Abuse of toxic chemicals is a widespread human hallmark documented only within the last 5,000 years, though it may well go back much earlier into pre-agricultural times. Unlike agriculture, it does not even rank as a mixed blessing but as a pure evil threatening the survival of individuals, though not of our species. Like art, drug abuse seems at first to lack animal precedents or biological functions. I shall argue in Chapter Eleven, however, that it fits into a broad class of animal structures or behaviours that are dangerous to their owners or practitioners, and whose function depends paradoxically on that danger. While animal precursors can thus be identified for all of our hallmarks, they still rank as human hallmarks because we are unique on Earth in the extreme degree to which we have developed them. How unique are we in the universe? Once conditions suitable for life exist on a planet, how likely are intelligent, technologically advanced life forms to evolve? Was their emergence on Earth practically inevitable, and do they now exist on innumerable planets circling other stars?
There is no direct way to prove whether creatures capable of language, art, agriculture, or drug abuse exist elsewhere in the universe, because from Earth we could not detect the existence of those traits on planets of other stars. However, we might be able to detect high technology elsewhere in the universe if it included our own capacity to send out space probes and interstellar electromagnetic signals. In Chapter Twelve I shall examine the on-going search for extraterrestrial intelligent life. I shall argue that evidence from a quite different field—studies of woodpecker evolution on Earth—instructs us about the inevitability of evolving intelligent life, and hence about our uniqueness, not only on Earth but also in the accessible universe.
EIGHT
BRIDGES TO HUMAN LANGUAGE
The gulf between animal vocal communication and human speech has traditionally been viewed as unbridgeable. In fact, recent studies of animal vocalizations show some of them to be far more sophisticated than we had previously suspected. On the other hand, there are dozens of cases in which humans have been forced by exceptional social circumstances to create simplified languages, possibly illustrating two primitive stages in the evolution of human language. Thus, we are beginning to understand how our most unique and important distinction from animals nevertheless arose from animal precursors.
The mystery of human language origins is the most crucial in understanding how we became uniquely human. After all, it is language that allows us to communicate with each other far more precisely than any animal can. Language enables us to formulate joint plans, to teach one another, and to learn from what others have experienced elsewhere or in the past. With it, we can store precise representations of the world in our minds, and hence encode and process information far more efficiently than any animal can. Without language we could never have conceived and built Chartres Cathedral—or V-2 rockets. For these reasons, I speculated in Chapter Two that the Great Leap Forward (the stage in human history when innovation and art at last emerged) was made possible by the emergence of spoken language as we know it. Between human language and the vocalizations of any animal lies a seemingly unbridgeable gulf. It has been clear since the time of Darwin that the mystery of human language origins is an evolutionary problem: now was this unbridgeable gulf nevertheless bridged? If we accept that we evolved from animals lacking human speech, then our language must have evolved and become perfected with time, along with the human Pelvis, skull, tools, and art. There must once have been intermediate language-like stages linking monkey grunts to Shakespeare's sonnets. Darwin diligently kept notebooks on his children's linguistic development, and reflected on the languages of'primitive' peoples, in the hope of solving this evolutionary mystery.
Unfortunately, the origins of language prove harder to trace than the origins of the human pelvis, skull, tools, and art. All of the latter may persist as fossils that we can recover and date, but the spoken word vanishes in an instant. In frustration, I often dream of a time machine that would let me place tape-recorders in ancient hominoid camps. Perhaps I would discover that australopithecines uttered grunts little different from those of chimpanzees; that early Homo erectus used recognizable single words, progressing after a million years to two-word sentences; that Homo sapiens before the Great Leap Forward became capable of strings of words that were longer but still without much grammar; and that syntax and the full range of modern speech sounds arrived only with the Great Leap.
Alas, we have no such retrospective tape-recorder, and no prospects for ever getting one. How can we hope to trace speech origins without such a magic time machine? Until recently, I would have said that it was hopeless to do more than speculate. In this chapter, however, I shall try to draw on two exploding bodies of knowledge that may allow us to begin building bridges across the gulf between animal and human sounds, by starting from each of its opposite shores. Sophisticated new studies of wild animal vocalizations, especially those of our primate relatives, constitute the bridgehead on the animal shore of the gulf. It has always been obvious that animal sounds must have been precursors of human speech, but only now are we beginning to sense how far animals have come towards inventing their own 'languages'. In contrast, it has not been clear where to locate the bridgehead on the human shore, since all existing human languages seem infinitely advanced over animal sounds. Recently, though, it has been argued that a numerous set of human languages neglected by most linguists truly exemplifies two primitive stages on the human side of the causeway.
Many wild animals communicate with each other by sounds, of which bird-songs and the barking of dogs are especially familiar to us. Most ot us are within earshot of some calling animal on most days of our lives. Scientists have been studying animal sounds for centuries. Despite this long history of intimate association, our understanding of these ubiquitous and familiar sounds has suddenly expanded because of the application of new techniques: use of modern tape-recorders to record animal calls, electronic analysis of the calls to detect subtle variations imperceptible to the unaided human ear, broadcasting recorded calls back to animals to observe how they react, and observing their reactions to electronically reshuffled calls. These methods are revealing animal vocal communication to be much more like language than anyone would have guessed thirty years ago. The most sophisticated 'animal language' studied to date is that of a common, cat-sized African monkey known as the vervet. Equally at home in trees and on the ground in savannah and rainforest, vervets are among the monkey species that visitors to East African game parks are most likely to see. They must have been familiar to Africans for the hundreds of thousands of years that we have existed as the species Homo sapiens. They may have reached Europe as pets over 3,000 years ago, and they certainly have been familiar to European biologists exploring Africa since the Nineteenth Century. Many laypeople who have never visited Africa are still acquainted with vervets from visits to the zoo.