The book The Sixth Extinction: An Unnatural History by Elizabeth Kolbert is not what I expected. Despite my apprehension about reading another depressing book, I noted that this one had been awarded the Pulitzer Prize and was also available in paperback, so I gave it a chance for the 2020 summer days of Trump and Covid 19 virus.
The New York Times quote on the cover said “... she can write with elegiac poetry about the vanishing creatures of this planet, but the real power of the book is the hard science and historical context ...” That is true. And her book gives accounts of her joining current scientists undertaking current science in different parts of the world. The trips take us to fossil fields, coral reefs and trails through upper Amazon forests. It is here that aspects of past extinctions and the current sixth extinction are set out. All very thoughtfully.
The histories – in geologic time – of the earlier five extinctions are the short times when the diversity of life suddenly and dramatically contracted. That means a huge sweep of history. We learn some geology, archaeology, botany and oceanography. And we learn the stories of the scientists who developed theories about what happened in the past and what is happening now.
To sum up, the depressing reality of dying species is somehow not overwhelming in this book. It is gentle, readable, and even enjoyable. There is education about science, past extinctions and the present extinction. Paradoxically, the sixth is a by-product of the success of our species. As usual, let me give you a bit more detail of the contents and a sense of how the book goes. There is a prologue and 13 chapters.
The prologue of two and a bit pages is the most succinct summary of a book that I remember reading. After a shaky start in Eastern Africa, the new species Homo Sapiens (or modern humans) grew and spread. Not strong but resourceful, Sapiens pushed into other areas with different climates, predators and prey. The new humans crossed rivers, and mountains, adapting and innovating. In Europe they encountered bigger stronger humans who had lived there for a long time. They interbred. In the end they somehow killed them off.
Sapiens crossed seas and encountered distinctive creatures that had evolved in isolation on islands and continents. These were overwhelmed by Sapiens - or by their rat fellow travelers. Although huge and fierce, the large animals that had evolved had not had any predator. They had slow rates of reproduction and over a time they died out.
Over a few thousand years Sapiens spread around the globe. Then in one century, the population doubled. Then it doubled again. Forests were cut to cultivate food. Organisms were moved from one place to another mixing up the biosphere. In the last century fossil fuels were found and exploited. Sapiens began to change the atmosphere and oceans. No other creature had so changed the world. However, other sudden major events had occurred in which the diversity of living things had plummeted - extinctions. Five of these were so catastrophic they are called the Big Five extinctions.
The prologue tells that the story of the Sixth Extinction comes in thirteen chapters. Each is the story about one emblematic species – the American Mastodon or the Great Auk, for example. The earlier chapters are concerned with past great extinctions. The later chapters explore the present – the fragmented Amazonian rainforest, the warming slopes of the Andes and the extremities of the Great Barrier Reef.
The author ends the prologue saying extinction is morbid and massive extinction is massively so. She says she tried to convey the excitement of what’s being learned as well as the horror of it. I think she succeeded.
The first chapter is about the early 21st century disappearance of once dominant poisonous golden frogs from central Panama. With deaths around 2002, local biologists rushed to save frogs in controlled buildings hoping for later release into the wild. Within a few years the blight that was killing them spread through Costa Rica and was affecting other frogs and amphibians. Mention of a sixth extinction occurred in scientific literature.
The first mass extinction was in the Ordovician period 450 million years ago. This was before continents formed, when living things were largely confined to water. The “mother of mass extinctions” came 250 million years ago in the Permian period. That came close to ending life. The most recent occurred at the end of the Cretaceous period. Famous for ending dinosaurs, this extinction ended many other species like ammonites. A sixth extinction would be a rare unnatural event that we humans are not only observing but causing. “Natural” extinction rates for a species are very, very slow: one species per thousand years for amphibians. But there can be a sudden rush of extinctions that removes what had seemed dominant species. That seems to be the case for amphibians now.
And what happened to the golden frogs? It seems they were vulnerable to a particular form of ubiquitous fungus “Bd.” This likely arrived in the Americas with other kinds of frog that carried it. Bull frogs were introduced. African frogs were brought for pregnancy tests in the 1950s. With Bd established in the region, there is little chance that the golden frogs in the human ark will ever be able to live in the wild.
Chapter two, The Mastodon's Molars, notes every child gets model dinosaurs and so knows about extinction, which is not an obvious notion. In the mid 18th century, only living animals were recorded, although strange artifacts, “fossils” - meaning dug out of earth - were in museums. Some were quite large – ammonite shells and mammoth bones from Russia. It was the Mastodon find and the writer Cuvier in revolutionary France that brought the notion of extinction.
French troops going down the Ohio river in 1739 came across a sulphurous smelling marsh with bones sticking out of it near what is now Cincinnati. The commander took a giant thigh bone, tusk and several teeth and carried them right until the disastrous end of the campaign and then back to France. The place of the find is now a State Park in Kentucky – Big Bones Lick. The bones resembled elephant or Mammoth bones, but the teeth were different, cusped.
By 1762 mastodon bones arrived in London. France’s expert Buffon suggested mixed bones including elephant but also a larger species now disappeared. In 1796 Cuvier reported on his examinations of bones. He distinguished separate species: a Ceylonese elephant; an African elephant; the Russian bones, mammoth; and the Ohio bones, what became mastodon. These last bones Cuvier described as a lost species. He also identified another lost species, a giant beast, the giant sloth. Species died out he said. Cuvier looked for and found more of them. Two full skeletons of the mastodon were assembled and finally in 1806 Cuvier gave the animal that name.
Cuvier established a history of life, with those fossils nearer the surface being newer, animals, and those lower, reptiles, and so on. At about the same time evolution was becoming a theory he postulated some catastrophe had led to the loss of species. And he correctly supposed that several catastrophes had occurred.
Some details of his theories were incorrect. His proposed “revolution” just before recorded history is debris left by the last Ice Age. The stratigraphy of the Paris basin is not from eruptions of water as he thought but from changes of sea level and the effects of plate tectonics. But he was correct in several areas. Life has been disturbed by terrible events and organisms without number have been their victims. Nature can change course. And the event just before recorded history was us.
The Original Penguin is chapter three, about the now extinct Great Auk. The chapter begins with the thinking of Lyell, an influential English geologist. He suggested that landscape features were the result of very gradual change: sedimentation; erosion; and vulcanization. Extinction was presumed to be similarly slow. Darwin was influenced by Lyell on his voyage on HMS Beagle that included Chile, the Galapagos islands, Tahiti, Australia, New Zealand, Mauritius, Cape of Good Hope and back.
Darwin did find finches, sea turtles and seafaring lizards. But the theory of natural selection came after his return to England with assortments of specimens, an account of his trip and his theory that coral reefs grew up to keep close to the surface on sinking land. Darwin supposed that as the landscape gradually evolved in geology, so did living things in biology. New species slowly arrived and old species departed. Yet extinction could be swift. In defiance of Darwin’s theory of gradual evolution, the end of the Great Auk came suddenly as Darwin even as wrote his theory.
The last Great Auk is stuffed, in a plexiglass case in a storeroom at the Institute of Natural History in Reykjavik Iceland where the last remaining group of this 2.5 metre tall flightless birds resided. It had been shot in 1821 and sold as a trophy to a Danish Count. Before humans raided its nesting grounds, the Great Auk ranged from Norway to Newfoundland and Italy to Florida. Auks were common as food when Iceland was first settled. Europeans sailing to fish for cod off Newfoundland passed a huge slab of granite just underwater that was covered with birds – mainly Great Auks. Boats picked up barrel loads of Auks as fresh meat for their travels. Auks were superb swimmers that went ashore to breed, producing around one egg a year. The huge colony survived two centuries of being taken as meat before feathers became valuable commodities. The last remaining colony of size was just off Iceland and it was destroyed by a volcanic eruption in 1830 leaving only the tiny colony on Eldey Island off Iceland.
By this time Auks were then sought out for skins, eggs and to become stuffed birds for gentlemen’s collections – the fate of the very last Great Auk. The only good news is that an 1858 attempt by British naturalists to visit the Eldey Island ended up with a naturalist bringing about a law to ban hunting during breeding season – the Act for the Protection of Sea Birds. That trip to Eldey Island took place as Darwin’s first paper on natural selection went to press.
Darwin had been made aware of human-caused extinction as can be seen in his On the Origen of the Species so it is puzzling that he never recognized the special status and role of the human species in the story of life.
The luck of the ammonites is the fourth chapter. The medieval Italian city of Gubbio north of Rome has a narrow gorge running north east from it. The walls have diagonal bands of limestone. Before people, Gubbio was at the bottom of the sea and the remains of marine life rained down to the bottom building up over the millennia. In the lift of land that created the Apennine mountains, that limestone formed by dead sea life was lifted and tilted to 45 degrees. Walking up the gorge a hundred yards takes one past a hundred million years.
In the late 1970s a geologist, Alvarz, rewrote the history of life by discovering the first signs of an asteroid that ended the Cretaceous period in a visible thin layer of clay halfway up the tilted limestone. Alvarez ended up working with a geologist expert on forams. These tiny Marine creatures create a variety of attractive little calcium shells that can be used to date rock. Alvarez had been trained to expect gradual changes in life. However, in the grotto walls the rich range of shells in the Cretaceous limestone vanished in the thin layer of clay.
It was Alvarez’ father at Berkley who suggested testing the clay for Iridium, an element extremely rare on Earth but common in meteorites. He tested the clay and the limestone above and below. The clay iridium level went off the charts. Alvarez went to other places with late Cretaceous rocks in Denmark and South Island, New Zealand with the same result – large amounts of iridium. The theory that Alvarez came up with was that a six mile diameter asteroid made a glancing impact with earth and exploded on impact with the force of millions of hydrogen bombs and searing temperatures. Debris spread. Day became night. Temperatures plunged. A mass extinction occurred. Darwin and earlier scientists had known of the apparent sudden transition in life forms but had argued that there must have been a long transition period. So the new iridium-backed theory was hugely controversial.
Slowly more evidence came in. Shocked quartz was found from this end-Cretaceous time – a phenomenon associated with nuclear test sites. And evidence of a tsunami in a curious layer of end-Cretaceous sandstone in Texas. Finally, a hundred mile wide crater was found under the Yucatan peninsula in Mexico with the right sedimentary deposits – cores with a layer of glass. Since then more sites have found the end-Cretaceous iridium layer – Tunisia, Biarritz, suburban New Jersey.
The late Cretaceous time was of a hot world of tropical forests in the Arctic and shallow seas. Ammonites floated through these seas for millions of years leaving fossilized shells all around the world. The theory of asteroid impact has by now been refined, with the timing moved earlier.
The chapter ends reflecting on the chance of it all. What could evolution have done to prevent extinction from a singular event like an asteroid? There came a blast of flying incandescent rocks, surface broiling, clouds of sulphurous dust and a multi-season winter. Ammonites and their tiny eggs that floated around the surface of the oceans found themselves suddenly in a highly toxic zone. Species that lived deeper in the oceans survived better. The scale of the extinction: 100% for land dinosaurs; 2/3 for mammals; 4/5 for reptiles. The forests were decimated.
Welcome to the Anthropocene is the title of chapter 5. It begins with some science of how we deal with unexpected incongruent facts. That moves to how science adapts. Science believed things evolve slowly – evolution theory. The iridium tests showed that sudden catastrophic events occur. Science adapted: mostly things evolve slowly unless they change rapidly.
The author travels with scientists to Dobb’s Lynn, a dramatic geological feature in the Southern uplands of Scotland. A jagged outcropping of rock has light and dark vertical stripes and a waterfall crashes down a narrow valley. The rocks go back 450 million years to the Ordovician period when most of the continents were fused into one giant land mass – Gondwana. England was on the now lost continent of Avalonia and Dobb’s Lynn was in the Southern Hemisphere at the bottom of an ocean – the Lapetus Ocean.
The Ordovician period followed the Cambrian that is known for an explosion of new marine life forms. The Ordovician also saw new life forms. Marine families tripled. Life forms we would recognize filled the seas. The first plants, mosses and liverworts, clung to the dry land. At the end of the Ordovician, the seas emptied and 85% of marine species died off. The survivors made the modern world.
At Dobb’s Lynn are fossils of Graptolites, which were colonies of connected tiny tubular shelters formed like letter V variations. The dark layers in the outcropping rock contain plentiful fossils, but the light layers have practically none. The transition looks sudden, from habitable sea floor to uninhabitable. One different Graptolite form did survive. What happened? There were searches for iridium. Then it was noted that extinctions came in bursts and no cosmic events were found. The current theory for the end-Ordovician is glaciation. After a greenhouse climate with high CO2 levels, high sea levels and high temperatures, temperatures fell, Gondwana froze, sea levels plummeted, and ocean chemistry changed. The reason is unclear.
However, the end-Permian extinction had the opposite cause. Around 252 million years ago there was a sudden massive release of CO2 into the air. Temperatures soared – the oceans by 18 degrees – ocean chemistry went wild, oxygen levels fell, many organisms suffocated, and reefs collapsed. At the end of the one to two thousand year transition, 90% of all species on earth had been eliminated. Since the losses are so big, other explanations are being sought.
Discussions with the scientists turn to the variety of causes for extinctions and the possibility of humans being a cause. One scientist speculates that rats would be in a good position to exploit an extinction, growing or shrinking in size! The impact of humans is already a stratum to be found in geological formations. One scientist named the human impact and called the period the Anthropocene in a short article in the journal Nature in 2002. Efforts are now underway to have that term formally adopted in geological circles.
The Sea Around Us is the title of chapter 6. It begins at the tiny island Castello Aragonese off the Italian coast near Naples. Volcanic activity sends bubbles of CO2 out of vents on the ocean floor around the island. Marine biologists take the author to the vents. Near them sea grass is particularly vivid because it lacks the usual coat of tiny organisms. and numbers of sea urchins, mussels and barnacles fall away. Some with almost transparent shells remain above the vents.
The burning of fossil fuels has meant CO2 levels are higher than at any point in the last 800,000 years. If this goes on the higher temperatures are expected to trigger world altering events. Since the CO2 is absorbed in the sea, the concentration there rises so that ocean acidity, pH, rises with CO2 in the air. The Castello Aragonse vents give a pre-view of the results. Several species are missing. If the projected 2100 pH level of the oceans (?) is reached, the eco-system is expected to crash. Species are affected differently, but it will change the microbial communities, change the availability of key nutrients like iron and nitrogen and change the way light and sound pass through the water. It could produce poisonous algae and poisonous compounds of dissolved metals. Organisms with shells can be particularly affected because the process of making the shell gets harder for them with higher pH.
Thus far 1/3 of the CO2 pumped out by humans has ended up in the oceans, but it is not just the amount that matters but the speed. Scientists have looked at past acidifications and the present one is unprecedented on account of its speed. The end-Permian extinction supposedly arose from a massive burst of vulcanism at where Siberia now is. But even that was less than our cars, factories and power plants produce. By burning oil and coal humans are putting back into the air CO2 sequestered for hundreds of millions of years. The human legacy could well be one of the most catastrophic events in geological history.
Chapter 7, Dropping Acid, takes the reader on a visit to part of the Great Barrier Reef off Australia, to “One Tree Island” where there is a tiny research station used by visiting teams of researchers from around the world. After Captain Cook rammed the reef in 1770 theories arose about its formation. Darwin theorized the coral grew up as the ocean floor subsided and, that was confirmed later by the US Navy’s drilling out cores.
Reefs are animal, mineral and teaming with life, but mainly dead. Tiny gelatinous creatures together create their community’s outer shell of calcium together. Billions of “polyps” of a hundred polyp species create a living structure that can extend for over a thousand miles and be 500 ft thick. Corals support other creatures. Many thousands of species have evolved to rely on the corals for food, protection or prey. But corrals are unlikely to survive the Anthropocene.
Some science underway was a repeat of 1970s low tide water sample measurements from a site labelled DK-13, so as to find the change in calcification rates. Corals like light but can’t withstand long exposure to air so they grow as high as the low tide mark then spread out. The author went out with a scientist to collect samples over the brittle brownish crust of the corral using a flashlight in the pitch black of the evening low tide. There is a band of such corals like a waistband around the tropics. The biggest is off Australia, the next largest is off Belize with others in the Indian Ocean, Red Sea and Caribbean.
Evidence that CO2 can destroy coral came from the ending of the Biosphere 2 project in Arizona. That project was supposedly a self-sufficient isolated ecosystem with rainforest, ocean, desert, agriculture. A small group lived in isolation for 2 years, grew their own food and breathed recycled air. Decomposition was supposed to be balanced by photosynthesis so the CO2 was replaced by O2. But decomposition won out, the CO2 level rose and the people got altitude sickness. The project was closed in 1995 and a university took it over.
The “ocean,” a huge swimming pool, was a wreck. Most fish had died. Corals were just hanging on. A marine biologist, Langdon, went to work. The pH was low. But fixing the pH was not enough. It was the saturation state with respect to carbonate, essentially the available carbonate ions, that mattered to the coral animals. Langdon showed that coral growth was in proportion to the carbonate saturation state. In the real world the saturation state has fallen around the world from 4-5 in the 1700s to below 4 now. Corals need to grow to replace losses from storms and from fish and sea urchins eating bits and from loss by burrowing worms. Using computer models and field data the scientists found that at current rates of CO2 emission, the corals would stop growing and start dissolving within 50 years.
The numbers and diversity of species in and around the coral is amazing and unexpected, because tropical waters are low in nutrients. Coral enables an oasis in tropical waters that should be deserts. If coral goes so does the ecosystem. Reefs have come and gone several times in geological time. All were limestone, but they were different. And there were times without reefs. The pH and CO2 are not the only threats. Overfishing and agricultural runoff promote algae that compete. Deforestation promotes silting. There are bacterial infections like white band disease that affects two types of coral. But too much warmth – and the globe is warming - is its own hazard. The polyps, animals, share accommodation with tiny plants that produce carbohydrates. The relationship breaks down with heat when the plant produces too many oxygen radicals. The coral dies and the colour – given by the plant – turns to white.
The author ends with her experience of a snorkel dip at the time of the annual, new moon event when coral polyps throughout a reef simultaneously send out tiny bundles of eggs and sperm. Her experience should to be read. The author leaves readers with a feeling of wonder at a world so different and so moving. It is both ancient and current. It involves amazing and different living things that have created and are growing an impressive ocean habitat with marine animals in a marine desert.
Chapter 8 takes us into the Andes for The Forest and the Trees. The author is with Miles Silman in Eastern Peru. They are in mountains above a tributary to the Amazon facing Manu National Park – a biodiversity hotspot. They are to visit a series of tree plots on a trail that slowly descends along a crest of mountains, in order to monitor changes in the very different forest communities in the plots at changing altitudes. Different altitudes come with different temperatures. The impact of climate change is not just vanishing ice in the arctic, but changes in the tropics.
The author shows how travelling south from the arctic the types and numbers of tree species get larger. Canada’s forest has lower numbers and fewer species compared to the Southern US. The abundance of flora and fauna keeps growing as one approaches the equator.
With a machete to clear undergrowth the little group of Silman, graduate students and the author set off down the trail. They have soon found 30 new species and an entirely new genus – like discovering “oak” rather than a type of oak. Even in the dry season the trail is muddy and it had worn a deep channel into the mountain side so the ground was at eye level and from time to time the vegetation closed over it to make it a tunnel. It was not just trees but a hanging garden of orchids, bromeliads, hanging vines and other vegetation that periodically held hanging soil mats. They passed plot 1 at 11,320 ft. Plot 2 at 10,500 ft had recently been scoured by a landslide and there was interest in returning species. By plot 3 they chewed coca leaves with baking soda – the author found it helped with altitude sickness! They spent the night in a clearing near plot 4 at 8,860 ft where there were signs that a spectacled bear had been active.
Each plot covers about 2.5 acres. Any tree over 4” in diameter is tagged, measured, given a species and numbered. Those previously tagged were remeasured. There were 777 trees. The different plots have different temperatures on account of their differing elevations. The temperature suits a particular range of species – they have temperature preferences. Some of the dominant trees have narrow temperature ranges.
The plots were set up in 2003. The thought was that trees would “move” upward as temperatures rose to find their favourite temperature. A re-census was done in 2007 only 4 years later but it did show the forest was moving. The average species moved upward 8 ft per year. But there was a surprising range of responses. One species, the dwarf umbrella tree, was moving up the ridge at 400 ft per year. Christmas holly was more or less unmoving.
Anywhere and everywhere there are temperature fluctuations, so some ability to handle temperature change is to be expected from any plant and animal. They have ways of coping. The last 40 million years has been a period of gradual cooling beginning at the end of the Eocene epoch when it was so warm that no ice existed anywhere. Then, 35 million years ago, glaciers formed in the Antarctic. Three million years ago an arctic ice cap formed. About 2.5 million years ago, at the start of the Pleistocene epoch, periodic ice ages began. Sheets of ice spread over the Northern Hemisphere and then melted away a hundred thousand years later. These supposedly result from changes in the earth’s orbit by gravitational pull from Jupiter and Saturn. This cycle repeated some 20 times.
In an Ice Age the water caught up in ice caused sea levels to drop some 300 ft. The weight of the ice pushed down the earth’s mantle. Britain and Sweden are still in a rebound! Darwin suggested living organisms moved in response to temperature change and there is scientific support for that. The magnitude of the projected temperature change in the next century is expected to be comparable – but the speed is not. Today’s warming is ten times faster.
The travellers have now arrived at a camp at plot 8 that had several groups of cocaleros, groups who carry coca leaves, pass through the camp during the night. The science story moves to the Species Area Relationship, SAR. Basically, the SAR says that the larger the area you sample the more of a species you find. However, the relationship is not just direct but to some mathematical power of the area. There are constants specific to a species and to the region but the terrain does not matter. Species are lost when humans reduce the area. If half a grassland is destroyed, it is possible to calculate the loss of particular species. Scientists have used such calculations since 2004.
Data on current ranges of over a thousand plant and animal species was collected and correlated to present climate conditions. Then two extremes were chosen. If all species were inert and stayed put like the holly, the amount of climatically suitable land shrank – even to zero. The projection was bleak. With minimal warming and no species mobility, 22-32% of species would be committed to extinction by 2050. If species were highly mobile, species still ended up with nowhere to go because there is less area as one approaches a mountain top. With minimal warming 9-13% of species would be “committed to extinction by 2050. Taking an average, about 1/4 of species would be headed for extinction. The study appeared in Nature and remains controversial. Climate change may not produce an extinction as great as one of the Big Five, but it would be on a par with one of the slightly lesser historic extinctions.
A different finding is that trees structure the eco system much like coral creates the ocean home for a marine ecosystem. Although animals and birds are more mobile, the immobility of the trees affects the whole ecological community. So Silman’s work suggests global warming will restructure ecological communities.
The trip down the trail ended in an area popular with birders and a rainbow assortment of brightly coloured bird species was visible. The author reflects that the golden tanagers and the cock of the rocks made it through the cold of the last ice age, but since then there has been little advantage for species able to deal with heat. The impending extinction could be “apocalyptic.”
Islands on Dry Land, chapter 9, begins on a road heading north from Manaus in Amazonas state. The paved road becomes dirt and finally ends at a gate, cows and Reserve 1202 – an island in the centre of the Amazon. There is a whole archipelago of similar metaphorical “islands” in the forest along the Amazon where the Biological Dynamics of Forest Fragments Project, BDFFP, has been underway for some 30 years. Back in the 70s Brazil opened up these lands for cattle farming on condition that half be left intact forest. Tom Lovejoy, a biologist, proposed letting scientists say which trees should be cut, in a giant experiment. Surprisingly Brazil agreed.
The current 50 million ice-free square miles on the planet is the baseline for human impact. Half of this has become cropland and pasture and also cities, malls, reservoirs, logging, mining and quarrying. The remainder is “natural but not necessarily virgin.” There are arguments about how to divide the lands – “biomes” of climate and vegetation or “anthromes” such as “urban,” “irrigated cropland,” “populated forest” and the like. Some areas mostly lack people: Siberia, part of the Amazon, Northern Canada, and parts of deserts. But even these are crossed by pipelines, hydro projects and the like. So the unnatural squares of the forest fragment project models the world. The trees are studied in the BDFFP project.
Ornithologist Cohn-Haft studies birds – including trapping them in nets, banding them, counting them, freeing them. (My wife and I are members of the banding station at the point in Prince Edward County, Ontario which does the same.) Cohn-Haft is expert on identifying bird sounds and, less frequently, seeing the birds. The author joins him to listen and look for birds from a tower above the canopy as dawn breaks. She catches glimpses of several exotic birds and loves the brilliantly coloured red-legged honey-creeper.
For the first year after trees were cut there was an increase in the bird count and number of species in the remaining forest fragment. As time went on the number and variety of birds in the fragments started to fall and kept falling. There was no new equilibrium, just steady degradation of diversity. And what went for birds, went for other species.
Islands of any kind tend to be species-poor whether volcanic islands or land-bridge islands. It’s not just a matter of suitable habitat. Smaller areas are populated by smaller populations and small populations are more vulnerable to chance. A study in the 80s showed that the main predictor of local extinction was population size. This is not limited to islands. When a species leaves normally other species move in. For islands, re-population is harder. And this holds true for any habitat fragment. Researchers at BDFFP found that re-population is species dependent. White crowned manikins will cross clearings made for roads whereas scale-backed antbirds are reluctant. Without recolonization, local extinctions become regional and eventually global.
BDFFP researchers have marked out areas beyond the fragments in the “undisturbed” rainforest for control experiments. The author and Cohn-Haft went there to camp 41. They examined insect life and encountered army ants. These are voracious little insects, but some 300 other species are associated with them – and there is a class of birds, obligate ant-followers. In the late 70s Erwin, a scientist, made studies and estimated that there are 2 to 7 million species of insects in the tropics compared with the 10,000 bird species and 5,500 mammals in the world. Thus threats to the tropics mean many potential victim species. The impact of tropical deforestation can be calculated with the species area relationship. If 1% are felled per year, that translates into 5,000 species extinctions per year – 14 per day. Other estimates after Erwin’s study sounded more dramatic: current extinction was 10,000 times greater than the natural background rate. The reality is slightly better, perhaps because there is some re-growth and because extinction takes time or because the numbers of species found are a fraction of the real total number there.
The author asked Lovejoy to sum up. He said extrapolating from part of the world is dangerous. For example, changes in land use in the Amazon could affect atmospheric circulation – rain could disappear. But most of the BDFFP projects have been on a theme of loss – vanishing of diminishing species from the lots. There is a synergy between fragmentation and global warming.
The chapter ends with a failed quest to find the army ants a second time. They had vanished into their dormant mode. There needs to be a place where the rules are steadily followed for there to be butterflies that feed on bird droppings of birds that have evolved to follow ants.
Chapter 10, The New Pangea, begins doing a bat census in winter. This is when bats hang by their toes in caves in a hibernation torpor until spring. In 2007 such a census near Albany found dead bats all over the cave floor – they had white power on their noses. The next winter – the same thing in 34 caves across four states. This continued. The white powder is a cold-loving fungus accidentally imported from Europe.
Without human help, long distance travel for species is difficult. Areas of Australia, South America and Africa with similar climates and topologies had very different plants and animal species until humans arrived. And land separated different marine life in the eastern Pacific and western Caribbean. Darwin found some species could attach to duck’s feet and that some seeds could survive long enough in sea water to be carried by the sea to grow on fairly distant shores.
There were some similarities of species however, and that led to theories of land bridges. Then came the idea that the continents had been side by side then shifted apart. This idea of “continental drift” was derided initially but has been largely vindicated by the theory of plate tectonics. Today’s global trade and global travel deny even the remotest islands their remoteness. In recent decades the remixing of the world’s flora and fauna has accelerated so much that in many places non-native plants outnumber the native ones.
The author joined a winter bat census in disused mine shafts near Albany where she lives. She learned the disease had spread killing millions of bats as far as West Virginia. Bats fluttered in and out and crawled on the snow. These are the local “little brown bats” of North America. The census team photographed and caught sample bats. The white powder is not limited to the nose and the way it kills the bats is not known. One theory is that the irritation wakes them and causes them to burn the fat they need to live out the winter and they die if they try to seek food. The census is made from a subsequent count using the photos taken.
Moving species often don’t survive the move. If they do, the species may survive to a next generation. This is called “establishment.” Then they often remain confined to a small area. A third possibility is that they spread. For example Japanese beetles from a nursery near Riverton, New Jersey in 1916 have reached Alabama and Montana.
An expert suggests 5-15 out of 100 invasive species establish and of these 1 will become a “bullet in the chamber.” Why? One factor it that the species in a new place has been freed from traditional enemies. Purple loosestrife is an example. Some of these enemies may then be introduced to try to control the invasion – but that can turn into disaster. Species in a new place also need to find native species to take advantage of – witness the devastation from the tree snake introduced somehow in Guam from Papua New Guinea. It is now running out of species to eat! A scientist author cautions this is not “evil”; it is a-moral – just a species in the wrong place. What the snake has done in Guam is what Homo Sapiens has done all over the planet.
When a new pathogen turns up, it is like a gun in an existing knife fight – particularly deadly. In the 1800s the American chestnut used to be the dominant species, good for lumber, sprouting from the root when cut and widely used in making furniture from cribs to caskets. A fungus responsible for chestnut blight that is resisted by Asian chestnut trees was accidentally introduced. It was almost 100% lethal for the American Chestnut and so for the several other species that depended on chestnut trees.
The story returns to the bats. It seemed likely the invasion began near Albany and it turned out that re-examination of old photographs in a popular tourist cavern about 40 miles from Albany showed some bats with white nose. The cave gets 200,000 visits per year and lots of opportunity for the fungus to somehow be brought in from overseas.
Introduced species are now part of the North American landscape. Plantains, dandelions, garlic mustard came from Europe. Most lawn grasses are from elsewhere. A third of all plant species in Massachusetts came from elsewhere. Earthworms displaced the North American salamander. Then there is the long-horned beetle, the emerald ash borer and the zebra mussel. In Australia, children are urged to help hunt and kill poisonous cane toads, which do not eat the pest they were imported to help manage, but which have had many adverse effects on the environment. And in Antarctica, 1/3 of vascular plants have been introduced by seeds from researchers and tourists. The old separation of continents is being reversed. There is now one unified supercontinent – New Pangaea.
A few weeks after her visit to the mine shafts for bats, the author joins the scientist for a visit to Aeolus Cave near Dorset Vermont. Before the white nose, this was a wintering place for some 300,000 bats from as far as Ontario and Rhode Island. Some bats fluttered despite the cold, and the floors were littered with dead bats. Bats have likely been hibernating there since the entrance emerged from the last ice age. Their deaths break the evolutionary chain.
The New Pangea project can be traced to when humans – the most successful invasive species - left Africa. By the time they crossed into North America 13,000 years ago by the Bering land bridge they had domesticated dogs and brought them. Polynesians colonized Hawaii 1500 years ago. They brought pigs, rats, lice and fleas. The Columbian biological swap with Europe was huge. The year The Origin of the Species was published rabbits were released in Melboune. They have been breeding in Australia since. In 1890 a New York group introduced foreign species that might be useful or interesting – starlings. And one member wanted to introduce all the birds mentioned in Shakespeare. Today Americans import plants into gardens and import exotic animals. Plants, animals and insects hitch rides in ship ballast, in aircraft and in suitcases. Rates of arrival of invasive species have increased in the last 200 years. An invasive species arrives each month in Hawaii and every 6 weeks in California. In some sense Hawaii has been enriched, but local species have been falling so that the global diversity of species has fallen.
Elton, a scientist, studied the effect of invasions and concluded that the world would become simpler and poorer. The species area relationship can be used to show compressing the land mass into one continent would mean 1/3 of the mammals now present and half as many birds. But looking millions of years further ahead, eventually travel and global commerce will have stopped. The continents will have become separate and the islands re-isolated, dominated by giant rats or rabbits!
The author visits the bat caves again in 2010, 2011 and 2013 and describes the falling numbers of bats until in 2013 white nose had spread to 22 states and 5 Canadian provinces killing 6 million bats.
The Rhino gets an Ultrasound is about the efforts human take to try to preserve endangered species. The author is at a zoo where staff and scientists are checking to see whether efforts of have a small female Sumatran rhino ovulate have just failed or not – the ultrasound shows failed. The species only ovulate if a male is around – not possible for an isolated female in a zoo. In 1984 conservationists gathered in Singapore with a plan to breed Sumatran rhinos. A group of them was captured and were sent to various zoos in the US. That was a disaster. Two died from injuries during capture, 1 died from tetanus, 1 from unknown causes, and 5 died in the Malayan peninsula from a parasitic disease. Three of the 7 in the US survived being given the wrong food. By 1990, none had given offspring. The program was, as a magazine article put it, helping them to become extinct.
Finally in 2000, after lost pregnancies, a US zoo rhino produced one offspring then another. A male was sent to Sumatra in 2007. By 2012, a calf was fathered there in Sumatra’s Way Kambas National Park. While not offsetting the deaths, the births were rare. Births in the wild continue to decline.
A similar story holds for other Rhinos. And the same is true for other big mammals like pandas. Unless they are locked up, such big charismatic mammals are in trouble. African elephants declined by 1/3 over the last 3 generations. A century from now, any of them will be only in zoos or wildlife areas so small they qualify as “quasi-zoos” as a zoologist put it.
The author visits the un-pregnant rhino at the zoo again. The effort calls for a huge quantity of imported food and the disposal of piles of manure. This small rhino appears affectionate, a bit like a dog, but it’s more related to a horse. And a sudden move of the head could break a human’s arm petting it. It’s big and heavy. Adults, like elephants and other big herbivores and bears and big cats, are beyond predators.
At various points in history such big creatures seemed at an advantage. Towards the end of the last ice age such jumbo creatures were in all parts of the world. Europe had woolly rhinos, cave bears, giant elk and oversized hyenas. North America had mastodons, mammoths, beavers the size of grizzlies, a group of sabre-toothed cats and a big sloth. South America had the giant sloth and, among other huge animals, a giant type of kangaroo. Even small islands like Cyprus had giant animals. New Zealand had moas – a large 12ft high flightless bird. However the enormous Haast’s Eagle, wingspan 10 ft, preyed on moas. These have gone. We now live in an impoverished world.
Near the Cincinnati zoo with the un-pregnant rhino is the Big Bone Lick marsh where the Mastadon tooth, a skeleton, and other ancient bones were found. It is now the site of a park with a museum and mini-golf.
The chapter ends with reflection on the theories about how big species disappeared – theories that now favour humans as an explanation. Extinction probably took thousands of years. For a human timeframe the change was too slow to perceive. Humans are capable of driving any great mammal to extinction, but also of going to great lengths to prevent an extinction.
Chapter 12, The Madness Gene, looks at the Neanderthals. The Neander valley, Das Neandertal, is about 20 miles north of Cologne on a bend in the Dussel, a tributary to the Rhine. There is a museum and theme park with shrubs from the ice age, Neanderthal beer and a statue of a smiling Neanderthal leaning on a stick and trails leading to the site where bones were found in 1856. More bones have since been found all over Europe and the Middle East as far south as Israel. Neanderthals lived in Europe for at least 100,000 years. This was mostly a time of cold, with ice sheets covering Scandinavia. It is thought they built shelters and fashioned clothing. Then, 30,000 years ago, they vanished. There have been many theories, but today it is thought that their bad luck was us. Modern humans arrived around 40,000 years ago and the archaeological record shows that when humans arrived in an area of Neanderthals, the latter disappeared.
There was however some interbreeding with modern humans so that people today can have about 4% Neanderthal genes. There is an Institute for Evolutionary Anthropology in Liepzig whose director, Paabo, invented the study of ancient DNA – starting with Egyptian mummies and moving on to mammoths and moas! In 2006, he began work to sequence Neanderthal DNA. Unfortunately, as soon as organisms die, the DNA begins to break down so that only fragments are left. Neanderthals are our nearest relative and finding the genetic differences was part of Paabo’s interest.
The original Neanderthal find was by workmen in a quarry, but the owner wanted the bones saved and a local schoolteacher realized they were special, and Darwin’s The Origin of the Species had just appeared. As more bones were discovered they were thicker than humans’ and the skulls were larger. A skeleton found in France led in the early 1900s to speculation about a hunched gait, lack of artistry and bestiality. By now, it is thought Neanderthals walked upright with a gait similar to our own. In the 1960s several Neanderthal skeletons that were found in a cave in northern Iraq were interpreted as showing evidence of caring for sick, interment with flowers, and spirituality. Those details are unlikely, but it is possible Neanderthals were intelligent individuals.
Gene analysis is a challenge. Maybe in permafrost the fragmenting of DNA would allow one to work back 500,000 years but not a million. Dinosaurs go back 65 million years, so Jurassic Park is pure fiction. But 500,000 years ago modern humans were not around. Despite difficulties of DNA fragments, the sequencing project was yielding some sequence results when a geneticist at Harvard Medical School noticed that the Neanderthal sequences were similar to human sequences – but were more similar to European and Asian DNA than African. Theories of human evolution had suggested that we came out of Africa, moving to the Middle East, then Europe where we encountered other humans that we “replaced.” In “the outstanding article of the year” published in Science 2010, Paabo and his team showed the “leaky replacement” of Neanderthals. Liaisons with Neanderthals produced children that helped to populate Europe, Asia and the New World. Even now, 30,000 years later, all non-Africans from New Guineans, to the French to the Han Chinese have 1-4% Neanderthal DNA. Neanderthals are 1-4% not extinct.
Our other nearest relatives are chimps and gorillas. The author goes to the Leipzig zoo and sees an orangutan performing intelligence tests. Small children and orangutans can figure out many of the same tests. We are apes but something makes us different. It seems other apes can’t do collective problem solving. You would never see two chimps carrying something heavy together. How would Neanderthals have done? Paabo doesn’t want to speculate.
Neanderthals were bigger boned and much stronger than humans. They were adept at toolmaking but they didn’t seem to change their tools over the years. There are signs they suffered bad injuries—perhaps because in hunting they don’t seem to have developed projectiles. Some of the injured survived their injuries. Others likely watched over them. So they likely had a capacity for empathy. They dispersed from Europe or Western Asia but they stopped at water or a significant obstacle. And that seems to be a significant difference. Modern humans ventured onto oceans, developed boats and travelled beyond the horizon. Paabo thought it might be possible in the DNA to find the source of our “madness.” One day we may know the freak mutation that made the human insanity and exploration thing possible.
Paabo can never know how significant a bone is. A finger bone with good DNA from a cave in Siberia was expected to be Neanderthal or Sapiens, but it turned out to be another human – called Denisovan after the cave where it was found. Surprisingly, modern humans have interbred with Denisovans too. New Guineans have 6% Denisovan DNA. It is not clear how Denisovans died out, but the timing fits the arrival of modern humans. If they have a long gestation periods like us, they had the vulnerability of large animals – a low reproduction rate. And that is true for our next of kin. Chimpanzees and mountain gorillas have declining populations. Sumatran orangutans are “critically endangered.”
One of the largest assemblages of Neanderthal bones was found at La Ferrassie, France near the famous painted caves of Lascaux. One of Paabo’s colleagues is excavating there. The site is beneath a limestone cliff that looks like half a vaulted ceiling. The bones on top are modern humans who occupied this cave when the Neanderthals had left. The Neanderthal skeletons are long gone. Students uncover bone fragments and flint fragments – axe heads. The author muses what it would have been like: cold; treeless; wandering elk and mammoths. People would have been young. And the smell would have been bad. Taught to identify a flint hand axe, the author finds it symmetrical and attractive. She is warned against imposing a significance onto the object from our time. Craftsmanship? There are no objects of personal adornment.
The author tells that the nearby human cave can only be entered by crawling through a low opening. It is so dark that only with fire could anything have been seen. The walls are covered with hundreds of engravings of animal images, many of them now extinct. Some possess an uncanny reality. The Neanderthals lived in this area for over 100,000 years and had no more impact than other large mammals. If humans had not arrived, they would likely still be there with the wild horses and woolly rhinos.
The Thing with Feathers, an allusion to a poem by Emily Dickinson, is the title of the short chapter 13. The chapter reinforces the human determining role – causing extinction in various ways but intervening heavily to try to prevent individual species from becoming extinct. There is a tank in San Diego zoo with a pool of liquid nitrogen at -320 degrees in which are towers of boxes full of upright vials. The author is shown the vial that contains what is left of the black faced honeycreeper that lived on Maui. The cells of the last bird that died are in the vial that is put back into the tank. Such frozen zoos have collections of species on ice. How may vials would be needed for the bats and for the frogs and the corals? Is there a better way?
Humans can be short sighted and destructive, but they can be forward looking and altruistic. DDT has gone. Bald Eagles are back. Great efforts were made to help condors – including vaccination against West Nile Virus! The author tells of the efforts to have one of the only remaining Hawaian crows produce sperm so there can be survival of this bird if only in captivity. These efforts could be a source of optimism, but they are not for the author.
The author has tried to give some sense of extinctions in the big picture of life’s history. It is up and down, neither uniformitarian nor catastrophic. Life is resilient, but not indefinitely so. There have been long uneventful stretches but then revolutionary changes. The causes are varied: glaciation; global warming and change of sea chemistry; an asteroid impact; and, now, human beings. When the world changes faster than species can adapt, they drop out. It doesn’t matter whether people care or not. People change the world. They always could. They always did. And modernity just makes that power greater.
“What happens to us?” asks the author. The sixth extinction will be our most enduring legacy. It will continue to determine the course of life long after everything people have created has become dust and the earth has been inherited by giant rats – or not.