Ten Million Aliens
Page 28
We warm-blooders, we mammals and birds, are high maintenance, and we have a high concept of busyness and a low tolerance of boredom. We have a high metabolism: we need to be busy in order to stay alive and our way of staying alive makes us constantly busy. We can’t afford to wait: if we wait, we die. Some shrews must eat almost all the time they are awake. Big carnivores like lions spend a fair amount of time dozing and cosying up to each other but if they don’t eat every couple of days or so they start to starve. Our mammalian, our warm-blooded concepts of time and life are radically different from those of the crocodile. Mammals and crocs live in the same world in three dimensions, but when it comes to the fourth dimension of time they are aliens. As I stood on the banks of the Grameti, I stood on what divides us. Step a little closer, they said, and we will move in a great deal less than a second from stillness to the most violent action. The fact that we haven’t moved much for 11 months and more doesn’t mean we can’t do so at a nanosecond’s notice. Try us. Step ten paces forward and pause for an instant of time while the water laps at your toes. Do you think you’re still out of range? Try us and see.
And then the sweet sibilant sounds of this watery glade were joined by a strange sort of gargling growl. Yes, mammal, we do mean you. You personally. I returned to the vehicle panting as if I’d just run the 100 yards.
Those are reptiles, then: vertebrates like us, but quite alien. Or are they? The concept of cold-bloodedness is deeply strange to us. How can we begin to imagine a life in which most of the body heat is generated from the outside rather than the inside? But reptiles are linked with birds and mammals by the fact that we are all amniotes, unlike other vertebrates. We have in common an amnion, a double membrane which permits reptile eggs to be laid on land rather than in water. That holds good for birds as well, and also for the egg-laying mammals, platypus and echidna. And confusingly, it is also true of mammals like humans. The foetus, carried within the female, is protected by several membranes, including the amniotic sac, which contains the foetus itself. Despite our radical differences, we are also one with the reptiles.
Modern taxonomists haven’t entirely settled the way the traditional class of reptiles should be ordered. The fact is that some reptiles – the crocodilians, for example – are more closely related to birds than they are to other reptiles. Some taxonomists have abandoned the concept of reptiles altogether, or redefined it to include birds. And if you look at some baby birds, those that don’t hatch out good-to-go,I you will see that they look unmistakably reptilian. A clutch of bird-of-prey chicks looks like a handful of little dinosaurs. Reptiles have been defined as “non-mammalian non-avian amniotes”. Crocodiles, us – what’s the difference?
But on an intuitive level the difference is very clear, just as the similarity is very clear when you meet one of the great whales and hear the great breath. Reptiles may be like us in some ways – number of limbs, backbone, amnion – and we certainly have an ancestor in common. But they don’t live in the same way, they don’t see life in the same way, they don’t think the same way about food and time and action and rest. A croc can afford to wait. I’ve seen 100 at a time in dry-season gatherings in the Luangwa River, in such deep pools as are left, outlasting the oppressive weather until the freedom of the rains comes: a sight straight from the Jurassic, for crocodilians have changed little since the time of the dinosaurs. I’ve seen them strike: or rather, I haven’t seen them strike. It seems that a croc has two speeds, slow and warp. Stand close to a croc and you are aware of a deep truth: that crocs, that reptiles, are a different class.
* * *
I. Newly hatched birds come in two kinds, precocial and altricial. The first are capable of moving around soon after they are hatched, the latter kind are not, and are pretty much helpless. Precocial chicks look like fluffy darlings; altricial chicks look like little (reptilian) monsters.
A suit of armour
My grandfather took me several times to Birmingham Museum. I was aware that it would be tactless to compare anything in Birmingham unfavourably with anything in London, so I didn’t say that the natural history collection was a bit thin compared with the great treasure-house in South Kensington where I had my early education. I can remember only two of the exhibits with any clarity. The first was an excellent Triceratops skull, the second a Japanese spider crab. This crab was displayed vertically: pinky-orange and with a leg-span of about 12 feet, getting on for 4 m. It was leggy to a disturbing degree. I couldn’t help throwing sneaky glances at it after we had passed it, in case it should come scuttling and rattling after us. Not that it could have done so even had it been alive: it needs the support of water to make those vast limbs and those endless pincers operate effectively. There was an unnatural look to it for that reason: it looked like a creature of diseased fantasy, for all that it was quite obviously real.
This is a crustacean, and the largest of all the arthropods. Crustaceans include crabs, lobsters, crayfish, krill and barnacles. Western civilisation regards many crustaceans as supremely edible but turns up its nose at their fellow-Arthropods. Insects,I for example. Insects have nothing to do with the sea, but the oceans are full of arthropods: there are crustaceans everywhere in the oceans. There are even a few land-dwelling crustaceans, like woodlice and some species of crab, and a few crustaceans are parasitic. Around 67,000 species have been described, but there are certainly many more awaiting discovery. Again, even the order of magnitude is in doubt: there may be ten times or 100 times more species.
Their stout suit of armour allows these somewhat ponderous and often slow-moving creatures to survive and prosper. They moult this exoskeleton as they grow. They are defined by two-part limbs and by the nature of their larvae. KrillII form a group more remarkable for their numbers than practically any other on earth. The stats defy belief: it has been estimated that the biomassIII of Antarctic krill totals 500 million tonnes: twice that of all humans on the planet. They can swarm at densities as great at 60,000 individuals in a square metre. These tiny creatures are food for other animals, many of them much larger: fish, squid, penguins, seals and the baleen whales. That the blue whale can survive by eating things that look like tiny shrimps is one of the head-spinning paradoxes of the wild world, and it baffles me as much as it did when I first learned such things in the Natural History Museum in London. Not that krill see themselves as a swimming larder: they have complex and sophisticated ways of evading predation, which involves both swarming and scattering techniques. Some krill have been observed performing an instant moult, leaving their discarded exoskeleton behind as a decoy. They filter-feed, mainly on phytoplankton: that is to say, planktonic species that operate by means of photosynthesis, rather than eating stuff – plants, in other words, and therefore different from animal plankton (zooplankton to be more technical). Ecologically, krill convert an unreachable and inedible resource into an edible form, which is themselves.
A further paradox of the wild world is that the prey population controls the predator population: the apex predators are always the most vulnerable animals in the food chain. Without krill there are no whales: so these little specks of marine life are controlling the largest animal that ever existed. Krill are harvested by humans for aquaculture and aquariums and as bait; they are eaten by humans in Russia and Japan. Climate change is having complex effects on the world’s oceans and it is possible that krill are vulnerable to this. Krill more or less hold the oceans together: their vulnerability is a looming problem for humans as well as whales.
* * *
I. But see the 1895 pamphlet by Vincent M Holt Why Not Eat Insects? Holt writes: “What a pleasant change for the labourer’s unvarying meal of bread, lard and bacon or bread and lard without bacon, would be a good dish of fried cockchafers or grasshoppers?” More recently, the Dutch scientist Marcel Dicke has recommended the consumption of insects for reasons of nutrition and ecological sense. “Locusts are nice cooked with garlic and herbs.” Amusing, I know. Is it more amusing to smash up the rainforest
to supply the world with beef?
II. The term krill is a little imprecise. It has sometimes been used to cover all kinds of planktonic animals, including small fish and fish-fry. Here it is used for the species of crustaceans that are found in the seas in such mind-spinning numbers.
III. The total dry mass of an animal or plant population – Larousse Dictionary of Science and Technology.
Snakes, unclad humans and a garden
I would sooner face a poisonous snake in my living room than a serious spider. I would do so naked and suffer fewer terrors than a harmless spider would give me. In fact, I have done so, and on more than one occasion; I used to live on Lamma Island, one of Hong Kong’s outlying islands, and snakes would occasionally come visiting. On two occasions these were bamboo vipers: a sumptuous green picked out with scarlet around the tail and a fine yellow underneath. They look exactly as poisonous snakes should. They are unlikely to kill you unless you are a child or have a weak heart, but all the same, anyone who got bitten was supposed to get helicoptered off the island. So they are serious snakes. I don’t claim any particular bravery in dealing with them: it’s all in the way these things take you. I was, as it were, rationally afraid of the snake, so I was careful. But big spiders, no matter how harmless, all give me the willies. I have known people express a still deeper terror of snakes: often people who have never clapped eyes on one. Snakes don’t kill as many people as you might think: most people who get bitten by a snake have been handing them, so there’s a hint.
There’s more complex mythology connected with snakes than with any other group of creatures on the planet. In western culture snakes are associated with the unapologetically evil, from the Book of Genesis to Harry Potter. Phallic, poisonous, legless, undulating, slimy, sinister, cold-blooded, unblinking: they stand for the wild world at its most unhuman and therefore most threatening. As a logical extension of this, snakes have come to represent all the evil in the world, everything that is dangerous and disturbing.
Which is a tough load for any creature to bear. It’s the poison thing that does it, I suppose. Actually the correct word is venom: poison is ingested or inhaled, venom is injected. Intuitive human taxonomy places snakes in two classes: venomous and non-venomous. There are around 3,000 species of snakes, and less than a quarter of them are venomous; of these, only about a third are capable of killing a human. However, it has to be admitted that the idea of 250 species all coming to get you at the same time is as compelling as it is irrational. It was a situation of high alarm and low farce when I found a snake in the living room: naked – they always seemed to be discovered first thing in the morning – I herded it into the middle with a broom. My then girlfriend, now my wife, was in the same state – there’s scriptural precedent for encountering snakes in this fashion – but without a broom. She was helpfully leafing through A Colour Guide to Hong Kong Animals, the very copy of which I consulted a few moments ago (she gave it to me) to check the colouration of the bamboo viper. “I think it’s this one, which means it’s not poisonous.”
“I think isn’t really good enough, Cind…”
Anyway, it turned out to be harmless and I swept it into the tiny front garden to sort itself out.
But snakes are not catalogued this way by zoologists, who divide them into 18 families. Venomous species crop up in three of these families, the elapids, which include cobras, kraits, mambas and sea snakes; the viperids, which contains vipers, rattlesnakes, cottonmouths and bushmasters; and colubrids, which include boomslangs. Most colubrids are non-venomous. I remember hearing a crashing sound on a drive through the bush at night in Malawi. We eventually found that a black mamba – it must have been at least 10 foot, 3 m long, though I didn’t get out and measure it – had fallen from the tree it had been creeping about in. Its truly colossal weight had been too much for the thin branches it had trusted itself to, and down it came. It lay out draped across a series of bushes like tinsel around a Christmas tree. It takes a lot for a snake to lose its dignity, but this one looked ridiculous. Which didn’t mean it couldn’t still kill you.
Venom is for disabling prey, not for menacing humans. Most snakes kill by other means: some by constricting, others by swallowing live prey,I all snakes being carnivorous. All snakes have many joints in their skulls, which means they can swallow prey larger than their heads, a particularly unnerving talent. They range in size from the thread snake, which is 4 inches, 10 cm long, to the reticulated python, which can get close to 10 m, 33 feet. There is a fossil snake, splendidly named Titanoboa cerrejonensis, that reached 15 m, almost 50 feet. Snakes probably evolved from lizards, but aren’t to be confused with legless lizards, like the slow worm, the lovely copper-coloured reptiles that can be found in this country if you get lucky and keep your eyes open. Legless lizards have eyelids and external ears: the snakes’ lack of such things gives them their singularly snake-like look; their eyes are covered by transparent protective scales. As arthropods have their being in legs, a snake has its own in length. Everything about a snake is about being long: so much so that many species have only one functioning lung, and paired organs, like the kidneys, are not placed side by side, like ours, but fore and aft to economise on width.
Their uncanny and unnerving reputation is enhanced by the senses they possess: an ability to smell with their tongues: more or less tasting the air, which is why they go in for the tongue-flickering. They repeatedly touch the tongue’s fork to receptors in the mouth to process information about the environment. Some species are equipped with infra-red sensors which allow them to home in on the heat produced by a warm-blooded vertebrate. They are all acutely sensitive to vibration. They have more than one way of moving, though not all snakes can do all of them. They can operate by lateral undulation on land, and a different version of the same technique in water. They can side-wind when there is nothing to push again (a great favourite of natural history documentaries, this) and they use a concertina motion when there is not enough room to side-wind. They can also move just by willing themselves forward – well, that’s what it looks like. Even from up very close, you can’t really see how the trick’s done: they just flow along. It’s called rectilinear motion: they lift and pull forward the scales of the belly and drag themselves along in a slow, effortless and wonderfully spooky way. Tree snakes use a complex combination of these techniques to climb. And some snakes can take to the air at will: the gliding snakes of Southeast Asia can spread their ribs to create an effective aerofoil surface. They can cover several hundred feet in the air and can even change direction while doing so.
Oh, and they’re not slimy. They are creatures of singular beauty that for some reason have given humans the willies across countless millennia.
* * *
I. Egg snakes kill their prey at a slightly earlier stage of development, by swallowing an egg whole and then crushing it.
Beloved barnacles
Brilliance is not enough. Charles Darwin grew aware of that hard truth long before he published The Origin. By 1845 he had published his The Voyage of the Beagle and had established a fine reputation as a naturalist-adventurer. He was now concerned with the biggest subject, the biggest adventure of them all. He had already drafted a paper on evolution but did not submit it for publication; he knew that it would face the most horrendous opposition. He was seen as a brilliant amateur: a speculative paper from such a source would be regarded as mere fireworks. He wasn’t really part of the club. He didn’t have a solid body of work behind him. Now Darwin was a great writer of letters (which, younger readers may care to learn, are like emails only different) and they show at the same time his breadth and depth of mind and an apparently bottomless fund of generosity and modesty. Joseph Hooker, the great botanist, was his closest friend and most trusted colleague. They were exchanging views on a recently-published book that was bursting with bright ideas. Hooker wrote: “I am not inclined to take much for granted from anyone [who] treats the subject in his way and who does not know what it is to be a specif
ic Naturalist himself.”
Darwin was mortified. He wrote back: “How painful (to me) is your remark that no one has hardly a right to examine the question of species who has not minutely described many.” Hooker was distressed that Darwin should have understood his words as a personal criticism, but Darwin was adamant that Hooker was right. He had a serious and terrible truth to unleash on the world: he needed to do it with an appropriate reputation for seriousness. He needed to show that his perfectly enormous and very general idea was backed up by detailed work on the very tiny and the very particular. He wanted to tell the world something about what species in general means: so he needed to devote himself to the questions posed by species in particular. So he spent the next eight years of his life (including two years off with illness) on the study of what he termed “my beloved barnacles”.I His initial intention was to cover just a few species, but the more deeply he got involved, the more he realised that the entire group needed intense and detailed work. And that is precisely what he gave it.II A series of monographs revolutionised our understanding of barnacles. It also gave Darwin the street-cred he needed when at last the big book came out in 1859. It was a book written by a man who knew what a species was when he saw one.III