rhythmic emanations of a pulsar. Pulsars are stars that give off rhythmic pulses of radio waves at intervals of a few seconds or less. When they were first discovered, by a group of Cambridge radioastronomers in 1967, there was momentary excitement as people wondered whether the signals might be a message from space. But it was soon realized that a more parsimonious explanation was that a small star was rotating extremely fast and sweeping a beam of radio waves around like a lighthouse. To date, {160} no authenticated communications from outside our planet have ever been received.

After radio waves, the only further step we have imagined in the outward progress of our own explosion is physical space travel itself: Threshold 10, the Space Travel Threshold. Science-fiction writers have dreamed of the interstellar proliferation of daughter colonies of humans, or their robotic creations. These daughter colonies could be seen as seedings, or infections, of new pockets of self-replicating information – pockets that may subsequently themselves expand explosively outward again, in satellite replication bombs, broadcasting both genes and memes. If this vision is ever realized, it is perhaps not too irreverent to imagine some future Christopher Marlowe reverting to the imagery of the digital river: “See, see, where life's flood streams in the firmament!”

We have so far scarcely taken the first step outward. We have been to the moon but, magnificent as this achievement is, the moon, though no calabash, is so local as scarcely to count as traveling, from the point of view of the aliens with whom we might eventually communicate. We have sent a handful of unmanned capsules into deep space, on trajectories that have no visualizable ending. One of these, as a result of inspiration from the visionary American astronomer Carl Sagan, carries a message designed to be deciphered by any alien intelligence who might chance upon it. The message is adorned with a picture of the species that created it, the image of a naked man and woman.

This might seem to bring us full circle, to the ancestral myths with which we began. But this couple is not Adam and Eve, and the message engraved beneath their graceful {161} forms is an altogether more worthy testament to our life explosion than anything in Genesis. In what is designed to be a universally understandable iconic language, the plaque records its own genesis in the third planet of a star whose coordinates in the galaxy are precisely recorded. Our credentials are further established by some iconic representations of fundamental principles of chemistry and mathematics. If the capsule is ever picked up by intelligent beings, they will credit the civilization that produced it with something more than primitive tribal superstition. Across the gulf of space, they will know that there existed, long ago, another life explosion that culminated in a civilization that would have been worth talking to.

Alas, this capsule's chance of passing within a parsec of another replication bomb is forlornly small. Some commentators see its value as an inspirational one for the population back home. A statue of a naked man and woman, hands raised in a gesture of peace, deliberately sent on an eternal outward journey among the stars, the first exported fruit of the knowledge of our own life explosion – surely the contemplation of this might have some beneficial effects upon our normally parochial little consciousnesses; some echo of the poetic impact of Newton's statue in Trinity College, Cambridge, upon the admittedly giant consciousness of William Wordsworth:

And from my pillow, looking forth by light

Of moon or favouring stars, I could behold

The antechapel where the statue stood

Of Newton with his prism and silent face,

The marble index of a mind for ever

Voyaging through strange seas of Thought, alone.

{163}

With a few exceptions I have limited this list to readily accessible books rather than technical works that can be found only in university libraries.

Bodmer, Walter, and Robin McKie, The Book of Man: The Human Genome Project and the Quest to Discover Our Genetic Heritage (New York: Scribners, 1995).

Bonner, John Tyler, Life Cycles: Reflections of an Evolutionary Biologist (Princeton: Princeton University Press, 1993).

Cain, Arthur J., Animal Species and Their Evolution (New York: Harper Torchbooks, 1960).

Cairns-Smith, A. Graham, Seven Clues to the Origin of Life (Cambridge: Cambridge University Press, 1985).

Cherfas, Jeremy, and John Gribbin, The Redundant Male: Is Sex Irrelevant in the Modern World? (New York: Pantheon, 1984).

Clarke, Arthur C, Profiles of the Future: An Inquiry into the Limits of the Possible (New York: Holt, Rinehart & Winston, 1984).

Crick, Francis, What Mad Pursuit: A Personal View of Scientific Discovery (New York: Basic Books, 1988).

Cronin, Helena, The Ant and the Peacock: Altruism and Sexual Selection from Darwin to Today (New York: Cambridge University Press, 1991).

Darwin, Charles, The Origin of Species (New York: Penguin, 1985).

– -, The Various Contrivances by Which Orchids are Fertilised by Insects (London: John Murray, 1882). {164}

Dawkins, Richard, The Extended Phenotype (New York: Oxford University Press, 1989).

– -, The Blind Watchmaker (New York: W.W. Norton, 1986).

– -, The Selfish Gene, new ed. (New York: Oxford University Press, 1989).

Dennett, Daniel C, Darwin's Dangerous Idea (New York: Simon & Schuster, 1995).

Drexler, K. Eric, Engines of Creation (Garden City, N.Y.: Anchor Press/Doubleday, 1986).

Durant, John R., ed. Human Origins (Oxford: Oxford University Press, 1989).

Fabre, Jean-Henri, Insects, David Black, ed. (New York: Scribners, 1979).

Fisher, Ronald A., The Genetical Theory of Natural Selection, 2d. rev. ed. (New York: Dover, 1958).

Frisch, Karl von, The Dance Language and Orientation of Bees, Leigh E. Chadwick, trans. (Cambridge: Harvard University Press, 1967).

Gould, James L., and Carol G. Gould, The Honey Bee (New York: Scientific American Library, 1988).

Gould, Stephen J., Wonderful Life: The Burgess Shale and the Nature of History (New York: W.W. Norton, 1989).

Gribbin, John, and Jeremy Cherfas, The Monkey Puzzle: Reshaping the Evolutionary Tree (New York: Pantheon, 1982).

Hein, Piet, with Jens Arup, Grooks (Garden City, N.Y.: Doubleday, 1969).

Hippel, Arndt von, Human Evolutionary Biology (Anchorage: Stone Age Press, 1994).

Humphrey, Nicholas K., Consciousness Regained (Oxford: Oxford University Press, 1983).

Jones, Steve, Robert Martin and David Pilbeam, eds., The Cambridge

Encyclopedia of Human Evolution (New York: Cambridge University Press, 1992).