Extraterrestrial Civilizations (26 page)

Such hard tissue was easily fossilized and thus by 600 million years ago, it seems (from the fossil record) that out of nowhere multicellular life, advanced and complex, was flourishing.

It was not until Earth was 4 billion years old, with a third of its life span gone, that such complex life forms existed.

If this, by the principle of mediocrity, is characteristic of completely Earthlike planets in general, then one-third of them are too young to have anything more than one-celled life. Conversely, two-thirds of them possess complex and varied multicellular life.

That gives us our tenth figure:

However complicated and specialized a life form becomes, it doesn’t interest us in connection with the subject matter of this book unless it is intelligent.

It cannot become intelligent unless it develops a large brain (or the equivalent—except that, on Earth at least, we know of no equivalent) and this, it would appear, cannot be done without the development of manipulative organs of some sort and of elaborate sense organs of considerable variety.

It is the flood of impressions entering the brain from the outside Universe, and the questing manipulative organs that respond to these impressions, which stretch the brain’s resources to its capacity and beyond, and lend survival value to any increase in the brain’s size and complexity. If a small brain is already sufficient to handle the coordinating needs of the information an organism collects, a larger brain is of no advantage; a larger brain would merely require the production of useless and energy-wasting highly complex tissue. If, on the other hand, the brain is being used to capacity, a larger brain can do more and is worth much more.

Viewed from this angle, the sea is ideal as an incubator of life, but is very poor as an incubator of intelligence. The most valuable and information-rich sense that we can imagine life possessing (without veering into fantasy) is that of vision. Under water, vision is limited, for water absorbs light to a far greater extent than air does. In air, vision is a long-distance sense; in water, only a short-distance sense. (To be sure, hearing is even more efficient in water than in air and can perform wonders, but the smallest sound waves used by life forms are still far longer than the tiny light waves, and therefore incapable of transmitting as much information.)

When it comes to manipulative organs, as I mentioned earlier in the book, the necessity for streamlining to allow rapid travel through the viscous medium of water eliminates almost any chance for developing a manipulative organ. What manipulation a sea organism can perform usually involves the mouth, the tail, or the full weight of the body, and it is rarely delicate in its nature.

One exception to this is the octopus and its relatives. The octopus has developed a set of sensitive and limber tentacles with
which there can be fine manipulation of the environment, yet when it wishes to travel quickly it can trail them behind and be streamlined. Then, too, the octopus has an excellent eye, the closest approach to the vertebrate eye in any nonvertebrate creature.

But though we may admire the intelligence of the octopus, it is certainly far from intelligent enough to build what we would consider to be a civilization.

There are, of course, sea animals far more intelligent than the octopus, but these—sea otters, seals, penguins—are all land creatures who had secondarily adapted to the water again. Even the whales and dolphins have land animals among their ancestry, and it is undoubtedly in the course of the period during which their ancestors inhabited the land that the cetacean brain developed.

For real intelligence of the level in which this book is interested, then, we must consider land organisms—land organisms who can make use of sight as a long-distance sense of incredible detail and richness; who can develop manipulative organs; and who live surrounded by free oxygen so that they can tame fire and develop a technology.

And yet when all life existed in the sea only, the land was an environment extremely hostile to life; as hostile as space is to us. We, at least, in conquering space can make use of our technology and devise artificial protective devices. Sea life, hundred of millions of years ago, had to develop protection as part of their bodies through the slow course of evolution.

Consider the difficulties they had to overcome:

In the sea, organisms need not fear thirst and drought; they are always surrounded by water, the essential chemical background to life. On the land, on the other hand, life is a continual battle to avoid water loss; water must either be conserved, or it must be replaced by drinking.

In the sea, oxygen is easily absorbed from the water in which it is dissolved. On the land, oxygen must first be dissolved in the fluid lining the lungs and then absorbed, and the lungs must not be allowed to dry out in the process.

In the sea, eggs can be laid in the water and allowed to develop and hatch without care (or with minimal care) in a congenial environment. On the land, eggs must be developed that have a shell that will prevent water loss while allowing gases to pass through
freely so that oxygen can reach the developing embryo.

In the sea, temperature scarcely varies. On the land, there are extremes of hot and cold.

In the sea, gravity is almost nil. On the land, it is a powerful force, and organisms must develop sturdy legs that can lift them free of the land, or else they are condemned to crawl.

It is no wonder that even after life in the sea grew energetic and complicated it took hundreds of millions of years to conquer the land.

But the conquest took place. The pressures of competition forced organisms of various sorts to spend more and more time upon the land, until such time as they could live on land more or less permanently.

About 370 million years ago, the first plants invaded the land. The land that had been lying sterile and dead for 4¼ billion years began to turn a faint green about its edges.

Animals followed the plants over the next few tens of millions of years. Insects and spiders appeared as the first true land animals about 325 million years ago. Snails and worms appeared on land. The first vertebrates to be entirely land animals, primitive reptiles, appeared 275 million years ago.

A rich land life appeared when the Earth was about 4.3 billion years old and had passed through 36 percent of its lifetime. By the principle of mediocrity, then, we can say that 64 percent of the habitable planets have a rich land life.

That gives us our eleventh figure:

Even a land species is not necessarily intelligent. To this day, cattle and other grazing animals are not particularly bright.

Nevertheless, one can see a steady progression of intelligence and a steady elaboration of the brain. Mammals, which first appeared about 180 million years ago, were on the whole an advance in intelligence over the reptiles.

The order of primates, the earliest records of which date back 75 million years, moved toward specialization in eyes and brains. About
35 million years ago, the primates split into the less brainy and smaller monkeys and lemurs on one side, and the more brainy and larger apes on the other.

Some 8 million years ago, a particularly brainy species developed that was the first hominid. About 600,000 years ago,
Homo sapiens
had developed, and about 5,000 years ago, human beings invented writing, so that written history began and civilization was in full bloom, in some parts of the world at any rate.

By the time civilization appeared, the Earth was 4,600,000,000 years old and had completed roughly 40 percent of its lifetime. That means, if we follow the principle of mediocrity, that 40 percent of the habitable planets in existence are not old enough to have developed a civilization and 60 percent
are
old enough.

That gives us our twelfth figure:

In other words, one star out of 770 in the Galaxy today has shone down on the development of a technological civilization.

We can go a little bit further. Our own civilization, if we count from the invention of writing to the first venture into space, has lasted 5,000 years. If we want to be glowingly optimistic about it, we can suppose that our civilization will continue to last on Earth as long as the Earth can support life—for another 7.4 billion years—and that our level of technology will advance in all that time.
^*
Suppose we say, then, that the average duration of a civilization is 7.4 billion years (we’ll have more to say about that later on in the book) and that space flight is reached in the first 5,000 years. That means that only 1/1,500,000 of a civilization passes before space flight is developed, and all the rest of it progresses to technological levels above and beyond that. Or, to put it another way, only 1/1,500,000 of the civilizations in our Galaxy are so unadvanced that they are barely at the brink of spaceflight or have not yet reached it. All the rest are beyond us.

That means that of the 390 million civilizations in our Galaxy,
only 260 are as primitive as we are—an inconsiderable number. All the rest (meaning just about all of them) are more advanced than we are.

In short, what we find ourselves to have been doing is to have worked out not merely the chances of extraterrestrial intelligence but the chances of superhuman extraterrestrial intelligence.

In a way, our speculations concerning extraterrestrial intelligence have ended on a triumphant note. Doing our best to make reasonable and conservative estimates and assumptions, we end with a Universe that may be incredibly rich in intelligence. Along with our own, 390 million sets of companions in the great adventure of learning and speculating have entered into civilization right here in our own Galaxy.

If those 390 million civilizations are spread evenly about the Population I outskirts of the Galaxy, then the distance between two neighboring civilizations would be, on the average, about 40 light-years. That is not very great as cosmic distances go.

But then there is a question that, in a way, spoils everything.

Where is everybody?

If there were indeed hundreds of millions of advanced civilizations in our own Galaxy, we should think that they might well have ventured beyond their own worlds; they might have formed alliances; they might have formed a Galactic Federation of Civilizations with
emissaries sent to other galactic federations beyond the intergalactic spaces. And, in particular, they should have visited us. Why haven’t they?

Where is everybody?

There are a number of possible explanations for this puzzle. It may be, for instance, that the analysis presented in this book is wrong in some key point after all, and there are, therefore, no habitable worlds except our own Earth.

Almost every stage in the analysis might hide an error arising out of our incomplete knowledge. Perhaps binaries are much more common than we think and much more influential in distorting planetary formation. In that case, there might be very few single Sunlike stars and very few planetary systems like our own Solar system.

It might be that the ecosphere is very shallow, as some calculations indicate, and it might be that almost no planets manage to be located in just the thin shell of space around a star that would make habitability possible.

It might be that, for some reason we as yet do not understand, planets with the mass of Earth form only rarely, and that in planetary system after planetary system, there are planets that are too large and others that are too small and virtually nowhere are there planets that are just right.

It might be an incredible cosmic accident that liquid water has collected on our world in appropriate amounts, or that other things are just so, and that we are, therefore, the only habitable planet in the Galaxy, or even in the Universe.

We have, however, no reason to think these things just yet. Evidence that will justify such thoughts may arrive at any time-tomorrow, for all we know. Until then, we have no choice but to stay with our line of reasoning and see if we can find an explanation for the absence of positive evidence of other civilizations elsewhere.

Perhaps it is not some error that arises out of our ignorance. Perhaps there is an error that arises out of something that is perfectly obvious but that we have been ignoring. For instance, is there something so unusual about the Sun, or its planetary system, or Earth itself, that we cannot truly make use of the principle of mediocrity?

As far as the Sun and the planetary system in general are concerned, there is nothing we know of. It may be unique in a dozen
different ways, but in nothing that is obvious on the face of it. Not so in the case of the Earth. Here we have something that cannot help but be unusual and that we have so far ignored; that we must now consider as a possible answer to the problem of the whereabouts of our space visitors.