Ever since the spark of life first flashed into existence on our planet, living things have expanded their domain, invading and making one habitat after another their own. The result has been a triumph of evolutionary change and a world of organisms so complex and varied that all living things should really be regarded as astonishing. Some living things, however, lead such different lives from the ones we have experience of that, from our narrow vantage point on the land, they appear almost alien. The ninety-seven creatures that populate these pages represent, in one way or another, the outer limits of life’s progress, and astonishing creatures they are indeed.
Despite three and a half billion years of evolutionary invasion and advance, the realm of life remains circumscribed, for it’s still only the skin of our heavenly sphere that is softened with a dusting of living things. The bacteria and other micro-organisms have ventured farthest. Some eke out an existence in the pores of rocks situated around ten kilometres in the Earth’s crust, while others are regularly hoisted by winds and currents a similar distance into the upper atmosphere.
Multi-celled animals, however, can exist only in a small part of this life-zone, and vertebrates—the creatures that are the focus of this book—are even more limited in their distribution. Despite the fact that man has touched the Moon, and vultures have collided with passenger jets 11,300 metres above the Earth, vertebrates can thrive only in a zone that ranges from the bottom of the Marianas Trench (a depth of around 11.2 kilometres) to a height of around 6400 metres in the Himalayas. The record for deep-living is held by an unidentified flatfish which was glimpsed by two submariners through the tiny window of a submersible as it touched down at the deepest point on Earth. In contrast there is a small, dull bird known as the wall-creeper (Typodroma muraria) which hops about among the bare rocks and scree slopes that sherpa Norgay Tensing and Edmund Hillary traversed in order to conquer Mount Everest. It says much about our ignorance of this living planet that we cannot identify the fish glimpsed at the bottom of the ocean, and that the next deepest record of a fish is from two kilometres nearer the surface—an undistinguished bag-like creature known as Bassogigas profundus.
If these are the geographical extremes to which life has pushed, there are other extremes as well—extremes of diet, of reliance on mysterious senses, and of sexual attraction. And it is the vibrant success of living things and their myriad ecological niches that has inspired this book.
Before embarking on our investigation of these natural wonders it is necessary to trace life’s long journey, from its obscure origins to its present success, for only then will we see these creatures in context. The expansion of life in time and space is, according to evolutionary biologist Michael Archer, “the saga of a four-dimensional bio-blob” (the fourth dimension being time), which is forever ramifying, splitting and terminating at the ends as it weaves its way through the obstacle course of extinction and opportunity that Earth has provided. Because all life shares a single origin, that bio-blob had to begin somewhere, and at some specific time, yet our knowledge of these matters remains frustratingly dim. Even the fundamental issue of which planet life originated on cannot be resolved at present, for some astronomers hold firmly to the view that life began on Mars and was carried inside rocks blasted from the red planet’s surface some four billion years ago.
Wherever its ultimate origin, life must have taken hold at a specific time and a specific place on the Earth’s surface. It seems to have done this so long ago, however, that at our current remove in time we have little hope of pinpointing that origin. Almost no rocks survive from that distant period, and many of those that remain are so distorted by pressure and heat as to have destroyed all fossils. And, of course, any fossils would be microscopic and simple in structure. These difficulties, and many others, mean that we may be doomed to live with an uncertainty of hundreds of millions of years in pinpointing the moment that earthly life began.
Mapping the precise geographic origin of life looks equally hopeless. Perhaps its cradle was a contained environment—a saline pool or a sandy beach, for example—or perhaps it was an entire ocean. Even the type of environment likely to have nurtured life’s first spark is contested by scientists. Some claim that the bottom of a frozen pool was the most likely spot, while others give the honour to volcanic vents in the ocean depths or the shores of the first oceans, where the sand acted as a sieve for the molecules that made life. The truth is we simply don’t know.
Wherever and whenever it happened, we do know that by 3.5 billion years ago our earliest ancestors (along with the ancestors of all living things) had established themselves on planet Earth, because it’s at this period that we find the earliest fossils. They are simple, single-celled xspecimens, but they inform us unequivocally that life was in existence within a billion years of our planet’s formation. Although considerable biochemical advances were made over the next three billion years, life remained microscopic. The first cells to possess a nucleus (where the chromosomes are stored) had evolved by 900 million years ago, and the sexual act was performed by them for the very first time. This last was a miraculous advance that greatly hastened life’s progress, because sex gives life variety (by this I mean that children are not just clones of their parents), and out of variety evolution can forge new species.
By 700 million years ago life had spread through the shallow waters of the oceans forming a thin, living soup of varied, complex, yet still mostly microscopic things. Some organisms lay on the surface sediments and formed recognisable structures like algae-filled mounds and bacterial films. More complex hydra-like creatures perched among them, and the waters themselves were filled with tiny floating beings. Then, rather suddenly around 600 million years ago, the pace of change picked up again. The first complex animals—the so-called Ediacaran fauna—sprang into existence. Now, had you swum in those early shallow seas, you wouldn’t have needed a microscope or magnifying lens to see life, for some Ediacaran creatures were true giants. One flatworm was nearly a metre long, while some seapens waved forty centimetres above the seafloor on which they were rooted.
The Ediacaran animals are diverse. As well as flatworms and seapens, some look like jellyfish while others resemble sea anemones. So obscure is their biology that researchers cannot agree on what they are, some claiming that even the most animal-like are nothing but bizarre marine lichens! Yet it is certain that they all lived suspended in the ocean’s sunlit waters, or lay gently on the shallow sea floor. The Ediacaran animals thrived for 58 million years, but 542 million years ago a revolution occurred. Life evolved a wondrous new capacity—the ability to grow a hard coating, and with that came the ability to dig and burrow. Soon a great host of creatures were turning the ocean floor into a turmoil of burrows, troughs and pits. This was a major breakthrough, for now the ocean sediments themselves became a prime repository for life. From this point on, the ability of life to adapt and diversify accelerated markedly.
Around 420 million years ago plants began to grow on land, greening the moister parts of the continents, and by 400 million years ago came the first creatures to venture onto land—the scorpions and their relatives, which hitherto had dwelt in the sea. Within 20 million years of this signal event fishes began to gulp air and 15 million years later some of these gulpers xii began to squirm out of the water and drag themselves through the shallows, eventually to colonise the dry land. Primitive insects crawled out of the sea at around the same time, and between 350 and 320 million years ago some began to develop wings, and so it was that life took to the air. From ocean to sediment to land and finally to air, life now occupied all of the major realms open to it, but still it continued to diversify, strengthening its grip, and giving our third planet from the Sun its unique signature.
A vital part of that process has been the creation of ever more living space for life, by life itself. Parasites have been perhaps the most direct beneficiaries, and they have become so prevalent and abundant that living bodies are almost like miniature planets colonised by ever tinier living things. By way of illustration, it’s been estimated that 10 per cent of the human body—even a well-groomed one—is made up of cells belonging to non-human parasitic or symbiotic organisms. They are a host of aliens inhabiting our body that we cannot rid ourselves of or indeed live without, for many help us perform vital functions such as digestion.
So interwoven are the tendrils of life’s four-dimensional bio-blob that Earth is considered by many scientists to be a single living entity that controls its temperature and the composition of its atmosphere so as to maintain optimum conditions for itself. The mechanisms are complex, but they include the photosynthesis of plants and the use of carbon by living things such as coral reefs. Because carbon dioxide is a greenhouse gas, taking it out of the atmosphere affects the Earth’s temperature. The scientist James Lovelock dubbed this great living, self-regulating entity Gaia, after the Greek personification of the Earth.
It is curious, though, that life has not leaped over all of the barriers that our planet has presented with equal alacrity. The various contexts in which life exists—water, the land’s surface, the air, and in the sediments themselves—present very different challenges and opportunities. Let’s consider that vital transition from water to land. The first step in making this transition was doubtless made by a fish, perhaps an inhabitant of a stagnant pond—and it involved gulping air. Thus the lung came before the leg by over 10 million years, but it was to take many more millions of years before other life functions could be performed by land animals. Judging from the habits of crocodiles (which must take their food into the water in order to swallow it), learning how to feed on land was a long and tortuous process. But it was reproducing in the absence of water that was the most difficult barrier to cross. The hard-shelled (amniote) egg was the key to success here, and it first appeared many tens of millions of years after the first fish hauled itself ashore.
The same sort of pattern can be seen in the transition from land to air. Although flying first evolved between 350 and 320 million years ago, to this day many flying creatures cannot feed while on the wing. And despite the 200 million years that have passed since the first vertebrate (a flying reptile known as a pterosaur) took to the air, not a single species has ever developed the talent of completing the reproductive cycle aloft.
We do not need to leave the solid surface of Earth to encounter many extreme and extraordinary environments, which even today remain virtually unexplored. Yet more people have been to the Moon than have been to the bottom of the ocean, and we know more about our satellite’s dark side than we do of the creatures that inhabit the Marianas Trench. We think of the ocean—with its intense pressure, cold and eternal darkness—as an incredibly hostile place, though in reality it’s the largest single habitat on Earth. Based on size, it is the land-dwellers that inhabit a marginal environment, and for the countless billions of creatures of the uncounted tens of thousands of species whose home is the ocean deep, conditions on land would seem as deadly and outlandish as those of outer space itself.
The changes life has made in order to survive in various environments are not always readily apparent to us. Consider the deep-sea fishes. Most people don’t realise that many of them have pathetically weak skeletons and terribly flabby bodies—in extreme cases they’re reduced to an almost gelatinous consistency, and seem to be composed merely of mouth and stomach. This is because so little food exists at such great depths that when it arrives it must be eaten come what may. Sometimes it arrives in the form of a creature larger than the predator itself, which accounts for the wicked-looking fangs and expandable stomachs of many deep-sea fish. This lack of food means that many deep-sea species do as little as possible between feeds in order to save energy. Researchers have discovered recently that parts of the deep ocean experience a “rain” of debris from the sunlit layers above that coincides with the spring plankton bloom, which forms an annual bounty that must keep many species alive until the next “rain.”
It is not necessary to live in the ocean depths for food to constrain your evolutionary development. The aye-aye (a lemur from Madagascar) and the great-tailed triok (a marsupial from New Guinea) eat similar foods—principally wood-boring grubs. Despite their very different origins they have evolved striking similarities of tooth, hand and tail in pursuit of their specialised diet. And a mammal (the long-beaked echidna), a bird (the kiwi) and a fish (a mormyrid) have come to share startling similarities through preferring a diet of worms.
Sex and magnificence are on intimate terms in the animal kingdom, sexual attractiveness being one of evolution’s greatest imperatives. Most of the spectacular birds featured in this book are males. This is because when it comes to reproduction, in most species it is the female that makes the critical choice. The male must provide what the discerning female eye (or nose or ear) wants. As a result, male birds of paradise have transformed their bodies into glorious if sometimes bizarre sexual attractions, often at the expense of escaping predators and feeding efficiently. But what is most astonishing about them is not that they attract female birds of paradise, but that they affect human sensibilities as well—eloquent proof of the idea that the aesthetics of beauty are shared by an astonishing variety of living things; a result, perhaps, of our common genetic heritage.
Not all male sexual appurtenances, however, are attractive to humans. It’s hard to discern the seductive powers of the “standards” borne by the standard-wing nightjar. Perhaps the female chooses the males with the largest standard feathers because they represent the greatest handicap to their owner. Although this sounds nonsensical, it makes good evolutionary sense, for the bearers of such “handicaps” are in effect proclaiming, “Look at me! I’ve grown into a big strong male even while carrying these cumbersome handicaps, so my genes must be extra good. They will benefit your daughters, who will not bear my handicaps, while your son’s handicaps will attract females as well!”
Despite our shared genetic heritage, our concept of beauty is largely dependent on the nature of our senses. We can appreciate the beauty of a bird of paradise because, like us, birds are visual creatures. For all their grotesquely, seadevils must be attractive to other seadevils, otherwise there would be none, though just where the attraction lies is beyond my reckoning. Perhaps it is scent, touch, or movement that makes the male seadevil swoon. Whatever it is, it’s a near-fatal attraction, for the male seadevil is tiny compared with his mate, and when he encounters her he does not seek to copulate, but instead bites her, never to let go. The two grow together, and in some species the male’s head becomes embedded in the body of the female. Nurtured solely by her blood, he becomes nothing but a dependent testicle that is somehow instructed by the female (perhaps through hormones) to release sperm at her command.
While the need for sex can lead to truly astonishing adaptations, a need for security can xvialso manifest itself in the most intriguing evolutionary strategies. The humble shield-tailed agama lizard has transformed its tail into a knobby door-stopper, while the flamboyant crest of the sail-tailed lizard may help it leap to safety. Vanishing is another form of defence. The bay owls are so good at it that one species, the African bay owl, remained unknown to science until 1951 when a single specimen was found. It was 1996 before another one was sighted. Some fish have elevated vanishing to an art form. The most spectacular disappearing acts are performed by pipefish and seadragons, yet outside their environment they are among the most flamboyant creatures imaginable. Some animals have even been driven to ignominy by their need to hide—witness the screaming Budgett’s frog, which looks like a turd left by a tapir at a waterhole.
We hope that this book provides an opportunity to consider animals outside the everyday perception of their place, and that of other creatures, in nature. Firstly consider how a dog lives—through its nose: tracking people by scent along a busy street, “smelling” illnesses such as cancer and somehow anticipating earthquakes, yet all the while seeing the world myopically in black and white. To imagine the very different life of the hairy seadevil, however, does lift us into another realm, for not only is its sex life bizarre but its habitat is too. Imagine living at pressures that would crush us in an instant, in a world of impenetrable darkness and frigid cold, where there exists no edges or ends—just an eternity of space.
When imagining such realms, remain alert, for things are not always what they seem. Even this book has its own trap. One of the creatures depicted here does not exist at all outside the imagination. I wonder if you can discover which one it is?