Mother Nature Is Trying to Kill You (24 page)

Some snake neurotoxic venoms disrupt the “sending” neurons by destroying the parts of the cell that send neurotransmitter molecules. The damage caused by this kind of neurotoxin is permanent because the neurons never recover. This is what makes snakes like taipans and pit vipers so deadly. Other snake venoms interfere with the “receiving” neurons by sitting on top of their receptors, physically blocking any neurotransmitters that arrive from other neurons. This second type of neurotoxin lasts only until the venom is broken down and moved out of the way by the human’s immune system. Once it’s gone, the neurons can talk to one another again. That means that if a person has been bitten by the right kind of snake, a medical team that knows what to do can bring the victim back from death’s door.

For example, the bite of a Malayan krait contains neurotoxins that cause paralysis of the whole body. First the person loses the ability to move voluntary muscles, but soon even the muscles around the lungs stop working. That means air is no longer coming into the lungs, so it doesn’t take long for the victim to die from a lack of oxygen. However, because Malayan krait neurotoxin is of that second, reversible type, there is hope for a victim who is lucky enough to get adequate medical care. If air is
pumped into that person’s lungs while they’re paralyzed, there’s never a shortage of oxygen, and no permanent damage occurs. So long as the medical staff keeps the patient “breathing,” that patient can fully recover from the total paralysis of a krait bite in just a few days.
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Because snake venoms work so well on humans, it’s easy to forget that they really aren’t there to hurt us. Snake venoms are primarily there to help snakes subdue their prey. After all, these are animals that don’t have any arms and that hunt other animals that can usually move much more quickly than they can. It’s pretty incredible that an animal like a rattlesnake can catch something as fast as a chipmunk at all. Fortunately for the rattlesnake, though, it only has to hunt successfully a few times each year.
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When hunting, a rattlesnake relies on its excellent sense of smell to find a spot in the forest that small mammals, like chipmunks, have been using as a trail. It would not be very easy for you or me to smell the residue on a branch from the soles of chipmunk feet that passed by four hours ago, but that kind of thing is right up a rattlesnake’s alley. In fact, that’s why they have forked tongues. The tongue comes out, touches different places in the forest, picking up chemicals that might be too heavy to float freely in the air, and then comes back into the mouth and touches
sense organs on the roof of the mouth. It’s kind of like when you go through security at the airport and they swab your bag with that little cloth and then put it into the chemical analyzer. Once the snake detects the chemical residues of mammal footprints, it sets up shop, coils, and waits.

The wait may last multiple nights, but snakes can be patient. They’re cold-blooded, so they use energy slowly. When a chipmunk does finally pass by, the snake strikes out, stabs the small mammal with its hollow fangs, injects it with venom, and then immediately lets the animal go. After all, there’s no sense holding on to a struggling chipmunk, since it might bite in self-defense. If the strike was successful, the chipmunk will be dead in just a couple of minutes anyway. As the chipmunk runs away, the snake slowly uncoils and then follows the scent of fresh footprints. Before long, the snake reaches the dead chipmunk at the end of that scent trail and sets to work eating it whole. None of that would be possible without venom. In fact, the venom even acts as a digestive juice, starting the breakdown of the chipmunk even before the snake eats it, easing the digestion that will take the snake several weeks to complete.
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When a rattlesnake’s venom enters a chipmunk, it first goes to work on the blood vessels. Within moments, capillaries and small veins near the bite start leaking blood uncontrollably into the surrounding tissue. This results in swelling, blistering, and overall breakdown of the tissue to its chemical components. As the blood carries the venom through the bloodstream, those problems spread to other parts of the body, including the heart.

Should a human be unlucky enough to step over a log and
onto a coiled rattlesnake, the animal might strike in self-defense. The potentially good news is that roughly half of rattlesnake defensive bites on humans are “dry bites,” which means that no venom is injected. Dry bites still hurt because a pair of daggers just pierced your skin, but at least you won’t suffer the chemical onslaught that eats away at your muscle tissues. Rattlesnakes sometimes deliver those dry bites because they’re just trying to get the human to go away. Whether or not they kill the human doesn’t really matter to the snake, so with all things being equal, it’s better to save venom for when it’s needed.
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To me, the scariest thing about being bitten by a snake is that you can’t tell at first if a snake bite was a dry one or not. The only way to find out is to wait for symptoms. If you’re lucky, the bite wounds swell up and become painful like any pair of deep puncture wounds would. But if you’re not so lucky, well, what happens next depends on which snake bit you, how much venom it delivered, and whether you have access to antivenin. If it is a rattlesnake, and you’re unlucky enough to have received a “wet bite,” you’ll probably still survive, though. The rapid tissue destruction will do permanent damage to the skin and muscles around the bite site, but rattlesnake venom happens to be nonlethal to humans . . . at least most of the time.

I understand that people want to believe that Mother Nature is looking after them, but how can they reconcile that idea with
the existence of jellyfish, cone snails, spiders, scorpions, bees, ants, wasps, and snakes? That’s not even starting on the centipedes, stingrays, scorpion fish, lizards, platypuses, shrews, beetles, and bugs that also use venom. If Mother Nature is so loving, why are there so many venomous creatures out there, and why do so many venoms contain chemicals that do nothing other than increase the pain of the victim?

Some would argue that venoms provide many useful chemicals to scientists trying to develop drugs, and that’s totally true, but I think it’s a stretch to pretend that’s why nature put them there. The fact is, we humans have learned to take advantage of nature in order to thrive as a species. Just as we eat plants and animals that didn’t volunteer for the job, we take apart the venoms that animals use against us. Through science, we can make antivenins, rendering those venoms less deadly, but even more amazingly, we can use venoms to gain access to parts of our own bodies we couldn’t reach before. If you’re making a drug that blocks pain, see what cone snail venoms are doing. If you’re making a drug that can temporarily block nerves, why not look at snake venoms? Venoms provide keys to the locks on millions of molecular machines within our bodies. With venoms we are making drugs that help us live long and healthy lives. Nature isn’t taking care of us. She’s trying to kill us, and we’re taking care of ourselves.

Animals kill other animals, and there’s no question that they often inflict pain when they do it. Whether it’s physical abuse or chemical abuse, animals give one another a beating out there every single day. But wrath in the natural world doesn’t just happen
on the scale of injured, tortured, or even killed individuals. Wrath happens on much larger scales than that. The wrath of nature is strong enough to wipe out entire species at a time, or even groups of species, without so much as a thought.

Whenever you mention extinctions, people usually think of dinosaurs, but the funny thing about dinosaurs is that they didn’t actually go extinct. There was an event 65 million years ago, at a point in time that separates the Cretaceous period from the Paleogene period. That moment in geological time is called the Cretaceous-Paleogene boundary, or K-Pg boundary. It was then that
almost
all the dinosaurs disappeared, but a few did survive. In fact, their descendants live on to this day, and you see them all the time. Those descendants are the birds, and because all birds are direct descendants of the dinosaurs, birds, by definition, are also dinosaurs.
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(Watch a chicken run and tell me it doesn’t look like a velociraptor from
Jurassic Park
.)

Because the dinosaurs didn’t go extinct, paleontologists are always careful to call the group that did die off at the K-Pg boundary the “non-avian dinosaurs.” That’s their way of saying “all the dinosaurs except the birds.”

The K-Pg extinction may have wiped out charismatic animals like
Tyrannosaurs
and
Triceratops
, but the non-avian dinosaurs weren’t the only ones that disappeared. Flying reptiles called pterosaurs did too (they weren’t technically dinosaurs), as did the big swimming reptiles that looked like Loch Ness monsters (also not dinosaurs) and a whole bunch of other plants and animals. In all, roughly 70 to 75 percent of all species on Earth disappeared.
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The evidence is very strong that the K-Pg extinction event
began when a massive meteor smashed into what is now Mexico, right near Mérida, on the Yucatán Peninsula. How big was it? For context, think back to that fireball that lit up the sky over Chelyabinsk, Russia, in February 2013. That meteor was about fifty-five feet across
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—big enough that when it burned up in the sky, it released a flash of light brighter than the sun and sent out a shock wave powerful enough to knock over building walls, shatter windows, and injure more than a thousand people. Millions of rocks of various sizes hurtle into our atmosphere each year, but the Chelyabinsk meteor is the biggest one Earth has seen in the past century.

The meteor that wiped out the non-avian dinosaurs? Oh,
slightly
bigger.

It left behind a crater about 125 miles in diameter, which means the asteroid itself was probably about 6 miles in diameter. Six miles! That makes it more than five hundred times wider than the Chelyabinsk meteor, and more than 200 million times heavier.
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Animals standing right under it would have been vaporized by the fireball when that impact occurred, and those nearby would have been killed by the wildfires and tidal waves that spread out from the impact site, but the global-scale problems came in the ensuing months. The dust kicked into the atmosphere by that impact would have blocked out sunlight, and since energy coming into the living world must be harnessed by plants from sunlight (as you’ll recall from the chapter on gluttony), this debris cut off the flow of energy not only to plants but also to all animals. By the time the dust settled, months or even years later, most of Earth’s species were dead.

Events like the asteroid at the K-Pg boundary are part of nature,
as are the smaller-scale events we’ve seen in our lifetimes, like earthquakes, tsunamis, hurricanes, tornadoes, and blizzards. When natural disasters happen, animals die, and when the event is big enough, a whole species or multiple species can vanish. Those extinctions are an important factor in how life has evolved on our planet. For one thing, mammals were only able to become things like horses, bats, and apes because the non-avian dinosaurs were gone.
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If that asteroid hadn’t hit, if all that death hadn’t happened, humans wouldn’t exist. By the same token, humans will surely someday experience an extinction of our own. That’s just how nature rolls.

The mass extinction at the K-Pg boundary wasn’t the only one in Earth’s history. In fact, it wasn’t even the biggest. Before dinosaurs ever existed, an extinction event 251 million years ago killed 95 percent of all species on Earth. That mass extinction, between the Permian and Triassic periods, is (not surprisingly) called the Permo-Triassic boundary, or P-Tr boundary. Some people, however, just call it the Great Dying. Almost every single kind of plant, insect, fish, amphibian, and reptile disappeared, including some reptiles as big as bears. All that was left was a tiny sliver of the biodiversity that had existed before.

The P-Tr extinction seems to have been triggered by giant volcanoes in what is now Siberia. Volcanoes don’t sound that threatening, but we’re not talking about lava flowing down a hillside. We’re talking about massive fields of volcanoes that burped up enough lava that it ultimately covered an area of 1.6 million square miles—roughly half the area of the contiguous United States. The lava would have been bad for the animals right at the volcanoes, but the gases that came out wreaked havoc worldwide. They triggered a cascade of environmental changes that animals on land
and in the oceans simply could not handle—poisonous gases, steep drops in aquatic oxygen levels, and runaway global warming with increases of around 11˚F (6˚C). To give you some idea of how bad it was, in some places the soil was completely wiped away, killing everything that had once lived there, except the molds and other fungi that could cling to the bare rock left behind. Despite the magnitude of that carnage, a few living things did manage to survive, and after a few million years, their descendants evolved to fill the roles of some of the creatures that had died. Some of those new creatures, for example, were the dinosaurs.
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