Top Quotes: “The Sixth Extinction: An Unnatural History” — Elizabeth Kolbert
Introduction
“This means that amphibians have been around not just longer than mammals, say, or birds; they have been around since before there were dinosaurs.”
“More or less from one day to the next, the zoo’s tank-bred frogs started dropping. A veterinary pathologist at the zoo took some samples from the dead frogs and ran them through an electron scanning microscope. He found a strange microorganism on the animals’ skin, which he eventually identified as a fungus belonging to a group known as chytrids.
Chytrid fungi are nearly ubiquitous; they can be found at the tops of trees and also deep underground. This particular species, though, had never been seen before; indeed, it was so unusual that an entire genus had to be created to accommodate it. It was named Batrachochytrium dendrobatidis-batrachos is Greek for “frog,” or Bd for short.
The veterinary pathologist sent samples from infected frogs at the National Zoo to a mycologist at the University of Maine. The mycologist grew cultures of the fungus and then sent some of them back to Washington. When healthy blue poison-dart frogs were exposed to the lab-raised Bd, they sickened. Within three weeks, they were dead. Subsequent research showed that Bd interferes with frogs’ ability to take up critical electrolytes through their skin. This causes them to suffer what is, in effect, a heart attack.”
“Even after it has killed off the animals in an area, it continues to live on, doing whatever it is that chytrid fungi do. Thus, were the golden frogs at EVACC allowed to amble back into the actual hills around El Valle, they would sicken and collapse. (Though the fungus can be destroyed by bleach, it’s obviously impossible to disinfect an entire rainforest.) Everyone I spoke to at EVACC told me that the center’s goal was to maintain the animals until they could be released to repopulate the forests, and everyone also acknowledged that they couldn’t imagine how this would actually be done.
“We’ve got to hope that somehow it’s all going to come together,” Paul Crump, a herpetologist from the Houston Zoo who was directing the stalled waterfall project, told me. “We’ve got to hope that something will happen, and we’ll be able to piece it all together, and it will all be as it once was, which now that I say it out loud sounds kind of stupid.”
“The point is to be able to take them back, which every day I see more like a fantasy,” Griffith said.
Once chytrid swept through El Valle, it didn’t stop; it continued to move east. It has also since arrived in Panama from the opposite direction, out of Colombia. Bd has spread through the highlands of South America and down the eastern coast of Australia, and it has crossed into New Zealand and Tasmania. It has raced through the Caribbean and has been detected in Italy, Spain, Switzerland, and France.”
“Today, amphibians enjoy the dubious distinction of being the world’s most endangered class of animals; it’s been calculated that the group’s extinction rate could be as much as forty-five thousand times higher than the background rate. But extinction rates among many other groups are approaching amphibian levels. It is estimated that one-third of all reef-building corals, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion.”
“Female African clawed frogs, when injected with the urine of a pregnant woman, lay eggs within a few hours.”
“Without being loaded by someone onto a boat or a plane, it would have been impossible for a frog carrying Bd to get from Africa to Australia or from North America to Europe. This sort of intercontinental reshuffling, which nowadays we find totally unremarkable, is probably unprecedented in the three-and-a-half-billion-year history of life.”
Discovering Extinction
“Aristotle wrote a ten-book History of Animals without ever considering the possibility that animals actually had a history. Pliny’s Natural History includes descriptions of animals that are real and descriptions of animals that are fabulous, but no descriptions of animals that are extinct. The idea did not crop up during the Middle Ages or during the Renaissance, when the word “fossil” was used to refer to anything dug up from the ground (hence the term “fossil fuels”). In the Enlightenment, the prevailing view was that every species was a link in a great, un- breakable “chain of being.” As Alexander Pope put it in his Essay on Man:
All are but parts of one stupendous whole,
Whose body nature is, and God the soul.
When Carl Linnaeus introduced his system of binomial nomenclature, he made no distinction between the living and the dead because, in his view, none was required. The tenth edition of his Systema Nature, published in 1758, lists sixty-three species of scarab beetle, thirty-four species of cone snail, and sixteen species of flat fishes. And yet in the Systema Nature, there is really only one kind of animal — those that exist. This view persisted despite a sizable body of evidence to the contrary. Cabinets of curiosities in London, Paris, and Berlin were filled with traces of strange creatures that no one had ever seen- the remains of animals that would now be identified as trilobites, belemnites, and ammonites. Some of the last were so large their fossilized shells approached the size of wagon wheels. In the eighteenth century, mammoth bones increasingly made their way to Europe from Siberia. These, too, were shoehorned into the system. The bones looked a lot like those of elephants. Since there clearly were no elephants in contemporary Russia, it was decided that they must have belonged to beasts that had been washed north in the great flood of Genesis.
Extinction finally emerged as a concept, probably not coincidentally, in revolutionary France.”
“Alvarez had been schooled in, to use his phrase, a “kind of hard-core uniformitarianism.” He’d been trained to believe, after Lyell and Darwin, that the disappearance of any group of organisms had to be a gradual process, with one species slowly dying out, then another, then a third, and so on. Looking at the sequence in the Gubbio limestone, though, he saw something different. The many species of forams in the lower layer seemed to disappear suddenly and all more or less at the same time; the whole process, Alvarez would later recall, certainly “looked very abrupt.” Then there was the odd matter of timing. The king-sized forams appeared to vanish right around the point the last of the dinosaurs were known to have died off. This struck Alvarez as more than just a coincidence.”
“The word “Anthropocene” is the invention of Paul Crutzen, a Dutch chemist who shared a l Nobel Prize for discovering the effects of ozone-depleting compounds. The importance of
this discovery is difficult to overstate; had it not been made-and had the chemicals continued to be widely used-the ozone “hole” that opens up every spring over Antarctica would have expanded until eventually it encircled the entire earth. (One of Crutzen’s fellow Nobelists reportedly came home from his lab one night and told his wife, “The work is going well, but it looks like it might be the end of the world.”)
Acidification and Coral
“1/3 of the species found in the vent-free zone were no-shows in the pH 7.8 zone.
“Unfortunately, the biggest tipping point, the one at which the ecosystem starts to crash, is mean pH 7.8, which is what we’re expecting to happen by 2100,” Hall-Spencer tells me, in his understated British manner. “So that is rather alarming.”
“Why is ocean acidification so dangerous? The question is tough to answer only because the list of reasons is so long. Depending on how tightly organisms are able to regulate their internal chemistry, acidification may affect such basic processes as metabolism, enzyme activity, and protein function. Because it will change the makeup of microbial communities, it will alter the availability of key nutrients, like iron and nitrogen. For similar reasons, it will change the amount of light that passes through the water, and for somewhat different reasons, it will alter the way sound propagates. (In general, acidification is expected to make the seas noisier.) It seems likely to promote the growth of toxic algae. It will impact photosynthesis — many plant species are apt to benefit from elevated CO, levels — and it will alter the compounds formed by dissolved metals, in some cases in ways that could be poisonous.”
“From a human perspective, calcification looks a bit like construction work and also a bit like alchemy. To build their shells or exoskeletons or calcitic plates, calcifies must join calcium ions (Ca]) and carbonate ions (CO, ) to form calcium carbonate (CaCO,). But at the concentrations that they’re found in ordinary seawater, calcium and carbonate ions won’t combine. At the site of calcification, organisms must therefore alter the chemistry of the water to, in effect, impose a chemistry of their own.
Ocean acidification increases the cost of calcification by reducing the number of carbonate ions available to begin with. To extend the construction metaphor, imagine trying to build a house while someone keeps stealing your bricks. The more acidified the water, the greater the energy that’s required to complete the necessary steps. At a certain point, the water be- comes positively corrosive and solid calcium carbonate begins to dissolve. This is why the limpets that wander too close to the vents at Castello Aragonese end up with holes in their shells.
Lab experiments have indicated that calcifiers will be particularly hard-hit by falling ocean pH, and the list of the disappeared at Castello Aragonese confirms this. In the pH 7.8 zone, three-quarters of the missing species are calcifiers. These include the nearly ubiquitous barnacle Balanus perforatus, the hardy mussel Mytilus galloprovincialis, and the keel worm Pomatoceros triqueter. Other absent calcifiers are Lima lima, a common bivalve; Jujubinus striatus, a chocolate-colored sea snail; and Serpulorbis arenarius, a mollusk known as a worm snail. Calcifying seaweed, meanwhile, is completely absent.”
“The Great Barrier Reef extends, discontinuously, for more than fifteen hundred miles, and in some places it is five hundred feet thick. By the scale of reefs, the pyramids at Giza are kiddie blocks.”
“Corals grew fastest at an aragonite saturation state of five, slower at four, and still slower at three. At a level of two, they basically quit building, like frustrated contractors throwing up their hands. In the artificial world of Biosphere 2, the implications of this discovery were interesting. In the real world — Biosphere 1-they were rather more worrisome.
Prior to the industrial revolution, all of the world’s major reefs could be found in water with an aragonite saturation state between four and five. Today, there’s almost no place left on the planet where the saturation state is above four, and if current emissions trends continue, by 2060 there will be no regions left above 3.5. By 2100, none will remain above three. As saturation levels fall, the energy required for calcification will increase, and calcification rates will decline. Eventually, saturation levels may drop so low that corals quit calcifying altogether, but long before that point, they will be in trouble. This is because out in the real world, reefs are constantly being eaten away at by fish and sea urchins and burrowing worms. They are also being bat- tered by waves and storms, like the one that created One Tree. Thus, just to hold their own, reefs must always be growing.”
“It is estimated that at least half a million and possibly as many as nine million species spend at least part of their lives on coral reefs.
This diversity is all the more astonishing in light of the underlying conditions. Tropical waters tend to be low in nutrients, like nitrogen and phosphorus, which are crucial to most forms of life. (This has to do with what’s called the thermal structure of the water column, and it’s why tropical waters are often so beautifully clear.) As a consequence, the seas in the tropics should be barren — the aqueous equivalent of deserts. Reefs are thus not just underwater rainforests; they are rainforests in a marine Sahara. The first person to be perplexed by this incon- gruity was Darwin, and it has since become known as “Darwin’s paradox.” Darwin’s paradox has never been entirely resolved, but one key to the puzzle seems to be recycling. Reefs-or, really, reef creatures — have developed a fantastically efficient system by which nutrients are passed from one class of organisms to another, as at a giant bazaar. Corals are the main players in this complex system of exchange.”
“Ocean acidification is, of course, not the only threat reefs are under. Indeed, in some parts of the world, reefs probably will not last long enough for ocean acidification to finish them off. The roster of perils includes, but is not limited to: overfishing, which promotes the growth of algae that compete with corals; agricultural runoff, which also encourages algae growth; deforestation, which leads to siltation and reduces water clarity; and dynamite fishing, whose destructive potential would seem to be self-explanatory. All of these stresses make corals susceptible to pathogens.”
“Tropical reefs need warmth, but when water temperatures rise too high, trouble ensues. The reasons for this have to do with the fact that reef-building corals lead double lives. Each individual polyp is an animal and, at the same time, a host for microscopic plants known as zooxanthellae. The zooxanthellae produce carbohydrates, via photosynthesis, and the polyps harvest these carbohydrates, much as farmers harvest corn. Once water temperatures rise past a certain point — that temperature varies by location and also by species — the symbiotic relation between the corals and their tenants breaks down. The zooxanthellae begin to produce dangerous concentrations of oxygen radicals, and the polyps respond, desperately and often self-defeatingly, by expelling them. Without the zooxanthellae, which are the source of their fantastic colors, the corals appear to turn white — this is the phenomenon that’s become known as “coral bleaching.” Bleached colonies stop growing and, if the damage is severe enough, die. There were major bleaching events in 1998, 2005, and 2010, and the frequency and intensity of such events are expected to increase as global temperatures climb. A study of more than eight hundred reef-building coral species, published in Science in 2008, found a third of them to be in danger of extinction, largely as a result of rising ocean temperatures. This has made stony corals one of the most endangered groups.”
“The corals of the Great Barrier Reef observe a lunar calendar. Once a year, after a full moon at the start of the austral summer, they engage in what’s known as mass spawning — a kind of synchronized group sex. I was told that the mass spawning was a spectacle not to be missed, and so I planned my trip to Australia accordingly.
For the most part, corals are extremely chaste; they reproduce asexually, by “budding.” The annual spawning is thus a rare opportunity to, genyouetically speaking, mix things up. Most spawners are hermaphrodites, meaning that a single polyp produces both eggs and sperm, all wrapped together in a convenient little bundle.
No one knows exactly how corals synchronize their spawning, but they are believed to respond to both light and temperature.
In the buildup to the big night — the mass spawning always occurs after sundown — the corals begin to “set,” which might be thought of as the scleractinian version of going into labor. The egg-sperm bundles start to bulge out from the polyps, and the whole colony develops what looks like goose bumps.”
Climate Change
“The only woody plant that grows on the island is the Arctic willow, which reaches no higher than your ankle. (The writer Barry Lopez has noted that if you spend much time wandering around the Arctic, you eventually realize “that you are standing on top of a forest.”)
A second theory posits that the tropics hold more species because tropical species are finicky. According to this line of reasoning, what’s important about the tropics is that temperatures there are relatively stable. Thus tropical organisms tend to possess relatively narrow thermal tolerances, and even slight climatic differences, caused, say, by hills or valleys, can constitute insuperable barriers.”
“Wood storks cool off by defecating on their own legs. (In very hot weather, wood storks may excrete on their legs as often as once a minute.)”
“It is now generally believed that ice ages are initiated by small changes in the earth’s orbit, caused by, among other things, the gravitational tug of Jupiter and Saturn. These changes alter the distribution of sunlight across different latitudes at different times of year. When the amount of light hitting the far northern latitudes in summer approaches a minimum, snow begins to build up there. This initiates a feedback cycle that causes atmospheric carbon dioxide levels to drop. Temperatures fall, which leads more ice to build up, and so on. After a while, the orbital cycle enters a new phase, and the feedback loop begins to run in reverse. The ice starts to melt, global CO, levels rise, and the ice melts back farther.
During the Pleistocene, this freeze-thaw pattern was repeated some twenty times, with world-altering effects. So great was the amount of water tied up in ice during each glacial episode that sea levels dropped by some three hundred feet, and the sheer weight of the sheets was enough to depress the crust of the earth, pushing it down into the mantle.”
“In its magnitude, the temperature change projected for the coming century is roughly the same as the temperature swings of the ice ages. (If current emissions trends continue, the Andes are expected to warm by as much as nine degrees.) But if the magnitude of the change is similar, the rate is not, and, once again, rate is key. Warming today is taking place at least ten times faster than it did at the end of the last glaciation, and at the end of all those glaciations that preceded it. To keep up, organisms will have to migrate, or otherwise adapt, at least ten times more quickly. In Silman’s plots, only the most fleet-footed (or rooted) trees, like the hyperactive genus Schefflera, are keeping pace with rising temperatures. How many species overall will be capable of moving fast enough remains an open question, though, as Silman pointed out to me, in the coming decades we are probably going to learn the answer, whether we want to or not.”
“In 2004, a group of scientists decided to use the species-area relationship to generate a “first-pass” estimate of the extinction risk posed by global warming. First, the members of the team gathered data on the current ranges of more than a thousand plant and animal species. Then they correlated these ranges with present-day climate conditions. Finally, they imagined two extreme scenarios. In one, all of the species were assumed to be inert, much like the Ilex trees in Silman’s plots. As temperatures rose, they stayed put, and so, in most cases, the amount of climatically suitable area available to them shrank, in many instances down to zero. The projections based on this “no dispersal” scenario were bleak. If warming were held to a minimum, the team estimated that between 22 and 31 percent of the species would be “committed to extinction” by 2050. If warming were to reach what was at that point considered a likely maximum-a figure that now looks too low-by the middle of this century, between 38 and 52 percent of the species would be fated to disappear.
“Here’s another way to express the same thing,” Anthony Barnosky, a paleontologist at the University of California-Berkeley, wrote of the study results. “Look around you. Kill half of what you see. Or if you’re feeling generous, just kill about a quarter of what you see. That’s what we could be talking about.”
In the second, more optimistic scenario, species were imagined to be highly mobile. Under this scenario, as temperatures climbed, creatures were able to colonize any new areas that met the climate conditions they were adapted to. Still, many species ended up with nowhere to go. As the earth warmed, the conditions they were accustomed to simply disappeared. (The “disappearing climates” turned out to be largely in the tropics.) Other species saw their habitat shrink because to track the climate they had to move upslope, and the area at the top of a mountain is smaller than at the base.
Using the “universal dispersal” scenario, the team, led by Chris Thomas, a biologist at the University of York, found that, with the minimum warming projected, 9 to 13 percent of all species would be “committed to extinction” by 2050. With maximum warming, the numbers would be 21 to 32 percent. Taking the average of the two scenarios, and looking at a mid-range warming projection, the group concluded that 24 percent of all species would be headed toward extinction.”
“The study has since been challenged on a number of grounds. It ignores interactions between organisms. It doesn’t account for the possibility that plants and animals can tolerate a broader range of climates than their current range suggests. It looks only as far as 2050 when, under any remotely plausible scenario, warming will continue far beyond that. It applies the species-area relationship to a new, and therefore untested, set of conditions.
More recent studies have come down on both sides of the Nature paper. Some have concluded that the paper overestimated the number of extinctions likely to be caused by climate change, others that it understated it. For his part, Thomas has acknowledged that many of the objections to the 2004 paper may be valid. But he has pointed out that every estimate that’s been proposed since then has been the same order of magnitude. Thus, he’s observed, “around 10 or more percent of species, and not 1 percent, or .01 percent,” are likely to be done in by climate change.
In a recent article, Thomas suggested that it would be useful to place these numbers “in a geological context.” Climate change alone “is unlikely to generate a mass extinction as large as one of the Big Five,” he wrote. However, there’s a “high likelihood that climate change on its own could generate a level of extinction on par with, or exceeding, the slightly ‘lesser’ extinction events” of the past.”
“At various points In Edoch, the sorts of creatures now restricted to the tropics had much broader ranges. During the mid-Cretaceous, for example, which lasted from about 120 to 90 million years ago, breadfruit trees flourished as far north as the Gulf of Alaska. In the early Eocene, about 50 million years ago, palms grew in the Antarctic, and crocodiles paddled in the shallow seas around England. There’s no reason to suppose, in the abstract, that a warmer world would be any less diverse than a colder one; on the contrary, several possible explanations for the “latitudinal diversity gradient” suggest that, over the long term, a warmer world would be more varied. In the short term, though, which is to say, on any timescale that’s relevant to humans, things look very different.
Virtually every species that’s around today can be said to be cold-adapted. Golden tanagers and cock-of-the-rocks, not to mention bluejays and cardinals and barn swallows, all made it through the last ice age. Either they or their very close relatives also made it through the ice age before that, and the one before that, and so on going back two and a half million years. For most of the Pleistocene temperatures were significantly lower than they are now — such is the rhythm of the orbital cycle that glacial periods tend to last much longer than interglacials — and so an evolutionary premium was placed on being able to deal with wintry conditions. Meanwhile, for two and a half million years, there’s been no advantage in being able to deal with extra heat, since temperatures never got much warmer than they are right now. In the ups and downs of the Pleistocene, we are at the crest of an up.
To find carbon dioxide levels (and therefore, ultimately, global temperatures) higher than today’s requires going back a long way, perhaps as far as the mid-Miocene, fifteen million years ago. It’s quite possible that by the end of this century, CO2 levels could reach a level not seen since the Antarctic palms of the Eocene, some fifty million years ago. Whether species still possess the features that allowed their ancestors to thrive in that ancient, warmer world is, at this point, impossible to say.
“For plants to tolerate warmer temperatures there’s all sorts of things that they could do,” Silman told me. “They could manufacture special proteins. They could change their metabolism, things like that. But thermal tolerance can be costly. And we haven’t seen temperatures like those that are predicted in millions of years. So the question is: have plants and animals retained over this huge amount of time — whole radiations of mammals have come and gone in this period — have they retained these potentially costly characteristics? If they have, then we may get a pleasant surprise.” But what if they haven’t? What if they’ve lost these costly characteristics because for so many millions of years they provided no advantage?”
“In the nineteen-seventies, the Brazilian government set out to encourage ranchers to settle north of Manaus, an area that was then largely uninhabited. The program amounted to subsidized deforestation: any ranchers who agreed to move to the rainforest, cut down the trees, and start raising cows would get a stipend from the government. At the same time, under Brazilian law, landholders in the Amazon had to leave intact at least half the forest on their property. The tension between these two directives gave an American biologist named Tom Lovejoy an idea. What if the ranchers could be convinced to let scientists decide which trees to cut down and which ones to leave standing? “The idea was really just one sentence,” Lovejoy told me. “I wondered if you could persuade the Brazilians to arrange the fifty percent so you could have a giant experiment.” In that case, it would be possible to study in a controlled way a process that was taking place in an uncontrolled fashion all across the tropics, indeed across the entire world.”
“A recent report by the Zoological Society of London notes that “the conservation status of less than one percent of all described in- vertebrates is known,” and the vast majority of invertebrates probably have not yet even been described.”
“One of the defining features of the Anthropocene is that the world is changing in ways that compel species to move, and another is that it’s changing in ways that create barriers — roads, clear-cuts, cities — that prevent them from doing so.”
Invasive Species
“Still today, it is not entirely understood how Geomyces destructans kills bats. What is known is that bats with white-nose often wake up from their torpor and fly around in the middle of the day. It’s been hypothesized that the fungus, which, quite literally, eats away at the bats’ skin, irritates the animals to the point of arousal. This, in turn, causes them to use up the fat stores that were supposed to take them through the winter.
On the edge of starvation, they fly out into the open to search for insects, which, of course, at that time of year are not available. It’s also been proposed that the fungus causes the bats to lose moisture through their skin. This leads them to become dehydrated, which prompts them to wake up to go in search of water. Again they use up critical energy stores and wind up emaciated and, finally, dead.”
“An expert on invasive species at the University of Massachusetts, has estimated that out of every hundred potential introductions, somewhere between five and fifteen will succeed in establishing themselves. Of these five to fifteen, one will turn out to be the “bullet in the chamber.”
Why some introduced species are able to proliferate explosively is a matter of debate. One possibility is that for species, as for grifters, there are advantages to remaining on the move. A species that’s been transported to a new spot, especially on a new continent, has left many of its rivals and predators behind. This shaking free of foes, which is really the shaking free of evolutionary history, is referred to as “enemy release.””
“The corollary to leaving old antagonists behind is finding new, naive organisms to take advantage of. A particularly famous-and ghastly-instance of this comes in the long, skinny form of the brown tree snake, Boiga irregularis. The snake is native to Papua New Guinea and northern Australia, and it found its way to Guam in the nineteen-forties, probably in military cargo. The only snake indigenous to the island is a small, sightless creature the size of a worm; thus Guam’s fauna was entirely unprepared for Boiga irregulars and its voracious feeding habits. The snake ate its way through most of the island’s native birds, including the Guam flycatcher, last seen in 1984; the Guam rail, which survives only owing to a captive breeding program; and the Mariana fruit-dove, which is extinct on Guam (though it persists on a couple of other, smaller islands). Before the tree snake arrived, Guam had three native species of mammals, all bats; today only one — the Marianas flying fox-remains, and it is considered highly endangered. Meanwhile, the snake, also a beneficiary of enemy release, was multiplying like crazy; at the peak of what is sometimes called its “irruption,” population densities were as high as forty snakes per acre. So thorough has been the devastation wrought by the brown tree snake that it has practically run out of native animals to consume; nowadays it feeds mostly on other interlopers, like the curious skink, a lizard also introduced to Guam from Papua New Guinea.”
“Already one plant species, Poa annua, a grass from Europe, has established itself on Antarctica; since Antarctica has only two native vascular plant species, this means that a third of its vascular plants are now invaders.”
Human-Driven Extinction
“Even many relatively small islands had their own large beasts. Cyprus had a dwarf elephant and a dwarf hippopotamus. Madagascar was home to three species of pygmy hippos, a family of enormous flightless birds known as elephant birds, and several species of giant lemurs. New Zealand’s megafauna was remarkable in that it was exclusively avian. The Australian paleontologist Tim Flannery has described it as a kind of thought experiment come to life: “It shows us what the world might have looked like if mammals as well as dinosaurs had become extinct 65 million years ago, leaving the birds to inherit the globe.” On New Zealand, different species of moas evolved to fill the ecological niches occupied elsewhere by four-legged browsers like rhinos and deer. The largest of the moas, the North Island giant moa and the South Island giant moa, grew to be nearly twelve feet tall. Interestingly enough, the females were almost twice as giant as the giant males, and it is believed that the task of incubating the eggs fell to the fathers. New Zealand also had an enormous raptor, known as the Haast’s eagle, which preyed on moas and had a wingspan of m more than eight feet.”
“”A very large mammal is living on the edge with respect to its reproductive rate,” he told me. “The gestation period of an elephant, for example, is twenty-two months. Elephants don’t have twins, and they don’t start to reproduce until they’re in their teens. So these are big, big constraints on how fast they can reproduce, even if everything is going really well. And the reason they’re able to exist at all is that when animals get to a certain size they escape from predation. They’re no longer vulnerable to being attacked. It’s a terrible strategy on the reproductive side, but it’s a great advantage on the predator-avoidance side. And that advantage completely disappears
when people show up. Because no matter how big an animal is, we don’t have a constraint on what we can eat.” This is another example of how a modus vivendi that worked for many millions of years can suddenly fail. Like the V-shaped graptolites or the ammonites or the dinosaurs, the megafauna weren’t doing any. thing wrong; it’s just that when humans appeared, “the rules of the survival game” changed.”
“Even a very small initial population of humans-a hundred or so individuals-could, over the course of a millennium or two, multiply sufficiently to account for pretty much all of the extinctions in the record. This was the case even when the people were assumed to be only fair-to-middling hunters. All they had to do was pick off a mammoth or a giant ground sloth every so often, when the opportunity arose, and keep this up for several centuries. This would have been enough to drive the populations of slow-reproducing species first into decline and then, eventually, all the way down to zero. When Chris Johnson ran similar simulations for Australia, he came up with similar results: if every band of ten hunters killed off just one diprotodon a year, within about seven hundred years, every diprotodon within several hundred miles would have been gone. (Since different parts of Australia were probably hunted out at different times, Johnson estimates that continent-wide the extinction took a few thousand years.) From an earth history perspective, several hundred years or even several thousand is practically no time at all. From a human m perspective, though, it’s an immensity. For the people involved in it, the decline of the megafauna would have been so slow as to be imperceptible. They would have had no way of knowing that centuries earlier, mammoths and diprotodons had been much more common. Alroy has described the megafauna extinction as a “geologically instantaneous ecological catastrophe too gradual to be perceived by the people who unleashed it.”
“Before humans emerged on the scene, being large and slow to reproduce was a highly successful strategy, and outsized creatures dominated the planet. Then, in what amounts to a geologic instant, this strategy became a loser’s game. And so it remains today, which is why elephants and bears and big cats are in so much trouble and why Suci is one of the world’s last remaining Sumatran rhinos. Meanwhile, eliminating the megafauna didn’t just eliminate the megafauna; in Australia at least it set off an ecological cascade that transformed the landscape. Though it might be nice to imagine there once was a time when man lived in harmony with nature, it’s not clear that he ever really did.”
“Modern humans arrived in Europe around forty thousand years ago, and again and again, the archaeological record shows, as soon as they made their way to a region where Neanderthals were living, the Neanderthals in that region disappeared. Perhaps the Neanderthals were actively pursued, or perhaps they were just outcompeted. Either way, their decline fits the familiar pattern, with one important (and unsettling) difference. Before humans finally did
in the Neanderthals, they had sex with them.”
“There was — and still is — no physical evidence to suggest that the [Neanderthals] were hairy.
In the nineteen-fifties, a pair of anatomists, William Straus and Alexander Cave, decided to reexamine the skeleton from La Chapelle. World War II-not to mention World War I-had shown the sort of brutishness the most modern of modern humans were capable of, and Neanderthals were due for a reappraisal. What Boule had taken for the Neanderthal’s natural posture, Straus and Cave determined, was probably a function of arthritis. Neanderthals did not walk with a slouch or with bent knees. Indeed, given a shave and a new suit, the pair wrote, a Neanderthal probably would attract no more attention on a New York City subway “than some of its other denizens.” More recent scholarship has tended to support the idea that Neanderthals, if not necessarily up to riding incognito on the IRT, certainly walked upright, with a gait we would recognize more or less as our own.”
“The process that turns an organism’s long strands of DNA into fragments — from a “text” into something more like confetti — starts pretty much as soon as the organism expires. A good deal of the destruction is accomplished in the first few hours after death, by enzymes inside the creature’s own body. After a while, all that remains are snippets, and after a longer while-
how long seems to depend on the conditions of decomposition — these snippets, too, disintegrate. Once that happens, there’s nothing for even the most dogged paleogeneticist to work with. “Maybe in the permafrost you could go back five hundred thousand years,” Pääbo told me. “But it’s certainly on this side of a million.” Five hundred thousand years ago, the dinosaurs had been dead for about sixty-five million years, so the whole Jurassic Park fantasy is, sadly, just that. On the other hand, five hundred thousand years ago modern humans did not yet exist.”
Conclusion
“When researchers from Leipzig performed a battery of tests on chimpanzees, orangutans, and two-and-a-half-year-old children, they found that the chimps, the orangutans, and the kids performed comparably on a wide range of tasks that involved understanding of the physical world. For example, if an experimeter placed a reward inside one of three cups, and then moved the cups around, the apes found the goody just as often as the kids — indeed, in the case of chimps, more often. The apes seemed to grasp quantity as well as the kids did-they consistently chose the dish containing more treats, even when the choice involved using what might loosely be called math-and also seemed to have just as good a grasp of causality. (The apes, for instance, understood that a cup that rattled when shaken was more likely to contain food than one that did not.) And they were equally skillful at manipulating simple tools.
Where the kids routinely outscored the apes was in tasks that involved reading social cues. When the children were given a hint about where to find a reward-someone pointing to or looking at the right container-they took it. The apes either didn’t understand that they were being offered help or couldn’t follow the cue. Similarly, when the children were shown how to obtain a reward, by, say, ripping open a box, they had no trouble grasping the point and imitating the behavior. The apes, once again, were flummoxed. Admittedly, the kids had a big advantage in the social realm, since the experimenters belonged to their own species. But, in general, apes seem to lack the impulse toward collective problem-solving that’s so central to human society.
“Chimps do a lot of incredibly smart things,” Michael Tomasello, who heads the institute’s department of developmental and comparative psychology, told me. “But the main difference we’ve seen is ‘putting our heads together.’ If you were at the zoo today, you would never have seen two chimps carry something heavy together. They don’t have this kind of collaborative project.””
“by the mid-nineteen- eighties the population of California condors had dwindled to just twenty-two individuals. To rescue the species — the largest land bird in North America — wildlife biologists raised condor chicks using puppets. They created fake power lines to train the birds not to electrocute themselves; to teach them not to eat trash, they wired garbage to deliver a mild shock. They vaccinated every single condor — today there are about four hundred — against West Nile virus, a disease, it’s worth noting, for which a human vaccine has yet to be developed. They routinely test the birds for lead poisoning — condors that scavenge deer carcasses often ingest lead shot — and they have treated many of them with chelation therapy. Several condors have been taken in for chelation more than once. The effort to save the whooping crane has involved even more man-hours, most provided by volunteers. Each year, a team of pilots flying ultralight aircraft teaches a new cohort of captive-raised crane chicks how to migrate south. for the winter, from Wisconsin to Florida. The journey of nearly thirteen hundred miles can take up to three months, with dozens of stops on private land that owners give over to the birds.”
