Read an Excerpt
Life in a Cave
By Paul Jordan
The History PressCopyright © 2011 Paul Jordan
All rights reserved.
People and Caves
Our earliest ancestors in Africa did not live in caves: they lived in the trees. Later they ventured onto the savannah and were able to spread around the tropical and subtropical world, even when the era of the ice ages was coming on, without needing the shelter of caves. Only in the cold environments of the northern latitudes in the times of full glaciation did people develop the way of life we can reconstruct for our 'caveman' forebears. Even then, they by no means in all times and places lived in caves.
This book tells the story of the lives of our fully human ancestors (Homo sapiens sapiens) and their close relatives the Neanderthalers (Homo sapiens neanderthalensis) who lived in Europe and Western Asia, often in caves, during the last ice age. (That epoch ended about 10,000 years ago before the invention of farming, urban living, writing, the wheel, and so much else we regard as natural to our lives.) Of course, for the 'caveman' way of life to have ever come about, there needed to be both human evolution and the formation of caves.
Caves and cave systems come into being as the result of natural processes and natural processes destroy them in the end: few caves are very old in geological terms, often younger in fact than the oldest fossils of our ancestors. Caves come in a variety of shapes and sizes because they are formed by different processes acting on different rocks and we know them at different stages of their creation and destruction. Some of the caves we know – and there must be many we do not – have been found in the course of mining operations. But most caves are evident to us, as they were to our ancestors, because they have visible openings. Some caves present themselves as a single, large and open cavern or little more than an overhanging shelter, while others form part of deep underground systems with negotiable passages including pits and chimneys or with quite impassable crawlways. In the depths of such systems there may be water in the form of streams, lakes and waterfalls and a myriad of exotic cave deposits including crystals and stalactites and stalagmites. The large open caves and rock overhangs offer people shelter from enemies and the elements, while the deep systems offer extraordinary experiences and mysteries. Our ancestors explored both situations.
Landscapes endowed with limestone cave systems are called 'karsts' and a world map of such landscapes shows the area around the Mediterranean and up into temperate northern Europe well pocked with such features. The same is true across the Middle East to the Far East, down East Africa to the south-west of the African continent, over Australasia and especially in southern Australia. Caves are found across the USA and down into Central America along with western South America. There are also stray pepperings into Scandinavia and across Russia and Siberia. It is especially the northern and eastern Mediterranean regions, together with Europe from northern Spain across to Russia, that set the stage for the story of prehistoric human life in the last ice age.
How Caves Begin and End
Rocks like limestone are soluble in water and the caves that form in them are called solution caves. Europe has some very impressive solution caves – in Belgium, France and Spain and eastwards in the Alps to the Adriatic. There are processes other than solution that can create caves, or at least start them off, but most caves have been largely 'excavated' by running water, not so much in the way that a river scours its course but rather by the sheer dissolving effect (solution) of running, circulating, percolating water.
Some caves were started when cavities were left in the layer formations of marine deposits (or in lava flows). The sea has played a big part in the making of coastal caves as a result of sea-driven erosion with sand and pebbles and boulders, or just pressure of the waves aided by chemical action or the boring of marine organisms. Bodies of water have also played a part in the generation of caves along stream banks and lake margins. Sometimes weather alone can eat out caves in the weaker members of rock structures with the action of rain, wind-driven sand and regular alternations of frost and thaw or wetting and drying. Even rock-splitting plants can initiate the process of cave making, but solution remains the chief cause of most caves, including the most complex and spectacular, whether working on cavities already available or creating its own from scratch. Plain water is enough – its natural acids do the dissolving as it soaks into the terrain and finds its way through the weaknesses in the rock. Of course, it has plenty of time to work in, by our standards, and there are many variables in the process of cave formation: of temperature, pressure, chemical concentrations, rate of refreshment with more water, to say nothing of the nature of the rock involved.
In the formation of cave systems, a complex pattern develops – of run-off variations, stream diversions, free discharges and blockages, of deepening runs of underground water along lines of joints and faults in the rock, of collapses above and below ground. By such means were the very varied cave systems of the world created: by such means, too, are cave systems eventually destroyed, with the occasional help of other factors like earthquakes and all against the background of the world's dynamic weather systems and ever-changing climate. Some caves just get silted up or blocked with larger rubble. Rock falls, whether due simply to ongoing solution or to seismic shocks, can be the beginning of the end for caves, as further solution works on the rubble and weather erosion enters the picture. While they last, caves can be subject to quite startling changes of circumstance: geological upheaval can place sea caves high above the waters that initiated them, while rising sea levels in the warm, melting times between ice ages can bring the sea to their door, so to speak.
Caves for People
The characteristic cave of what we may think of as the 'caveman' era, handily overlooking a watercourse with plenty of game passing by, comes about when the stream's erosion of its course exposes caves along its banks and goes on to cut its way down below them. There are caves just like that, notably in the Périgord region of France where so much important evidence of our relatively recent Neanderthal cousins and Crô-Magnon ancestors has come to light in the valleys of rivers like the Dordogne. But most of the very earliest human remains – the bones of the people and the stone tools they made – have not come from caves. This is partly because some of the caves they may have used have not survived to our day and their contents are lost. It is also because caves were not the only or even the main places where very early people lived and laboured. Caves were never available (or required) in some of the regions occupied by evolving humanity and even where they were occupied there was still a need for open-air camps and work sites. The archaeological remains of these open-air sites are harder to find than those from caves, in which materials can survive in much better shape and order, with layers of stratigraphy to help date them. Stone tools transported and rolled in old river gravels (their makers were working on the welcoming banks of long lost or wandered streams) are all we have to chart some epochs of human evolution. In some places, like Eastern Europe which does on occasion afford us some magnificent open-air sites, the advance and retreat of the ice ages' glaciers and their floodwater run-offs have erased a great deal of evidence for the highly significant open-air aspect of 'caveman' times. But its significance must be remembered, along perhaps with an appeal for the abolition of this 'caveman' notion altogether, not least in view of its lingering sexist connotations. The people whose lives we shall be considering belonged to the Old Stone Age, before the development of polished stone implements let alone of metal ones, though they employed wood and sometimes bone and antler too: archaeologists call them palaeolithic people and we can now fix our sights on their appearance in the archaeological record after millions of years of evolution in Africa.CHAPTER 2
Humanity has evolved against a backdrop of climatic change: whatever the future holds it is fair to say that the past 7 million years or so, during which time we parted evolutionary company with our closest relatives the chimpanzees, have been coldish and sometimes very cold times. There have been warmer fluctuations during this period, but the world was once very much more dependably warm with little difference in warmth between the poles and the equator: after very dim and distant ice ages of the remote past, these generally very warm conditions went on and on until about 55 million years ago (mya). Thereafter there was a slow decline in world temperatures reaching a low (though not as low as today) between 35 and 25 mya. The factors that interact to change the earth's temperatures include the heat output of the sun, the degree of transparency of the earth's atmosphere (influenced, for example, by volcanic eruptions or degree of cloud formation) and the variability of the shape of our planet's orbit around the sun and of its axis of spin relative to orbit; of course, we have been busy adding a human factor to this picture of late.
The Primates, the order of mammals to which we belong, begin to emerge in the fossil record a little before 55 mya, evolving out of small fruit - and insect eating animals. By 55 mya, the distinctive Primate trait of large brain for body size is evident – the brain capacity partly evolved to handle high quality vision to help with the identification of good ripe fruit and fresh leaves against the clutter of the dark forest in which these creatures lived. Large brains also help with complex social relations, which was to be very important as the human line evolved.
By the time of that long cooler spell between 35 and 25 mya the Primates had greatly diversified, with the presence of monkey-like creatures at the start of this time span and ape-like ones too at the end. A peak of warming occurred thereafter, at around 16 mya, but it was followed by a series of drops in temperature at about 12, 10 and 7 mya, ushering in the long epoch of fluctuating ice ages and 'interglacials' during which human evolution has taken place and in which we still live, with permanent ice in Antarctica. While the high latitudes got colder, the low got drier, causing a shrinkage and retreat of the forests that had lavishly clothed the tropical zones in the very warm and moist times. The forest-living apes retreated with the forest and a new ecological niche began to open up, in the shape of spreading savannahs, for exploitation by a suitably evolved 'ex-ape'. From about 7 mya, the separation of the human line first from the gorillas and then from the chimpanzees was under way. It is at times of rapid environmental change that small populations of animals evolve fastest: the slightest advantage conferred by some random mutation may allow an individual to thrive better in a new niche and leave more descendants behind, themselves to thrive better than less well-adapted individuals. And so genetic lines are selected by nature and perpetuated.
It is not in caves that the evidence for the evolution of our earliest ancestors in the human line is to be found – as we have seen, scarcely a cave from times as far back as 6 mya survives. They would not have wanted to be confined in caves in any case, though no doubt their carcasses sometimes found their way into caves that formed part of other creatures' lairs. These remote ancestors of ours frequented the stands of trees that were maintained along watercourses where food, both vegetable and to some extent animal, might be found. Erosion out of the deposits of old river valleys in East Africa has turned up skull fragments and even limb bone pieces of 'ex-apes' who were shedding their more ape-like traits and evolving towards the bipedal walking-on-two-legs mode of the human line. Continuing forest shrinkage during these ongoingly dry and coldish times was extending the range of the grassland habitat and our remote ancestors were standing up on two legs in it - if only at first to be able to run back to the shelter of the remaining trees. Finds from Kenya and Ethiopia cover a time span from about 5.5 to 4 mya to shed light on these human beginnings.
Evidence turns up more widely in Africa after 4 mya, showing a trend to brain size now going beyond the ape range in absolute terms and big in any case for the body sizes indicated, up to about 1.25 m in height. These creatures are likely to have been capable of the sort of limited tool use seen in chimp hands today, though as with the chimps the materials employed were mostly of a perishable nature and very little modified. In South Africa the fragmentary fossils of these early ape-men are sometimes found in caves of around 3 mya, but almost certainly not because they lived in them (they probably still slept in what trees they could find and their hand and foot bones show they were still practised climbers); rather their remains were taken back to the caves by the more ferocious beasts that preyed on them. In one case it looks as though a leopard was in the habit of chewing up its prey, which included some of these proto-humans, in a tree that grew over a cave fissure: the complete skeletons of an apeman and a leopard are now coming to light during painstaking excavation, which rather suggests that the leopard ended up chasing an apeman over the edge and both perished in the cave below.
The passage of time brought bigger brains, more human-looking teeth and fuller bipedalism until, about 2.4 mya, the archaeological record shows a definite association of deliberately knapped stone tools alongside the bones of their makers – in fact, stone tools found away from any association with proto-human fossils go back a little further in time. In making stone tools to a regular pattern, however simple at first, these creatures were doing something that today's apes struggle and fail to do even under instruction. Meat eating is attested by the added association of deliberately broken animal bones, running at a rate above the occasional level seen among chimps. Some at least of the tools were being used to butcher meat. The sheer efficiency of meat eating as a mode of nutrition, especially to fuel big brains, was vital to human evolution. The sharing of meat that had been cooperatively acquired, whether by scavenging or hunting, was a cornerstone of human social development in a feedback process that promoted complex social relations and fed the big brains that could handle them.
The Beginnings of Humanity
Toolmaking suggests the use of some form of speaking. Both involve a process of logic through time, with the accomplishment of steps along the way to the goal of the finished tool or the finished expression. From an early stage, there is moreover evidence of 'handedness' (usually right-handedness) in the production of the tools and humans are the only markedly 'handed' primates, which goes with a certain assymmetry of our brains that is also associated with speech; meanwhile our upright posture, a concomitant of bipedal walking, has facilitated the evolution of the chest musculature and throat anatomy necessary to produce the sounds of speech. Speech and the development of language in all its rich complexity have played such a crucial part in the creation of humanity.
Meat eating, toolmaking and ground living were the trinity of adaptations that set our remote ancestors on the way to full humanity. Ground living, of course, brought its dangers which only quick-witted resourcefulness could avoid. On some sites, collections of unworked rocks suggest the stockpiling of throwing stones to see off the wild enemies of these proto-humans: the stones also indicate the likely place of these people in the natural order, as second-level scavengers following the big predators (like lions) around and scaring off the first line of scavengers (hyenas) with their throwing stones.
At the point we have now reached in the human story, about 2.5 mya in rather cold and dry times, there is no unambiguous evidence of the making of 'home bases' with any sort of built structures or of the use of fire: nothing like the repertoire of the cave people of some million years and more later. But the quality of the stone tools got very slowly better and we can speculate that language use was making similarly slow progress. By about 2 mya, if not before, some of these early humans were beginning to spread out of Africa into the wider world, via the region of the Red Sea and the Near East and along the southern shores of the Mediterranean.
The classification of proto-human types identified in the African fossil record before these times of expansion is very complicated and contentious and prone to shift with new discoveries, but by 1.8 mya at least we have arrived at a form of humanity, increasingly worldwide in its scope, that we can conveniently assign to a single genus and species: Homo erectus. There is a particular specimen of H. erectus from East Africa, a young man, whose nearly complete skeleton illustrates for us this stage of human evolution at about 1.6 mya, where everything below the skull was more or less of a form and stature like our own, while the brain in the heavily-built skull above remained about one-third smaller in volume than our average. The tall physique of such examples of the erectus species as this 'Nariokotome Boy' amply justify the species name: H. erectus was the great upright strider of the savannah.
Excerpted from Life in a Cave by Paul Jordan. Copyright © 2011 Paul Jordan. Excerpted by permission of The History Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.