The disaster, whatever it was, that cleared the dinosaurs from the world stage removed the pressure on the mammals. Our ancestors no longer had to live in the shadow of voracious reptiles. We diversified exuberantly and flourished. Twenty million years ago, our immediate ancestors probably still lived in the trees, later descending because the forests receded during a major ice age and were replaced by grassy savannahs. It is not much good to be supremely adapted to life in the trees if there are very few trees. Many arboreal primates must have vanished with the forests. A few eked out a precarious existence on the ground and survived. And one of those lines evolved to become us. No one knows the cause of that climatic change. It may have been a small variation in the intrinsic luminosity of the Sun or in the orbit of the Earth; or massive volcanic eruptions injecting fine dust into the stratosphere, reflecting more sunlight back into space and cooling the Earth. It may have been due to changes in the general circulation of the oceans. Or perhaps the passage of the Sun through a galactic dust cloud. Whatever the cause, we see again how tied our existence is to random astronomical and geological events.
After we came down from the trees, we evolved an upright posture; our hands were free; we possessed excellent binocular vision – we had acquired many of the preconditions for making tools. There was now a real advantage in possessing a large brain and in communicating complex thoughts. Other things being equal, it is better to be smart than to be stupid. Intelligent beings can solve problems better, live longer and leave more offspring; until the invention of nuclear weapons, intelligence powerfully aided survival. In our history it was some horde of furry little mammals who hid from the dinosaurs, colonized the treetops and later scampered down to domesticate fire, invent writing, construct observatories and launch space vehicles. If things had been a little different, it might have been some other creature whose intelligence and manipulative ability would have led to comparable accomplishments. Perhaps the smart bipedal dinosaurs, or the raccoons, or the otters, or the squid. It would be nice to know how different other intelligences can be; so we study the whales and the great apes. To learn a little about what other kinds of civilizations are possible, we can study history and cultural anthropology. But we are all of us – us whales, us apes, us people – too closely related. As long as our inquiries are limited to one or two evolutionary lines on a single planet, we will remain forever ignorant of the possible range and brilliance of other intelligences and other civilizations.
On another planet, with a different sequence of random processes to make hereditary diversity and a different environment to select particular combinations of genes, the chances of finding beings who are physically very similar to us is, I believe, near zero. The chances of finding another form of intelligence is not. Their brains may well have evolved from the inside out. They may have switching elements analogous to our neurons. But the neurons may be very different; perhaps superconductors that work at very low temperatures rather than organic devices that work at room temperature, in which case their speed of thought will be 107 times faster than ours. Or perhaps the equivalent of neurons elsewhere would not be in direct physical contact but in radio communication so that a single intelligent being could be distributed among many different organisms, or even many different planets, each with a part of the intelligence of the whole, each contributing by radio to an intelligence much greater than itself.* There may be planets where the intelligent beings have about 1014 neural connections, as we do. But there may be places where the number is 1024 or 1034. I wonder what they would know. Because we inhabit the same universe as they, we and they must share some substantial information in common. If we could make contact, there is much in their brains that would be of great interest to ours. But the opposite is also true. I think extraterrestrial intelligence – even beings substantially further evolved than we – will be interested in us, in what we know, how we think, what our brains are like, the course of our evolution, the prospects for our future.
* In some sense such a radio integration of separate individuals is already beginning to happen on the planet Earth.
If there are intelligent beings on the planets of fairly nearby stars, could they know about us? Might they somehow have an inkling of the long evolutionary progression from genes to brains to libraries that has occurred on the obscure planet Earth? If the extraterrestrials stay at home, there are at least two ways in which they might find out about us. One way would be to listen with large radio telescopes. For billions of years they would have heard only weak and intermittent radio static caused by lightning and the trapped electrons and protons whistling within the Earth’s magnetic field. Then, less than a century ago, the radio waves leaving the Earth would become stronger, louder, less like noise and more like signals. The inhabitants of Earth had finally stumbled upon radio communication. Today there is a vast international radio, television and radar communications traffic. At some radio frequencies the Earth has become by far the brightest object, the most powerful radio source, in the solar system – brighter than Jupiter, brighter than the Sun. An extraterrestrial civilization monitoring the radio emission from Earth and receiving such signals could not fail to conclude that something interesting had been happening here lately.
As the Earth rotates, our more powerful radio transmitters slowly sweep the sky. A radio astronomer on a planet of another star would be able to calculate the length of the day on Earth from the times of appearance and disappearance of our signals. Some of our most powerful sources are radar transmitters; a few are used for radar astronomy, to probe with radio fingers the surfaces of the nearby planets. The size of the radar beam projected against the sky is much larger than the size of the planets, and much of the signal wafts on, out of the solar system into the depths of interstellar space to any sensitive receivers that may be listening. Most radar transmissions are for military purposes; they scan the skies in constant fear of a massive launch of missiles with nuclear warheads, an augury fifteen minutes early of the end of human civilization. The information content of these pulses is negligible: a succession of simple numerical patterns coded into beeps.
Overall, the most pervasive and noticeable source of radio transmissions from the Earth is our television programming. Because the Earth is turning, some television stations will appear at one horizon of the Earth while others disappear over the other. There will be a confused jumble of programs. Even these might be sorted out and pieced together by an advanced civilization on a planet of a nearby star. The most frequently repeated messages will be station call signals and appeals to purchase detergents, deodorants, headache tablets, and automobile and petroleum products. The most noticeable messages will be those broadcast simultaneously by many transmitters in many time zones – for example, speeches in times of international crisis by the President of the United States or the Premier of the Soviet Union. The mindless contents of commercial television and the integuments of international crisis and internecine warfare within the human family are the principal messages about life on Earth that we choose to broadcast to the Cosmos. What must they think of us?
There is no calling those television programs back. There is no way of sending a faster message to overtake them and revise the previous transmission. Nothing can travel faster than light. Large-scale television transmission on the planet Earth began only in the late 1940’s. Thus, there is a spherical wave front centered on the Earth expanding at the speed of light and containing Howdy Doody, the ‘Checkers’ speech of then Vice-President Richard M. Nixon and the televised inquisitions by Senator Joseph McCarthy. Because these transmissions were broadcast a few decades ago, they are only a few tens of light-years away from the Earth. If the nearest civilization is farther away than that, then we can continue to breathe easy for a while. In any case, we can hope that they will find these programs incomprehensible.
The two Voyager spacecraft are bound for the stars. Affixed to each is a gold-plated copper phonograph record with a cartridge and stylus and, on the aluminum record jacket, instructions for use. We sent something about our genes, something about our brains, and something about our libraries to other beings who might sail the sea of interstellar space. But we did not want to send primarily scientific information. Any civilization able to intercept Voyager in the depths of interstellar space, its transmitters long dead, would know far more science than we do. Instead, we wanted to tell those other beings something about what seems unique about ourselves. The interests of the cerebral cortex and limbic system are well represented; the R-complex less so. Although the recipients may not know any languages of the Earth, we included greetings in sixty human tongues, as well as the hellos of the humpback whales. We sent photographs of humans from all over the world caring for one another, learning, fabricating tools and art and responding to challenges. There is an hour and a half of exquisite music from many cultures, some of it expressing our sense of cosmic loneliness, our wish to end our isolation, our longing to make contact with other beings in the Cosmos. And we have sent recordings of the sounds that would have been heard on our planet from the earliest days before the origin of life to the evolution of the human species and our most recent burgeoning technology. It is, as much as the sounds of any baleen whale, a love song cast upon the vastness of the deep. Many, perhaps most, of our messages will be indecipherable. But we have sent them because it is important to try.