story is grounded in reality. The limestone hills around Castleton really are as picturesque as he describes. There really is a semi-precious, purple–blue mineral called Blue John and, in the UK, there are only two places it can be found: Blue John Cavern and Treak Cliff Cavern, both of which hide under a triangular-shaped hill called Treak Cliff a mile or so away from Castleton. And Blue John really was mined. Indeed, extraction continues to this day albeit on a reduced scale—mainly to service the day-trippers who come to explore the show caves and marvel at the Blue John formations. (These popular visitor attractions repeat one of the details mentioned in Doyle’s story, namely that the Romans discovered these banded fluorite veins. In truth, there is no evidence the Romans were aware that Blue John existed in Derbyshire. The mineral was probably first mined in about 1750.) The background aspects of “The Terror of Blue John Gap” are, therefore, realistic. But how convincing is the main thrust of the story? Could the caves under Treak Cliff—or caves anywhere else for that matter—be home to a monster? 1910
The monster in Blue John Gap would now be classified as a
—an animal, according to the
Oxford English Dictionary
, “whose existence or survival to the present day is disputed or unsubstantiated”. Although not part of the
definition, size and aggression surely also play a role: when we talk about unfamiliar life forms we tend to think in terms of
creatures that might hurt us. As Doyle demonstrated, they make for the best stories. And there are many such stories. One book devoted to
—literally, the study of hidden animals—lists more than a thousand cryptids. Some are of world renown: surely everyone has heard of Bigfoot, the Kraken (see Fig.
), and the Loch Ness Monster. Most are of purely local fame—anyone heard of Amaypathenya, Batutut, or Chipekwe? (No, me neither.) What the book demonstrates, however, is that cultures all across the world tell tales of strange lake monsters or fearsome, hairy, manlike beasts. Given the prevalence of these stories, could they be hiding a grain of truth? Are cryptids creeping about out there?
The legendary Kraken, seizing an unfortunate ship. The artist Edgar Etherington produced this wood engraving to illustrate John Gibson’s 1887 book “Monsters of the Sea: Legendary and Authentic” (Credit: Public domain)
At first glance it seems unlikely.
The ubiquity of monster stories signifies little in itself—after all, the pervasiveness of ghost stories is seldom taken as proof of an afterlife. And, if cryptids
did exist, is it credible that hard evidence of their existence would be lacking? Earth is now home to 7.5 billion human beings, many of whom possess a smartphone, so if cryptids were around YouTube would be filled with amateur footage of Nessie and the Abominable Snowman.
And yet …
Biologists accept that they haven’t found every large creature currently living on Earth. As I was re-reading Doyle’s story, for example, a journal article announced the discovery on the island of Vangunu of a hitherto unknown giant rat—a rodent that lives in trees and feeds on coconuts. Biologists were only searching for the creature because of tales told by natives of the Solomon Islands. Of course, a nut-munching rat isn’t as exciting as Doyle’s monster but inevitably science will continue to uncover creatures that previously have been hidden from view. Indeed, since the turn of the century dozens of new mammals have been described. That’s just land-based mammals. The deep sea offers a vast unexplored reservoir of ecological niches. Scientists have yet to catalogue many of the creatures that live far below the surface, a region where sunlight doesn’t penetrate and pressures are high. It’s not impossible that some of the creatures who dwell in the deep are large beasts—sea monsters, if you will. (There are countless tales of strange sea creatures. As a young man, serving in the navy, my father kept a diary. An entry from 1960 describes a couple of sailors fishing one day in the Med. One of the sailors caught something and began to pull. A giant tentacle came out of the water, grabbed hold of the fishing line, and snapped it … The shocked anglers dropped their poles and ran.)
Although it would be unwise to bet on the existence of cryptids, and certainly on cryptids of the kind described by Arthur Conan Doyle, it’s not entirely unreasonable to believe “monsters” exist somewhere on our planet. And if a creature such the Yeti
were discovered, just imagine the peaks of excitement that journalists would scale! But what would be the impact of such a discovery on science? I don’t believe it would necessarily be profound. Ultimately—depending upon the details, of course—the discovery might merely indicate that creatures can survive in niches away from the ever-increasing influence of humans. Indeed, this thought raises a question. More than a century after the publication of Doyle’s story, are there any discoveries in biology that would have a profound impact? The answer is: of course! Let’s briefly consider one example of just such a profound discovery, based on work that took place in the 1970s. We can then consider a suggestion which, if it were proved true, would represent a biological discovery of far more significance than that of a bipedal carnivore in Blue John Gap.
Big creatures are made up of eukaryotic cells—cells that possess a nucleus, a cytoskeleton, and flexible cell walls (or no cell walls at all). These cells have the ability to combine, pass on genetic information through sex, and evolve different body shapes in response to environmental pressures. The eukaryotic grade of life thus contains all the complex life we see around us, in all its wonderful variety—from aardvarks, bats, and camels through to xerus, yaks, and zebras. Bigfoot, Nessie, and the monster of Blue John Gap would all be examples of the eukaryotic grade of life. By many measures, however, the most successful organisms on Earth aren’t the big, complex, life forms. The most successful creatures are single-celled microorganisms like bacteria.
Prokaryotic cells—those that possess rigid cell walls—have been on the planet for 3.6 billion years or so. These cells evolve biochemical rather than morphological responses to environmental pressures, an approach that helped them survive the various mass extinctions which have wiped out so many biologically complex species in the past. Bacteria constitute a large fraction of Earth’s biomass. So when we talk about the dominant form of life on Earth we shouldn’t be so human-centric: bacteria might be unable to ponder the mysteries of the universe, but they are important. And although land-dwellers with the size of the Blue John Gap monster are unlikely to have eluded us, surprises surely await biologists in the microcosmic world. There’s more space for discovery in the world of microorganisms than there is in the ocean depths.
The microbial world has already sprung one big surprise: the revelation that life is so adaptable it can evolve to thrive in niches once thought deadly. Some organisms require high acid levels in order to survive and some require high alkaline levels. Some organisms require the absence rather than the presence of oxygen. Some organisms thrive in salt, or at high temperatures, or in ice. So-called
extremophiles can be found in deserts, subsurface Antarctic ice, hydrothermal vents … life is pretty much everywhere you look.
In the late 1970s, the American microbiologist Carl Richard Woese discovered that a certain class of extremophile wasn’t a type of eukaryote, but neither was it a type of bacteria. This particular prokaryote represented a completely new domain of life. The discovery was as much a shock to the scientific community as the sighting of the Blue John monster was to James Hardcastle. Biologists had got used to the idea of there being two domains of life: eukarya and bacteria. Woese showed there are
domains: eukarya, bacteria, and archaea. Archaea and bacteria are no more related to each other than they are to eukaryotes. (Fig.
shows a simplified version of the tree of life.)
This tree of life shows the relationships between those species with sequenced genomes as of 2006 (the same image now would contain much more detail). The diagram’s central point represents LUCA—the last universal common ancestor, the organism from which all current life on Earth ultimately evolved. The three colours represent the three domains of life. Green = archaea (the relatively recent discovery made by Woese). Lilac = bacteria. Pink = eukarya (animals, plants, fungi). The reader with eagle eyes—or a magnifying glass—might make out Homo sapiens in the tree: we are in the pink segment, second from the edge with the lilac. Tree diagrams such as this emphasise just how inconsequential we are in evolutionary terms; we are just one of leaf in a vast forest of species, and each leaf can trace its ancestry back to LUCA (Credit: image generated using the online phylogenetic tree viewer iTOL Interactive Tree of Life; retraced by Mariana Ruiz Villarreal)
For a while biologists believed all archaea were extremophiles, eking out a living in harsh environments. In recent years, however, archaea have been found in a wide range of moderate habitats; they have even been found in the human gut and on human skin. They are among the most abundant organisms on the planet.
Four decades on and Woese’s discovery has transformed our understanding of microbial diversity, provided us with new perspectives on our thinking about evolution, and improved our knowledge of the history of life on Earth. It was a key breakthrough in biology. Is it possible that an even more exciting discovery might be waiting to be made?
Although there are three separate domains—archaea, bacteria, and eukarya—all forms of life on Earth possess certain common features. For instance, all life forms are able to metabolize; in other words, they can draw nutrients from their environment, convert them into energy, and excrete the waste products. And all life forms are able to reproduce. Indeed, one can argue that metabolism and reproduction are necessary factors in order to define something as being alive. But some common features of life on Earth seemingly
aren’t necessary. Some features of life appear to be mere accidents. Consider, for example, chirality.
Chirality is a fancy word for handedness. If an object is different to its mirror image then it displays chirality; human hands provide the clearest example, since the mirror image of a person’s right hand cannot be superimposed on the left hand. Well, the laws of chemistry are blind to chirality. Although many molecules can have a “handedness”—they can come in left-handed or right-handed varieties, just as a glove can be left-handed or right-handed—as far as chemistry is concerned the handedness doesn’t much matter. A molecule is a molecule, just as a glove is a glove. In
biochemistry, however, chirality is crucial.
Large biochemical molecules come in two mirror-image forms, and the molecules must be compatible in order to assemble more complex structures. All life on Earth uses amino acids to construct proteins, and those amino acids are all left-handed. Sugars are all right-handed. And DNA is a right-handed double helix. If life were starting now, from fresh, there would presumably be a 50–50 chance of it using right-handed amino acids or a left-handed double helix for DNA.
Chirality isn’t the only example of chance when it comes to the history of life on Earth. Consider the genetic code—a set of rules that enables cells to translate information stored within nucleic acids (DNA or RNA) into proteins. In DNA, information is preserved in the sequence of nucleotide bases —adenine, cytosine, guanine, and thymine; A, C, G, and T. The genetic code is based on nucleotide triplets—called
codons—and different codons spell out the names of different amino acids. The codon GGU, for example, codes for the amino acid glycine. Within a gene, a particular sequence of triplets dictates the sequence of amino acids that are chained together to form a particular protein—and proteins are the molecules that allow cells to function. (When genetic engineering is mentioned in films or news reports it’s often to the backdrop of a string of bases: … ATGGCTAC … or whatever. Whenever you see these strings, it helps to picture groupings of three bases—in the same way that the seemingly meaningless string “thefatredhatwastoobigfortheboy” can be decomposed into meaningful three-letter groupings: “the fat red hat was too big for the boy”.)
Apart from some minor exceptions, all life uses the same 20 amino acids to build proteins. The point to make here, however, is that a three-letter genetic code based on four bases could produce up to 4 × 4 × 4 = 64 different amino acids. Life employs only a limited number of amino acids even though further types exist—chemists can synthesise them—and the genetic code is large enough to contain them. Perhaps the particular genetic code used by life is an accident rather than an inevitability.
Or consider the basic chemicals upon which all life on Earth is based: carbon, hydrogen, oxygen, nitrogen, and phosphorus. It’s possible to imagine life making use of arsenic instead of phosphorus. (Arsenic is a poison precisely because it acts in a similar fashion to phosphorus. For an arsenic-based life form it would be phosphorus that was the poison.) Or, to take the classic science-fictional scenario (see Chapter
: “Life on Mars”), perhaps life could make use of silicon rather than carbon: the silicon atom, like carbon, has four electrons in its outermost shell and so could form the rings and long chains required of biological molecules. 4
And the point of all this? Well, scientists don’t understand the details of
abiogenesis—the original formation of life from inorganic material—but we do know that Earth gave rise to life at least once. Eventually this primitive organism, whatever it was, evolved into the so-called last universal common ancestor, which then split into the domains of bacteria and archaea; some time later the more complex eukaryotic cell came into being. Suppose, though, that abiogenesis happened more than once! It’s possible. After all, several biologists argue that if environmental conditions on a young planet are such that life can come into being then life will come into being. This viewpoint, if correct, means it’s entirely possible life started from non-life on several different occasions in Earth’s distant history. Those ancient organisms would be examples of life—but not life as we know it. Alien life, in a sense. Such life forms might be arsenic based, or use a different genetic code, or require left-handed sugars. Furthermore, those different forms of life would not be in direct competition with familiar life forms—they might not be able to consume the same food, for example and there would be no possibility of swapping genes with everyday organisms. Therefore, “alien” microorganisms descended from other abiogenesis events could in principle still be around today. And because biologists haven’t spent much resource in looking for such microorganisms—the deep sea is better explored than this putative “shadow biosphere”—alien life might be widespread. It could even be living on you, right now!
This is, of course, pure speculation. But if it turned out to be true? Well, the discovery of microscopic “alien” organisms descended from different creation events here on Earth—life, but not life as we know it—that would be of tremendous scientific importance. For one thing, it would confirm that the creation of life from non-life can occur in a number of different ways; it would increase the likelihood of there being aliens out there in the Galaxy. And encountering extraterrestrials would be much more exciting than finding a Bigfoot-like creature in a Derbyshire cave.
Nature perhaps contains only the creatures with which we are by now familiar. But biotechnology is advancing to the stage where scientists can
make new life forms. Perhaps some future biotechnologist could create a creature similar to the monster of the Blue John Gap? We continue that thought in Chapter . 2