The Seven Mysteries of Life

by Guy Murchie

  ALTITUDE

  The vertical limits of known animal life in the earth's biosphere are of interest here, as relating to air and water pressure, which derive from gravitation. Life thins down drastically by the 20,000-foot level above the sea, and mountaineers in the Himalayas report seeing only a few kinds of birds above that height - an occasional eagle or lammergeier (eaglelike vulture), perhaps a snow partridge, some crowlike choughs (ranging to 27,000 feet) or a string of bar-headed geese flying over Mount Everest on their annual migration to the lakes of Tibet. Although mammals lack the very efficient lungs of birds, not only yaks but sheep (including domestic ones) wander as high as edible plants will grow, and cushion plants have been collected at 20,130 feet. Mice and conies sometimes get about that high too, expectably pursued by weasels, foxes, wolves and snow leopards. Choughs by the way commonly alight on the backs of sheep and search their wool for insects, a service the sheep encourage by patiently holding still as long as the birds are near. And jumping spiders have been observed at 22,000 feet preying on flies and exploited by parasites. And aphids, moths, butterflies, beetles and centipedes about equally high, as well as semi-microscopic glacier fleas, mites and springtails, not to mention bacteria or smaller creatures. This level is known as the aeolian zone, for most of these tiny animals ride gracefully aloft on warm rising winds, along with pollen and dust, including spores and minute shreds of fungus or lichen on which they may graze as hungrily as birds and rodents feed on them in turn.

  In light of the fact that the Air Force requires its flight crews to use extra oxygen above 10,000 feet, one might think that humans and other breathing mammals dwelling above that height could hardly live normal lives. Yet Tibet is largely 14,000 feet high and has many a bustling town above the common cloud levels. And I have seen reports of a permanent mining camp in Peru at 17,500 feet, where the air pressure is only half that at sea level, up from which men climb daily to work at 19,000 feet! There are also a few big cities with the pressure around 70 percent such as La Paz, capital of Bolivia, a metropolis of more than 375,000 people at 12,800 feet, the loftiest big city on Earth, with railroad stations, hospitals, department stores, a university and about everything else you would expect in a municipality the size of Miami. So life more than two miles up in the sky is sanctioned with a kind of normality - at least for an estimated ten million people here and there upon the scattered mountains of Earth.

  Life in the abysmal depths of the oceans of course is much more difficult to observe than at comparable heights above sea level. But the greater volume of habitable, oxygen-rich room down there may make it all the more important, for the area of Earth covered by water 2 1/2 miles deep is as vast as all the continents put together, and even the scattered abysses deeper than 4 miles total almost half the area of the United States.

  It imposes more than a little strain on the imagination to visualize life in the sea-bottom world of utter and inky blackness, of passing mysterious shapes and unexpected encounters, of eternal cold (perpetually less than ten degrees above freezing) and of pressures thousands of times greater than in the air. But that there is life down there we know without doubt, for fine steel nets on cables several miles long have hauled its organisms up to the light of day and Jacques Piccard and Lieutenant Don Walsh who descended in their bathyscaph to the nadir nigritude of the Mariana trench in 1960, the deepest abyss known on Earth and more than seven miles straight down, saw flounderlike flat fish at the very bottom blithely swimming through water under a pressure of seven tons per square inch, their carefree relaxation certainly attributable to the pressure being equalized inside and outside the body and its cells.

  Most abyssal animals, however, seem to be bug-sized burrowing forms such as bristle worms and brittle stars, mollusks, crustaceans and a few larger, crawling sea cucumbers. Fish with backbones remain very scarce below the top two miles because of the dearth of creatures they eat. And, even where they are plentiful about a mile down, their lives are made precarious by the fact that smaller edible creatures retreat into the darkness the instant they are sensed at a range of a few inches, while the fish themselves must flee in turn from bigger ones who want to eat them and, should they encounter still others of their own species but opposite sex, it becomes a rare opportunity for mating, with any effective choice between these alternatives requiring both discriminating decision and resolute action within a few seconds. And perhaps it was just such nerve-racking dilemmas that forced the evolution of the nightmarish denizens of the deep: the black swallowers and rattail grenadiers with needle-sharp fangs protruding through cheek holes even when their huge mouths are shut, and whose stretchable balloonlike bellies permit them to specialize in devouring unsuspecting fish twice their own size; the gulpers consisting of practically nothing but a swimming mouth trailed by a long lash ending in a red taillight that lures victims close enough so they can be lassoed by the lash and swished between the gaping jaws; and many other varieties of anglerfish with dorsal fishing rods from which hang lines with floats and luminous bait dangling in front of waiting teeth or, in a few species, displaying a tempting morsel even inside the already open mouth!

  Below the two-mile depth there not only are very few luminescent fish or predators of any kind but virtually none that graze on fresh vegetation, which is absent because of remoteness from the sunshine and photosynthesis on which it depends. This may be why life is found to be slower in rough proportion to depth with the deepest fish breathing and metabolizing at only one third the rate of upper fish. In any case the only reliable food below two miles is the steady "snowfall" of organic debris settling very slowly from above: crumbs of decaying seaweed, barnacle shells, shrimp skins, waterlogged driftwood and half-dissolved excrement full of bacteria, taking years to get there. Seldom does anything like an edible carcass slip past the upper scavengers - only a rare and fast-sinking dead whale or maybe the forty-foot remains of a giant shark or humans entombed in a broken ship.

  And not only are the creatures of the deepest chasms isolated by pressure and five miles or more of black water above them, but they are separated from all the other deeps of the oceans because of the vast subsea plains, plateaus and mountain barriers standing between these pockets with pressures far too low to permit them to pass over. Each abyss thus is like a solitary peak or ridge in reverse, a unique world that may have had no traffic with other such depressions for hundreds of millions of years. And the fact is shown also in the distinct high-pressure species dredged up from each trench, which in all cases have differed from trench to trench, each great abyss being the home of an entirely separate evolution, most of which are still so little known that it has not yet been quite ruled out that some one of them may have evolved a considerable degree of intelligence or conceivably even some sort of a sightless dexterity approaching that of man.

  TEMPERATURE

  If pressure is a factor imposing limits on life's domains on Earth, temperature must be an even more critical factor. Did you know that a brook trout will die at room temperature or a frog when as much as one leg is placed in lukewarm water for a few hours, and polyps that build coral reefs may perish from temperatures only one or two degrees warmer than that of the ocean in which they have lived all their lives? Even we adaptable human beings will rarely survive a fever of 9°F. above normal, because the fluid cytoplasm in body cells coagulates in heat almost as does the white of an egg being cooked.

  So animals have developed various ways of stabilizing their temperatures within tolerable limits. The one percent of them that are warm-blooded have the most elaborate physiological systems, which amount to remarkably efficient heat pumps and cooling radiators that use blood, lymph, sweat and air to transfer heat to and from the vital organs as needed - plus all sorts of supplementary devices, like the African elephant's wing-sized ears which, it is calculated, add an important 15 percent to his radiating surface when he holds them out from his head in hot weather. The much more numerous cold-blooded creatures such as fish, on the other
hand, simply seek to stay in water that feels livably cool or warm enough, which can be a hazardous problem, as it is often difficult to know which way to swim up or down a gradient of only a tenth of a degree per mile.

  Insects and land reptiles (not quite so "cold blooded") when exposed to the vagaries of the atmosphere, which is generally much less stable in temperature than water, must resort to many tricks of behavior to avoid roasting or freezing. Thus the greater earless lizard of the southwestern United States has been found, when active, to keep its temperature within 3.3°F. of its day mean of 101°F. 75 percent of the time. It does it by basking judiciously, by sensitively orienting its body at right angles to the sun's rays when it feels cold and therefore needs to absorb heat at the maximum rate. Later, as it warms up, it progressively turns more nearly parallel to the daylight until, attaining its normal temperature, it is directly facing the sun and exposing a minimal surface. Should its temperature rise uncomfortably higher, it will purposefully move into the shade of a rock or bush for a while to cool off, sometimes climbing into the branches to get away from the hot ground. And in the evening it is fond of burrowing into warm sand, tucking itself snugly under a granulated quilt for the night. In the morning, rather charily it will poke its head out into the sunlight, the while keeping the rest of its by-then-cooled body still under the covers, discreetly waiting until the sun has heated the blood coursing through a large sinus in its head enough to raise the temperature of its whole body. Only after it is thus prudently preheated all over does this wary reptile shake off its remaining bedding to venture forth primed for possible emergency speed and efficiency.

  Snakes do better than lizards in some ways, their long flexible bodies enabling them to expose more surface (per unit of mass) when they want to absorb or radiate their heat yet without forgoing their capacity to condense (by coiling) into a compact mass at noon or night or whenever they want to conserve either coolth or warmth. Another animal device for temperature control is having a skin that can change color or shade. By such means, many small reptiles and amphibians turn paler when hot, thereby reflecting more and absorbing less of the sun's rays.

  Heat adaptation being vital to the diverse thousands of species of desert animals, it is not surprising that they have evolved a wide variety of drought strategies such as the spade-foot toad's way of sleeping through the nine driest months in a burrow sealed with his own jelly, the zebra's sniffing out and digging wells in dry stream beds, the tortoise's storing of a summer's supply of water in two sacs under his upper shell, the elf owl's quenching of thirst with wet spiders, the rabbit's sipping cactus water while radiating body heat from his giant ears, the deer's cooling himself with belches, desert birds nesting not according to sun declination but at the coming of rain, the bats that fly each spring to a cooler clime. And there are at least twenty species of desert fish swimming in the permanent oases, lungfish that sleep through long droughts caked in dried mud, eels that slither through wet grass at night from well to well, and dozens of kinds of snails and shrimps creeping and wiggling in brief puddles all over the desert after a rare downpour who, before drying up, lay eggs that can wait for decades, perhaps centuries, in the parched salty soil to hatch whenever the next rain comes.

  But the animal most famous of all for its adaptation to drought is surely the Arabian camel, whose introduction as the ideal vehicle for desert transport, probably during the second millennium B.C., brought the incense land of Sheba into practical contact with Egypt and Babylon - a welcome and dramatic change after the age-old frustrations of trying to drive parched and emaciated donkeys from oasis to oasis, as did the Jews in their 40-year exodus. Camels have long been reputed to have a special water reservoir in their humps or, as some say, in their "fifth stomachs," but camel research in the Sahara in the 1950s by Knut Schmidt-Nielsen and others since has not revealed any such localized container. The fact that healthy camels can go without drinking for months, particularly in winter, and still refuse good water when offered it (as they sometimes do) does not prove they have been tapping a secret internal storage tank. For many animals from goats to desert rats can get along nicely without drinking, and even a human can abstain comfortably in cool weather if he eats plenty of juicy vegetables and fruits and does not sweat. But in warm weather, particularly if he exercises, a man must lose water from his body so fast that he is likely to want to drink several times a day. This of course becomes inevitable in very hot weather if he is to keep his temperature within a couple of degrees of normal through the cooling effect of moisture evaporation, for a man suffering from heat cannot lose even 12 percent of his body weight in water and hope to survive. As he gets drier, his blood literally thickens and eventually becomes so sticky that his heart is overworked and his circulation too slow to conduct his internal heat to his skin, which throws him into a runaway fever that quickly accelerates into what is called "explosive heat death." If you "oiled" an engine with glue and neglected its cooling system, no doubt something similar would befall it.

  The camel circumvents such a disaster, however, by keeping the loss and evaporation of his body water to a minimum. He does this through such devices as highly efficient kidneys that use much less water to eliminate the same amount of uric waste and a wonderfully specialized liver that sifts out a goodly portion of such wastes before they even reach the kidneys by shunting them back through the blood to the stomach for digestive reprocessing (along with incoming lowgrade fodder) into new protein. He also largely seals off the watery plasma of his blood from the rest of his body water by means of albumin, so that he can be dehydrated to the extent of 25 percent of his normal weight without appreciably thickening his blood. And he saves a great deal of water by sweating much less than horses, cattle or men, which he manages by a delicate combination of heat insulation in his efficient camel's-hair coat and his hump that places reserve fat where the sun beats most fiercely, and less insulation where he has almost no fat on his flanks, belly, neck and limbs, from which in consequence any excess heat can radiate away most easily. Despite all this, however, the camel's temperature rises as much as 12°F. during a hot day. Yet the very fact that he can tolerate 105°F. internally Without feeling feverish or losing strength saves him the evaporation of sweat or breath it would cost to keep him cooler. On the other hand, his ability to cool down to 93°F. on chilly nights - a kind of semihibernation - spares him both energy and the inevitable evaporation that would have been added if he had stayed warmer. This fluctuation may give you the impression that a camel's temperature is unregulated, but actually it is confined within strict limits, for his body will sweat hard to avoid rising above 105°F. and, if he has free access to water, he will seldom get warmer than 100°F., while 93°F. is his bottom limit, than which (until he is dying) he may cool no colder.

  As for animals' ability to withstand heat without dryness, probably the palm should go to an odd fish called Barbus thermalis who lives in the warm springs of Ceylon at temperatures as high as 122°F. Or maybe to a pond snail who dwells in almost equally hot springs, despite the fact that some of them contain a lot of sulfur.

  On the other hand there is a polar codfish named Boreogadus who swims about actively in saltwater at 29°F., several kinds of "ice fish" who do equally well in Antarctic seas (getting along virtually without red blood cells or hemoglobin) and penguins in Antarctica who routinely raise their families in air temperatures that sometimes drop below -100°F. And there is an insect known as Grylloblatta who looks like a cross between a cricket and a cockroach but dwells in the predominantly frozen soil of polar and subpolar mountains and is so far from being able to withstand normal insect temperatures that, if placed on a human palm, he will "burn" to death in a few minutes.

  A crucial factor in an animal's adaptation to temperature is the fluidity of his fats and oily juices (as distinct from his watery juices) for it has been noted that cold-resisting species like the northern salmon have a more liquid type of fat than tropical fish - that is, a fat with a significa
ntly lower freezing point that would qualify it as an antifreeze, four varieties of which have already been discovered in fish, all with a high content of the amino acid alanine. In addition there is the critical matter of enzymes which are very sensitive to temperature, slowing vital metabolism when too cool, enervating themselves by overactivity when too warm.

  Easier to understand of course is simple insulation, a vital boon to large animals yet amazing in its variety. While insects are too small to carry enough insulation to effectively stabilize their temperatures, birds and mammals have evolved the enfolding of wonderful mantles of air in their feathers and fur. Eskimos do something similar in wearing their fur parkas extremely loose, so body-warmed air can flow about their limbs. Deer fur in winter not only holds air between the hairs but each hair itself is hollow and sealed at both ends, so a protective snow blanket may lie unmelted upon a sleeping doe's back for days if she remains still that long. The insulation value of fat and flesh also largely explains why Eskimos tend to be fatter than people of warmer latitudes, and why arctic animals such as walruses, polar bears and ptarmigan have stockier necks, legs and tails than most tropical ones. This effect indeed has recently been studied in laboratories where mice raised at 90°F. (close to their blood heat) grow up scrawny with fine long tails while others raised at 60°F. turn out fat with stubby tails. Then, some animals solve the temperature problem by maintaining two internal temperatures: a tropical one for their main body mass and a semipolar one for such extremities as hoofs, tail, ears and nose, an expedient that not only reduces the heat loss of radiation from areas that do not need to be kept very warm but, for example, keeps arctic gulls' feet cold enough so they don't ever melt ice, which might risk their later becoming frozen in. It works through an extraordinary circulatory heat-exchange in which the warm arterial blood flowing toward an extremity is cooled by passing close to the returning cold venous blood, which, in the same exchange, is rewarmed preparatory to reentering the heated central parts of the body.