Masters of the Planet (25 page)

In this new means of tool production we clearly see a new layer of cognitive complexity introduced into the hominid behavioral repertoire. Not only did the toolmaker have to envision the form of the finished tool before the process began, but he or she had to be able to plan and conceptualize several stages ahead, instead of heading straight for the desired shape. Whether this new approach to making tools was invented in Europe or Africa or independently in both regions is unclear, as is the exact identity of the inventor(s); but it represented an idea whose time had come, and it was an innovation that occurred on
Homo heidelbergensis
's watch. Interestingly, in the parent continent of Africa there is early evidence of the production, using stone hammers, of “blades”—basically, flakes with parallel sides and more than twice as long as wide—at a site in Kenya dating to over half a million years ago, also within the time span of
Homo heidelbergensis.
The appearance of blades in Africa that long ago is particularly intriguing because such implements, struck from cylindrical cores, are only found in Europe many hundreds of thousands of years later, with the arrival of fully cognitively modern humans. Blade production is no mean feat, involving as it does a complex sequence of actions, together with a firm grasp of the properties of the material being worked; and, whatever exact species the Kenyan early blademaker belonged to, he or she had completed a very demanding cognitive task.

The tenure of
Homo heidelbergensis
on Earth, approximately between 600 and 200 thousand years ago, thus witnessed a large number of lifestyle and technological innovations among hominids. And though we cannot identify the authors of these innovations with any certainty,
we
can with reasonable confidence attribute them to
Homo heidelbergensis
or something very like it. These were hardy, resourceful folk, who occupied and exploited a huge range of habitats throughout the Old World through the deployment of an amazing technological and cultural ingenuity. They were adroit hunters who pursued large game using sophisticated techniques, built shelters, controlled fire, understood the environments they inhabited with unprecedented subtlety, and produced admirable stone tools that at least occasionally they mounted into composite implements. Altogether, they lived more complex lives than any hominids had ever done before them.

Yet in isolation we cannot confidently read symbolic thought processes into any techniques of stone-knapping; and throughout the period of
Homo heidelbergensis
's tenure no hominid produced anything, anywhere, that we can be sure was a symbolic object. Perhaps only a couple of very late items even qualify for consideration in this category. One of these is a “Venus” recovered at Berekhat Ram, a 230-thousand-year-old site on the Golan Heights excavated by Israeli archaeologists in 1981. The “Venus” is a small pebble that is vaguely shaped like a human female torso. It has been argued that this object's anthropomorphic aspects have been amplified by three deliberately incised grooves, though it remains uncertain that any purposeful human action was involved. The second contender is a couple of small round perforated disks of ostrich eggshell from Kenya that may arguably have been objects of personal adornment (and therefore symbolic), and are even more arguably up to 280 thousand years old. But both the dating and the interpretation are speculative, and there is certainly nothing in the material record to suggest that the symbolic manipulation of information was in any way a regular part of the cognitive repertoire of
Homo heidelbergensis.
Had it been, we would surely expect to see more material evidence of it.

Homo heidelbergensis
was certainly remarkable, and in their day its members were undoubtedly the most intelligent creatures that had ever existed on Earth. But although we can see numerous similarities to ourselves in them—as indeed it's also easy to do, albeit to a lesser extent, in chimpanzees—members of
Homo heidelbergensis
were not merely simpler versions of us. If I had to wager a guess, it would be that the intelligence of these hominids, formidable as it may have been, was
purely
intuitive and non-declarative. They neither thought symbolically as we do, nor did they have language. As a result, we can't usefully think of them as a version of ourselves, certainly cognitively speaking. Instead, we need to understand them on their own unique terms. As I've already emphasized, this is not easy to do even at the best of times; and in the case of
Homo heidelbergensis,
where the clues we have about these hominids' lives are hugely tantalizing yet so few, it is particularly difficult.

NINE

ICE AGES AND EARLY EUROPEANS

The continent of Africa has consistently been the fount of innovation in hominid evolution. But—and only partly because it has been scoured more intensively than any other part of the globe for traces of the human past—Europe also has a huge amount to offer us in terms of understanding just how it is that we differ even from our closest extinct relatives. The key to this understanding lies in the breadth of our knowledge of the endemic European hominid species
Homo neanderthalensis.
This species is better documented than any other of our extinct hominid relatives, and, very importantly, its members boasted brains as large as our own, if not even fractionally larger. The Neanderthals are thus ideally placed to act as a sort of mirror to our own uniqueness: an alternative take on the theme of the large-brained hominid that helps us to gauge whether or not our vaunted mental prowess is simply a sort of passive byproduct of the metabolically expensive “more brain is better” theme that—for whatever reason—seems to have dominated the history of the genus
Homo.
To make the comparison more complete, we can contrast our own behaviors with what we can infer of theirs in unaccustomed detail, because the Neanderthals left us an unusually complete material record of their existence. By making this comparison we may hope to gain some perspective on exactly what it is about us
that
has made us the lone hominid in the world today, and a species that interacts with that world in an unprecedented way. But before we look at what the Neanderthals add to the human story, let's quickly look at the climatic backdrop against which the events of later hominid evolution took place. For environmental change (on various scales) has been the most important single driver in the evolution of the organic world, human beings not excepted.

THE ICE AGES

We've already seen that, well before the time at which our genus
Homo
originated, climates worldwide were undergoing the gradual deterioration that spurred the development of the relatively open African habitats colonized by the early hominids. This trend received a huge impetus about three million years ago, when the collision of North with South America produced the Isthmus of Panama. The new land barrier blocked the circulation into the Atlantic Ocean of warm Pacific water, producing an acceleration of the cooling and drying trend in Africa, and initiating the formation of an ice cap in the Arctic. We see the results of this event dramatically expressed in the African fossil record beginning around 2.6 million years ago, with a proliferation of grassland-adapted grazing mammals and the disappearance of older browsing forms. Some authorities believe that the environmental shift reflected in faunal change around this time was the most significant stimulus to the emergence of our genus
Homo;
and whether or not this was actually the case, it is certainly true that the underlying event ushered in a new climatic cycle that exerted a profound influence on later phases of hominid evolution. In Africa temperatures remained relatively warm, but the continent was deeply affected by major fluctuations in rainfall. In Eurasia the effects were greater yet, since the more northerly latitudes into which hominids began moving some two million years ago were also influenced by significant excursions in temperature.

The initiation of the Arctic ice cap at around 2.6 million years ago marked the beginning of the “Ice Ages” cycle of alternating glacial and interglacial episodes, as the ice caps at both ends of the Earth regularly expanded and contracted. These fluctuations occurred because of differences
in solar radiation received at the planet's surface due to variations in its orbit around the Sun. By about a million years ago, when vast Serengeti-style savannas were becoming established in parts of Africa, this cycle had settled down into a fairly steady rhythm, swinging every hundred thousand years or so from cold troughs to warm peaks (of the kind we are experiencing today). Between the extremes, numerous shorter-term oscillations occurred. Sometimes those oscillations were very short-term indeed, rather like the “Little Ice Age”—which itself showed three distinct temperature minima—that spanned the sixteenth to nineteenth centuries.

At the peaks of cold, the Arctic ice cap expanded to cover much of Eurasia as far as 40 degrees south, and subsidiary ice caps on the Alps, Pyrenees, and other Eurasian mountain chains grew and sometimes coalesced to form formidable geographical barriers. Environments in proximity to the ice varied substantially, depending on local topographic features and how far away the ocean was. But in most places the ice masses yielded rapidly to tundra, where sedges, lichens, and grasses grew on a thin layer of soil above the permafrost and supported large populations of grazing mammals such as musk ox and reindeer. Farther south, and in sheltered areas, the vegetation grew taller, with pine forests ultimately giving way to mixed conifer and deciduous formations in which deer roamed. As the climate warmed up, the ice retreated northward and the vegetation bands followed, taking their faunas with them. In the south, broadleaf forests dominated during milder periods, giving way to Mediterranean-style scrublands in drier areas. As all this was going on geography itself changed, due to the locking up of seawater in the ice caps during colder periods. At times of maximum ice cover, world sea levels fell as much as three hundred feet compared to today's, thereby uniting such warm-period islands as Britain and Borneo with the adjacent mainland, and extending continental coastlines far seaward. In warmer times the encroaching sea doubtless repeatedly swamped many major sites of human glacial habitation.

The latest official geological determination (with which not everyone is happy) is that the start of the glacial cycle around 2.6 million years ago marks the beginning of what geologists call the Pleistocene (“most recent”) epoch, which runs right up to the last major ice cap retreat
about
12 thousand years ago. The time since is known to geologists as the Holocene (“entirely recent”) epoch—although, human impact apart, there is no good reason for thinking we are out of the glacial cycle. However you may choose to define our genus
Homo,
it is thus a product of the Pleistocene; and the bottom line here is that our ancestors evolved in a period of increasingly unsettled environmental conditions. This was true both in the home continent of Africa, where rainfall varied dramatically on compact timescales, and in Eurasia, where vast swaths of the continent were periodically rendered uninhabitable to hominids of the time. There is thus no way in which we can realistically think of hominid evolution during the Pleistocene as a matter of steady adaptation to a specific environment, or even to an environmental trend. Instead, the story is a much more dramatic one, as tiny hominid populations were buffeted by changing conditions, often retreating or becoming locally extinct, simply victims of being in the wrong place at the wrong time.

It's worth noting, though, that by regularly fragmenting already sparse hominid populations both in Africa and Eurasia, the Pleistocene offered ideal conditions for the local fixation of genetic novelties and for speciation. Both of these are processes that in creatures such as hominids depend on physical isolation, and small population sizes. Ice Age conditions were often tough for the hominid individuals concerned; but never had circumstances been more propitious for meaningful evolutionary change than among our highly mobile, adaptable, and resourceful Pleistocene ancestors. Taken together, this combination of internal and external factors may well account for the amazing rapidity with which hominids evolved during the Pleistocene. For there can be no doubt that the evolutionary history of hominids during this epoch was hugely more eventful than that of any comparable group of mammals of the period. We differ today far more from our earliest Pleistocene ancestors than do any other of the creatures with which we share the planet.

Ironically—because ecological generalists normally have much lower speciation and extinction rates than specialists—this rapid evolution was almost certainly due to our generalist ancestors' combination of flexibility and resilience, combined with a propensity to spread readily into new environments in a rapidly fluctuating world. The process would have been helped along by the sparse and scattered population
structure
that resulted from the hominids' secondary adoption of a predatory lifestyle. And very recent findings have also pointed to something quite unexpected: the possibility that, under fluctuating Pleistocene conditions, new genes may have been introduced into hominid populations by occasional intermixing between closely related and poorly differentiated hominid species.

But one important final factor that is totally unique to hominids, and which appears in some respects paradoxical, is the possession of complex culture, especially as it is expressed in technology. The exploratory inclinations of our ancestors could never have been indulged in the absence of their ability to accommodate technologically to unfamiliar and extreme conditions. Culture is usually—and justifiably—viewed as a factor that has helped insulate hominids from their environments and thus from biological selection. But in this particular context, its role in facilitating the huge geographical dispersion of thin-on-the-ground hominids may actually help explain how the genus
Homo
contrived to evolve so fast during the Pleistocene.