Gulliver's Travels (part 1) Jonathan Swift

On the 16th day of June, 1703, a boy on the top-mast discovered land.  On the 17th, we came in full view of a great island, or continent (for we knew not whether;) on the south side whereof was a small neck of land jutting out into the sea, and a creek too shallow to hold a ship of above one hundred tons.  We cast anchor within a league of this creek, and our captain sent a dozen of his men well armed in the long-boat, with vessels for water, if any could be found. I desired his leave to go with them, that I might see the country, and make what discoveries I could.  When we came to land we saw no river or spring, nor any sign of inhabitants. Our men therefore wandered on the shore to find out some fresh water near the sea, and I walked alone about a mile on the other side, where I observed the country all barren and rocky. I now began to be weary, and seeing nothing to entertain my curiosity, I returned gently down towards the creek; and the sea being full in my view, I saw our men already got into the boat, and rowing for life to the ship.  I was going to holla after them, although it had been to little purpose, when I observed a huge creature walking after them in the sea, as fast as he could: he waded not much deeper than his knees, and took prodigious strides: but our men had the start of him half a league, and, the sea thereabouts being full of sharp-pointed rocks, the monster was not able to overtake the boat. This I was afterwards told, for I durst not stay to see the issue of the adventure; but ran as fast as I could the way I first went, and then climbed up a steep hill, which gave me some prospect of the country.  I found it fully cultivated; but that which first surprised me was the length of the grass, which, in those grounds that seemed to be kept for hay, was about twenty feet high.

I fell into a high road, for so I took it to be, though it served to the inhabitants only as a foot-path through a field of barley.  Here I walked on for some time, but could see little on either side, it being now near harvest, and the corn rising at least forty feet.  I was an hour walking to the end of this field, which was fenced in with a hedge of at least one hundred and twenty feet high, and the trees so lofty that I could make no computation of their altitude.  There was a stile to pass from this field into the next. It had four steps, and a stone to cross over when you came to the uppermost. It was impossible for me to climb this stile, because every step was six-feet high, and the upper stone about twenty.  I was endeavouring to find some gap in the hedge, when I discovered one of the inhabitants in the next field, advancing towards the stile, of the same size with him whom I saw in the sea pursuing our boat. He appeared as tall as an ordinary spire steeple, and took about ten yards at every stride, as near as I could guess.  I was struck with the utmost fear and astonishment, and ran to hide myself in the corn, whence I saw him at the top of the stile looking back into the next field on the right hand, and heard him call in a voice many degrees louder than a speaking-trumpet: but the noise was so high in the air, that at first I certainly thought it was thunder.  Whereupon seven monsters, like himself, came towards him with reaping-hooks in their hands, each hook about the largeness of six scythes. These people were not so well clad as the first, whose servants or labourers they seemed to be; for, upon some words he spoke, they went to reap the corn in the field where I lay. I kept from them at as great a distance as I could, but was forced to move with extreme difficulty, for the stalks of the corn were sometimes not above a foot distant, so that I could hardly squeeze my body betwixt them.  However, I made a shift to go forward, till I came to a part of the field where the corn had been laid by the rain and wind. Here it was impossible for me to advance a step; for the stalks were so interwoven, that I could not creep through, and the beards of the fallen ears so strong and pointed, that they pierced through my clothes into my flesh. At the same time I heard the reapers not a hundred yards behind me. Being quite dispirited with toil, and wholly overcome by grief and dispair, I lay down between two ridges, and heartily wished I might there end my days.  I bemoaned my desolate widow and fatherless children. I lamented my own folly and wilfulness, in attempting a second voyage, against the advice of all my friends and relations. In this terrible agitation of mind, I could not forbear thinking of Lilliput, whose inhabitants looked upon me as the greatest prodigy that ever appeared in the world; where I was able to draw an imperial fleet in my hand, and perform those other actions, which will be recorded for ever in the chronicles of that empire, while posterity shall hardly believe them, although attested by millions. I reflected what a mortification it must prove to me, to appear as inconsiderable in this nation, as one single Lilliputian would be among us.  But this I conceived was to be the least of my misfortunes; for, as human creatures are observed to be more savage and cruel in proportion to their bulk, what could I expect but to be a morsel in the mouth of the first among these enormous barbarians that should happen to seize me? Undoubtedly philosophers are in the right, when they tell us that nothing is great or little otherwise than by comparison. It might have pleased fortune, to have let the Lilliputians find some nation, where the people were as diminutive with respect to them, as they were to me. And who knows but that even this prodigious race of mortals might be equally overmatched in some distant part of the world, whereof we have yet no discovery.

Gulliver is best known for being shipwrecked and washing ashore in Lilliput, where all the inhabitants are tiny. Immediately after his return from that first adventure, he implausibly finds himself on another undiscovered shore, this time the native inhabitants are so enormous as to make him feel tiny. He says that the “philosophers are in the right, when they tell us that nothing is great or little otherwise than by comparison.” but in biology, that isn’t strictly true. Could there be giant corn plants, livestock and humans? It turns out that there are some limits on the size of biological systems because of intrinsic scaling properties. 40 foot tall corn is extremely tall for a corn plant, but not for a pine tree. Sequoias grow to be hundreds of feet tall, but sequoias have some very special adaptations that allow them to grow to such prodigious heights. Obviously the wood fibers of trees gives much more strength than a corn stalk, but the wood of sequoias isn’t as strong as the wood of oak trees which don’t even grow to be half as tall. The sequoia relies on flexibility as much as pure strength, like how a modern steel skyscraper can be much taller than a limestone pyramid, partly because it is flexible and able to sway in the wind.

Sequoias are so tall that they’ve baffled a lot of biologists with how they are able to bring water all the way from their roots up to the leaves in their crown (pine needles are specialized leaves). In a system that lifts water by suction from above, there is a limit to how high the water can be lifted. It’s no problem for us to suck up a gulp of soda through a drinking straw, because the height that we lift the liquid is only a few inches. If that height got much taller, the suction needed would collapse the straw. If you had a rigid steel pipe and an industrial strength suction motor, there would still be a limit of how high you could lift water which is about 30 feet. This is because it is actually the difference in pressure between the inside of the pipe and the outside of the pipe that drives the water in to fill it. The pressure outside the pipe is due to the weight of the atmosphere, which is a touch under 15 pounds per square inch. As that pressure drives more and more water up the steel pipe, eventually the weight of the water equals the pressure driving it, and it can’t be sucked up any higher. This is why deep wells have the pump located at the bottom, the water is then lifted by adding pressure, but this isn’t how trees work. Water evaporates out of the leaves, which creates the suction that lifts more water into place.

Most trees that are taller than 30 feet rely on two other tricks to lift water up to their leaves, capillary action and osmotic pressure. The tubes within a tree that lift the water are called xylem and they are sort of a one way circulatory system for plants. Water is sticky to itself, we see this in surface tension. The surface tension in a skinny tube can lift water like a suction pump. Osmotic pressure is the tendency of water to move towards where there is the most salt (or other stuff). If you put a raisin into a glass of drinking water, all the sugar (and other stuff) in the raisin suck the water into the raisin. Tree sap, like the sugar in a raisin, is sticky to water. The tissues of the tree have so much sap that it sucks water up the xylem from the roots. Trees are relying on all of these mechanisms to grow as tall or taller than the corn that Gulliver found in Brobdingnag, but sequoias have yet another trick: they drink from the clouds themselves. Instead of relying on bringing all the needed water up from the roots, sequoias have evolved adaptations that let them capture clouds and fog directly into their crowns, sometimes even creating their own rain that quenches their roots as well.

So the corn in Brobdingnag is big (but not as big as our trees) but the animals and inhabitants of Brobdingnag are equally oversized. Is it possible to grow a human to be as tall as a spire steeple? Nope. Again we bump into some problems of scaling, and how hard it is to lift water. Animals like people or livestock all use the contraction of their heart to add pressure to their blood (blood is essentially just water with some protein and cells in it). This means that we have a positive pressure circulation system, just like the well with the pump at the bottom. The astute reader will notice at this point that we differ from sequoias in at least this one major regard (there may be other ways in which we differ from sequoias too). The overly eager reader may at this point try to jump ahead of me and say “great! We’ve solved the problem of lifting water, we can now be as tall as we want”. Turns out, there is a paradox here. Having high pressure circulatory system, powered by our muscular hearts, aren’t nearly as good at lifting to very high heights as the low pressure system of trees. Why is that? Everytime your heart beats, what it’s doing is squeezing the blood inside it. That squeeze is the pressure that lifts blood up to important parts of our bodies, like our brains. A typical blood pressure for an adult is 120/80 mmHg. What is a mmHg and why do we use it? It is a measure of pressure, telling us how high in a tube (measured in millimeters) we can lift liquid mercury. Why mercury? Because it is really, really dense, so the tube doesn’t need to be nearly as tall. In fact, mercury is 13.5 times denser than water, so the same amount of pressure could lift water 13.5 times higher in a tube. Remember, this is how high our hearts can lift the blood in our bodies. If we do some arithmetic, and multiply 13.5 X 120mm, we get 1620mm or just over five feet. This is good news, because it means that when you raise your hand in class to answer a question, your fingertips will still get blood to them. If your arms were much longer, we would need our hearts to squeeze harder. To squeeze harder, our hearts would need more muscle. Giraffes have really big hearts because they are so tall. Some dinosaurs like sauropods had much longer necks than giraffes, did they have enormous hearts? Sure they were big, but probably not big enough to hold their heads upright. We can make good guesses about how big the hearts would have to be by looking at the scale of hearts in other animals and how high they can lift blood.

So if sauropods couldn’t hold their heads up, what is the point of having such a long neck? After all, we’re taught as kids that they ate the leaves from the tops of trees, and our upright necked dinosaur toys and pictures confirm that. Well, a long neck does help to get leaves that are well out of the way, but sauropods might have been using their reach to get to leaves that were very low instead of very high, like maybe from the bottom of ponds. If sauropods spent most of their time wading in lakes, it would solve their blood pressure problems and they could hold their head up above the surface. This is because the water pressure on the outside of their bodies increases with depth at the exact same rate that the water pressure on the inside of their body increases with depth, so the weight of the water in the pond would squeeze the deepest parts the most and the shallowest parts the least. The pond water would help take some of the burden off the heart. Whales are the biggest animals ever, and they don’t have any issues fighting against gravity to lift the weight of their blood because in the ocean it is neutrally buoyant. Think of how hard it is to hold a gallon of milk at arm’s length, and compare that to holding that same gallon at arm’s length underwater in a swimming pool.

Living the pond life would help sauropods with a few other problems of being big. Big animals get very hot. Animal tissues generate heat during metabolism, more tissue means more heat. Animals shed heat through the surface area of their skin and the surface area of their lungs. If you were to measure the surface area and the volume of your childhood dinosaur toy you could divide them together to get a surface area to volume ratio. If you took that toy and zapped it with a magic alien grow-really-big gun until the toy was the size of a real dinosaur, and then re-measured the surface area and volume, that ratio would be very different. What you would find would be that the volume increased by much more than the surface area did. This means that the full size sauropod has lots of tissue that generates heat, but not nearly enough surface area to shed that heat. That is, not enough surface area… unless it’s in a nice cool pond. Whales take advantage of this also. Whales generate enormous amounts of heat but thrive in cold polar waters because of their immense size. Overheating is just one of many reasons why you never see any blue whales in Phoenix Arizona.

All that body mass that creates heat for the sauropod is also really heavy to carry around. We know from their skeletons, that they had really, really (yeah, really) strong leg bones. In fact, their legs were mostly bone. Hippos and elephants have much more bone in their legs compared to smaller animals, because of that scaling relationship of volume. Cats have thin little bones but can leap many feet into the air, elephants can’t jump at all because they’re so heavy. If you zapped your housecat with our convenient magic alien grow-really-big gun, you’d find that the poor thing’s legs wouldn’t be strong enough to even hold up it’s body weight.

So what does all this mean about the giants that Gulliver found? Well, I guess you could say that the only fictional parts about them is that they weren’t all overheated, with broken legs, and passed out from low blood pressure. But they certainly would enjoy going for a swim.