CHAPTER 2 
CHAPTER 2 It is only natural that we should measure everything in the world around us in terms of our own size. An elephant is bigger than we are, and a mouse is smaller. Some years ago, TimeLife was publishing a series of illustrated books on various subjects, and they called me up to ask for advice on a book they were doing on the general subject of growth—would I please come in to New York to discuss the matter with their editors, for they had numerous questions they wanted to ask an interested biologist. I no longer remember what those questions were, but at the end of our conference they said they were having difficulty thinking of a suitable photograph for the cover of the book. I thought about it as they were talking, and suggested they should have the large open hand of a man and in his palm have the hand of an infant. They did not seem very enthusiastic about the idea, but when they sent me the finished book, that was exactly what they had on the cover. We see and are conscious of the size of everything that surrounds us, whether it is smaller or larger, and nothing makes the point more clearly than the growth of children. Who has not remarked upon seeing—after an absence—the child of a friend or family, “My, you are so much taller than when I saw you last.” Once I visited Louis Pasteur’s house outside of Paris, and one of the doorways still had pencil marks recording the annual growth of his children, something that will sound familiar to everyone. Either consciously or, because it is so much part of our natures, unconsciously, we are forever taking note of the size of things and gauging any increase or decrease.
Our world is the world we see with our naked eyes, and that is what we use for our everyday measuring stick. We are also aware that there are worlds that are larger and smaller than we can see in our normal existence—in fact, how to see the things above and below our vision was among the great discoveries in our history. The telescope was one of the profound technical advances in our civilization. The first to see huge, distant bodies was Galileo, who in the seventeenth century devised an improved way to put lenses together to greatly magnify the heavenly planets and stars (fig. 1). Following this discovery of great importance and consequence, there has been a continuous improvement in telescopes to explore the sky. Today we have the Hubble (and similar) telescopes carried by a satellite orbiting the earth which not only has an enormously powerful telescope, but it can operate free of the optical disturbances created by the earth’s atmosphere. The universe is unimaginably large, yet with this tool we are learning things about it that are totally beyond the reach of unaided human eyes.
Figure 1. Galileo’s telescope. (Drawing by Hannah Bonner)
The microworld is too small for us to see without help. That help first came in the seventeenth century when Anton van Leeuwenhoek ground very small lenses to greatly magnify objects (fig. 2). He not only invented the microscope, but he went on to illuminate a whole world that had never before been known to exist. He described for the first time all sorts of microscopic animals and plants that live in ponds and rain barrels: he even, for the first time, described bacteria, which are exceedingly small. He was the discoverer of spermatozoa in human semen, although it was not until much later that their nature was correctly understood. The technical advances in microscopes over the years has been no less remarkable than those of telescopes; their complexity and their power bears little resemblance to the tiny lenses ground out by van Leeuwenhoek many years ago.
Figure 2. Van Leeuwenhoek’s microscope. (Drawing by Hannah Bonner)
It has often struck me that, conscious as we are of our own size and of those around us, we do not ordinarily think that once we were microscopic. It is possible to believe that at one time we were infants, and there are all those old family photographs to prove it. It is even possible to imagine that earlier we were a foetus, but the idea that we were once a microscopic, single cell—a fertilized egg—is not something that ordinarily crosses our mind. In our own growth we go from the world of van Leeuwenhoek to the world we see around us every day. Perhaps if we were to have eyes and senses and a memory at that single cell stage of our life—an absurd possibility—we would look at the world differently, for our sense of size does not come to us until we are a small child. (In any event, an egg does not have much to look at in the darkness of a Fallopian tube.) One of my early recollections is being so small that I could not reach a light switch on the wall and had to get help from some giant adult. I had a psychologist friend who wanted to apply for a grant to build a huge room with gigantic furniture exactly as a small child would see it, and study the effect it might have on an adult who reenters his childhood world. The university committee that had to pass on research done on human subjects turned the request down: the effect might be too dangerous for the human psyche!
Clearly children are especially conscious of their size as they are surrounded by huge adults. This is reflected in fairy stories and children’s tales. A good example is Lewis Carroll’s Alice in Wonderland, where Alice keeps changing her size to go down rabbit burrows and back to her normal large self. She begins with the bottle which says “Drink Me” and shrivels to a size that allows her to join the underground world. Later, the hookah-smoking caterpillar puts her on to a magic mushroom: a bite from one side makes her larger, and a bite from the other smaller. What a perfect child’s dream to go back and forth from one size world to another. At one point she worries that she will shrink to nothing, which has special resonance for me. When I was a very small boy I had a terrifying recurrent nightmare that I would enter a room with adults and I would instantly shrink to something minute, like an untied balloon letting out its air. I never knew my final size—I always woke up shrieking. Perhaps that was the first spark of an early interest in the role of size in biology, a subject that has pursued me these many years.
Another way in which we show our fascination with size is our sustained interest in human dwarfs and giants. In the nineteenth century, Barnum had great success in his circus exhibiting the midget Tom Thumb along with the giant Angus MacAskill, who were so extraordinarily small and large compared to everyday human beings. MacAskill came from Cape Breton in Nova Scotia, now an hour’s drive from where I write these words. He was unusual in that he was not only huge—he was 7 feet and 9 inches tall—but he was phenomenally strong. His palms were almost eight inches across and he could hold Tom Thumb, who was a mere 3 feet tall, in his hand.
Both Tom Thumb and Angus MacAskill suffered from a malfunctioning pituitary gland: in Tom Thumb’s case there was a deficiency in the secretion of growth hormone, and in MacAskill’s case an oversecretion. It is a powerful hormone that controls our size during our growing years, and if it is not tuned just right, as it normally is, a dwarf or a giant will be the result. Today if the pituitary malfunctions, abnormal size can be prevented by controlling the amount of growth hormone. In the case of pituitary giants it is rarely the case that the individual will have the strength of MacAskill, and in general sufferers of the disease do not live to an old age. (MacAskill died at the age of 38 of “brain fever,” presumably meningitis.) The excess of growth occurs mostly by stimulating the cartilage at the ends of the long bones, so it is possible to produce gigantism only in a growing youth. If too much hormone is produced after the long bones become sealed off and their layer of cartilage is gone, which usually occurs around the age of 20, only those parts of the human anatomy that still have cartilage will have a growth spurt. This will happen mainly in the hand and the face—a disease called acromegaly—and those unfortunates stricken with it will have enlarged jaws, broadened noses, and distorted finger joints. The cause is usually a tumor on the pituitary gland.
The fascination with giants and dwarfs goes way back in literature. Children’s stories are replete with them, from Jack the Giant Killer to the Seven Dwarfs and innumerable others. The wonderful Icelandic sagas have diminutive, evil trolls as well as heroes of huge proportions who pitilessly slice off parts of the enemy with their gigantic broad swords.
Perhaps one of the best known and most enduring tales is Gulliver’s Travels by Jonathan Swift. Lemuel Gulliver was about twelve times taller than the Lilliputians, and the Brobdingnagians were that amount again taller than he was. Swift sensed some of the problems, and in order to feed Gulliver, the Lilliputians cubed their difference in height and for their half pint of wine they gave him 1,728 (123) half pints. We know today that this calculation does not take into account the relative differences in metabolic rate, and it would have made Gulliver roaring drunk, but Swift was taking a step in the right direction. In other things he made pure fictions, but interesting ones. According to Swift, being smaller meant being able to see smaller things; everything in the natural world of Lilliput was to scale—not just the people. The horses, the chickens, the sheep, the trees, the corn in the fields were all miniature so that their world appeared to them as ours does to us. From this perspective, the Lilliputians’ ability to see small things was far greater than ours. “I have been much pleased with observing a Cook pulling a Lark, which is not so large as a common Fly, and a young Girl threading an invisible Needle with invisible Silk.” A Lilliputian microbiologist would not need much of a microscope to help her see microbes. The corresponding difference is seen between Gulliver and the Brobdingnagians; he viewed their huge bodies as though through a magnifying lens. He watched the gigantic queen’s maids of honor undress, “before their naked Bodies; which, I am sure, to me was far from being a tempting Sight, or from giving me any other Motions than those of Horror and Disgust. Their skins appeared so coarse and uneven, so variously coloured when I saw them near, with a Mole here and there as broad as a Trencher, and Hairs hanging from it thicker than Pack-threads, to say nothing further concerning the rest of their persons.”
As we shall see, none of this is physically possible; no matter how big or how small a living object, the same physical laws will govern it, and those laws will make for differences in shape and form with differences in size. So the three size levels in Gulliver’s world, with man and all the beasts being of similar proportions no matter their size, is impossible; it is the world of fantasy. Yet Gulliver is correct when he says, “Undoubtedly Philosophers are in the Right when they tell us, nothing is great or little except by Comparison.”
My plan is first to give the reader some feeling for the enormous variety of animals and plants and all the lower forms. Then in later chapters I will go on to examine what these size differences mean for all aspects of their existence: for their shape, for their complexity and their division of labor, for their evolution, for their abundance in nature, and for all those time-related activities such as metabolic rates, generation times, speed of movement, and even the pitch of their voices and songs.
Big animals and plants have a special fascination, beginning for us all in our childhood. My first biology book was a huge volume by H. G. Wells, Julian Huxley, and G. P. Wells called The Science of Life (1931). It was exciting reading for a small boy, and in fact it trapped me into becoming a biologist. In particular I was fascinated by a section on the size of organisms, which no doubt psychologically imprinted me so that after all these years I am writing this book! I still have my battered copy, and to this day I find the figures on the extreme size of a variety of plants and animals engrossing. They have a rather antique appearance, but they send a clear message.
Consider their figure of the largest forms (fig. 3). To make it easy to understand relative sizes, a man is included alongside the largest of all animals, a blue whale (1). As Galileo understood, it is to be expected that the champion would be an aquatic beast because the whale’s specific gravity is close to that of water, and therefore it is essentially weightless and need not have supporting limbs.
Well-known dinosaurs, such as Tyrannosaurus (2) and Diplodocus (3), were among the biggest terrestrial animals, but there were larger ones. In fact, it was known since the early part of the twentieth century—well before the book was published in 1931—that the biggest of them is not among the popular ones shown in the figure. The record giant is Brachiosaurus, first discovered in Colorado in 1900, but a complete skeleton was not unearthed until a dozen or so years later in what was then German East Africa, now Rwanda and Burundi. The reconstructed skeleton can be found in the Humboldt museum in Berlin—standing in imperial elegance in a huge hall built especially to house it. It stands 40 feet tall, and its weight has been estimated to be about 80 tons; this compares to approximately 30 tons for the Diplodocus we see in the figure. The tallest living mammal is the giraffe.
Figure 3. The largest animals and plants, from H. G. Wells, J. S. Huxley, and G. P. Wells, The Science of Life (1931). The names of the organisms are given in the text.
The largest living animals that can fly are condors, and albatrosses (5) have a record wingspan of 11 feet, but they seem very small compared to the fossil pterosaurs (4) (see also fig. 4). Pterosaur remains were discovered in the late eighteenth century, and the celebrated French anatomist Georges Cuvier showed that they were reptiles and gave them their name. They appeared long before birds and bats and existed for about 215 million years, then became extinct at roughly the same time as the dinosaurs at the end of the Cretaceous era. Even though there were some small ones of birdlike proportions, the larger ones are truly huge (fig. 4). The record holder was discovered in Texas a few decades ago: it was estimated to have a wingspan of at least 36 feet, far bigger than a small airplane. The bones of these huge fliers were hollow and very light; their musculature must have been formidable. These record holders were not known to exist in 1931 when The Science of Life was published; if we were to add these giants they would have a much larger wingspan than the pterosaur shown in figure 3. It is tempting to imagine that the mythical, immense flying bird, the roc of the Arabian Nights, was a pterosaur that lifted Sinbad to safety. However, our credibility is stretched beyond the limit when Sinbad says the roc could lift an elephant in its talons.
Figure 4 (facing page). Soarers. (a) The magnificent frigate bird has a wingspan of more than 6.5 feet; (b) the wandering albatross can have a wingspan of as much as 11 feet, the greatest of any living bird; (c) the largest flying animal of any age was the pterosaur, with a wingspan estimated at 36 to 39 feet. (From T. A. McMahon and J. T. Bonner, On Size and Life, 1983)
We are all familiar with the fact that flightless birds have become much larger then their flying relatives. There are many examples: emus, rheas, cassowaries, and the champion of them all, the ostrich (7), which seems especially large if we compare it in our minds to a chicken (8). But all the real record breakers are now extinct: the moas and the huge Aepyornis (6). Some recent evidence reinforces the view that their extinction was caused by the advent of early colonization by human beings of the Pacific islands where they lived. Large, flightless birds are not only easily captured by wily hunters, but they are big enough to provide a substantial meal. There is the story of Charles Darwin, who, on his famous voyage on the HMS Beagle, shot a rhea on the Pampas and only after he and his compatriots had half eaten it did he realize that it was a new species and had to carefully resurrect what was left of the uneaten parts.
The largest snake is a fossil form (9) that exceeded 50 feet in length. I am particularly fond of the drawing that appears to be no more than a straight line (10), showing no anatomical detail, for it would be too slim to depict on this scale. It is a record tapeworm found in a human being, and the fact it is so long means that our intestine is also long and highly convoluted.
Lizards can be very big, the largest being an extinct, fossil species (14), which is considerably bigger than a record crocodile from West Africa (12). The huge and ferocious Komodo dragon (13) is modest by comparison, but seen alongside a man or a sheep (11) it appears fairly large. Those who have seen nature films of these inhabitants of Komodo Island near Bali, and watched them tear a carcass apart in a viscous frenzy, do not think of them as being small; they are indeed dragons.
Among invertebrates the largest jellyfish is Cyanea (16), which was made famous in one of the Sherlock Holmes stories, The Lion’s Mane, where it turned out to be the murderer. The biggest specimen known was found in the North Sea: its tentacles spread about 8 feet below the huge bell of jelly. No doubt it is a threat with all its innumerable tiny, poisonous nettle-like stinging cells; but so far as I know, Conan Doyle’s fictional account is the only one in which it has actually killed a man. The largest related polyp is of comparable size (15). The giant clam (18) of the southern Pacific Ocean is very big compared to the ones we normally eat—all the invertebrates depicted here are in the same size bracket as a horse (17). Clams feed by bringing a current of water in between the valves and consuming the microscopic plankton they draw in; the valves are held together with a strong muscle that shuts them when the beast is disturbed. It has often been claimed that they can be accidental murderers if a diver inadvertently happens to get a foot inside the closing valves of a giant clam, but apparently it is no more than a tall tale, for no such lethal accident has ever been recorded.
To continue with the invertebrates, crustaceans can become quite large, such as the Japanese spider crab (20), which towers over a large Atlantic lobster (21). Even bigger is an extinct sea scorpion, or Eurypterid (22), a common fossil form. The biggest invertebrate of them all is a mollusk, the giant squid (25) that lives deep in the ocean and is a prey of the sperm whale.
Among fishes, a large tarpon (19) seems small alongside the huge whale shark (23), yet it in turn seems modest in size compared to a blue whale (1), which, of course, is a mammal.
The plant kingdom is less well represented in this figure, although this kingdom produces the biggest organisms of them all. A huge sequoia (26) is so big that only less than a third of it will fit on the page, and for comparison a 100-foot larch tree is superimposed. However, the size of trees is special in that a large part of their bulk consists of dead wood and the living tissue is a relatively thin layer under the bark, besides of course the leaves.
The largest flower is Rafflesia (24), which is found in Malaysia and Indonesia (fig. 5). Sir Thomas Raffles, the extraordinary British explorer and statesman who founded Singapore, discovered it in 1818. He encountered the flower in Sumatra and wrote in a letter,
Figure 5. The largest flower, Ralesia. (Drawing by Hannah Bonner)
The most important discovery . . . was a gigantic flower, of which I can hardly attempt to give anything like a just description. It is perhaps the largest and most magnificent flower in the world . . . its dimensions will astonish you—it measured across from the extremities of the petals rather more than a yard . . . and the weight of the whole flower fifteen pounds.
It is a parasitic plant that feeds off the roots of vines—it has no leaves. Not surprisingly, considering its weight, the flower lies on the ground, and it blooms for a brief but glorious four days. It has huge red petals that look like seat cushions, and produces a wonderfully offensive odor of putrefying flesh—irresistible to flies that pollinate the flowers.
Also not shown in the figure are some very large brown algae. These are the very big marine forms known as kelp. They have a holdfast that anchors them to the bottom of the ocean, and a long stem leads to the blades near the surface where they can bask in the sun for photosynthesis. There is an old account from one of the early sea voyages that a species of kelp (Macrocystis) can be over a 1000 feet long, and here lies an interesting tale: in the early part of the twentieth century, the longest measured was 138 feet, which is not inconsiderable.1
The older account of vastly exaggerated length died hard after the modern measurements were made in 1914. When I was a student, textbooks of elementary biology and botany still carried the tall tale even though quite a few years earlier it had been shown to be untrue. It was not until midcentury that the fiction began to fade, proving that we like large organisms, and if nature does not provide ones large enough we manufacture improvements.
A few years ago there was a big splash in the newspapers announcing that the biggest organism ever had been discovered.2 It was a fungus that parasitized the roots of evergreen trees and spread huge distances in the forest, attacking and killing the trees as it advanced. It traveled over thousands of acres about 3 feet underground, and all the tips of the spreading fan of fungal filaments were shown to be part of the same individual; all were genetically identical. This is, however, a spurious individual organism; in no way does it qualify as a record giant organism. Soil fungi start from a germinated spore at one point and spread outward. It is commonly observed that they give rise to “fairy rings,” a circle of mushrooms that form along the edge of the spreading filaments. On aerial photos of the Salisbury Plain in England they can be seen as discolored circles, and knowing how far they grow in a year one can estimate that some are 500 years old. The parasitic fungus mentioned above spread much farther and is estimated to be well over a 1000 years old. The difficulty is that the peripheral filaments become separated from their common stem—they are clones, not one giant beast. They are like groves of aspen (and some other plants) that spread by runners, but we do not consider the entire grove one individual.
Wells, Huxley, and Wells also examined the other end of the scale and show a rather old-fashioned drawing of a variety of small organisms that surrounded us: the microscopic world that van Leeuwenhoek opened up with his microscope (fig. 6). In a pond or in a swamp we are likely to find a number of protozoa that are single-cell animals. Mostly they are free swimming, although sometimes they are attached to the bottom, as in Vorticella (8). The one we remember from our elementary biology course is Paramecium (9), and the largest ciliate protozoan is Bursaria (1); note its huge nucleus that looks like a long piece of rope. Number (11) is a human liver cell, and (10) an amoeba that causes dysentery. A very small wasp is seen in (4), a species of rotifer, which is a very small multicellular animal, in (5), and a cheese mite in (6). A human sperm (7) seems small alongside a human egg (6). Also shown is the foreleg of a flea (2). If this figure were done today it would include the recently discovered smallest vertebrate, a fish in Australia that is about 7 millimeters long and lives for only two weeks.3
Figure 6. Some smaller organisms, from H. G. Wells, J. S. Huxley, and G. P. Wells, The Science of Life (1931). The names of the organisms are given in the text.
While all of these organisms are very small, they are by no means the smallest. The most abundant of all the microorganisms are bacteria, and they would be about the size of the stipple dots in the figure. There are even smaller organisms, the so-called mycoplasmas. Unlike bacteria, they lack cell walls and are a fraction of the size of bacteria. At the other extreme is a very large and curious bacterium that is big enough to be seen with the naked eye and lives in the intestine of some fish.
It is interesting to note that at one point in the early history of our Earth bacteria were the only organisms, and they have not only failed to become extinct, but are found everywhere today in incredibly vast numbers—a genuine case of multizillions. They have even been found in the deepest trenches in the ocean floor, and most remarkably in the crevices of rocks in the deepest mines. They also exist in great abundance in the intestines of animals. It is estimated that we harbor in our own gut 1013 bacteria (ten trillion), which is considerably more than the number of cells in our bodies. It is mostly the big beasts, such as the dinosaurs, that die out; the smallest ones started off as a success and have remained so ever since.
