The Seven Mysteries of Life

by Guy Murchie

  The difference between sauna steam and boiling water of course is that the former is gaseous, the latter liquid. And, as any fish knows, a liquid is a very concentrated and penetrating medium to be in - certainly as compared with air or ordinary steam. It accounts for the fish's temperature sensitivity, especially since he is a "cold blooded" animal without the thermostat system of mammals and birds, who speed up their glandular and muscular activity (sometimes to the point of shivering) when their blood starts to cool, but sweat or pant to cool themselves by evaporation when their blood heats up. Lacking internal means of stabilizing body temperature, the poor fish must try to swim into water that has the temperature he wants, which means he usually heads down to cool down or up to warm up - often with only a few degrees of leeway between getting paralyzed with the cold or dying of the heat. The deadly seriousness of this problem to a fish was dramatically demonstrated at Harvard a few years ago when some goldfish were provided with a special and very delicate valve that could be pushed open by a fish, whereupon it would squirt cold water for a second into their bowl, lowering the temperature about half a degree. After a little training, most of the fish learned what the valve was for and how to use it. Then whenever their bowl got uncomfortably hot (above 96°F.), they would work the valve to cool it, and, when it was heated to 106° (which would kill a goldfish in a few minutes) they worked frantically, pressing the valve continuously and keeping at it until the water got back to their optimum 96°

  A few creatures living in air are about equally heat-sensitive in their individual ways. A dog's internal temperature is known, for example, to rise as much as 6°at the sight or smell of an approaching strange dog or human. And humans, using biofeedback and "thinking warm" (presumably to expand their outer capillaries), have raised the skin temperature of their hands as much as 15°F. If a dog (or human) sheds a few fleas and lice at such a time, it is presumably because fleas and lice are very sensitive to heat. In fact in some primitive societies lice living, in one's hair are considered a prime proof of good health because such creatures have been observed to abandon anyone falling ill with fever. The great bubonic plagues of medieval times are now attributed to infected heat-sensitive fleas fleeing from feverish rats or humans, since, by doing so, they obviously advanced the spread of the disease.

  The rattlesnake, in common with all pit vipers, seems to be a leading candidate for the championship in heat measurement (actually infrared vision) with his extremely precise thermal organ in each of two pits located between the nostril and eye on either side of his head, neatly focused to converge and overlap at striking distance a foot or so in front of him. Three thousandths of a degree Fahrenheit has been found to be the threshold acuity needed to alert the snake to any significant living presence in his neighborhood, to which he responds by turning immediately toward a warm-blooded potential prey or enemy, using his conical fields of heat vision to "see" the size, shape, motion and range of his adversary.

  In humans the senses of heat and cold are less acute than in most animals and are usually described as twin senses using differentiated sets of specialized nerve cells: a set of about 150,000 in the outer fiftieth of an inch of the skin to register cold and another of 16,000 deeper in the skin to register heat. While human skin fluctuates a good deal in temperature, averaging around 81°F., and doesn't seem to be thermostatically controlled like blood, a mysterious skin area has been discovered in the center of the forehead that registers temperature differences as small as one sixtieth of a degree. I haven't heard any anatomist associate it with the "pineal eye," an eyelike structure in the forebrain believed by some to be a vestigial sense organ or "third eye." But I notice that, in the case of hagfish, lampreys and a few reptiles, the counterpart of this lobe evidently evolved what have been described as "visual structural adaptation," and there is growing evidence that it produces at least a little actual vision.

  Probably the most interesting thing about this comparison of infrared and visual seeing is that these brother senses caught the world's attention only recently with the discovery that the hypothalamus is not only the body's thirst center and central "eye" of temperature awareness, but that, significantly, the temperature eye and the visual eye both evolved from the same matrix at the bottom of the third ventrical of the brain, out of which the visual eye moved forward to view the outer world, while the temperature eye turned inward to monitor the blood, their relation becoming one of the most elegant instances of sense complementarity in all the kingdoms of life.

  ELECTROMAGNETIC SENSE

  Every creature on Earth, including plants and probably rocks, seems to react to electricity one way or another and thus may be said to possess an electrical sense. Man certainly possesses it and, though the occasion seldom arises, he can feel static electricity accumulating in his body just before a lightning strike when he still may have the seconds needed to reach a safer location. A young couple who barely escaped death from lightning on a 10,400-foot peak in British Columbia in 1948 remembered afterward (in the words of the girl, Ann Strong) that "there was a slow, inevitable rhythm about it. After each strike we moved in silence for a while, with only the tearing wind and slashing rain. Then the rocks would begin a shrill humming, each on a slightly different note. The humming grew louder and louder. You could feel a charge building up in your body. Our hair stood on end. The charge increased, and the humming swelled, until everything reached an unbearable climax. Then the lightning would strike again - with a crack like a gigantic rifle shot. The strike broke the tension. For a while we would grope forward in silence. Then the humming would begin again ..."

  Some animals, notably about 500 species of fish, not only feel electricity but generate it in large enough quantities to use it either as a weapon or a sort of electric eye for "seeing" their surroundings and navigating waters too/murky for optical vision. Most spectacular of these is the electric (eel whose fifty-pound, eight-foot body may be stacked with half a million wafer-thin plates called electroplaques, hooked up in series to compose a living 1000-volt battery that can kill a horse. This has been known to happen in shallow South American rivers where horses ford and may step on an eel burrowing in the mud. Men have been killed too, in several cases drowning after becoming dazed and paralyzed from repeated shocks.

  The Nile catfish and the giant electric ray are two other dangerous electric fish, but most of the species generate too little current to mount an effective weapon, evidently using it almost exclusively as a sense system, of which they have evolved dozens of varieties. One variety, investigated in detail in an eel-like African fish called Gymnarchus, produces a spherical electric field around the animal with the negative pole in the tail and positive pole in the head. Such a dipole field clearly does not work on the radar principle of sending out radio waves to bounce off objects and return with information as to distance and shape - because radio waves don't penetrate water. But any objects near the fish do distort the paths of electrons circulating around the field, inevitably converging them toward those that are good conductors, diverging them from bad conductors, the distortions being "seen" by the fish through its many porelike electric "eyes" that are distributed about its body, especially near the head, and connected to internal nerve centers that lead to the brain. Like a bat broadcasting sonar (page 206), Gymnarchus thus puts out its field of electric current in pulses (about 300 a second), giving every sign that it visualizes the distortions as the shape of the surrounding world - with understandable supersensitivity to anything electromagnetic out there like, say, an approaching electric fish, who just might turn out to be an enemy or a mate. And, speaking of mates, many fish have recently been discovered to woo electrically, each of several kinds broadcasting its

  own characteristic pattern of discharge, through which not only its species but its age and sex can be recognized. One researcher, Carl Hopkins in Guyana, using equipment that converts electric signals into sound, reported that when a typical female fish (Sternopygus macrurus) ready to breed entered
the electrical field of a mature male, his "steady drone" changed abruptly to an electric serenade.

  While the research is still far from conclusive, there are also indications that electric fish may navigate long distances by sensing the intensity and angles, if not the polarity, of the geomagnetic lines of force they almost continuously cross in the ocean. Here of course we are dealing with the magnetic aspect of the electromagnetic fields that enclose and permeate the earth, even the illusive emptiness between them, and which incidentally make it easy to accept the accumulating evidence that birds, fish, insects and other navigating animals must be influenced by magnetism, even as that lowly mineral called the lodestone. It may be enough in fact to cite the pioneering work of Frank Brown, zoologist at the Marine Biological Laboratory in Woods Hole, Massachusetts, who showed in 1960 that the mud snail "could actually distinguish between different magnetic intensities and was also aware of the direction at which magnetic lines of force passed through its body." In any case, this breakthrough in biomagnetic research was followed by experiments on volvox, the planarian worm, paramecium, many species of insects from fruit flies to beetles, several kinds of birds, fish and man; and, in every case, the creatures tested showed reaction to magnetic forces. Planarian worms, for example, navigated along magnetic lines and repeatedly followed them within an angular tolerance of 15° And human subjects in darkness could actually "see" magnetic fields, particularly a rapidly alternating field that would consistently register on the retina as a luminous glow, a type of nonoptical (closed eye) image known as a phosphene (page 237). There is still plenty of mystery about these magnetic senses, but at least a promising clue turned up recently when it was discovered that protons in hydrogen atoms all over the earth align themselves like compass needles parallel to the geomagnetic field. For hydrogen is abundant in living tissue and the solitary proton in/the nucleus of each hydrogen atom, in effect a tiny spinning magnet a trillionth of a millimeter thick, just might somehow convey its bias to whatever organism it is in and so play the part of an infinitesimal compass.

  Such a hypothesis, at any rate, is reasonably consistent with the facts that the electromagnetic polarity of a frog embryo (and presumably of other embryos) is irrevocably fixed before it starts to develop a skeleton or a shape, and that seedlings grow faster when their roots follow magnetic lines leading toward a natural or artificial south pole. All animals and vegetables are believed to generate electricity and put forth associated electromagnetic fields that are important in the workings of nerves, muscles, heart, brain and other organs. And Dr. Robert 0. Becker, an orthopedic surgeon and researcher in New York's Upstate Medical Center, has said that "subtle changes in the intensity of the geomagnetic field may affect the nervous system by altering the body's own electromagnetic field."

  In animals and man this field is found to be negatively charged at the forehead, positive at the back of the head and down the spine, gradually becoming negative again along the arms and legs. How important such body polarity can be is suggested by Becker's experiment in reversing it in a rat - which knocked the animal unconscious. He also found that electric fields can significantly help the healing of wounds and that the electrical potential of the human head, comparable to the electrical charge in a thundercloud, is directly related to the level of consciousness - so closely-related, in fact that anesthesiologists have begun to use the discovery in determining when their patients are ready for the surgeon's knife.

  HEARING

  If the eye is the most notable organ for detecting radiation, many of whose sense variations we have been describing, the ear is hardly less important or complex as the outstanding organ of feeling - in this case feeling sound waves that mechanically vibrate the eardrum - and it may have an even longer evolution. At least its earliest discovered form seems to have been that of a simple balance indicator in primordial planktonic sea creatures who could not hear a sound. Known as a statocyst, it was a microscopic hollow cell containing an even smaller pebble of limestone, called a statolith, balanced on sensitive bristles so that, whenever the swimming creature got tilted, the pebble would roll toward the cell's down side, instantly triggering the down bristles' nerves and making them signal the animal how to shift back to an even keel. Such an organ hardly seems to have anything to do with hearing, yet, consistent with the interrelatedness of all senses, it evolved during hundreds of millions of years into the central gas bladder of modern fish which acts as a buoyancy balance or float to keep them at their accustomed depth in the sea. But it also vibrates when reached by sound waves, serving as an eardrum to convey hearable patterns through amplifying bones to the liquid channels of the inner ear, where they are transformed by hairs (more sensitive than the statocyst's bristles) into nerve impulses that go to the hearing center of the brain.

  This successful fish ear in some species can even be shifted into reverse, giving the fish a voice through muscular control of little drumstick bones that beat rhythmically on the bladder to "talk back" to whoever has addressed it. All fish and some amphibians in addition have an earlike organ along their sides known as the lateral line, through which they hear low-pitched sounds and feel water pressure fluctuations, including faint waves made by other fish - a sense indispensable to formation maneuvering in fish schools.

  By the time birds evolved some 140 million years ago, hearing had taken another step forward with invention of the cochlea, an improved inner ear shaped like a spiral seashell and containing ducts of fluid separated by delicate membranes that vibrate and move around a kind of microscopic empyrean harp called the organ of Corti in which (as adapted to the human ear) some 23,500 hair cells somehow transform sound's mechanical motion into electric current that conveys it through about an equal number of fibers of the auditory nerve to the brain, where it is consciously heard. The organ of Corti presumably has thousands of resonators, each of which, like a harp string, responds only to one precisely pitched note, and there is evidence that it works on the piezoelectric principle (page 45!). Certainly it is comparable to the retina, which transforms light waves from the eye into electrical optic nerve impulses and vision, but such organs are far too complex (not to say controversial) for detailed discussion in a book of this scope.

  Before the cochlea appeared, insects, living on land and in the air, evolved their own type of ear. Unlike the ears of fish, birds and man (all of which originated underwater), this bug ear had no fluid transmission of sound and therefore developed a simpler and more direct transition by running an auditory nerve from the eardrum directly to the brain. And it was this simple ear, I like to speculate, that heard the first messages ever uttered in the atmosphere of Earth. Three hundred and fifty million years ago it undoubtedly was much simpler than it is now, for it has evolved unceasingly, no doubt still increasing its sensitivity range in species after species, still trying out new body locations. The ears of moths and butterflies, for instance, are often in the base of their wings, mosquitoes hear with their antennae, and many kinds of insects have ears in their midsections, usually at the lowest point so they can detect the ground reverberating with the tread of terrestrial predators. Katydids, tree crickets and some grasshoppers, however, have slit-shaped ears just below their knees which are efficient for directional hearing because they can be widely separated and aimed in different directions, this being particularly important at mating time when males and females are out calling and sometimes work themselves up to the point of desperation to provoke positive and explicit responses.

  Some ears, as you've probably noticed, serve more than one purpose like the gigantic ones of the African elephant and the dainty fennec, a fox of the Sahara (see chapter heading, page 177), which not only hear acutely but act as radiators to dissipate excessive body heat. This must be true also of the spotted bat of Mexico whose pink ears are as long as himself, not to mention the earlike petals and leaves of plants which may "hear" music (page 640), while they transpire moisture, refract and reflect light, attract pollinators and function in
ways still unknown. Most aspects of vision have counterparts in hearing and other senses, you see, including aural camouflage and smell illusion.

  The range of pitches heard by various kinds of ears varies widely, each animal family tending to evolve the range that will enable it to hear its predators or prey soon enough to escape or attack, and between times to converse and mate with its own species. Humans, incidentally, have a hearing range from about 20 to 20,000 vibrations a second, with maximum sensitivity at around 3000, which, significantly, is the pitch of a woman's scream! But hearing capacity is not constant, varying from man to man to woman to child and diminishing with age and masculinity for, although a young girl may hear bats twittering at an ultrasonic 25,000 cycles a second (as an acoustic engineer would put it), her mother can hear only a warbler singing at 15,000 and her aging father barely catch the top note of the piano at 4100. In fact, tests on men in their forties have shown that the upper limit of human hearing descends inexorably at an average 160 cps (cycles per second) for every year lived.

  THE SONAR OF BATS

  The thought of inaudible, ultrasonic frequencies naturally brings to mind the echo-location technique called sonar that is used by so many high-pitched chirpers like bats, night birds and sea mammals. Bats, the most fantastic of these, have lived on Earth for 60 million years evolving some 1300 species from chickadee-sized ones to the "flying foxes" of Java with wingspreads exceeding five feet. Although they are mammals without feathers and cannot fly as fast as birds, they are champions of maneuverability - superior even to hovering chimney swifts and backward-flitting hummingbirds - for they can turn at right angles at full speed in little more than their own length.