Asimov - Fecundity Limited [1957]

Fecundity Limited

by Isaac Asimov
(Copyright: 1957)


   I have hinted at the disasters that await mankind if the present rate of increase in population is allowed to continue indefinitely.  There are many, however, who take a casual view of the matter and assume that "science" will always find a way; that no matter how large our numbers become, scientific advance will discover a way to feed, house, and amuse us.
   Is that so?
   Let us ask then:  How far can we increase our numbers on earth and how long will it take us to reach our limit?
   Let's give mankind every possible break in this matter so that there is no question of being anything but supremely optimistic.  Suppose energy to be no problem; hydrogen fusion and solar power to give us all we need.  Suppose we have worked out artificial photosynthesis and can form all the food we want as fast as we want out of water and air, as plants now do.  Suppose we solve all the organizational problems of dealing with a tremendously crowded planet (from coping with waste disposal to the handling of racial tensions).  Suppose, even, that we can wipe out all competing life to make the maximum room for ourselves.
   If we suppose all that, what can limit man's population increase?  Well, one thing cannot be avoided if we are restricted to our own planet.  Sooner or later, we will run out of at least one of the chemical constituents of the human body — we get to the point where there just isn't enough left anywhere on earth to make another human being.
   Actually, the element which is in the most critical supply, and which is the one that will probably be used up first if mankind increases without limit, is phosphorus.  However, let us give mankind a further break by considering carbon, a less critical component of life from the standpoint of sheer mass-availability, and see what conclusions we can come to.
   To begin with, not all the carbon on earth is in a form that is readily available to life forms.  Let us begin then with merely the "available carbon."
   Ninety percent of the available carbon occurs in the ocean as bicarbonate ion.  A small amount is in the air in the form of carbon dioxide, and the rest is contained in living creatures.  You can add to this the ordinarily unavailable carbon content of earth's oil and coal, since these are being rapidly burned and converted to carbon dioxide, which enters the air or dissolves in the sea and becomes available to life.
   The total amount of carbon present on earth in these forms comes to about 51,000,000,000,000,000,000 grams (which is equivalent to about fifty-six trillion tons).
   This is truly a sizable quantity but wait, some 90 percent of that carbon must be reserved for man's food supply (assuming that he isn't reduced to cannibalism).  After all, man must eat, and he must eat carbon-containing food, whether it is grown in the soil or in chemical tanks, whether it is meat, wheat, yeast, or a mixture of nutritious chemical compounds.  And an over-all organic food supply ten times the mass of humanity is necessary to allow a safe margin, as well as to allow for the production of nonedible organic by-products such as textiles, plastics, and so on.  That still leaves us with something over five trillion tons of carbon that can actually be incorporated into human beings.
   Now let us suppose the average human being on earth (including children) weighs 100 pounds.  Each one would contain an amount of carbon coming to 18 percent of his total weight.  This would be 18 pounds or some 8,100 grams.  The number of human beings required, then, to exhaust ten percent of the available carbon on earth would be 630,000,000,000,000.
   This number, six hundred and thirty thousand billion, certainly dwarfs our present population of a mere three billion and makes it seem that we have ample time in which to expand; that the problem of pushing near the maximum potential is far, far in the future.  But is it?
   Earth is currently doubling its population every half-century but let us be conservative and say it is doubling its population every 80 years.  If this rate of doubling continues, then in about 1500 years, that is, by 3500 A.D., we would have reached maximum.  The living matter on earth would then consist only of human beings, and their necessary supply of food and organic by-products.
   If earth's population were to spread itself evenly over earth's land area, each person would, in 3500 A.D., have about 2½ square feet to stand on, and this includes Greenland, Antarctica, the Amazon Valley, the Sahara Desert.  That's what I call crowding.
   I think you will agree that no reasonable extension of scientific ability will make such a condition tolerable; or even a condition approaching it.  Therefore, if the population explosion continues unchecked, an intolerable crisis will be upon us in much less time than 1500 years, no matter what science does.
   But just for fun let us suppose that through some unimaginable scientific advance, even this population can be taken care of.  What next?
   Well, as I said earlier, there is far more carbon on earth than is ordinarily available.  There is the carbon tied up in limestone and other materials making up the crust of the earth.  This carbon is not generally available to living creatures until slow geologic processes move it into air or sea.  But let us be optimistic.  Let us assume that mankind can burrow as far as necessary into the crust and make all of the carbon available.
   The quantity of carbon in the earth's crust is nearly 500 times the amount available in air and sea, so mankind might be envisaged as multiplying to 500 times the 3500 A.D. population.
   This would bring the total population of the earth to 300,000,000,000,000,000 or three hundred million billion.  If this mighty number were spread over the earth (and this time, we can suppose the oceans to be covered over with planks from end to end so that people could stand on them, too) each individual would have about one-eighth of a square foot to stand on.  They would have to be stacked like cordwood.
   And how long would it take for humanity to incorporate all the carbon on earth, available and unavailable, into their bodies and their food?  Only an additional seven centuries after the 3500 A.D. mark.  In 4200 A.D. there would be an absolute end.
   But, then, why restrict ourselves to our own puny planet of earth?  The Space Age has come upon us.  Science is making tremendous strides.  Out there the vast illimitableness of space beckons.  Surely there is room out there for any number of human beings, and we don't have to worry about population expansion.
   Don't we?
   There are 135,000,000,000 stars in our galaxy and perhaps 100,000,000,000 galaxies in the known universe.  Let's suppose that every known star in the universe is surrounded by ten planets, each capable of supporting as much life as earth can.
   Let's suppose moreover that there is no problem whatever in moving earthmen to any planet in the universe at a moment's notice.  Just snap your fingers and it is done.
   Now, then, in what year will all the universe be filled, to the same extent as earth of 4200 A.D.?  In what year, will earthmen be stacked like cordwood over the entire surface of every one of a couple of trillion trillion planets?
   Why, roughly speaking, by 11,000 A.D.
   In short at the present rate of increase in population, Homo sapiens can fill the universe far beyond any question of tolerability in a mere nine thousand years.
   There is no room, you see, and science can do nothing.  The rate of population increase must decrease, and this can be done in one of two ways — either by increasing the death rate or decreasing the birth rate.
   Take your pick.