Reproduction And Heredity

( Originally Published 1909 )

THE facts referred to at the close of the last chapter prove that physical or material life is regulated throughout by natural laws. These laws are just as natural as the laws of chemistry and of physics, and therefore science is properly concerned in endeavoring to discover what they are. This statement involves the conclusion that each living form, whether plant or animal, comes into being as naturally as an icicle or a waterfall. But this conclusion by no means implies that the laws of life, however natural, are the same in kind with other natural laws, such as those of chemistry or of physics, or with any conceivable modification of them.

This question must be judged on its own merits until the decision can be given according to the facts. After that is done, we contend that a consideration of the most essential elements in the existence and in the development of life shows that they are totally different from all other facts or laws and cannot possibly be derived from them. This is our. contention; that life is not physico-chemical in origin or in nature we would emphasize from the outset.

When men began to think about the phenomena of Nature, their readiest ex-planation for everything was furnished by the consciousness of their own personality. As they acted according to their own wishes, hopes or fears, which led to their creating objects or causing events to come to pass, so they concluded that everything in nature, good and bad alike, must have a corresponding designing personality to account for it. The progress of knowledge, however, dispelled all that, until it changed thunder itself from an awe-inspiring voice into only a loud noise.

But it was in accounting for the phenomena of life in Nature that this old conception lasted the longest. A sort of supernatural, vital force was imagined to be the only explanation here, and in medical science particularly this imaginary vital force arrested all progress for many centuries.

But this once crudely conceived mythical vital force remains as a name to disturb the reasoning of those who repudiate its existence. Because there is no vital force, therefore it is concluded that what things and forces we know of must ac-count for life by supplying everything needed both for its origin and for its developments. Those things are, first, matter as a substance, and then such forces we know of that act on matter, like light, heat, chemical affinity, electricity, etc. Hence it is maintained that because we know nothing else except the properties of matter and of force, there-fore there is nothing besides these for life to come from.

We demur from this conclusion most decidedly, on the ground that the chief laws of life are now pretty well understood, and so also are the chief laws of matter and of force, and that there is no correspondence between these two whatever. Every alleged instance of living matter becoming so without the agency of previous life proves on examination to be erroneous. That all life is from life, and from nothing else, is therefore the proposition which we will discuss.

It is just here that, as it seems to us, some reputable biologists have failed to perceive the real point at issue. Because some processes of growth and of nutrition have been experimentally proved to be profoundly affected by purely chemical agents, they appear to accept this as evidence that it is all of a piece throughout, and that further investigation will show that one after another of supposed vital phenomena will take their place in the list of physico-chemical effects until no such thing as vitality will remain.

Thus one of the hitherto most mysterious of living processes, that of the cleavage and arrangement of cells in the early stages of animal development, has been shown to be fundamentally modified by varying the chemical composition of the fluids in which the animal living cells are bathed. Professor Loeb, for example, more than confirmed similar experiments by other biologists, by demonstrating that unfertilized eggs of echinoderms, or sea urchins, when dipped in a dilute solution of magnesium chloride, then went on to grow into complete parthenogenic forms of that animal. But these results are only in line with what was well known before, that living matter, while living, can both be affected by, and also itself give rise to every kind of physical, chemical, and electrical reactions, just as any other active agent does. Loeb had to have living embryos to experiment with, and all he did was to affect their processes of development by his solution of magnesium chloride. He could no more thus originate these animals than he could make a new egg.

But what is demanded is how to account by non-living agencies for the really essential elements in life. These, and not the accompaniments of vital activities, are the things to explain.

Thus we may well ask what physical, mechanical, chemical, electrical, or other non-living agency comes anywhere near accounting for the really basic fact about life, namely, Reproduction, because by its processes vital reproduction excludes its being classified with anything else on earth. Thus a whale is, to be sure, a large living thing whose circulation, respiration, muscular and nervous activities illustrate many physico-chemical laws. But how can these laws account for the biological history of this animal himself ? As we have already stated in the preceding chap-ter he began his individual existence, as every other living thing, animal or plant, large or small, has to begin, as a microscopic unicellular entity. It is the be-ginning of things which settles the nature of things, and when a whale begins, he is certainly a whale, though 1,500,000 such whales might be got into a space not larger than a pin's head. He also is then nothing else than a whale, and by no possibility can he grow into a fish any more than he can grow into a bird, for whales are mammals and therefore separated by an impassable biological gulf from all fishes. Likewise an elephant, an onion, and a grasshopper all begin in single primordial cells of about the same size. Therefore, in their first microscopic cells it is all determined what they are going to be. But determined by what? By physico-chemical laws? Again, in that vanishing speck of matter constituting the unicellular whale is already settled just how all the billions of cells of his future body are to grow, how many of them there are to be, and where the bone cells, the muscle cells, the nerve cells, and all the other bodily cells are to find their places to the end of that whale's life.

But what thing in physics, or what force among forces, acts in that way whether singly or in conjunction with other things or forces? A thing may become larger by accretion, but never by the working of complex, internal organization. No thing on earth can grow unless it be living. So no force or forces can shape any form of matter so that it will reproduce itself. Force and matter can make an icicle, but the icicle remains as lifeless as both the force and the matter which produced it.

But a new and portentous factor in the problem now challenges our consideration, namely, that of Heredity. Again, as al-ready mentioned, in the wonderful organization of this minute particle of whale matter we find that in a minuter portion of it, namely its nucleus, there is a minuter portion of this in turn, which goes by the name of the chromatin substance, and that this latter substance chiefly bears the indelible impress of all the whale's ancestry back to the first whale. On that account this whale, as he grows, will demonstrate that whales used to walk, for in his adult state he has legs just where legs ought to be and complete in every bone thereof, but as they are now no longer usable in the ocean where he lives, they are deeply imbedded under his skin, much as an English nobleman of ancient lineage hangs up in his halls the coats of armor of his ancestors, as mementos of days long gone by, on account of rifle bullets.

But a physical atom or ion with the attribute of heredity is as unthinkable as hereditary hydrogen. We must therefore take leave here from matter and all its known properties, and restrict our attention to the familiar forces above mentioned, which play on matter according to their well ascertained laws. All admit that these forces are themselves lifeless, but it is imagined that somehow they can vivify matter and make it living. This is momentarily thinkable, but soon ceases to be so when we are really confronted with the facts of both reproduction and heredity. No one of the known forces can re-produce itself, still less can it go through the cycles. of successive generations, any more than matter itself can. A hereditary unit of heat is as absurd as hereditary helium. But life without coming by hereditary descent and then going on to reproduction does not exist. Both these elements are as inseparable from life as attraction is inseparable from gravitation. But where else is there even an analogue, not only to both, but to either one of them? Vital reproduction is difficult .enough, but heredity is ten-fold more so, and we have already seen to what grievous mental strain some biologists have been subjected in trying to explain how every cell and part in an adult body exists, potentially if not actively, in the single primordial cell " when as yet there were none of them," and exists there according to that which has been transmitted to it through countless successions, not of adult bodies but of previous minute primordial cells.

Of what avail then in our discussion is it to cite the peculiar set of electrical cur-rents in functionating nerves, or processes of growth affected by mineral salts? We might as well say that fire is caused by the smoke which generally accompanies it. In view of the infinitely complex processes fundamentally related to vital reproduction, through most ancient descent, what is the probability of experimenters being able some day to give us a formula or receipt for making life altogether de novo?

Meantime, the reader should now note that though in the primordial cell the mat-ter associated with life is so near nothing, life itself, so far as its most specific properties and potentialities are concerned, exists to an unexampled degree. The microbic whale, for example, starts with more vital elements in his microscopic body than ever he will possess afterwards, for by the time he has grown into an adult whale, and bulks as much as a brigade of men, he has spent much the greater part of his original capital stock of vital capacities. There remains in him no potential reserve of that living power to form an eye or an ear or any new tissue or organ which he had when he counted only one cell to his physical being. All he does when he is full grown is to keep what he has until it begins to decay with age.

It is true that there are still traces in him of his original capacity for making new tissues in his power of repairing bodily injuries. In animals lower in the scale of life than whales, this power of re-pair is sometimes strikingly illustrated. Thus, if the crystalline lens of the eye of a larval salamander be extracted, this creature soon makes a new lens out of the posterior cells of his iris, as complete and as good as his original lens. Many biologists seem to think that this behavior of a mutilated salamander greatly deepens the mysteries of living processes. If it did not actually occur it would otherwise seem as likely as that the sides of a man's pocket should spontaneously replace the same as before a stolen pocket-book, even to the dollar bills which were in it when it was lost. But after all there is no more mystery in this salamander's making a new lens, than there is in his making his first lens. He only shows that as he did it once he can do it again by the same old power which was in his primordial cell. The only difference seems to be that animals higher in the scale than the salamander, lose, as they grow, most of that original, all-creating capacity to make new parts, until nothing is left of it except a limited capacity for repairs. But the power to repair and that entirely to regenerate are only different degrees of that inherent living endowment residing in the first microscopic cell.

When a whale is full grown he has matter in quantity sure enough. Every action then of his nerves, especially his motor nerves, gives rise to electrical currents ; every contraction of his muscles liberates heat, and all his secretory activities are accompanied with chemical changes. But do any of these elements, or all of them together, constitute his life? Not at all. What life he has comes from the life of his primordial cell, and from nothing else.

But the mysteries of heredity are not confined to the potentialities of the primordial cell. All cells and tissues in the body are ruled by its sway, and can never depart from it. No body cell in a walrus, from its head to its tail, can take on the pattern of a whale's body cell, because each cell of a living body, whether it be plant or animal, has its own special pat-tern. The pattern of a walrus' body cells is wholly different from that of a whale's, however identical they may be in chemical composition.

Moreover, we encounter here one of those biological marvels by which science has recently revealed the fact that the blood is the most hereditary thing about us, for its hereditary elements override everything in the make-up of the physical animal body, whether it be the shape of the skeleton, of the lungs, of the alimentary canal, or of the skin. It even overrides ancestral habits as to the great Food Question—Darwin's chief creator, which works by the strife in Nature about how to eat or keep from being eaten. This discovery of the hereditariness of the blood came about in this way.

Some of the most recondite investigations in the history of medicine have been about the mechanism of Immunity, or why a single attack of certain infectious diseases renders a person immune from a second attack. It was through these investigations that some valuable antitoxins were discovered in the immunized blood serum, which raise hopes that we may yet find the antitoxins for the worst forms of our deadly infections, just as an anti-venom has been found for the cobra's poison, and another for that of the rattle-snake. But each of these antitoxins is specific in that it does not afford any protection except just against its own poison. This led Professor Wasserman of Vienna to investigate whether the blood of each kind of animal did not contain some ingredients which would be specific to that animal, that is, not to be found in any other animal, a fact which, if found, might be of use in medico-legal cases.

His results made this so probable that Professor Geo. H. F. Nuttall, F.R.S., of the University of Cambridge took the subject up, and has so extended its application that a single drop of blood from any animal now suffices not only to show by its peculiar chemical reactions what animal it comes from, but also how nearly related, or the opposite, an animal is by his blood to other animals. It begins, therefore, to look as if the whole classifications of zoology may have to be rearranged according to these blood tests. Thus, a drop of the blood of a walrus shows no relation with a drop of whale's blood, or of the blood of any other cetacean, such as seals or porpoises, which, like the walrus, are mammals that have taken to the sea. Instead of that, the blood of the walrus immediately reacts with the blood of horses, asses, and zebras, thus proving that he is an equine that no longer crops grass, but goes where he can live on an exclusively fish diet. Likewise, the hippopotamus is shown to be a modified pig.

Where blood relationship exists, but is distant, these reactions are proportionately faint, but where no reactions occur there is no relationship at all. Thus, geology indicates that birds are descended from reptiles, and oddly enough, the blood of a bird shows a distinct, though very faint, reaction with the blood of a snake, but none whatever with that of the winged bat or the flying squirrel, for these are mammals.

On the other hand, the marsupials, once such a great family, but now reduced to the kangaroo, the opossum, and a small creature in South America, have now not a single blood relation left. As to man, he has no relationship to monkeys, but the blood of anthropoid apes shows a very faint reaction with his. Meantime, all the races of man are unmistakably of one blood, whatever their color or abode.

Heredity, therefore, is inseparable from living matter, whether it be in man, in animals, or in trees, or whether in the smallest microscopic particle thereof. In one sense it and physical life are one, for no matter can be living without it. It is absolutely unique, for what else is hereditary? Certainly nothing physico-chemical that we know of. It doubtless has its own laws as everything else has. But laws explain only sequences, and never origins. At every turn we find mysteries connected with heredity which no known law ex-plains. But so accustomed do we become to associate heredity directly with parent and child, linking the one to the other, that we do not know what to say about the worker bee, which for the past hundreds of thousands of years never had a working father nor a working mother to impart to it that wonderful skill which it shows in constructing the cells of its honeycomb. But bees abound in unaccountable inheritances. Darwin's survival of the fittest, however, may contribute a ray of light on one of their constitutional laws. With a do-nothing male, after his case has been duly considered, two of his spinster sisters take him outside and put him to death, thus ridding their community of such a make-weight. We have not yet reached that utilitarian stage of development, but Darwin thinks that if we only had the useful moral standards of bees we would see nothing wrong in such a performance.

But bees are not the only hymenoptera which illustrate the puzzles of heredity.

In one particular species of wasps, the Eumenes, the female makes a most peculiar provision for the nourishment of the offspring which she will never herself live to see, and as the same was thus provided by her mother who likewise died before her, she could not have learned this remarkable proceeding from her. This wasp first makes a secure papier machélike box, as it may be called, and having finished that, she then goes on a hunt for the proper spiders, which she stings one by one, and then deposits in the. end of the box. This sting does not kill the spiders, but only benumbs them, so that they remain hypnotized, as it were, awaiting their doom from the larval wasp when it hatches out of the egg which the wasp lays only after enough spiders have been deposited for the hatched larva to feed upon. Here this wasp shows an accurate knowledge of the nervous anatomy of spiders, as she stings only that ganglion which does not include the respiratory centres, for that would be fatal. As the adult wasp does not often feed upon spiders herself, this benevolent arrangement is for the purpose of providing proper baby food for her young. But how in the world did she inherit this most complex way of doing things? It would not have done at all to kill the spiders with her sting, for this larval wasp must have only living meat, and not even meat kept in cold storage.

But the genus hymenoptera includes not only bees, wasps, hornets, and other insects, but also the ants, and we might fill pages with the curious hereditary habits of the ants alone, which are as inexplicable as any of the rest. To ascribe them to Instinct is simply to get behind the most expansive of all words for veiling blank ignorance.