The Seven Mysteries of Life

by Guy Murchie

  In the very beginning of course sex was without gender. There was literally no such a thing as male or female anywhere on Earth in that pre-Cambrian time about a billion years ago. No creature had sex organs, and the organisms that mated were more similar than any two brothers or two sisters you ever met, with the possible exception of identical twins. Under the biologist's microscope one can see the same thing still going on among many single-celled plants and animals, where it is an enduring trend of elementary life. As these cells divide and multiply and divide again, or sometimes sprout buds that cast off on their own, once in a long while, particularly under stress conditions, a new and intrusive urge seems to pervade them. Some flagellate, say, instead of splitting in two as its ancestors did for too generations, will hesitate and probe about. It may be getting a giddy, reckless feeling of sociability it never knew before. It will show interest in some other flagellate and, after only the briefest of introductions and perhaps a moment to screw up its "courage," the two will touch and melt and merge completely into one, as if they were two minds with a single thought.

  If this happened every time two cells met, of course their number would steadily diminish - but it does not; it can be deadly dangerous to both cells (which they seem to sense), and most of them go on dividing and disregarding their neighbors, only resorting to this risky population-reducing merger at rare intervals. Although the two merging cells are clearly almost identical when they first try this "exciting," liquid hug, evolution gradually brings on greater complexity, a protohermaphroditism followed by increasing polarity and disparity between them, permitting them eventually to specialize, which is the real beginning of sex. Since some traveling must be done to get them together, and some food must be provided to keep them nourished afterward, their specializing takes the logical direction of dividing these duties, one kind of cell going in for mobility by growing a tail, the other kind concentrating on food storage by growing fat. The first kind, we soon realize, is evolving into a sperm, the second into an ovum. The first therefore emerges in time as the male, whose essential function is to be active, to hunt and travel. The second becomes the female, whose essence is passivity, who stays home and nurtures the young.

  Of course many variations of the basic idea of sexual polarity as demonstrated in merging or swapping of genes are tried out. This is nature's wont and, while some free cells become simple sperms and ova that merge into one cell before they start their reproductive multiplication, others just touch or conjugate long enough to exchange material, then separate and one or both may reproduce later, depending on their degree of maleness, femaleness, hermaphroditism or other sexuality. The paramecium (page 86) is a one-celled animal that briefly conjugates to swap genes, using this primitive protosexual technique to ease the stress of life, on the principle that "two do better than one." The mating pair express themselves in what might be described as the oldest known language of love, a sort of chemical conversation in which each partner puts forth a substance that influences the other, both of them seeming to feel better and more relaxed for this discourse evolving into intercourse. It may not be as limited a dialogue as you would think either, for there is no fundamental reason why there can't be more than two sexes and biologists already have discovered eight sexes just among paramecia. On hearing this I once asked an authority on sex at the Harvard Biological Laboratories (whose name not inappropriately turned out to be Dr. Raper) whether these eight sexes could have any sort of mechanical manifestation because, in my innocence, I had imagined lovemaking among octosexed paramecia as analogous to a kind of baseball game in which each player had to touch all four bases twice in order to make a home run. But he said, "No, the sexual differences in parameciums are only chemical."

  Yet the complications of multisexed life remain both fascinating and baffling. Just think of the dilemma of a hostess faced with the etiquette problem of seating guests of eight different sexes harmoniously and congenially at the banquet table. Then consider some of the higher varieties of fungi which, according to Raper, have as many as 24,000 sexes - only, as he points out, they aren't really sexes as the word is commonly understood but rather mating types, properly called syngams, each of which is intrasterile within itself and intersterile with certain other syngams, while interfertile with the great majority of its own species. Incidentally this is a more liberal arrangement than it may seem - for, I was given to understand, if one were a fungus and should happen to meet another fungus of one's own species, say in some shady nook, one would have about a 98 percent chance of being able to mate with it successfully. Which is a much higher batting average than anybody, including Jacques Casanova, ever attained as a human.

  Some of the multiplicity of sexes may perhaps be explainable through the relativity of sex, an aspect one doesn't ordinarily become aware of much, outside homosexual circles. In saying relativity, I mean that sexual characteristics, notably in primitive creatures, seem to depend on how much of this or that chemical the organism contains, with the implication that there are many degrees or even gradients of sexuality. If true it would explain why a microbe is so often observed to be male in relation to one companion at the same time it is female in relation to another. For all I know, there could be individual organisms with a whole arsenal, repertoire or spectrum of sexes, each sex chemically (if not mechanically) specific to one of dozens of potential mates it might someday feel a yen to get intimate with. Almost anything appears possible. Bacteria are now known to swap genetic material at random or by accident, as when two or more of them are mangled by an intruding object, by the action of viruses adept at lugging genes around or by "deliberate" conjugation. Cutting is one of the most familiar means of reproduction among worms, almost any species of which, no matter how you slice it, seems able to grow its parts into whole new worms. And since multicelled organisms, unlike single-celled ones, do not need their whole bodies for reproduction, most of them soon evolve the more efficient system of keeping just a relatively few special cells for the purpose: like sperm and ova. Since sea to the land (where the more variable environment particularly demanded the adaptability of sex), it had to bring a little sea along with it or find a substitute in order to get to the ova and reproduce. That is why animals still either lay their eggs in water or retain wet internal ducts for the sperm.

  Primitive plants naturally evolved something similar, most of them living in wet places or, if crowded away, perforce waiting for rain, as do ferns and mosses, whose sperms still swim, but the majority of their descendants eventually found this dependence such a fatal drawback that they "taught" their sperms to fly or hitch rides, mostly by progressively miniaturizing them into pollen. And not a few species (of animals as well as vegetables) even compromised between sex and nonsex by alternating generations between sperms and spores.

  It would be only natural for humans to think of nonsexual reproduction or virgin birth as limited to the most primordial or simple creatures, but actually it is found here and there through practically all levels of life, including our own. Sometimes it is a phenomenon of only half the year, as among aphids, water fleas, etc., where males are unknown in spring and summer but normally show up every autumn. But there are at least two species of lizards and four of fish that have no males ever, their embryos developing unfertilized by what is known as gynogenesis. Frogs' eggs, moreover, can be "fertilized" without any sperm at any season by pricking them with a needle, or sea urchin eggs by adding sugar, salt or other substances to the water, and they grow up into real frogs and urchins.

  In such cases, as you would suspect, it's the mother who is the virgin. Yet if a sperm is "fertilized" by being allowed to enter a fragment of egg that has no nucleus, the young that develop from out of it have no genetic mother - so in this instance, oddly enough, it's the father who is the virgin! Animals as big and advanced as turkeys have recently been raised by the U.S. Department of Agriculture without any fathers at all, their ova evidently produced by mitosis instead of meiosis (page 164), and have lat
er begotten their own offspring. So the principal biological evidence that the Virgin Mary had to have experienced a miracle - if not an immaculate misconception to have given birth to Jesus is his maleness, and a human race of Amazons is theoretically possible. Besides, has it not long been known to science that there exists such a thing as human sexless reproduction: notably in the case of the embryo that, without aid from the opposite sex, somehow divides into two and becomes identical twins?

  Winding up this chapter on sex, we might revert for perspective to the question of the relative importance of space and time in all of life's reproductive methods, for there is obvious significance in the observation that encapsulated spores (which are tough and have no sex or fertilization problems) can go almost anywhere in space but are not very adaptable over a period of time, while sperms (which can survive only where they find an ovum) are very limited in space yet can adapt to almost any environment if only they (and their descendants) have time enough.

  Such an issue is admittedly too unfamiliar to us humans to be easy to grasp but, I can imagine, it might seem a lot nearer fetched to the mind (if any) of a sperm or an ovum, or any other kind of sex cell. Sex cells, you know, are practically immortal - potentially so anyway - and for that reason, if for no other, it would seem worth the effort to try to visualize their extraordinary outlook. Generation upon generation they live on and on without dying, being passed "down" from parent to child, repeatedly conceiving and sprouting out a body in which to shelter, feed and renew themselves, indeed diverging again and again into many bodies at once, tantalizing them with wild lusts so they will be sure to free them before they have lost the power to find their way and sprout the next body - and so on indefinitely.

  Thus, in a sense, you and I are nothing but a sperm's (or ovum's) way of duplicating itself and staying alive. And what is a chicken but an egg's way of producing another egg? Come to think of it, what really evolves in evolution may not be so much the obvious vegetables and animals we see around us as their hidden cells of sex - not the mortal individuals so much as their immortal lifelines of genetic continuity. For evolution is essentially a kind of perpetual living flux, a turbulent continuum of interrelatedness that as a whole must be much greater than any sums of its parts.

  We will be returning to the subject of interrelations in Chapter 13, but, before that, we need to delve deeper than sex and its cells. I mean we must dig into the very core of whatever it is in these germs of generation that enables them not only to preserve everything our ancestors evolved during billions of years but whatever, in each reproductive cycle, still makes it possible to move each of their descendants one more step forward into the unknown future. And this, should our endeavor meet with success, means simply that we shall have come that much closer to the ancient and elusive elixir of life.

  Chapter 6

  Secret Language of the Gene

  * * *

  WHEN I LOOK upon the earth and moon and other worlds so patiently going their rounds, each sticking to its own well-defined beat like so many territorial animals, I can't help but wonder at the order and discipline of it all. If these rotund organisms are alive, as I am more and more convinced they are (at least in a cosmic sense), there must be some factor regulating their growth and behavior, just as is true of raindrops, bubbles, apples, seeds, eggs and other globoid forms that come and go - something that directs the motion not only of whole entities but even of the atoms, molecules and other substances that enter and leave them in the endless exchange of life.

  So I ask myself: if life is a flow, isn't it because only the fluid state permits matter to maintain enough molecular motion to give it the chemical complexity that spells life? Of course I know the solid state of bones includes metabolic drift, but far surpassing this movement are the torrents of blood, lymph, water and air that keep the body alive by supplying it with vital secretions plucked out of the passing world. The processes involved are naturally abstract in essence, like an ocean wave that continuously advances through vast populations of molecules, shaping them as it goes - or like a candle flame fed by liquid wax and air so that its fluctuating form persists as a pattern in the invisible currents of oxygen, hydrogen, carbon, nitrogen...

  The abstract aspect of life thus revealed is as inescapable as it is elusive, since it leaves no room to doubt that life is essentially only a pattern in a metabolic current of elements and not really dependent on any particular atom or molecule or cell. What, then, should we think of as the physical basis of life? And from what, if anything, is a body ultimately derived?

  It is an ancient enigma. Like Chopin's first prelude (sometimes called "The Question") it does not expect an immediate answer. Rather must it glean satisfaction from being truly heard.

  HEREDITY'S UNIT

  The first inklings of an answer, by a growing consensus, are believed to lurk somewhere in the nucleus of the living cell - particularly in the genes that direct the cell's growth and behavior. But what is a gene? Perhaps the surest explanation one can give is that it is a letter or a word in nature's message to a seed or an egg telling it how to be a tree, a bird, a turtle, a snake, a platypus ... A gene is one step in the secret recipe for growing up, for living. It is a wave of the unseen wand that turns a tadpole into a frog, a caterpillar into a butterfly. It is a basic unit of heredity. It is what controls the mysterious automation that heals a wound, regenerates a lizard's tail or guides a migrating bird with the help of the stars.

  Such automation is called genetic because it is presumably provided by genes in each cell, but just how they provide it is still in process of being unfolded. Last-century biologists, who knew little of the microcosm, theorized that whatever hereditary controls are in a fertilized egg inevitably must be parceled out as the egg divides and grows so that each new cell can be directed as to what it is to do. One of the two cells created in the egg's first division, they reasoned, contained directives for all the structures on the right side of the body, while the other held the plans for those on the left. The second round of division (at right angles to the first) in turn separated the instructions for the upper half of the body from those for the lower half, while every subsequent division in like manner reduced the number of determinants per cell until finally, at the birth of the animal, each of its cells carried only about one unit (gene) of hereditary information. In other words each fingertip contained only genes with fingertip information, each eye contained only eye information, and so on.

  Though such a hypothesis had the appeal of logic and simplicity, it was proved untrue in a classic experiment early this century by a German zoologist named Hans Spemann, who operated on an embryo salamander, using semimicroscopic glass threads and tubes of his own devising. Most of the cells of the unborn creature (still attached to its mother) apparently had not yet committed themselves to specialization, for the tiny animal looked as blank as a baked bean, with barely perceptible nubs where the head and limbs had begun to form. Yet Spemann knew from experience exactly where an eye would appear in a few more days' development, and carefully cut a square piece of prospective-eye flesh out of the emerging head and exchanged it for a piece of the same size and shape dissected from the emerging tail, immediately transplanting both into their respective new positions to see how they would grow. Would the eye appear in the tail, as it should if each cell had been given instructions only for itself? Within a week it was clear that the answer was no - for the eye showed up in its regular place in the head, notwithstanding the fact that it fashioned itself out of cells that would have become a tail had they not been moved. Obviously, then, all body cells must have genes fully qualified to make any body part required of them - like men building a house, each of whom has been given blueprints for the whole job, so that, no matter what section he finds himself in, he can build correctly in relation to the whole. When a body composes itself, therefore, it is immaterial what flesh is used to form its features. Any of its flesh is good enough to make an eye, even as God the Potter may mold any cl
ay to His creative wish.

  This revelation of a complete genetic blueprint in every cell, extravagant and wonderful though it seemed, inevitably left a lot to be explained as to how life grows. Students of embryology had long been aware that when a cell begins to specialize it generally commits itself to a particular task and ones with such different functions as eyes and tails had never been known to tolerate an exchange after they were established. However, Spemann continued his imaginative experiments, and it was not long before he realized and proved that development is controlled not just by genes but to a great extent by a continuous "interplay" between them and the rest of the cell. He did not fail to take into account also the ceaseless influence on a cell's growth of all its surrounding cells and every manner of far-ranging hormones, chemicals, viruses and other intrusions. The process in which a fertilized ovum thus divides in order to multiply itself into 2, then 4, 8, 16 ... cells came to be recognized as more and more subtle and complex - an unfathomably sophisticated natural increment of cells, in which each organism diverges into its own pattern, the cells by the time their number approaches 50 forming one of various models of a hollow sphere known as the blastula. This round and growing speck sooner or later, for some little understood reason, finds itself compelled to draw its single-layered surface inward at a certain point like a rubber ball sucking a dent into itself, usually thus becoming a cup-shaped two-layered body, the gastrula, which will later shape the dent into the beginnings of a gut. And, along with the gut, the outer gastrula will fold inward to make a groove that, if the embryo is to become a chordate, will steadily work itself into a spinal column, while other foldings, unfoldings and sproutings of increasing intricacy form the head, limbs, muscles, organs and detailed features of the being-to-be.