The Seven Mysteries of Life

by Guy Murchie

  By such a process all animals literally organize their organs and themselves. So do human embryos, dramatically increasing their weight ten-thousand-fold in the first month. And I note with interest that the body's original single opening, the one that formed when the blastula dimpled inward to become a gastrula, first served as a mouth that was increasingly expected to double as an anus until, this crudity becoming intolerable, a new mouth broke through at the other (now forward) end, at last permitting sensible throughway digestion. Later feelers, nose and ears appeared (also forward), followed by the eyes. At the same time undoubtedly appendages of locomotion were developing (aft) through relentless trial and selection - tail, fins, flippers, legs, toes, wings - to produce the million-odd different creatures we know today. One can readily recognize the main phases in human embryos, whose heads bulge like bladders in their early liquid period, only gradually solidifying, and who, like others, have gills and flippers before they develop lungs and hands. By the time he is halfway to birth, obstetricians point out, the human fetus has learned to move and turn and kick, to drink his surrounding fluid and, in some cases, to suck his thumb, practicing for the outside world. When he is hurt he will cry, strengthening his lungs with liquid breathing. At eight months he can hiccup, sneeze and begin working his kidneys and bowels. Although he sleeps most of the time in the womb, he intermittently wakes and hears continuous throbbings, rumblings, occasional voices, scary bangs and soothing music from another world. There is even evidence that he may see changes of reddish light and darkness through briefly opened eyes. And a doctor in Toronto, watching unborn twins through a fluoroscope, saw them actually fighting.

  THE ORGANIZER

  The mechanisms hidden within such a miraculous luxuriation of flesh and function were almost completely unreachable until Spemann, still experimenting, made his greatest discovery in locating specific growth spots he named "organizers," which at every developmental stage proved to be the actual inducers of the next step. The salamander eye, for instance, begins as a tiny swelling upon its brain sprouting a stalk with a cup at the end that soon reaches nearly out of its skin. The stalk does not have to go farther because the cup is a potent organizer that promptly induces the nearest skin cells to dip down into it and form an eyeball: transparent lens, cornea and all. Spemann even demonstrated the cup's power by embedding one from an embryo salamander under the skin of its belly, with the result that the following week he had a baby salamander with a belly eye!

  The same kind of induction, as he called it, is known to multiply a fertilized egg's cells through the blastula stage, in which the "dorsal lip" of its indentation becomes the "primary organizer" of the future body by defining its spinal axis. If any very young embryo tissue is grafted upon such an organizer, Spemann found, it will be organized into a new organizer, which in turn can induce new specialized growth, including the sprouting of an entirely new embryo. In certain situations even organizer tissue that has been established as "dead" by all the standard tests will still induce some such development in a graft. In others a normally living organizer may kill its brother cells by the thousands in order to shape a living body - producing, for example, a frog by degenerating a tadpole's tail, a development sometimes called ungrowth. A striking example of ungrowth is Pseudis paradoxa, a species of frog in Trinidad who ungrows to such lengths that when he 15 an adult frog (measuring two inches) he can be literally less than a quarter as long as he was just after he lost his tail when a juvenile frog (almost ten inches).

  All kinds of cases could be cited of the ways of organized development, for there are whole hierarchies and successions of organizers that step by step turn the gastrula's outer layer of cells into skin and nerves, its inner layer into lungs and digestive tract, its ensuing intermediary layer into bone, muscle, blood. The organizer seems to give orders that a basic structure be made, trustingly leaving it to local influences to produce the details, as was pointedly demonstrated when Spemann grafted a piece of prospective brain from a frog embryo into the prospective mouth region of a newt, which then obligingly grew a usable mouth in the right place. Yet, surprisingly, it turned out to be not the toothed mouth of a newt, but unmistakably the gaping mouth of a frog. All this suggests that the genes, whatever they are, act something like tones in a tune. Certainly they have a time axis of some sort, each following and fuffilling the gene before it as if they can somehow sense that they are unit parts of a sequential whole, footsteps in a procession, notes in the melody of life.

  His experiments understandably gave Spemann's laboratory something of the reputation of a "monster factory," but they were only the most prominent among several similar early research efforts in the field of growth which continued to make significant discoveries, such as that if you cut off a shrimp's protruding eye, leaving the nerve ganglion in its stalk, a new eye will grow out of it - but if you amputate the ganglion along with the eye, an antenna will sprout in place of the eye. Or if a mantis's antenna is cut off, two sections from the head, a new antenna will regenerate, while, if only one section of stump is left, a leg will grow instead. Findings of this kind reinforced the conclusion that body cells have full repertoires of potentialities within their genes and that they depend on local organizers only to decide which potentiality to materialize. This points to an interesting genetic variant of the ancient Mosaic Law of an eye for an eye and a tooth for a tooth, which may have to yield place among some creatures to a wider range of possibilities, perhaps even more fantastic than this automatic substitution of an antenna for an eye or a leg for an antenna.

  GENETIC PUZZLES

  It may be worthwhile to take a quick look at regeneration in general, which seems to be a fundamental organizing property of living matter. Why can a salamander regrow an amputated limb when a mouse cannot? The significant difference between these animals must be in the degree of their evolvement or specialization. A primitive creature such as an ameba is, so to speak, a blob of unspecialized goo, more than 95 percent of which, as we have seen, can become a foot, mouth, nostril, stomach or anus as occasion demands. Its protein and other protoplasm seem as flexible and uncommitted as a batch of freshmixed cement. But a slightly higher form of life - say, a hydra - is specialized at least to the degree of maintaining a tentacled form. Although here again almost any sizable piece of flesh cut from the hydra will regenerate into a whole new hydra, the tentacles turn out to be an exception and will not grow into hydras because they have become too specialized, having in some genetic way committed themselves beyond the capacity for that much adaptability. The age of the individual organism of course is a major factor, for its early growth swiftly repeats its ancestors' evolutionary history, with the primitive, simple, embryonic stages retaining much more regenerative potential than will later be possible to the mature, specialized, complex animal. In consequence any creature, including a human, may regenerate any part if called to do so early enough; identical human twins, triplets, etc., are nothing less than a single embryo that broke into two or more pieces, each of which then regenerated into a complete human being. In the case of the famous Dionne quintuplets, the original female embryo is known to have split into five parts in 1933, every one of them developing into a consummate woman by 1950. That is, five full skeletons, five human brains, five pairs of seeing eyes and hearing ears and the complete bodies and minds that go with them - all springing from one disintegrated embryo under what was left of its own guidance.

  The older or more developed an embryo is, of course, the less it can regenerate any lost part. Yet it has been found that in some mysterious way the inhibiting effect of age can be largely offset by artificially increasing the number of nerve fibers at the site of required regrowth, which seems to indicate that the nerve impulse conveys not only information but a stimulus actually vital to growing. Electricity is an important factor here too, working specifically through the natural flow of electrons in skin over a stump. Even artificial electric current applied from outside is known to have accelerated the
healing and regenerative process in many cases. There is a limit to it though for, beyond a certain stage of development, the only hope of recouping a loss has been found to be by grafting - and grafting in turn has its own narrow limits attributable to the long-known reluctance of any flesh to accept any other kind but its genetic equal, which has traditionally meant flesh from either the same body or that of its identical twin.

  The most obvious reason for flesh's inhospitality to strangers is the need for a defense against abnormal growths, such as tumors or invasions from outside, particularly the subtle intrusion of germs and viruses. But immunity is not all that simple. In fact the new science of immunology has sprung up mainly to deal with its spreading complexities that involve the body's production of defensive protein molecules called antibodies. For, although the antibodies usually do a good job of disarming dangerous invaders, they cannot unaided discriminate between good invaders and bad, and naturally tend to oppose helpful ones such as a transplanted kidney even when that kidney represents a last hope for life. That is why modern researchers have made a major effort to learn how to control the antibodies by typing, studying and comparing them. From their viewpoint the immune system is one of the most important organs in the body - and it weighs two pounds.

  Another and even more fundamental approach to this basically genetic problem has resulted in the experimental procreation of a black-and-white-striped mouse who genetically had two mothers and two fathers ... It was done in 1964 by mixing and transplanting genes from the fertilized ova of two newly pregnant mice, one black, the other white, to assemble the first four-parent creature in history. Later other experimenters went a step farther to produce a series of previously "impossible" hybrid creatures by using viruses to integrate the genes of species as classically disparate as mice and men and, very recently, of a chicken and a tobacco plant to create the first artificial cross between a plant and an animal, a so-called plantimal that lived for five hours! The viruses that made this possible were of infectious strains that, for some reason, are wont to dissolve cell membranes wherever two cells touch, at the same time fusing what remains of the membranes into a single composite membrane around what has thus become one compound cell with two nuclei. Since there are no antibodies or other mechanisms for recognizing incompatibility within a single vertebrate cell, such corralled nuclei do not reject each other, and even larger hybrid cells with three entirely different nuclei have been created, which produced daughter cells that thrived and continued duplicating themselves.

  THE VIRUS

  Part of the explanation for these phenomena is in the nature of a virus (page 102), now known to be the smallest biological structure possessing all the information needed for its own reproduction, and whose discovery finally filled the perplexing gap between molecules and organisms. In a sense a virus is a gene with a coat on, out wandering about the world, for its core is made of either deoxyribonucleic acid (DNA) or its subsidiary ribonucleic acid (RNA), carrying hereditary information and wrapped in protein. Yet it is far from complete unto itself - in fact it is a very special but fundamental kind of parasite that cannot reproduce itself without entering a cell and using the cell's own genetic and reproductive machinery. For this reason its protein coat is often equipped with chemicals enabling it to dissolve cell membranes (as mentioned above) presumably to assure it of admittance to a host when it finds one.

  Most of the time a virus just lies around as an inert crystal, "lifeless as a rock" and perhaps staying that way for centuries or millenniums. Yet, unlike a rock, it may "wake up" at any moment. All it needs is the warmth and moisture of some vulnerable cell that it can swiftly enter and infect, in the same motion reproducing itself hundreds of times within the hour - in some cases (apparently by chance) breeding a new type of offspring that may spread fast enough in a year to kill 20 million people, something a new, deadly influenza virus actually did as recently as 1918. The submicroscopic size of most viruses of course is the most obvious factor in their ability to slip inside cells, For notwithstanding the fact that they are gigantic compared to the simple molecules of water, air, etc., their atoms numbering in the millions, they are still so unbelievably tiny that one quintillion of them could fit inside a Ping-Pong ball. And if this spatial comparison makes little impact on you, you can make it a temporal one by realizing that, if the viruses had commenced pouring into a Ping-Pong ball at the supposed beginning of the universe (18 billion years ago) at a steady rate of one virus a second, the ball would now be only half full.

  Of course not all viruses are the size of the polio virus used in the above calculation. In fact some are a thousand times bigger, yet would still need 30 million years to fill the Ping-Pong ball. And others are eighty times smaller and couldn't fill the ball in two trillion years.

  Significantly it took only thirty years for science to figure out the structure of the newly discovered viruses through electron microscopy, x-ray diffraction analysis and other sophisticated methods. It is now known that these infectious particles are assemblies of identical protein subunits stacked symmetrically around cores of nucleic acid into the shapes of gemlike polyhedrons, including some of Plato's five famous regular solids, plus prisms, spirals and a few more complex forms. The smallest virus yet discovered is made of nothing but a core of nucleic acid (RNA), while another, a little larger and known for its beauty, is the polio virus, a dodecahedron of 12 perfect pentagonal facets, probably made up of 30 spherical subunits. Another is the polyoma virus of rodent cancer, an icosahedron of 20 equilateral triangles composed of 42 hexagonal prisms. The tobacco mosaic virus is like a long tubelike pine cone with 2130 protein "seeds" in a continuous spiral, the mumps virus a spheroid full of endless helical RNA "spaghetti," the influenza virus perhaps something of a bristling "sea spider" (page 92) around a coiled core, the T4 virus a kind of hexagonal mosquito with 6 leglike triggers and a beak for injecting bacteria.

  One is apt to think of viruses as swimmers like amebas, propelling themselves where they wish. But actually they are generally as inert as grains of sand and get to their destinations only by being swept along willy-nilly in their surrounding tide of liquid, occasionally following magnetic gradients but continually buffeted by the agitations of molecules collectively known as Brownian movement, in trees wafted by sap, in animals by blood and lymph, in the sky by wind and rain ... Nevertheless, through patient willfulness or blind chance, they get wherever they are going and a percentage of them manages to attack their prey like a pack of dogs around a bear, as in the case of the T type (also called the bacteriophage or "phage" for short) that punctures a bacterium with its syringelike beak to pour in its DNA. Such an attack, interestingly enough, is as much rape and suicide as it is murder, for it injects genetic material that merges with the bacterium's own genes, while neither the virus nor his victim survives the act. Once the long thread of viral DNA has been shot into the bacterium, you see, the virus's residue of protein is but an empty husk, and the injected DNA disintegrates in the very act of insinuating itself into the bacterial genes, somehow deceiving them into accepting it piecemeal as parts of themselves. Although there is no remaining sign of the virus in the bacterium, since it has fused with the nucleus already there, about 20 minutes later new viruses begin to form by the hundreds and within 30 minutes the bacterium pops open like a burst balloon, liberating a horde of viral offspring identical with their virus "father," who only half an hour ago raped their "foster mother," whose torn corpse now is all that remains of "her."

  Although such a virus attack on bacteria is very common, it is not always so one-sided. Indeed there is at least one species of bacterium, called Flavobacterium virurumpens, that lives in mud and can kill viruses, specifically the tobacco mosaic virus, which it attacks with enzymes at certain points in the spiral protein coat, literally dissecting it into irregular clusters of one or more of its 2130 "seeds." Not many kinds of viruses are yet considered exactly "good" by man, but one kind "infects" tulips with beautifully colored patterns t
hat increase their value, and another stopped the midcentury plague of rabbits in Australia with frightening efficiency.

  Undoubtedly man's greatest benefit from viruses, however, is what they teach him about genetics, because viruses are the simplest of all reproducing creatures. In fact geneticists already have such a detailed concept of viral genes that one of them states that the difference between a mild virus and a killer could be the replacement of only 3 of 5,250,000 atoms in a particular species. All sorts of viral crossbreedings can be made experimentally by letting different varieties of viruses simultaneously infect the same cell, the offspring often inheriting traits from more than one "parent" through this most primitive level of "sexual" intercourse. Also, since it has been proven now that viruses can cause and cure certain kinds of cancer, evidently by changing the genes of cells (a phenomenon called mutation) and, since science is learning to influence mutations (by radiation, etc.) as well as to manipulate viruses, it looks as though viruses may soon be made to order by man, possibly including some that will destroy cancer cells but leave normal ones alone.

  DISCOVERY OF THE GENE

  To round out the genetic story, we need now to look back to the mid-nineteenth century when the first great discoveries about genes were made. It was in Brunn in Moravia (now Brno in southern Czechoslovakia) that a young Augustinian monk named Gregor Mendel, who had studied mathematics at the University of Vienna, experimented methodically with peas and other plants, trying to find out the laws of inheritance. The accepted belief of the day was that animal and human heredity was directly transmitted through blood, while vegetable heredity presumably worked through some element in plant juices, the progeny in either case receiving a mishmash of all their ancestors' characteristics. On the-rare occasions when black-haired parents unexpectedly had a baby with red hair it was supposed to be because the baby somehow miraculously happened to derive a few drops of relatively unmixed blood from a red-haired ancestor further back. If a red flower that had been crossbred with a white flower produced pink progeny it was because any red liquid mixed with a white liquid must yield some blend of pink. Charles Darwin, aware of the naivete of these notions, which, if true, would have progressively eliminated the natural variations in organisms on which (he had discovered) evolution depends, had been experimenting quietly with plants for years in a serious effort to learn precisely how colors and other traits passed from generation to generation, but his results were inconsistent and confusing, eventually leading him to abandon the project in favor of more promising lines of endeavor.