In fact, the great apes are completely silent most of the time. The primatologist Allen Gardner described his experience in Tanzania as follows: "A group of ten wild chimpanzees of assorted ages and sexes feeding peacefully in a fig tree at Gombe may make so little sound that
an inexperienced observer passing below can altogether fail to detect them."
Homo sapiens, by contrast, can rightfully be called the babbling ape. Humans communicate vocally all the time; it is far easier to start them talking than to shut them up. They begin in infancy during ex- changes with adults, who urge them on with the slow, vowel-heavy, emotionally exaggerated singsong called motherese. Left alone, they continue with "crib speech," composed of squeaks, coos, and nonsense monosyllables, which evolve over a few months into a complex play of words and phrases. These early verbal repertories, conforming more or less to adult vocabularies, are repeated ad nauseam, modified, and combined in experimental mixtures. By the age of four the average child has mastered syntax. By six, in the United States at least, he has a vocabulary of about fourteen thousand words. In contrast, young bono- bos play and experiment freely with movements and sounds and some- times with symbols, but so far progress toward the Kanzi level depends on the rich linguistic environment provided by human trainers.
Even if the great apes lack true language, is it possible they possess culture? From evidence in the field it appears they do, and many ex- pert observers have so concluded. Wild chimps regularly invent and use tools. And the particular kinds of artifacts they invent, just as in human culture, are often limited to local populations. Where one group breaks nuts open with a rock, another cracks them against tree trunks. Where some groups use twigs to fish ants and termites from the nests for food, others do not. Among those that fish, a minority first peel the bark off the twigs. One chimp group has been observed using long hooked branches to pull down branches of fig trees to obtain fruit.
It is natural to conclude from such observations that chimpanzees have the rudiments of culture, and to suppose that their capability dif- fers from human culture by degree alone. But that perception needs to be accepted with caution: Chimpanzee inventions may not be culture in any sense. The still scanty evidence on the subject suggests that while chimps pick up the use of a tool more quickly when they see oth- ers using one, they seldom imitate the precise movements employed or show any clear sign of understanding the purpose of the activity. Some observers have gone so far as to claim that they are merely stirred into greater activity by watching others. This kind of response, which zoologists call social facilitation, is common in many kinds of social animals, from ants to birds and mammals. Although the evidence is in-
conclusive, social facilitation alone, combined with trial-and-error ma- nipulation of materials conveniently at hand, might guide the chimps to tool-using behavior in the free-ranging African populations.
Human infants, on the other hand, do engage in precise imitation and with astonishing precocity. As early as forty minutes after birth, to cite the ultimate example, they stick out their tongues and move their heads from side to side in close concert with adults. By twelve days they imitate complex facial expressions and hand gestures. By two years they can be verbally instructed in the use of simple tools.
In summary, the language instinct consists of precise mimicry, compulsive loquacity, near-automatic mastery of syntax, and the swift acquisition of a large vocabulary. The instinct is a diagnostic and evi- dently unique human trait, based upon a mental power beyond the reach of any animal species, and it is the precondition for true culture. To learn how language originated during evolution would be a discov- ery of surpassing importance. Unfortunately, the evidences of behavior rarely fossilize. All the millennia of campsite chattering and gesticula- tion, and with them all the linguistic steps up from our chimplike an- cestors, have vanished without trace.
What paleontologists have instead are fossil bones, which tell of the downward migration and lengthening of the voice box, as well as possible changes in the linguistic regions of the brain impressed upon the inner cranial case. They also have steadily improving evidence of the evolution of artifacts, from the controlled use of fire 450,000 years ago, presumably by the ancestral species Homo erectus, to the con- struction of well-wrought tools by early Homo sapiens 250,000 years ago in Kenya, then elaborate spearheads and daggers 160,000 years later in the Congo, and finally elaborate painting and the accouter- ments of ritual 30,000 and 20,000 years ago in southern Europe.
This pace in the evolution of artifactual culture is intriguing. We know that the modern Homo sapiens brain was anatomically fully formed by no later than 100,000 years before the present. From that time forward the material culture at first evolved slowly, later ex- panded, and then exploded. It passed from a handful of stone and bone tools at the beginning of the interval to agricultural fields and vil- lages at the 90 percent mark, and then—in a virtual eyeblink—to prodigiously elaborate technologies (example: five million patents so far in the United States alone). In essence, cultural evolution has fol- lowed an exponential trajectory. It leaves us with a mystery: When did
symbolic language arise, and exactly how did it ignite the exponentia- tion of cultural evolution?
TO O BAD , but this great puzzle of human paleontology seems insol- uble, at least for the time being. To pick up the trail of gene-culture co- evolution, it is better to defer reconstruction of the prehistoric record and proceed to the production of culture by the contemporary human brain. The next best approach, I believe, is to search for the basic unit of culture. Although no such element has yet been identified, at least to the general satisfaction of experts, its existence and some of its char- acteristics can be reasonably inferred.
Such a focus may seem at first contrived and artificial, but it has many worthy precedents. The great success of the natural sciences has been achieved substantially by the reduction of each physical phe- nomenon to its constituent elements, followed by the use of the ele- ments to reconstitute the holistic properties of the phenomenon. Advances in the chemistry of macromolecules, for example, led to the exact characterization of genes, and the study of population biology based on genes has refined our understanding of biological species.
What then, if anything, is the basic unit of culture? Why should it be supposed even to exist? Consider first the distinction made by the Canadian neuroscientist Endel Tulving in 1972 between episodic and semantic memory. Episodic memory recalls the direct perception of people and other concrete entities through time, like images seen in a motion picture. Semantic memory, on the other hand, recalls mean- ing by the connection of objects and ideas to other objects and ideas, either directly by their images held in episodic memory or by the sym- bols denoting the images. Of course, semantic memory originates in episodes and almost invariably causes the brain to recall other epi- sodes. But the brain has a strong tendency to condense repeated episodes of a kind into concepts, which are then represented by sym- bols. Thus, "Proceed to the airport this way" yields to a silhouette of an airplane and arrow, and "This substance is poisonous" becomes a skull and crossbones on the side of a container.
With the two forms of memory distinguished, the next step in the search for the unit of culture is to envision concepts as "nodes," or ref- erence points, in semantic memory that ultimately can be associated with neural activity in the brain. Concepts and their symbols are usu-
ally labeled by words. Complex information is thus organized and transmitted by language composed of words. Nodes are almost always linked to other nodes, so that to recall one node is to summon others. This linkage, with all the emotional coloring pulled up with it, is the essence of what we refer to as meaning. The linkage of nodes is assem- bled as a hierarchy to organize information with more and more meaning. "Hound," "hare" and "chasing" are nodes, each symbolizing collectively a class of more or less similar images. A hound chasing a hare is called a proposition, the next order of complexity in informa- tion. The higher order above the proposition is the schema. A typical schema is Ovid's telling of Apollo's courtship of Daphne, like an un- stoppable hound in pursuit of an unattainable hare, wherein the dilemma is resolved when Daphne, the hare and a concept, turns into a laurel tree, another concept reached by a proposition.
I have faith that the unstoppable neuroscientists will encounter no such dilemma. In due course they will capture the physical basis of mental concepts through the mapping of neural activity patterns. They already have direct evidence of "spreading activation" of differ- ent parts of the brain during memory search. In the prevailing view of the researchers, new information is classified and stored in a similar manner. When new episodes and concepts are added to memory, they are processed by a spreading search through the limbic and cortical systems, which establishes links with previously created nodes. The nodes are not spatially isolated centers connected to other isolated cen- ters. They are typically complex circuits of large numbers of nerve cells deployed over wide, overlapping areas of the brain.
Suppose, for example, you are handed an unfamiliar piece of fruit. You automatically classify it by its physical appearance, s
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