Now you used the board neither to write with nor to write upon directly. It simply offered you a surface on which what you wanted to do could be done. Further, it was in no way used up. If you had a trillion notations to make on a trillion pieces of paper, the same board could be used for all, given enough time.

  The writing board is an example of a catalyst.

  There are molecules or conglomerates of molecules which do not take part in a chemical reaction but which offer surfaces upon which that chemical reaction can take place speedily. Protein molecules are particularly good for this purpose because their surfaces are so varied from spot to spot.

  Every protein of respectable size contains at least 19 different kinds of amino-acids, dozens of each, perhaps. Each kind of amino-acid is made up of different combinations of atoms and even when they are bound together to form proteins, portions of them, known as ‘side-chains’, are present on the surface of the protein molecule.

  These side-chains vary in several ways. Some are made up of carbon and hydrogen atoms only. Some of carbon, hydrogen and oxygen; or carbon, hydrogen and nitrogen; or carbon, hydrogen and sulfur. Some have an electrical charge on them and some have not. Of those with an electrical charge, some have a negative charge and some a positive.

  The result is that the surface of a protein, any protein, has a particular pattern of atoms and of electrical charges.

  A molecule which could be involved in some type of reaction may happen to find on some portion of the protein surface a kind of atom and charge distribution which just fits its own. It snuggles in and forms a ‘complex’. Such a complex (for reasons I can’t go into now) reacts more easily than the molecule alone would.

  For this reason, a molecule which would seem perfectly aloof ordinarily, would, upon hitting the appropriate portion of a protein molecule, instantly undergo changes. It might break apart or pick up a molecule of water or transfer some of its atoms to another compound or any of a million different things.

  A protein with such a surface is a catalyst and such proteins are called enzymes. The human body contains thousands of different enzymes, each of which catalyzes one particular reaction or one particular kind of reaction.

  A protein formed at random by the chemical processes discussed in the previous article would have a vast number of different types of patterns on its surface. None of them might be suitable for any useful reaction. On the other hand, some of them might be.

  It’s like those multi-bladed pocket-knives that used to be fashionable; the ones that carried screwdrivers, awls, knives, scissors, corkscrews, files, can-openers and things for taking pebbles out of horse’s hooves. If you had a job to do, you might find a blade that would do it and you might not. The greater the number of blades and the greater the variety, the better your chances.

  Well, with a nucleoprotein containing a million amino-acids, the chances of finding a spot on the molecule where a reaction involving the splitting of glucose could be catalyzed were not completely negligible. And maybe another spot could catalyze the formation of an acyl mercaptan, and still another the formation of a high-energy phosphate.

  It may be that millions of nucleoprotein molecules were formed before one was found with the proper surface patterns. Only that ‘proper’ nucleoprotein molecule could develop the energy to form another nucleoprotein molecule and only that nucleoprotein molecule would be ‘alive’.

  We can see now that in order for a nucleoprotein molecule to reproduce itself it must break down appropriate molecules in the ocean about it; the complex molecules that had been built up by the action of the sun’s ultraviolet rays to some point short of life. This would be the nucleoprotein molecule’s ‘food’.

  And as the nucleoprotein molecules duplicated and reduplicated, the strain on the ‘good’ supply would be ever greater. The ocean would begin to be scoured clean of complex organic molecules as some of them would be converted to simpler compounds for energy purposes and the rest would be built up into nucleoprotein, these joining the ravenous horde and looking for food in its turn.

  Eventually, an equilibrium would be reached. The nucleoprotein population would remain at a number where the rate at which the organic material was consumed would be just equal to the rate at which it was produced by the random effect of solar energy. Since the rate at which ultra-violet light produced organic compounds was probably slow indeed, the nucleoprotein population of the ocean would have to be very low.

  Furthermore, if things continued in that fashion, it would have to remain low for as long as life existed. Life would be only a rare phenomenon of the ocean surface—a scavenger molecule living on the occasional sugar molecule it happened to bump into.

  To progress further than that, one thing was necessary—the capacity for change; and that, fortunately, the nucleoprotein molecule possessed.

  In the course of this book, I have said several times that the nucleoprotein had the capacity of causing molecules of the simpler units that composed it to line up next to it until an atom for atom duplicate was built up. Each individual unit is probably lightly bound to the corresponding unit that forms part of the nucleoprotein molecule. The individual units are then knit together strongly and the new nucleoprotein molecule is released.

  Now the nucleoprotein molecule doesn’t want such a duplicate built up. It has no consciousness as far as we know and no desires. It is just that a symmetrical arrangement, like-next-to-like, is the stablest possible arrangement (due to something called resonance) and therefore the most probable arrangement. However, the most probable arrangement is not that which occurs always; it is merely that which occurs most often. Occasionally, a less probable line-up of units occurs. At longer intervals still, a still less probable line-up, and so on.

  For instance, if unit A and A1 are fairly similar, it will happen once in so many duplications that an A1 will line up next to an A in the nucleoprotein molecule. The resulting molecule will be an A1 modification. When the modified molecule duplicates itself, an A1 will line up next to the A1 and another A1 modification will be produced. In this way, different series of nucleoprotein molecules will be continually coming into existence.

  Imperfect duplications are not the only changes that take place. The nucleoprotein molecules are being continually bombarded with the sun’s ultra-violet light and with cosmic rays and with gamma rays from radioactive materials. Every once in a while, a quantum of such radiation will strike a nucleoprotein molecule in such a way as to change the arrangement of its atoms somewhat. If it remained still capable of duplication, it would duplicate this new arrangement.

  In either case, when a nucleoprotein molecule changes its structure for any reason and passes that change on to its ‘descendants’, the process is known as a mutation.

  Now consider the mutated nucleoprotein. With a new unit in place, the pattern of atoms and charges on its surface is changed in at least one spot. Its catalytic properties may be changed if that one spot is a catalytic spot. It may be that it loses a vital ability as a result and can no longer develop the energy necessary to duplicate itself. In that case it is no longer ‘alive’ and can serve only as food for its more fortunate companions. This is probably the result of most mutations.

  Occasionally, though, a mutation occurring entirely by chance may actually improve the catalytic ability of a vital spot, or form a catalytic spot on the surface where no such spot existed before. Such a mutated molecule might have the ability to utilize its food more efficiently, use energy less wastefully, reproduce itself more quickly. Whatever it is, the new molecule may displace and crowd out the old ones.

  You will notice that this is a form of molecular evolution exactly similar to the evolution on a larger scale with which we are familiar. (In fact, the evolution that leads from lizards to birds and from tree-shrews to man is just a reflection of the tiny molecular changes going on in the nucleoproteins of the genes of these creatures.)

  In what directions can this molecular evolution go? Judging from what we see about us now, one of the directions must have been toward the development of an ability for several nucleoprotein molecules to form a more or less permanent union with one another.

  You can see the advantage of such co-operation. A single nucleoprotein molecule must be able to catalyze all the necessary reactions involved in self-duplication; all without exception. As soon as one ability was lost, the molecule was dead. If several such nucleoproteins banded together, the loss by one molecule of a particular catalytic ability was no longer fatal. The others in the chain still possessed it. Furthermore, as time went on, each gene might begin to specialize in certain of the catalytic abilities or even in one only and do that one with particular efficiency.

  The more complex viruses that exist today may actually consist of as many as 25 nucleoprotein molecules (or genes, as we may now call them) in close co-operation. The human cell, it is estimated, has somewhere between 2,000 and 14,000 genes.

  Another direction in which molecular evolution took place was in the formation of a protective membrane about the nucleoprotein molecule (or molecules). In some way, the nucleoprotein molecule managed to collect a film of fatty molecules about itself. This film was ‘semi-permeable’; that is, it let some molecules through and not others, depending on the size and chemical properties of the molecules.

  For instance, such a membrane would not let protein molecules through and that made possible the invention of enzymes.

  You see, the nucleoprotein molecule could reproduce itself only when all the necessary units were in line. But what if only a portion of the units could be found at a particular time? In that case, only a fraction of the molecule could be formed. It wasn’t alive, this fractional molecule, and it just drifted away to be food for some other nucleoprotein molecule.

  Yet this might easily represent a waste, since the portion of the nucleoprotein molecule that had been duplicated might have been one of the catalytic spots.

  Once the nucleoprotein molecules had surrounded themselves with a membrane, though, such incomplete fragments could not escape, and the fragments would serve as detached catalytic spots; as enzymes, in short.

  In this way, the nucleoprotein would be able to ‘delegate authority’. It would no longer have to do everything itself, but could create any number of enzymes to take care of the individual reactions that needed catalysis, while it alone remained ‘alive’.

  The cell nucleus, which is surrounded by a membrane separating it from the rest of the cell, and which contains the genes, may be the direct descendant of these primordial nucleoprotein sacs. It is interesting to note that the cell nucleus (even of our own cells) is incapable of handling molecular oxygen. It has no enzymes fit for the purpose. It gets its energy only by glycolysis—as though it had evolved in an atmosphere that lacked oxygen.

  All of this would increase the efficiency of life’s use of what organic molecules could be found in the primordial ocean, but it wouldn’t increase the supply.

  In order for life to advance, the cells had to guide the formation of new organic matter. It had to make sure that such formation was not simply the result of chance collisions of sunlight and molecules. It had to trap the sun. It had to create a molecule which could absorb solar energy and transfer it to high-energy phosphate bonds.

  The deed was accomplished. How long it took we have no way of knowing. The key molecule was chlorophyll, which is made up of a porphyrin ring system and a magnesium ion. The materials were common enough. The porphyrin ring system is very stable and was probably swarming in the primordial ocean just as were other stable organic molecules. And magnesium ion is one of the commonest in the ocean.

  Apparently, then, a nucleoprotein molecule was formed through random mutation which could form an enzyme out of one of its catalytic spots which could latch on to such a chlorophyll molecule and put it to use.

  Any nucleoprotein sac that developed such an enzyme was fortunate indeed. All such a sac needed was water, carbon dioxide, certain simple ions and sunlight. All these were inexhaustible and now the nucleoprotein sacs required the drifting food of the ocean surface no longer and could multiply almost without limit.

  But in order to do so, one more invention was required—cells. The nucleoproteins could form their own carbohydrates and fats now but once formed there was a tendency for them to drift away. To be sure, the nucleoprotein molecules might be content simply to fill the oceans slowly with food, as it had been filled in the beginning. Perhaps this was what happened at first, but obviously it is an inefficient process.

  Then it must have happened that one sac developed a second membrane about itself, further away than the first membrane. Between the two membranes food might now be stored.

  As the nucleus formed a glucose molecule it would travel out through the inner membrane into the space between the membranes. Or if the cell (as we may now call it) bumped into a glucose molecule floating in the ocean, that glucose molecule would travel in through the outer membrane into the space between the membranes.

  In either case, in the space between the membranes, a phosphate group would be added to the glucose and its properties would be so changed that it could no longer cross the films again. It would be trapped within the cell. Once enough sugars were collected, they could be hooked together to form a starch molecule, and starch could be converted into the still more concentrated energy store represented by fats.

  You see, by storing starch and fats, the cell could make sure it profited from its exertions and didn’t distribute the sweat of its brow, so to speak, over the vast reaches of the ocean.

  Naturally, the outer portions of the cell, called the cytoplasm, had to possess enzymes with which to catalyze the reactions involved in forming starch and fat and breaking them down when necessary, too. For that reason, a new type of nucleoprotein molecule was developed which is characteristic of the cytoplasm and which can also duplicate itself and make enzymes.

  The cytoplasm may have been developed after photosynthesis had continued long enough to place some oxygen in the atmosphere, because it is the cytoplasm of the cell that has the capacity to utilize molecular oxygen.

  Chlorophyll-containing cells, which we may now call plant cells, multiplied extensively and filled the oceans once again with food—in the form of cells rather than of individual molecules. Cells without chlorophyll could now develop which could live, parasitically, on the food painstakingly stored by the plant cells.

  Such animal cells, as we may call them, could engulf plant cells whole, strip them of the energy of their food content and build up their own store of carbohydrates and fat. They, in turn, could be the prey of still other cells.

  Animals cells, making use, as they did, of plant cells, did not depend on the presence of light. They could spread into deeper layers of the ocean.

  When plants invaded the land, they were tied to their roots, because they had to have a lot of water continuously. Animals let the plants worry about that, ate the plants, and developed independent locomotion.

  Plants had to build up their food supplies slowly and were sessile, inert things. Animals broke down plant food (or other animal food) rapidly and had enough energy to develop active muscles and nerves capable of concentrating electric charges and carrying sensory impulses.

  That meant, eventually, the development of a nervous system, and of a brain. That, in turn, meant that someday intelligence could be achieved and a creature like man would evolve, a creature capable of wanting and trying to puzzle out how it had all come about.

  CHAPTER NINE—THE SEA-URCHIN AND WE

  In any free association test, the chances are appreciable that the word ‘evolution’ will evoke the response ‘fossils’. And fossil remains are usually of bones, teeth, shells, scales and other hard parts of a body. Evolution, as most of us think of it, is thus largely a history of morphological change (that is, changes in shape) of the hard parts of the body, plus what can be deduced therefrom (which is often precious little) about the soft parts.

  We’ve got the shape of the hard parts neatly categorized from the trilobite to the Neanderthal. We can trace the steps in the morphological development of the horse, the elephant and man in a series of skeletal gradations. See any museum of natural history.

  But think of the questions morphology can’t answer. Did Eohippus have any vitamin requirements the modern horse does not have, or vice versa? Did Neanderthal man utilize his amino-acids in any way differently from us? What, precisely, was the clotting mechanism involved in the blood of Tyrannosaurus Rex?

  Barring time-travel, we’ll never know. But we might be able to make reasonable guesses, perhaps, if we study and compare the biochemistry of the various living species that exist today.

  Biochemical evolution is less spectacular than morphological evolution. A morphological invention such as wings has been made at least four independent times (insects, pterodactyls, birds and bats) in four different styles, but biochemical inventions are usually made once, or if more than once, then in identical style. The uses to which the various B vitamins are put were decided very early in the game and all living cells today, from bacteria to those of man, use them in the same way. There are many other examples of the biochemical uniformity of life despite tremendous morphological variations.

  But uniformity isn’t universal. Biochemical differences among species do exist and then things become really interesting.

  Take the case of fat digestion among mammals. Fats are one of the major food components and an important body fuel. To be utilized by the body, the fatty substances in food must first be digested by the action of enzymes in the intestines. There is one catch. Fats are not soluble in water and digestive fluids are mostly water. Fats will not be digested with anything approaching efficiency unless something is done to enable them to mix with the watery digestive fluids.