by Tim Flannery
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* In Fowler’s terms, a barbarism is a word minted using words from more than one language.
* Liquidambar maintains a European foothold in a small area of southwestern Turkey.
* Owen would take over the Natural History department there in 1856.
* William of Occam was an English Franciscan Friar who lived in the fourteenth century. He is remembered for his dictum that: ‘among competing hypotheses, the one with the fewest assumptions should be selected’.
CHAPTER 22
The Pleistocene—Gateway to the Modern World
In 2009—the same year that Arribas and his colleagues published their stimulating research on the two-million-year-old ‘late Pliocene’ fauna of southwestern Europe—the panjandrums at the International Union of Geological Sciences moved the beginning of the Pleistocene back by more than half a million years—from 1.8 million years ago to 2.6 million years ago. Their reasoning was that the glacial cycles (of which the ice ages are a part) should be included in their entirety in the Pleistocene, and that the first glacial cycle began 2.6 million years ago. It was a worthy and sensible decision, not least because it further reduced the rump-like Pliocene.
It was that veteran namer of geological periods Charles Lyell who coined the term Pleistocene. It means ‘most new’, in recognition of the fact that about 70 per cent of mollusc fossils from the Sicilian deposits studied by the venerable professor belonged to still-existing types. While the beginning of the Pleistocene has been appropriately designated, I cannot say the same for its termination. The International Union of Geological Sciences recognises the Pleistocene as ending 11,764 years ago, because that is when the last advance of the ice—known as the Younger Dryas—ended. After that comes the shortest geological epoch of all: the Holocene.
I hate to quibble, but if glacial cycles characterise the Pleistocene, then we are (or were until a few decades ago) still in it—for the simple reason that the ice would have advanced again, in accordance with the Milankovich cycles. But over the past 20 years or so, the burden of greenhouse gases has built to such an extent, and the planet so warmed, that scientists are confident that the ice will not return.
A proposal currently before the International Union of Geological Sciences argues for the recognition of yet another geological period: the Anthropocene. It is defined as commencing at the moment that human activity began to leave an indelible and widespread stamp on Earth’s sediments. Perhaps the moment that our greenhouse gases prevented the future return of the ice is the appropriate marker. Under that reading, the Pleistocene should last until around the end of the twentieth century, when it was succeeded by the Anthropocene.
The Pleistocene is characterised by rapid shifts in climate, including eleven major glacial events—ice ages—along with many minor ones. On each occasion glaciers and ice sheets spread and remained for extended periods, before being melted by brief warm spells. Over the Pleistocene, ice ages have prevailed for 90 per cent of the time, and at their greatest extent, glaciers and ice covered 30 per cent of the surface of the Earth. In the northern hemisphere, permafrost or glacial desert extended for hundreds of kilometres south of the ice sheets. With a bit more cooling, it’s possible that the glaciers could have extended to the equator.*
These dramatic climatic shifts left behind much evidence, in the form of glacial features and altered rainfall patterns. But it was not until 1837 that the Swiss scientist Louis Agassiz (he who named the megalodon shark) introduced the idea that much of the Earth had recently been in the grip of ice. He migrated to the US in 1847, taking up a position at Harvard, and in New England discovered abundant evidence, including massive boulders shifted by the ice, to support his hypothesis. But just what caused the ice ages remained a mystery until Milutin Milanković, a Serbian mathematician and a highly successful civil engineer, turned his mind to the problem.
Born on the banks of the Danube in what is now Croatia, Milanković began researching the causes of the ice ages in 1912. But, what with building bridges and experimenting with concrete, he lacked the time to make much progress on matters celestial. When World War I broke out, Milanković was on his honeymoon in his natal village, where he fell foul of the complex and shifting politics of Eastern Europe of the time. Considered a hostile foreign national, he was arrested by the Austro-Hungarians and taken to Esseg fortress, where he was locked up as a prisoner of war. He wrote that:
The heavy iron door closed behind me…I sat on my bed, looked around the room and started to take in my new social circumstances…In my hand luggage which I brought with me were my already printed or only started works on my cosmic problem; there was even some blank paper. I looked over my works, took my faithful ink pen and started to write and calculate…When after midnight I looked around in the room, I needed some time to realise where I was. The small room seemed to me like an accommodation for one night during my voyage in the Universe.
Mrs Milanković, it appears, was less sanguine about the arrangement. Through a colleague in Vienna she organised for Milutin to accompany her to Budapest. And there, through the good graces of other colleagues, he was given the run of the libraries of the Hungarian Academy of Sciences and the Hungarian Meteorological Institute. Milanković spent almost the entire the war happily studying the climates of other planets, as well as the great problem of the ice ages, and in the fragile peace that followed he became a professor of mathematics in Belgrade.
In 1930 Milanković published research showing that the ice age was caused by slight variations in the Earth’s orbit around the sun and the tilt and wobble of the Earth on its axis. By mid-1941 he had finished a book explaining his full theory, Canon of Insolation of the Earth and Its Application to the Problem of the Ice Ages, which included an explanation of the trigger for the advance of the ice: when celestial factors led to cool summers in the northern hemisphere, not all the winter snow would melt; year by year the ice caps would grow, and because ice is very bright and reflects sunlight, it accelerates the cooling trend.
On 2 April 1941 Milanković delivered his manuscript to a printing house in Belgrade. Just four days later, disaster struck when Germany attacked the Kingdom of Yugoslavia and destroyed the printery in a bombing raid. What one war had given, a second threatened to take away. But, thankfully, some printed sheets survived in a warehouse. A month later, in May 1941, two German officers called on Milanković, bearing greetings from Professor Wolfgang Soergel. They explained that they were students of geology, and Milanković entrusted them with the only remaining complete copy of his work. Soergel ensured that the book was published—in German—but in the decades after the war Milanković’s Canon was ignored. When the first English translation was made in 1969, it revolutionised our understanding of the ice ages immediately.
The cycles that Milanković identified had been in existence for hundreds of millions of years. So why did they trigger an ice age beginning 2.6 million years ago? It seems that, in earlier times, the configurations of the continents, and the higher level of greenhouse gases present in the atmosphere, prevented a full chilling, regardless of the influence of Earth’s orientation relative to the sun. From about 2.6 million years ago, however, these buffering effects were removed, and Milanković’s cycles began to play Europe’s biota like a piano accordion. At first, the duration of each cycle was about 41,000 years, and the effects were gentle. But about a million years ago the cold spells (known as glacial maxima) got deeper and longer, the cycles extending from 41,000 to 100,000 years.1 Just why this shift—from 41,000- to 100,000-year-long cycles—occurred is hotly debated. But the impact was clear: two faunas started to develop across Eurasia; a new one adapted to the cold phase, and an older one acclimated to the warmth.
The ice ages were not kind to the warmth-loving fauna. As the cycles intensified they blew entire species from the cosy café of temperate Europe. At each contraction of the bellows, frigid northern winds blew outwards from the pole, forcing the warmth-lovi
ng elements of its flora and fauna into shrinking refuges in Spain, southern Italy and Greece, where they would be confined until the orbital patterns ushered in a brief warming. The European ice age is thus marked by migration and extinction on a massive scale. More than half of Europe’s mammal species disappeared with the onset of the ice ages; surviving was all about adaptation, and migration.
What was it like to live in ice-age Europe? During the last glacial maximum, which peaked about 20,000 years ago, the sea level was between 120 and 150 metres lower than it is today, courtesy of all the water locked up as ice. A broad plain was exposed across the north of Europe, connecting Ireland to Britain and the continent. To the north a great field of ice and snow extended across land and sea to the pole. In the south, only the shallower northern Adriatic was exposed, though some of the Mediterranean islands became connected (Sardinia with Corsica, and Sicily with the mainland, for example). Sea temperatures were as much as 13° Celsius lower than they are today, and the now-extinct great auk bred on the coast of Sicily, while gulls, auks and gannets nested by the million on the Mediterranean cliffs of Iberia, France and Italy.
On land, temperatures were probably 6–8° Celsius lower, on average, than those of today, and winters were much colder, with permafrost extending as far south as Provence. Strong winds blew from the high ice cap, carrying fine dust from the polar deserts throughout Europe. Where London, Paris and Berlin are today, a vast polar desert, all but devoid of plant life, extended to the line of ice on or beyond the northern horizon. Frostbite, grit in the teeth and lungs full of dust would have been the lot of anyone venturing so far north.
To the south of this frigid desert, in a band stretching from northern Spain to northern Greece, were steppe lands and a stark forest of taiga-like conifers grew, similar to that which covers areas of Siberia today. Further south, deciduous trees and Mediterranean scrublands (maquis) found a refuge. Though limited in extent, these warm-adapted habitats were remarkably diverse. Around Gibraltar, for example, one could walk in a pine or oak forest, harvest blueberries and stroll through the maquis now typical of the region, all in the one day.2
The cold periods that characterise the ice ages end abruptly, accelerated by the outgassing of CO2 from the oceans when they begin to warm. But it takes thousands of years for the climate to reach a new, warmer equilibrium. At the end of the last glacial maximum it took the ice between 12,000 and 13,000 years to melt, and for the sea to regain its current levels. Before that, the Black Sea was a freshwater lake, with people living along the coasts, which were about 150 metres below current sea levels. Then, 8000 years ago, the Mediterranean broke through the Dardanelles and the Bosphorus, and within a few years the Black Sea filled, displacing those living around its ancient shore. The melting of the ice released weight on lands across Europe. Some areas, including Basilicata in southern Italy, the Gulf of Corinth, and northwestern Scotland, were uplifted by several hundred metres. There are many strange consequences of this history. One is evident if you are a birdwatcher standing in a mature Mediterranean forest. You will not hear a single species unique to the Mediterranean region. Yet in the nearby maquis you can hear plenty. That’s because, even as far south as the Mediterranean, tall forests were so devastated by the ice ages that none of the surviving patches was large enough to support the species of birds that were restricted to them.3
Between 2.6 million and 900,000 years ago, when the ice-age cycles were 41,000 years long and relatively gentle, a characteristic fauna developed. The giant hyena, Pachycrocuta brevirostris, was a metre high at the shoulder and 190 kilograms in weight, making it the largest hyena that ever lived. It evolved in Africa and its earliest appearance in Europe dates to about 1.9 million years ago.4 The giant hyena used caves as den sites, and the remains of past meals are well preserved in some. Even the bones of large creatures like hippos and rhinos bear its distinctive chew marks, though whether the hyenas killed such beasts or merely scavenged their carcasses is not known. Giant hyenas were probably social and were certainly powerful enough to kill creatures the size of wisent, or perhaps to drive Homo erectus from its caves.
The giant hyena arrived from Africa at about the same time that our ancestors, Homo erectus, reached Europe. The hyenas thrived, but our ancestors remained rare almost to invisibility. But then, about 400,000 years ago, the great hyenas vanished, and new members of our genus, in the form of early Neanderthals, started to become abundant, and to use caves.5, 6 What caused the giant hyena to become extinct is not clear. But some researchers tie it to the decline of the sabre-toothed and scimitar-toothed cats, as giant hyenas scavenged the big cats’ kills. The European sabre-toothed cat (a relative of the Smilodon) had become extinct about 900,000 years ago, while the giant scimitar-toothed cat, Homotherium, had begun to decline in Europe by half a million years ago.
The European jaguar inhabited the continent from about 1.6 million years ago until around 500,000 years ago. Larger than the living jaguar of South America, it is sometimes considered to be a giant version of the South American species that was replaced in the Old World by the leopard. Another spectacular cat of the early European ice age was the giant cheetah: it was the height of a lion, though considerably lighter. It had disappeared from Europe by about a million years ago.
Early ice-age Europe was also home to giant beavers of the genus Trogontherium. At almost two metres long they had similar gnawing habits to today’s beavers, but lacked flattened tails, instead having longish cylindrical ones. They survived in parts of Russia until about 125,000 years ago. Europe’s giant beavers lived at the same time as the first moose, Libralces gallicus. Its two-million-year-old remains have been found in southern France, where it inhabited warm grasslands.
An unexpected African immigrant was a kind of hippo, Hippopotamus antiquus. It had arrived by 1.8 million years ago and was happily settled into the Thames, among other rivers, by the time a warm spell known as the Eemian occurred between 130,000 and 115,000 years ago.* At the time, temperatures briefly rose to become slightly higher than those of the pre-industrial period, making the Eemian the warmest time in the last million years.
A small, ancestral red deer had appeared in Europe by about two million years ago.7 Its leg bones suggest that it may have been adapted to rugged mountain environments. It shared the forests with an early form of fallow deer. By a million years ago larger red and fallow deer had evolved, that were very similar to living types. Another group that flourished during the early ice ages was the ancestral cattle, bison and muskox, and an ancestral form of the giant deer Megaloceros.8 By 900,000 years ago—just as the 100,000-year glacial cycle takes hold—the ancestors of the cave lion, the first lions to be seen in Europe, stalked into the continent.
Ancestral wolves, Canis etruscus, had arrived in Europe from Asia over three million years ago, but they did not flourish until the ice ages. They can survive in many habitats, but wolves are really at home on the tundra.9 In European fossil deposits their bones are often accompanied by the remains of a coyote-sized canid, Canis arnensis. Over time this smaller canid became restricted to the lands adjacent to the Mediterranean, until about 300,000 years ago when it died out in Europe. Today, dogs may be our best friends, but strangely, in the whole fossil record of Europe there is only one site where a primitive human-like creature and a primitive wolf co-occur: the 1.85 million-year-old Dmanisi site in Georgia.
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* Just why the ice did not grow and grow until it covered the Earth is still debated. One factor may have been the polar deserts, the dust from which may have coated the ice, dulling it. The oceans played an important role in accelerating the weak warming trend triggered by the celestial cycles because warm water holds less gas than cold water.
* The Eemian is also known as Marine Isotope Stage Five E.
CHAPTER 23
Hybrids—Europe, the Mother of Metissage
Advances in DNA analysis, particularly in the study of ancient DNA, are unlocking a hith
erto unsuspected aspect of hybridisation (or metissage as the French might call it). It is increasingly shown to have been important in the origination of species, and in helping species adapt, with many examples coming from Europe. But perhaps most strikingly hybridisation has been a very important influence on human evolution in Europe. We often think of hybrids as something inferior—a sort of bastard or mongrel type. Pejorative associations of the word ‘hybrid’ were particularly common in the first half of the twentieth century, when misguided ideas about genetics made purity of race a dangerously attractive concept. The pioneering geneticist R. A. Fisher—who was a keen promoter of eugenics (the idea that societies could be improved by selectively breeding ‘superior’ humans)—believed that hybrids resulted from ‘the grossest blunder in sexual preference which we can conceive of any animal making’.1
The idea that species are discrete entities—carriers of a unique genetic heritance, is deeply embedded within us, perhaps reflecting some sense of a perfect, pre-human world, so hybrids can threaten our sense of order. They certainly complicate the work of the taxonomists, some defying easy classification and threatening the Linnaean system of classification that has ruled biology for more than 250 years.
Yet we have long known that hybridisation is widespread. By 1972, about 600 kinds of mammal hybrid had been identified (many from zoos or other captive situations).2 By 2005 it was estimated that 25 per cent of plant species, and 10 per cent of animal species, were involved in hybridisation.3 Over the last few years, research into ancient DNA has revealed that such figures are gross underestimates, even for wild species living in nature. Two recent studies, one involving bear species and the other elephants, illustrate what is being learned.