CONSERVATION OF ENVIRONMENTAL SPECIES
The prehistoric massacres
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In the previous issue I stated that our prehistoric ancestors committed ecological misdeeds as much and in some cases more than our contemporaries. In this issue we will see a "case" of that kind, that of the Clovis.
The contemporary evolution of several species in the same places normally causes some of them to evolve characteristics corresponding to the evolution of the others; thus, if the cheetah gets faster, even its usual preys tend to improve speed, by natural selection. This is exactly what happens in Africa, between the Homo species and its prey: these evolve defensive strategies, while Homo hones his hunting skills. Thus, the only continent in which the species of large animals have not become extinct en masse, in the last fifty thousand years, is precisely Africa, the one in which Homo has lived for the longest time (1).
Big, slow ones first
Where Homo sapiens suddenly arrived, the first to pay for it were the large, slow-moving animals. The giant sloth, which we see here grabbing a tree (pictured left), weighed up to four tons. The gliptodonti (reconstruction below) in some cases had the size of a Fiat 500; their armor evidently was not enough to protect them from the weapons of the newcomers. Both were probably very slow: ideal for being quickly transformed into large roasts. However, the bones and armor have come down to us, and we can see them in museums (photo in the center).
Where evolution did not take place in parallel, the sudden arrival of very skilled hunters will have much more disastrous consequences for the most sought-after prey. Most of the extinctions occurred before a few thousand years ago, by populations who used bows, arrows and spears. By comparison, modern extinctions (at least of large animals) are certainly fewer, and not because moderns are wiser hunters: they simply haven't had as many large species available to destroy. Some think that the massacre was practically global; there is no shortage of clues: the first are discovered in North America. Starting around 12,000 years ago, over a period of just over a thousand years, three quarters of the large mammals in North and South America disappear. Many point the finger at the Clovis, the people who probably owe the first significant human presence in the Americas. The story that comes out of some research on Clovis is one of the most significant examples of the influence that our species has on nature, and will help us understand what happened in the past almost everywhere.
The Clovis are named after an American location in New Mexico, where traces of their culture were discovered for the first time in 1927. The identification mark of this are very sophisticated spear heads; their props are in fact very large (up to almost thirty centimeters in length), and at the end that is towards the weapon shaft they are shaped in the shape of a large inverted V. That shaping was used to facilitate the attachment of the tip to the shaft.
Spears for big game
With spear heads of this type, the Clovis probably hunted large animals: mammoths, mastodons, camels, horses, cave bears, bison, yaks, giant sloths, glyptodons. The tips should not have broken when they were brandished with force inside the belly of the prey. In fact, they were precious, and it was important to recover them whole.
Remains of their culture have been found in various locations throughout most of North America; the dating of the finds goes systematically from 11,500 years ago for the Clovis sites of the American northwest, up to a few hundred years later, for the sites in the southeast of the continent.
It is believed that they came from Siberian lands; they reached North America by the only possible route, passing through Beringia, the land now covered by the Bering Sea, which at that time was a dry isthmus and connected eastern Siberia to Alaska. It is thought that a little before 11,500 years ago an ice-free corridor was formed, linking Beringia to the area where Edmonton is located today, in the Canadian state of Alberta.
That corridor was a possible transit route between two large ice masses.
The figure sketches the situation of the territory of Beringia and part of North America around 11,000 years ago. The two great ice masses are indicated by their names: Cordilleran and Laurentide; the arrows represent the Clovis migration through the ice-free corridor.
The presence of Sapiens in eastern Siberia is proven by finds that are at least 20,000 years old; twenty thousand years ago the last glaciation was almost at its peak, and would have continued, albeit gradually decreasing in intensity, until beyond the time when the Clovis migration took place. Given the great scarcity of rainfall, those lands were free from ice, and were covered with herbs and shrubs suitable for an arid and cold climate. In those conditions, which also seem prohibitive to us, some large herbivorous animals managed to survive. There were probably only very large animals in that area of Siberia: those small or medium-sized could not live at those temperatures without getting too cold. Certainly there was the mammoth, and it was perhaps the most widespread animal; perhaps here and there there were musk ox, woolly rhinoceros, bison, grizzly bear.
Mammoth under the snow
With its large body, the mammoth certainly did not fear the cold, as long as it had enough forage to feed on. This looks comfortable under heavy snow; but it's not in Siberia: I caught it just outside the Natural History Museum in Paris.
Below, one of his companions in misfortune is depicted, who disappeared from North America at the same time: the mastodon.
For Sapiens in that environment, hunting was not an option, but it was the only possible life strategy. The collection of spontaneous vegetables and fruits, assuming that there were any suitable for its diet, could contribute to sustenance only during the summer months. Certainly he had to know how to defend himself from the cold, and therefore cover himself with the fur of available mammals, build shelters, govern and produce fire at will. But most of all he had to be an excellent hunter and have adequate weapons for large prey, as well as cunning and courage.
It is enough to look at the Clovis spearheads, which probably derive from those Siberian peoples, to realize how those points were in practice the maximum that can be obtained with a lithic technology, having to produce a weapon capable of killing a large animal. such as a mammoth.
We can imagine that those spears were not only thrown, to obtain that force of penetration, but that they were brandished with force inside the belly of the prey, therefore from almost no distance. Such a great risk is explained by an absolutely probable reason: those prey were vital for those populations; without them they could not have survived.
In those cold climates, a culled pachyderm could provide food for more than a month for a whole group of Sapiens. An extremely hard existence, however, always poised between life, frostbite and hunger. Those harshness in all likelihood shaped a culture that valued the great prey at its greatest, a culture that could not devote time and energy to the superfluous. Those populations lived to hunt, precisely because hunting was the only way to survive, and they probably moved more or less continuously, in search of areas richer in large game.
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- On the Clovis, their culture, and the Overkill Hypothesis, that is the hypothesis that it was that people who caused the extinction of the great North American mammals, see:
- Prehistoric Overkill, by Paul S. Martin, is part of the volume Quaternary Extintions, a Prehistoric Revolution, published by Paul S. Martin and Richard G. Klein, with contributions from various authors; University of Arizona Press, 1995;
- Overkill, in The End of Evolution, Peter Ward. Bantam Books, New York, 1994;
- The Call of Distant Mammoths, Peter Ward. Copernicus by Springer-Verlag, New York, 1997;
- Peopling the New World, in Timewalkers; Clive Gamble. Harvard University Press, Cambridge, Massachusetts, 1994;
- Human Impacts of the Past, in The Sixth Extinction, Richard Leakey & Roger Lewin. Doubleday, New York, 1995. Published as Laesta Extinction. The complexity of life and the future of man, by Bollati Boringhieri, 1998.
- On the evolution of the horse, see: Fellow Creatures, in The Day before Yesterday; Colin Tudge. Jonathan Cape, London, 1995.
- On climate swings in the ice age, see: The Ice Age World, in In Search of the Neanderthals, Christopher Stringer & Clive Gamble. Thames & Hudson, New York, 1993.
NotePaul Martin used a specially developed model to simulate on a computer the advance of a population in the conditions of the Clovis, and the density of large mammals that that population hunted. Some of the details of the Clovis story told in this article stem from the results obtained with that model.