Mother Nature Is Trying to Kill You (3 page)

“Absolutely,” says the student, finally getting up from his seat. “But I don’t have to outrun the lion. I just have to run faster than one of you.”
^I

That joke’s been around forever, but it doesn’t get old because it’s basically true. A predator is only going to catch you if it doesn’t catch someone else first. Every year in South Africa, plenty of zebras get killed by lions, but they don’t die randomly.
¹
Some zebras are better at avoiding lions than other zebras are, because they’re faster, more attentive, healthier, or maybe just luckier. Lions do the killing, but
which
zebras live or die is determined by the zebras. They’re like the three people in the bar: so long as a zebra can run faster than other zebras, it has a better chance of survival than the slower ones do.

The first of the seven deadly sins on our tour of the living world is greed, and by that I mean an all-consuming focus on yourself. I’m talking about Ebenezer Scrooge–ness. In
A Christmas Carol
, Scrooge didn’t want to have to pay his clerk, Bob Cratchit, for Christmas Day if Cratchit wasn’t coming to work. Scrooge also refused to give even a shred of his considerable wealth to the poor. All Scrooge cared about was himself. Period. That’s how animals make decisions—except while Scrooge was greedy about money, animals are greedy about passing on their genes. Animals will screw one another over without any hesitation, just so long as it helps get copies of their own DNA into the next generation.

Some of the most aggressive actions animals take in the name of selfishness are carried out against members of their own species. They do this because often the most threatening animals in the world are those that are most like you. Members of your own species want to live in the same place as you, they want to eat the same food as you, they want to have their babies in the same place as you, and they want to feed their babies the same kind of food you want to feed your babies. If you ever have to fight a member of your own species, there’s a good chance you’ll be injured. To pass on its DNA, an animal has to make sure it doesn’t get the short end of the stick compared to those other members of its own species, and the best way to do that is to be as greedy and selfish as possible.
²
This might sound jaded, but it’s absolutely true, and a recent study demonstrated this point beautifully using sheep as an example.

It’s been known for a long time that when a predator like a wolf approaches a flock of sheep, the sheep in the flock will cluster closer together. People have assumed that this was because the sheep were all running away from the same predator and
therefore just ended up in the same location, but that’s not what happens at all. Sheep are smarter and far more conniving than people give them credit for.

Researchers fitted an Australian flock of sheep with GPS collars so that they could see how individual sheep moved in response to an approaching predator (in this case, a herding dog). When the dog approached, the whole group closed in on itself as expected, but not because the sheep were all running away from the predator in unison. Instead, the GPS data showed that individual sheep reacted to the dog by moving toward the center of the flock—even if that wasn’t directly away from the dog. In other words, the direction chosen by a sheep wasn’t determined by the location of the predator, it was determined by the locations of the other sheep. Using the same strategy as the student in the bar, a sheep can survive without having to outrun its predator. It just has to put other sheep between itself and the source of danger. A sheep can live, just so long as someone else dies instead.
³

There’s a similar story with emperor penguins in Antarctica. During the impossibly cold and dark winters there, males huddle together for more than three months while each incubates a single egg. Males don’t eat anything over that time, and by spring, each penguin has lost more than a third of his body weight. Penguins are extremely well insulated, but they still leak a little heat to the world around them. Because all the other penguins are giving off heat the same way, the best possible place for a penguin to stand is right in the middle of the huddle, with other penguins leaking heat on every side of him.
^II

This works better than I would have ever imagined. A penguin in the middle of a huddle experiences temperatures like those on a tropical island, between 68˚F and 99˚F, while those near the edges are exposed to some of the coldest temperatures on Earth.
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On the surface, this huddling behavior looks like a great example of teamwork. In fact, it was part of a very popular documentary released in 2005 called
March of the Penguins
, narrated by Morgan Freeman, who said,

Though they can be aggressive during the rest of the year, at this time the males are totally docile—a united and cooperative team. They brace against the storm by merging their thousand bodies into a single mass. They will take turns, each of them getting to spend some time near the center of their huddle, where it’s warmer.

That’s a nice way to describe it, Morgan Freeman, but they’re not really a team. None of the penguins is keeping track of who’s taken his turn in the middle or at the edge, and none of them willingly leaves that warm middle for a turn on the cold edge. Instead, all the penguins act selfishly, and the morphing huddle is what happens as a result.

A detailed analysis based on hours of video showed that the overall movement of the group is exactly what you would expect if penguins follow a simple, selfish set of rules: If you have penguins on all sides, don’t move; if you’re on the edge, try to shove your way back into the middle. You
could
call that “taking turns,” as Morgan Freeman does, but when you think about it,
it’s really what would happen if every penguin was just trying to stay as warm as possible.
^III
The decrease in aggression among male penguins that the movie mentions makes sense from that selfish perspective too; for a huddling penguin it would be counterproductive to kill the heat source next to you. But for other animals in other situations, killing thy neighbor is the best possible strategy, and when that’s the case, they don’t hesitate at all.

A male zebra who comes across a baby zebra that isn’t his own will kick and bite it until it dies.
^IV
By doing that, he reduces the competition that his own offspring will face in life. Similarly, when a male lion displaces a rival and takes over his group of females, the first thing he does is kill the babies in his newly inherited pride so that he can start making babies of his own.
^V
Killing babies means more food for his (soon-to-be-conceived) babies and also has the added bonus that the females will come into heat sooner than they would if they were still nursing their young. Killing babies might at first seem unthinkable, but for many animals it’s just another way to look after their own selfish interests.

Remarkably, babies are even sometimes killed by their own siblings. Take snowy owls, for example. These large white birds are found in the Arctic, where they eat lemmings—small rodents that go through population explosions every once in a while. That
means that in some years lemmings are very hard to find while in other years you can’t swing a dead lemming without hitting a lemming. The problem is that those population explosions are unpredictable, so the owls don’t know ahead of time how many eggs to lay. In some years there are enough lemmings for a pair of owls to feed a whole nest of owlets, but in other years there’s hardly anything around. Fortunately, the owls don’t have to guess. They can just let their owlets fight it out themselves.

First, mama owl lays one egg. Then she waits two days and lays another. And so forth, until a total of five to ten eggs are laid. When the first owlet hatches, it gets all the food it needs from the parents and starts growing instantly. By the time the second egg hatches, that first owlet is quite big, putting the new, younger sibling at a real disadvantage. Whenever mom arrives at the nest to barf up lemmings for the babies, that first chick pushes its weaker sibling out of the way and gets as much vomit as it wants. Only after number 1 can’t eat any more does the younger owlet get to eat. As the subsequent eggs hatch, that system continues. Only after number 2 has had enough will number 3 get any, then 4, and so forth. This system’s brilliant, because it means in a lean year, instead of having six chicks so hungry that none of them has a chance of survival (which is what would happen if all the eggs hatched at once), the parents end up with one or two very healthy chicks. In a great year they end up with more healthy chicks. Owls can use this system to raise exactly the right number of chicks every year, no matter what the lemming populations are, and all it requires is that the parents let the babies enforce their age-based pecking order.
⁵

To be fair, the snowy owls don’t actually kill their brothers and sisters, they just starve them by leaving them no food. But that’s not the case with Verreaux’s eagles of Africa. I don’t know
if you ever suffered abuse at the hand of your older sibling, but it can’t possibly compare to what Verreaux’s eagles go through. A female of that species always lays two eggs, but only one survives. The older sibling gets about a three-day head start on its little brother or sister. Then, as soon as the second bird hatches, the physical abuse begins. It’s relentless. In one study, a researcher watched an older sibling peck its younger one 1,569 times, until it died at the age of three days. This abuse happens every single time. Out of two hundred observed nests, the younger sibling has been observed surviving in just one.
⁶

It’s not just birds either. Baby sand tiger sharks eat their own brothers and sisters before any of them are even born. At first, they develop within egg capsules inside their mother’s uterus, where each embryo gets its energy for growth from a yolk, just as in a chicken’s egg. But eventually that yolk runs out, and unfortunately, that happens before the shark is ready to be born. So the first shark to reach that stage of development (the oldest) swims around the uterus, eating other egg capsules and the siblings inside them. In fact, it doesn’t just eat the other egg capsules at random but actually seeks out the egg sac of the next-largest sibling and eats that one first. That way, there’s no chance of a strong competitor in the uterus later on.
⁷

The fact that animals will even kill their own brothers and sisters is a good reminder that animals aren’t born to be nice. They don’t try to preserve their own species, and they certainly don’t care about the other species of the ecosystem living around them. Instead, each animal looks after itself. An ecosystem is what emerges when every animal in nature follows Scrooge’s philosophy. (In fact, Scrooge comes off looking like a pretty good guy when you compare him to a Verreaux’s eagle.)

But of course, at the end of
A Christmas Carol
(spoiler alert), Scrooge changes his ways. The ghosts of Christmas past, present, and future collaborate to scare the crap out of him and convince him that no matter what the short-term benefits of greed, it’s a bad strategy in the long term. The ghosts tell Scrooge that if he doesn’t give up on his greed, he’ll become a ghost like them instead of going to heaven. That scares Scrooge enough that he immediately changes his attitude, making Christmas better for everyone, including his faithful clerk, Bob Cratchit.
^VI

So what about all these selfish animals? Won’t their greed ever bite them in the ass? What would ghosts from the past, present, and future say to them? The truth is, greed usually goes unpunished, but in some instances that shortsighted strategy can lead to catastrophe in the longer term. And there’s no more wonderful example of that than the giant carnivorous mice of Gough Island.
⁸

Gough Island is a cold and rainy rock in the middle of the South Atlantic Ocean, but millions upon millions of seabirds breed there. After all, many of these birds feed on fish out in the middle of the ocean, so they don’t have a lot of places available to lay their eggs. The island is only thirty-five square miles in area—that’s less than half the size of Lincoln, Nebraska—but it’s been called “the most important seabird island in the world” because more than twenty species breed there, some of which live nowhere else on Earth.
⁹
There aren’t any trees, so the birds lay
their eggs on the ground, and their chicks live there until they’re old enough to fly. That nesting strategy worked wonderfully for millennia because there were no predators on the island. But everything changed about two hundred years ago, when humans visiting the island by boat accidentally dropped off some common house mice.

Mice are usually vegetarians, but every once in a while, if food is scarce, a mouse will scavenge on the carcass of a dead animal. It’s rare, but it does happen.

When those mice first got to the island, around 1810, some of them might have scavenged on the corpses of whatever dead birds happened to be lying around. But at some point, a few of the mice on Gough Island figured out that you don’t have to wait for a seabird chick to die before you can eat it. Having lived on an island free of predators for so long, the seabirds had no strategy for defending themselves from land predators. The mice realized they could pretty much just start eating seabird chicks alive.