The Scientist as Rebel (37 page)

Leaving aside genetic surgery applied to humans, I foresee that the coming century will place in our hands two other forms of biological technology which are less dangerous but still revolutionary enough to transform the conditions of our existence. I count these new technologies as powerful allies in the attack on Bernal’s three enemies. I give them the names “biological engineering” and “self-reproducing machinery.” Biological engineering means the artificial synthesis of living organisms designed to fulfill human purposes. Self-reproducing machinery means the imitation of the function and reproduction of a living organism with nonliving materials, a computer program imitating the function of DNA, and a miniature factory imitating the functions of protein molecules. After we have attained a complete understanding of the principles of organization and development of a simple multicellular organism, both of these avenues of technological exploitation should be open to us.

I would expect the earliest and least controversial triumphs of biological engineering to be extensions of the art of industrial fermentation. When we are able to produce microorganisms equipped with enzyme systems tailored to our own design, we can use such organisms to perform chemical operations with far greater delicacy and economy than present industrial practices allow. For example, oil refineries would contain a variety of bugs designed to metabolize crude petroleum into the precise hydrocarbon isomers which are needed for various purposes. One tank would contain the n-octane bug, another the benzene bug, and so on. All the bugs would contain enzymes metabolizing sulfur into elemental form, so that pollution of the atmosphere by sulfurous gases would be completely controlled. The management and operation of such fermentation
tanks on a vast scale would not be easy, but the economic and social rewards are so great that I am confident we shall learn how to do it. After we have mastered the biological oil refinery, more important applications of the same principles will follow. We shall have factories producing specific foodstuffs biologically from cheap raw materials, and sewage treatment plants converting our wastes efficiently into usable solids and pure water. To perform these operations we shall need an armamentarium of many species of microorganisms trained to ingest and excrete the appropriate chemicals. And we shall design into the metabolism of these organisms the essential property of self-liquidation, so that when deprived of food they disappear by cannibalizing one another. They will not, like the bacteria that feed upon our sewage in today’s technology, leave their rotting carcasses behind to make a sludge only slightly less noxious than the mess that they have eaten.

If these expectations are fulfilled, the advent of biological technology will help enormously in the establishment of patterns of industrial development with which human beings can live in health and comfort. Oil refineries need not stink. Rivers need not be sewers. However, there are many environmental problems which the use of artificial organisms in enclosed tanks will not touch. For example, the fouling of the environment by mining and by abandoned automobiles will not be reduced by building cleaner factories. The second step in biological engineering, after the enclosed biological factory, is to let artificial organisms loose into the environment. This is admittedly a more dangerous and problematical step than the first. The second step should be taken only when we have a deep understanding of its ecological consequences. Nevertheless the advantages which artificial organisms offer in the environmental domain are so great that we are unlikely to forgo their use forever.

The two great functions which artificial organisms promise to perform for us when let loose upon the earth are mining and scavenging.
The beauty of a natural landscape undisturbed by man is largely due to the fact that the natural organisms in a balanced ecology are excellent miners and scavengers. Mining is mostly done by plants and microorganisms extracting minerals from water, air, and soil. For example, it has been recently discovered that organisms in the ground mine ammonia and carbon monoxide from air with high efficiency. To the scavengers we owe the fact that a natural forest is not piled as high with dead birds as one of our junkyards with dead cars. Many of the worst offenses of human beings against natural beauty are due to our incompetence in mining and scavenging. Natural organisms know how to mine and scavenge effectively in a natural environment. In a man-made environment, neither they nor we know how to do it. But there is no reason why we should not be able to design artificial organisms that are adaptable enough to collect our raw materials and to dispose of our refuse in an environment that is a careful mixture of natural and artificial.

A simple example of a problem that an artificial organism could solve is the eutrophication of lakes. At present many lakes are being ruined by excessive growth of algae feeding on high levels of nitrogen or phosphorus in the water. The damage could be stopped by an organism that would convert nitrogen to molecular form or phosphorus to an insoluble solid. Alternatively and preferably, an organism could be designed to divert the nitrogen and phosphorus into a food chain culminating in some species of palatable fish. To control and harvest the mineral resources of the lake in this way will in the long run be more feasible than to maintain artificially a state of “natural” barrenness.

The artificial mining organisms would not operate in the style of human miners. Many of them would be designed to mine the ocean. For example, oysters might extract gold from seawater and secrete golden pearls. A less poetic but more practical possibility is the artificial coral that builds a reef rich in copper or magnesium. Other mining organisms would burrow like earthworms into mud
and clay, concentrating in their bodies the ores of aluminum or tin or iron, and excreting the ores in some manner convenient for human harvesting. Almost every raw material necessary for our existence can be mined from ocean, air, or clay, without digging deep into the earth. Where conventional mining is necessary, artificial organisms can still be useful for digesting and purifying the ore.

Not much imagination is needed to foresee the effectiveness of artificial organisms as scavengers. A suitable microorganism could convert the dangerous organic mercury in our rivers and lakes to a harmless insoluble solid. We could make good use of an organism with a consuming appetite for polyvinyl chloride and similar plastic materials which now litter beaches all over the Earth. Conceivably we may produce an animal specifically designed for chewing up dead automobiles. But one may hope that the automobile in its present form will become extinct before it needs to be incorporated into an artificial food chain. A more serious and permanent role for scavenging organisms is the removal of trace quantities of radioactivity from the environment. The three most hazardous radioactive elements produced in fission reactors are strontium, caesium, and plutonium. These elements have long half-lives and will inevitably be released in small quantities so long as mankind uses nuclear fission as an energy source. The long-term hazard of nuclear energy would be notably reduced if we had organisms designed to gobble up these three elements from water or soil and to convert them into indigestible form. Fortunately, none of these three elements is essential to our body chemistry, and it therefore does us no harm if they are made indigestible.

I have described the two first steps of biological engineering. The first will transform our industry and the second will transform our earthbound ecology. It is now time to describe the third step, which is the colonization of space. Biological engineering is the essential tool which will make Bernal’s dream of the expansion of mankind in space a practical possibility.

First I have to clear away a few popular misconceptions about space as a habitat. It is generally considered that planets are important. Except for Earth, they are not. Mars is waterless, and the others are for various reasons basically inhospitable to man. It is generally considered that beyond the sun’s family of planets there is absolute emptiness extending for light-years until you come to another star. In fact it is likely that the space around the solar system is populated by huge numbers of comets, small worlds a few miles in diameter, rich in water and the other chemicals essential to life. We see one of these comets only when it happens to suffer a random perturbation of its orbit which sends it plunging close to the sun. It seems that roughly one comet per year is captured into the region near the sun where it eventually evaporates and disintegrates. If we assume that the supply of distant comets is sufficient to sustain this process over the billions of years that the solar system has existed, then the total population of comets loosely attached to the sun must be numbered in the billions. The combined surface area of these comets is then a thousand or ten thousand times that of Earth. I conclude from these facts that comets, not planets, are the major potential habitat of life in space. If it were true that other stars have as many comets as the sun, it then would follow that comets pervade our entire galaxy. We have no evidence either supporting or contradicting this hypothesis. If true, it implies that our galaxy is a much friendlier place for interstellar travelers than it is popularly supposed to be. The average distance between habitable oases in the desert of space is not measured in light-years, but is of the order of a light-day or less.

I propose then an optimistic view of the galaxy as an abode of life. Countless millions of comets are out there, amply supplied with water, carbon, and nitrogen, the basic constituents of living cells. We see when they fall close to the sun that they contain all the common elements necessary to our existence. They lack only two essential requirements for human settlement, namely warmth and air. And
now biological engineering will come to our rescue. We shall learn to grow trees on comets.

To make a tree grow in airless space by the light of a distant sun is basically a problem of redesigning the skin of its leaves. In every organism the skin is the crucial part which must be most delicately tailored to the demands of the environment. The skin of a leaf in space must satisfy four requirements. It must be opaque to far-ultraviolet radiation to protect the vital tissues from radiation damage. It must be impervious to water. It must transmit visible light to the organs of photosynthesis. It must have extremely low emissivity for far-infrared radiation, so that it can limit loss of heat and keep itself from freezing. A tree whose leaves possess such a skin should be able to take root and flourish upon any comet as near to the sun as the orbits of Jupiter and Saturn. Further out than Saturn the sunlight is too feeble to keep a simple leaf warm, but trees can grow at far greater distances if they provide themselves with compound leaves. A compound leaf would consist of a photosynthetic part which is able to keep itself warm, together with a concave mirror part which itself remains cold but focuses concentrated sunlight upon the photosynthetic part. It should be possible to program the genetic instructions of a tree to produce such leaves and orient them correctly toward the sun. Many existing plants possess structures more complicated than this.

Once leaves can be made to function in space, the remaining parts of a tree—trunk, branches, and roots—do not present any great problems. The branches must not freeze, and therefore the bark must be a superior heat insulator. The roots will penetrate and gradually melt the frozen interior of the comet, and the tree will build its substance from the materials which the roots find there. The oxygen which the leaves manufacture must not be exhaled into space. Instead it will be transported down to the roots and released into the regions where humans will live and take their ease among the tree trunks. One question still remains. How high can a tree on a comet grow? The answer
is surprising. On any celestial body whose diameter is of the order of ten miles or less, the force of gravity is so weak that a tree can grow infinitely high. Ordinary wood is strong enough to lift its own weight to an arbitrary distance from the center of gravity. This means that from a comet of ten-mile diameter trees can grow out for hundreds of miles, collecting the energy of sunlight from an area thousands of times larger than the area of the comet itself. Seen from far away, the comet will look like a small potato sprouting an immense growth of stems and foliage. When humans come to live on the comets, they will find themselves returning to the arboreal existence of their ancestors.

We shall bring to the comets not only trees but a great variety of other flora and fauna to create for ourselves an environment as beautiful as ever existed on Earth. Perhaps we shall teach our plants to make seeds which will sail out across the ocean of space to propagate life upon comets still unvisited by humans. Perhaps we shall start a wave of life which will spread from comet to comet without end until we have have achieved the greening of the galaxy. That may be an end or a beginning, as Bernal said, but from here it is out of sight.

In parallel with our exploitation of biological engineering, we may achieve an equally profound industrial revolution by following the alternative route of self-reproducing machinery. Self-reproducing machines are devices which have the multiplying and self-organizing capabilities of living organisms but are built of metal and computers instead of protoplasm and brains. It was the mathematician John von Neumann who first demonstrated that self-reproducing machines are theoretically possible and sketched the logical principles underlying their construction. The basic components of a self-reproducing machine are precisely analogous to those of a living cell. The separation of function between genetic material (DNA) and enzymatic machinery (protein) in a cell corresponds exactly to the separation between software (computer programs) and hardware (machine tools) in a self-reproducing machine.

I assume that in the next century, partly imitating the processes of life and partly improving on them, we shall learn to build self-reproducing machines programmed to multiply, differentiate, and coordinate their activities as skillfully as the cells of a higher organism such as a bird. After we have constructed a single egg-machine and supplied it with the appropriate computer program, the egg and its progeny will grow into an industrial complex capable of performing economic tasks of arbitrary magnitude. It can build cities, plant gardens, construct electric power-generating facilities, launch spaceships, or raise chickens. The overall programs and their execution will remain always under human control.