Linguistics 001     Lecture 4    A Biological Perspective

Where did human language come from, and why?

This is not an easy question to learn to ask. We think of ourselves as being the pinnacle of development, the most perfect of earth's creatures. As Alexander Pope put it in his Essay on Man,

Far as creation's ample range extends,
The scale of sensual, mental pow'rs ascends:
Mark how it mounts to man's imperial race,
From the green myriads in the peopled grass:
Remembrance and reflection how ally'd;
What thin partitions sense from thought divide?
And middle natures, how they long to join,
Yet never pass th' insuperable line!
Without this just gradation, could they be
Subjected, these to those, or all to thee?
Vast chain of being! which from God began,
Natures aethereal, human, angel, man,
Beast, bird, fish, insect, what no eye can see,
No glass can reach; from infinite to thee,
From thee to nothing.

We tend to view the quirks and peculiarities of our species as The Right Thing to Do, and assume that if other species don't do the same, it's because they just haven't evolved to our level. Surely our most complex and perfected language must be what all other species aspire to "in just gradation," mounting a scale of communicative complexity from worms to insects to fish to birds to mammals to us.

However, one authority on animal communication tells us:

For most relatively social adult fishes, birds and mammals, the range or repertoire size [of communicative displays] for different species varies from 15 to 35 displays.

Curiously, there appears to be little correlation between repertoire size and location in the "vast chain of being." Cuttlefish, as far as we know, have about as many different communicative displays as chimps do. Biologists who study the evolution of behavior speculate that there are selective pressures that prevent the overall number of displays from growing beyond a certain point, even though it is clear that new displays are developed to suit new adaptive circumstances. In the same way, although specialized physical organs develop in response to new evolutionary opportunities, other specializations tend to be lost, so that creatures do not over time accumulate indefinitely many humps, horns, ruffs, claws and so on.

Thus human language, with its hundreds of thousands of words, is not just the logical endpoint of some obvious evolutionary "scale of sensual, mental powers." Rather, it seems to be a behavioral counterpart of the peacock's tail or the elephant's tusk: a specific, enormously hypertrophied development of structures with rather different original functions.

How and why did this happen? If complex systems of communication are so great, why hasn't evolution been developing them in other species for the last few hundred million years -- as eyes, ears, horns, claws etc. have repeatedly been developed?

Is language in our genes?

Does it make sense to ask about the genetic evolution of language?

The essence of life is the transmittal of genetic information. Words like "communication" are sometimes used to talk about the expression of genetic information within the cell, and the transmittal of genetic information to new cells. There are good reasons for these verbal analogies -- there are interesting mathematical affinities between computational linguistics and computational biology.

However, we share this genetic language with every other living thing on earth, while it is only our fellow humans that we can talk with. Although molecular genetics is not the kind of "language" we are investigating, it provides one framework for interpreting our question about the origins of human spoken language.We can ask: what aspects of the human genome make spoken language possible? What selective pressures on our ancestors led these characteristics to develop?

It's conceivable that looking for this genetic basis of human language is not very enlightening. For example, we would not learn much by asking for the genetic basis of certain other uniquely human traits, such as the practice of wearing baseball caps backwards. There are things we could say -- humans have heads, for instance, and a tendency to be dazzled by sunlight when looking for things in the air on bright days, whence hats with brims -- but in fact the main issues are cultural, not biological. The human species has not adapted genetically to wearing caps, whether forwards, backwards or sideways. Instead, the design and use of caps has "evolved" as part of the culture of a particular time and place, among people no different genetically from those with very different tastes in headgear.

Human language and culture are deeply interconnected, to the point that it would absurd to study the evolution of language without considering its role in broader social and cultural questions. However, the human species has in fact adapted genetically to facilitate the use of spoken language. Thus it is worthwhile to look into what these adaptations are, and also at some theories about what selective advantage they offered to our ancestors.

What we hominids did

We are talking about evolution during the roughly five million years since we separated from the ancestors of today's great apes (Chimpanzee, Gorilla, etc.).

We are going to sidestep several controversies:

  • how many distinct species should be recognized in the fossil record (expert opinions vary from three to fifteen)?
  • where along the line from Australopithecus to Homo erectus (about 1.8 mya)  to Homo sapiens (about 100,00 ya) did how much of the various changes take place?
  • where on the family tree do various particular species or subspecies (e.g. the Neanderthals) fit in?
  • did the recent change from erectus to sapiens happen in one place (the "out of Africa hypothesis") or over a wide area (the "multiregional hypothesis")?

The language-related changes took place from the neck up. These changes took place in two areas: the mouth and throat (the "vocal tract"), and the brain.

Vocal tract changes in hominid evolution

One set of changes occurred between neck and nose, and served to adapt our vocal tracts for speaking.

Specifically, we shortened our muzzle and the oral cavity it contains, and stretched out our pharynx (throat, in ordinary language) by lowering the larynx (what is behind your Adam's apple). The comparison below of human and chimpanzee vocal-tract anatomy shows the changes:

The result of these changes is to make it possible for our tongue to move forward and back, up and down, in a way that creates resonant cavities of different sizes in various places in the vocal tract, as this synthesis demonstration shows.

The picture below shows that the skull of Homo erectus, our immediate ancestor who lived between about 1.8 million and 100,000 years ago, appears to be intermediate in these respects between the great apes and our esteemed selves.

These changes are great for making a wide variety of different vowels and consonants. However, they are otherwise a bad idea!

The expansion of the pharynx creates some real problems. For instance, it means that laughing while drinking tends to propel liquids out the nose. Much more seriously, it's relatively easy for us to get a chunk of food lodged in the larynx, with potentially fatal results. To quote from Holloway 1996, The evolution of the human vocal apparatus:

    The lower position of the larynx alters dramatically the way humans... breathe and swallow. The loss of the ability of the epiglottis to make contact with the soft palate means that the possibility of having two largely separate pathways, one for air and one for liquid, no longer exists. The respiratory and digestive tracts now cross each other in the area of the pharynx... This new configuration can, and does, have unfortunate drawbacks. The major problem is that a bolus of food can become lodged in the entrance of the larynx. If this material cannot be expelled rapidly an individual may literally choke to death... Another disadvantage of the crossed pathways is the relative ease with which vomit can be aspirated into the trachea, and thus pass into the lungs.

This problem is even worse for men than for women, because as a secondary sexual characteristic of male humans, the larynx increases in size and moves lower in the throat at puberty. None of the other great apes show this laryngeal sexual dimorphism, or indeed any other vocal tract dimorphism -- though they have much greater dimorphism in overall size, and also show dimorphism of canine teeth, which humans entirely lack.

The unique human development of sexual dimorphism in larynx size and position presumably means that vocalization is important to us in ways that it is not to gorillas and chimps.

 Brain changes

One thing that happened to our brain was that it just got bigger. This chart (from Holloway 1996, Evolution of the Human Brain) shows that the relationship of brain weight to body weight is roughly linear on a log-log scale across a large range of primate sizes. The data point for humans is obviously above the trend line by a significant factor:

However, the hominid brain did not just get uniformly larger. According to Holloway's discussion:

There are four major reorganizational changes that have occurred during hominid brain evolution, viz.: (1) reduction of the relative volume of primary visual striate cortex area, with a concomitant relative increase in the volume of posterior parietal cortex, which in humans contains Wernicke's area; (2) reorganization of the frontal lobe, mainly involving the third inferior frontal convolution, which in humans contains Broca's area; (3) the development of strong cerebral asymmetries of a torsional pattern consistent with human right-handedness (left-occipital and right-frontal in conjunction); and (4) refinements in cortical organization to a modern human pattern, most probably involving tertiary convolutions. (this last 'reorganiziation' is inferred; in fact, there is no direct palaeoneurological evidence for it.)

Of the four changes cited, the first three straightforwardly involve language in whole or in part. Wernicke's area in modern humans is involved in comprehension of language. Broca's area is involved in motor control of speech. The cerebral asymmetries in the third point involve a localization of language skills in the dominant (generally left) hemisphere of the brain, and of other abilities (visuo-spatial and emotional) in the non-dominant hemisphere.
Like the vocal-tract changes, the brain changes have a cost. For one thing, brain tissue is expensive to maintain, about ten times more expensive than other tissue. The human brain, although only about 2% of our body weight, consumes about 20% of our energy.

For another thing, increased brain size normally translates to increased gestation period, because fetal brain tissue is laid down at a relatively constant rate. This graph shows the relationship for a sample of species from rhesus monkeys to elephants:

Humans are on this graph -- as the triangle down and to the right from the circles representing the other animals. If the human data point were brought in line with the trend for the rest of the species, it looks like human babies ought to be born about 15-17 months after conception, rather than 9. However, this would be a bad idea. Anyone who has ever given birth, or witnessed a birth, knows that an 6-8-month-old baby  would just not make it out, even if the mother could manage the extra period of pregnancy.

Instead, full-term human infants are in fact born "premature" by the standards of the rest of the animal kingdom. In fact, since development is slowed down after birth as well, human infants are not as mature as new-born chimps until they are a year old or more. Taking care of these "premature" infants imposes considerable burdens on human parents, and especially on the mother, during the first year of life.

Why'd we do it?

This is a key question: what was the source of selective pressure?

Before trying to answer it -- and all answers are speculative ones -- let's look at some background.

A "forest of symbols" -- the cybernetic imperative

Signals are everywhere -- for those who can understand them.

As Charles Baudelaire wrote, nature is a "forest of symbols." Light, sound, air and water currents, drifting chemicals, temperature gradients, all carry information about the structure of the world and the activities of its inhabitants.

Critters that are better at reading the world's signs tend to eat better, live longer, and reproduce more effectively, so there is selective pressure to develop sensors of all types. These may be simple sensitive molecules in the membrane of a single cell, or more complex subcellular assemblies, or elaborate structures of many specialized cells, like eyes and ears.

A pure sensor, connected to nothing, is worthless. Its owner needs to evaluate the information it provides, and to act appropriately. In fact, sensory evaluation is also necessary for effective action. To move towards a goal or around an obstacle, to manipulate an external object, and indeed to do almost anything, an organism needs feedback about the consequences of its actions. "Open loop" action, where no information comes back, only works where the environment is so well known that nothing unexpected can happen. The real world is a complicated and ambiguous place, full of unexpected obstacles, dangers and opportunities, and in this world, perception without action and action without perception are equally useless.

The basic mathematics of this integration of perception and action was worked out during WW II, motivated by the need for radar-guided anti-aircraft guns, auto-landing devices for airplanes, homing torpedoes, and the like. Fundamental work in this area was done by Norbert Wiener at MIT and by Andrey Nicolaevich Kolmogorov at MSU (that's Moscow State, not Michigan State). These two were among the greatest mathematicians of the century. After the war, Wiener went on to develop the underlying metaphor of "control and communication" -- that is, the integration of perception, information and action --  into the field of cybernetics.

Private signals

At the cellular level, the signals that organisms interpret are mainly chemical ones (though there are receptors for light, motion and electromagnetic fields as well). These signals may come from the organism itself, for purposes of internal development and control, or they may come from the outside world.

Larger organisms need cybernetic systems at multicellular scales. Chemical diffusion is not always fast enough for such purposes, so specialized cell types developed to transmit electrical signals, leading to the development of nervous systems.

Organisms benefit from communicating with nearby relatives and other members of the same species. For organisms that reproduce sexually, locating prospective mates is critical. Warning of danger and drawing attention to available food are a way to help nearby relatives, offering selective advantage for social organization.

Chemical signals will work for communication between individuals. For example, tobacco plants infected with certain viruses give off methyl salicylate vapor, which travels through the air to healthy leaves on the same or neighboring plants, causing increased expression of a gene connected to viral resistance. In many animals, sexual receptiveness is signaled chemically, and special organs may develop to deal with such chemical signals. For instance, the Pittsburgh zoo's page on the African elephant tells us that

    "All elephants possess two small holes in the roof of their mouths, called vomeronasal organs, and these detect pheremones, especially important in the breeding process. Bull elephants can tell when a female elephant is sexually receptive (in estrus) from pheremones in her urine, and since she is in estrus for only three days or so every four years, this accurate analysis is imperative for maximum reproductive success. "

Curiously, the pheremones involved seem to be the same as those used by some insects. Interpretation of chemical signals is also important to humans, pervasively for physiological regulation, but also for perception of the environment.. Humans also secrete chemicals that act as pheremones in other species, such as androstenone, which will induce a sow to adopt the mating posture when it is sprayed on her. However, according to a recent review:

Given the importance of vision to human beings and the apparent irrelevance of olfaction to most important social behaviour, it should not be surprising that odours do not produce the same reliable and strong sex-related effects in humans as they do in other animals. Vision is our dominant sense. There may also be another reason why pheromones 'don't work' in humans. There is evidence to suggest that the organ in the brain responsible for detecting and acting on these pheromones (this is called the vomeronasal organ) may be absent in humans (Moran et al, 1995). If this organ is important for sensing pheromones then humans will have difficulty sensing pheromones. Meanwhile, however, the evidence suggests that if you want to attract a member of the opposite sex, a bottle of good perfume or cologne would be a better option than would exposing your armpits, or investing in a can of Boarmate.

Making noise: the evolution of vocalization

With or without a volmeronasal organ, chemical signals have definite limitations. They travel fairly slowly, and don't travel upwind at all.

Neural signals are not an option for communication between individuals -- you have to be "plugged in."

This leaves a few other options:

  • Tactile signals are possible, but require direct contact.
  • Signaling by manipulation of electric fields does not seem to be biologically reasonable, except for short-distance systems in water.
  • Visual signals are common. The visual channel is an especially rich one for many animals, especially primates. However, visual signals have some drawbacks. They are limited to line-of-sight, and require visual attention on the part of the recipient.
  • Acoustic signals are also very common. The acoustic channel has an inherently lower capacity than the visual one does, but has the advantage of going around or through most obstacles, and being available regardless of the direction the organism is "looking".

Nearly all organisms have acoustic sensors, developed to help figure out "what's going on out there." There are lots of ways to make sounds -- tapping or scraping limbs, whistling or grunting with the respiratory apparatus.

The somatic portfolio: how much to invest in what?

Although cybernetic systems are useful, they come at a cost, to organisms as well as to defense contractors (or rather taxpayers). Not every military aircraft carries the electronic-warfare sensors and countermeasure devices of highly specialized planes like the AWACS shown in the picture.

Its manufacturer boasts that "its radar" (the big saucer-shaped device on its back) " has a 360-degree view of an area, and at operating altitudes it can detect targets more than 320 kilometers (200 miles) away. AWACS mission equipment can separate, manage and display these targets individually on situational displays." These are enviable capabilities compared to those of a typical fighter plane. However, to put the same systems on individual fighter aircraft would cost a lot, in money, weight, and aerodynamic compromises. Designers have decided that the cost is not worth the benefit: a fleet of fighters carrying such radars would be defeated by a larger number of cheaper, faster, more maneuverable opponents.

The evolution of biological organisms is subject to similar trade-offs. All sorts of incredible sensory systems, integrated in stunning ways with action capabilities, are possible. The use of sonar by bats in catching insects and by barn owls in catching mice, the odor sensitivity of dogs or pigs, the magnetic navigation of some birds, are all available in principle. However, specialized sense organs and specialized neural circuits are "expensive", in the sense that it takes energy to build them, and they may compromise other functions.

Evolution is constantly carrying out a sort of experimental cost-benefit optimization. Our hominid ancestors, when they split off from the lineage of chimps and gorillas some 5 million years ago, might have gone on to develop built-in sonar or an improved sense of smell. They might also have stayed about the same, as indeed Homo Erectus, the species that is our immediate anscestor, did for almost two million years. Instead, they learned to talk. Why?

OK, so why'd we do it?

What are these physical changes -- in jaw, throat and brain -- good for, that would outweigh their many selective disadvantages?

They're definitely good for spoken language.

The redesigned vocal tract is good for making lots of different vocal sounds. The reorganized and expanded  Broca's area deals with control of sound structures -- aspects of what we will call phonology and phonetics when we get to them. The reorganized and expanded Wernicke's area, along with the larger cortex in general, allows us to have lots and lots of words, each one connecting a meaning with a pronunciation.

Somewhere along the line, we learned to think about what others believe -- what philosophers call the "others minds" problem -- and this made us better at communicating regardless of the medium.

But why? Why did our ancestors make such a big investment in talking? As the biological anthropologist Terence Deacon has recently written, it's easy to think of plausible reasons:

From the perspective of hindsight, almost everything looks as though it might be relevant for explaining the language adaptation. Looking for the adaptive benefits of language is like picking only one dessert in your favorite bakery: there are too many compelling options to choose from. What aspect of human social organization and adaptation wouldn't benefit from the evolution of language? From this vantage point, symbolic communication appears "overdetermined." It is as though everything points to it. A plausible story could be woven from almost any of the myriad of advantages that better communication could offer: organizing hunts, sharing food, communicating about distributed food sources, planning warfare and defense, passing on toolmaking skills, sharing important past experiences, establishing social bonds between individuals, manipulating potential sexual competitors or mates, caring for and training young, and on and on.

Another theory, proposed in a recent book by the linguist Derek Bickerton, is that hominids invested in language so as to be able to think better. This hypothesis views rational thought as being at least in large part made up of inner speech..

Each of these theories has some positive aspects -- the cited advantages certainly do exist to some extent. However, one may doubt how strong many of these effects could have been. For instance, in documented modern hunter-gatherer cultures, language does not play a very large role either in coordinating hunts or in teaching tool-making. Packs of wolves and wild dogs are extradinarily clever at group hunting, without being able to talk about it. Many kinds of human thought do not seem to involve language at all.

The evolutionary process that got human language started -- as opposed to reasons to make it bigger, faster, or more powerful once it existed to some degree -- must have been able to accomplish something pretty special, even with the small, poor, stumbling kind of approximation to language that hominids would have been able to manage before any language-specific adaptations took place. Then, because even simple and crummy language was a big success, natural selection would have a chance to create adaptations for complex, excellent language.

Most of the recent theories that meet this test assume that the crucial selective advantages of language were social. Perhaps something about the development of language made the creation and maintenance of larger social groups possible, at a time when larger social groups were essential to survival; or perhaps language permitted a different kind of social organization, enabling our ancestors to move into a different ecological niche.

Two recent theories of language origins: gossip and marriage contracts

Two recent examples of such theories of language evolution are especially striking. In Grooming, Gossip, and the Evolution of Language, Robin Dunbar proposes that our ancestors evolved language so as to use gossip as a more efficient substitute for the grooming behavior that other primates use to establish and maintain social relationships. In The Symbolic Species, Terence Deacon argues that hominid brains and human language have co-evolved over the past two million years, driven by "a reproductive problem that only symbols could solve: the imperative of representing a social contract," which in turn was required to take efficient advantage of the resources available via systematic hunting and scavenging for meat.

In outline, Dunbar's argument is as follows:

Among primates, "encephalization" (brain size normalized for body size) varies in proportion to social group size. Apparently, the larger the group a primate lives in, the more brain it needs to keep track of social relationships within the group. This is plausible, given the intricate micro-politics of primate society, as documented by ethologists. If we take the step from correlation to causation, and assume that larger brains evolved in primates in order to permit larger social groups (e.g. for better intra-species competition or better defense against predators), we have what has been called the "Machiavellian Intelligence Hypothesis."

If we look at human brain size from the perspective of this hypothesis, and extrapolate the relationship between brain size and social group size found in other primates, we predict a "natural" group size for humans of about 150.

In primate societies, grooming (picking nits out of fur) is a major factor in establishing and maintaining social bonds. There are interesting hypotheses about why grooming fulfills this function, but for now, we can just note that the bigger the primate group, the more time on average each member spends in grooming others. If we look at human social relations in this perspective, then with a group size of 150, we should have to spend 40% of the day in grooming. This is far too high to be practical -- the highest actual proportion observed among primates is 20% (Gelada baboons).

Dunbar suggests that our ancestors, facing hard times on the African plains, very badly needed to live in larger groups. "Gossiping" (in whatever form it first arose) made it possible to form and maintain social bonds more efficiently than grooming, both because more than two can do it at once, and also because you can actually do some useful work (like gathering or processing food) at the same time. The development of sense and reference -- and especially of proper names for group members -- enabled political maneuvering at a higher level in larger groups.

Here are two of Dunbar's graphs, first showing predicted group size for various hominids:

The same graph, with the Y-axis labelled as "grooming time" -- it's the same graph because both as derived from models of the relationship of group size and grooming time to encephalization.


Deacon's argument is a complex one, depending on a number of results from ethology and other allied fields.

He argues that the key point is a shift to a symbolic mode of communication, in which new linguistic tokens (i.e. words) can be created with an arbitrary relation to their meanings. He stresses that the first steps in developing symbolic communication look very difficult for a non-linguistic species, helping us to understand why no non-human species has gone very far down that road:

Even a small, inefficient, and inflexible symbol system is very difficult to acquire, depends on significant external social support in order to be learned, and forces one to employ very counterintuitive learning strategies that may interfere with most nonsymbolic learning processes. The first symbol systems were also likely fragile modes of communication: difficult to learn, inefficient, slow, inflexible, and probably applied to a very limited communicative domain. . . . Neurologically and semiotically, symbolic abilities do not necessarily represent more efficient communication, but instead represent a radical shift in communicative strategy. It is this shift, not any improvements, that we eventually need to explain.

As a rule, he argues, significant changes in communicative systems in other species occur "in the context of intense sexual selection."

It is at the point in the life cycle where choice of mate takes place that evolutionary theory predicts we should find the greatest elaboration of communicative behaviors and psychological mechanisms in both pair-bonding species and polygynous species, though the communicators and the messages may differ significantly in these two extremes. Between these extremes there are many more complex mixtures of reproductive social arrangements that add new possibilities and uncertainties, and thus further intensify selection on the production and assessment of signals.

Deacon then points out that human mating arrangments, though diverse across societies, share some characteristics that make our speciesnearly unique: "cooperative, mixed-sex social groups, with significant male care and provisioning of offspring, and relatively stable patterns of reproductive exclusion, mostly in the form of monogamous relationships." According to Deacon, "reproductive pairing is not found in exactly this pattern in any other species." The reason this pattern is not found, he argues, is that it's a recipe for sociosexual disaster: "the combination of provisioning and social cooperation produces a highly volatile social structure that is highly susceptible to disintegration."

In evolutionary terms, a male who tends to invest significant time and energy in caring for and providing food for an infant must have a high probability of being its father, otherwise his expenditure of time and energy will benefit the genes of another male. As a result, indiscriminate protection and provisioning of infants will not persist in a social group when there are other reproducing males around who do not provision, but instead direct all their efforts towards copulation.

These tensions get worse if males and females spend a lot of their time apart, as necessarily happens if males are out hunting and scavenging while females are gathering plants with children in tow. "Hunting and provisioning go together, but they produce an inevitable evolutionary tension that is inherently unstable, especially in the context of group living. Besides ourselves, only social carnivores seem to live this way."

Carnivores that engage in cooperative group hunting include wild dogs, wolves, hyenas, lions and meercats. All such creatures exhibit particular ecological and reproductive patterns that defuse the resulting evolutionary tension. Among lions, provisioning takes place among a "pride" of closely-related females (sisters, aunts etc.). One, two or rarely three male lions take over a pride and guard it against other males -- who will try to kill the cubs to bring the females into estrus -- but do not provide food. Among wild dogs and wolves, the cooperative hunting pack includes both males and females, and they provision both pups and a nursing mother. However, in a given pack there is usually only one reproducing female, who is typically the mother of many of the hunters. Other females are kept from becoming sexually receptive by social pressures and perhaps pheromones. There is usually also only one reproductively active male in a pack.

The typical human pattern involves many reproductively active males and females living in a group while maintaining patterns of sexual exclusivity, with male provisioning of children although mated males and females spend considerable time apart, is never found among the social carnivores.

Deacon suggests that this background helps to explain why the evolution of systematic hunting as a major food source for our hominid ancestors posed a difficult problem in social engineering.

The acquisition and provisioning of meat clearly would be a better strategy for surviving seasonal shortages of more typical foods than shifting to nutrient-poor diets of pith, bark, and poor-quality leaves, as do modern chimpanzees. But this is only possible if there is a way to overcome the sexual competition associated with paternity uncertainty. The dilemma can be summarized as follows: males must hunt cooperatively to be successful hunters; females cannot hunt because of their ongoing reproductive burdens; and yet hunted meat must get to thoese females least able to gain access to it directly (those with young), if it is to be critical subsistence food. It must come from males, but it will not be provided in any reliable way unless there is significant assurance that the provisioning is likely to be of reproductive value to the provider. Females must have some guarantee of access to meat for their offspring. For this to evolve, males must maintain constant pair-bonded relationships, and yet for this to evolve, males must have some guarantee that they are provisioning their own progeny. So the socio-ecolgogical problem posed by the transition to a meat-supplemented subsistence strategy is that it cannot be utilized without a social structure which guarantees unambiguous and exclusive mating and is sufficiently egalitarian to sustain cooperation via shared or parallel reproductive interests.

Deacon argues that this problem required -- or at least invited -- a solution mediated by symbols.

[C]ertain things cannot be represented wthout symbols. . . . Although there is a vast universe of objects and relationships susceptible to nonsymbolic representation, indeed, anything that can be present to the senses, this does not include abstract or otherwise intangible objects of reference. This categorical limitation is the link between the anomalous form of communication that evolved in humans and the anomalous context of human social behavior.

For hunting and provisioning to co-exist in large groups of reproductively active hominids, Deacon argues, it was necessary to establish a certain sort of social contract. If this contract can be establishing and maintained, then everyone is better off. However, it will not work until nearly everyone observes the terms and also enforces observance among others.

Essentially, each individual has to give up potential access to most possible mates so that others may have access to them, for a similar sacrifice in return.

Accomplishing this requires two things. First, you have to establish a shared understanding of who is bonded with whom. According to Deacon, "this information can only be given expression symbolically", because it "is a prescription for future behaviors," not just a memory or an index of past behavior, or an indication of current social status or reproductive state, or even a prediction of probably future behavior.

The pair-bonding relationship in the human lineage is essentially a . . . set of promises that must be made public. These . . . implicitly determine which future behaviors are allowed and not allowed; that is, which are defined as cheating and may result in retaliation.

Second, you have to get everyone else that might be involved to agree not to cheat, and to help protect against cheating.

For a male to determine he has . . . paternity certainty, requires that other males also provide some assurance of their future sexual conduct. Similarly, for a female to be able to give up soliciting provisioning from multiple males, she needs to be sure that she can rely on at least one individual male who is not obligated to other females to the extent that he cannot provide her with sufficient resources.

A marriage contract is a social contract, not just an agreement between the bonded pair. It is typical in human societies for the social group as a whole to play an active part in maintaining sexual exclusivity between individuals; this is something that happens in no other species. Deacon argues that it happens among humans because all members of the group "are party to the social arrangement, and have something to lose if one individual takes advantage of an uncondoned sexual opportunity."

Deacon is less clear about the first steps in the process of establishing such social contracts. He suggests that the ability of apes to acquire limited symbolic abilities in laboratory settings give us an indication of what our species' symbolic beginnings might have been.

In a word, the answer is ritual. Indeed, ritual is still a central component of symbolic "education" in modern human societies, though we are seldom aware of its modern role because of the subtle way it is woven into the fabric of society. The problem for symbol discovery is to shift attention from the concrete to the abstract; from separate indexical links between signs and objects to an organized set of relations between signs. In order to bring the logic of token-token relationships to the fore, a high degree of redundancy is important. This was demonstrated in the experiments with the chimpanzees Sherman and Austin. It was found that getting them to repeat by rote a large number of errorless trials in combining lexigrams enabled them to make the transition from explicit and concrete sign-object associations to implicit sign-sign associations. Repetition of the same set of actions with the same set of objects over and over again in a ritual performance is often used for a similar purpose in modern human societies. Repetition can render the individual details for some performance automatic and minimally conscious, while at the same time the emotional intensity induced by group participation can help focus attention on other aspects of the objects and actions involved. In a ritual frenzy, one can be induced to see everyday activities and objects in a very different light.

To sum up: Deacon thinks that early hominids developed symbolic communication as a way to establish social contracts permitting stable family and group structures, which otherwise would not have permitted hunting and scavenging for meat as a systematic source of supplemental food during times of drought. This set the state for nearly two million years of evolutionary adaption for improved symbolic communication, probably due to sexual selection (crudely, females preferred males who could make more convincing promises).

Note that Dunbar and Deacon might both be right: perhaps the development of gossipy chatter as an extension of grooming behavior created a substrate for symbolic reference -- maybe originally involving personal names -- that in turn opened the way for the kind of public "contracts" about mating that Deacon sees as crucial to permit systematic hunting.

Needless to say, all of these proposals are speculative, although Deacon and Dunbar provide a considerable range of supporting fact and argument. There appears to be fairly general current agreement, at least, that humans are extensively adapted for language, and that establishment and maintenance of social structure was a key source of selective pressure in the evolutionary development of human linguistic adaptations.

The "spandrel" theory

Another perspective on the initial development of language treats it as a sort of accidental side-effect of larger brains, which on this view developed for some other reason (say to facilitate tool use and/or social dynamics).

This "side-effect" theory would be an example of what Stephen Jay Gould has called evolutionary spandrels. The original meaning of "spandrel" is a space between two arches and a horizontal cornice above them; this space began as an accidental (but unavoidable) consequence of architectural techniques based on the use of arches and domes; because this accidental space is a convenient place to put paintings, it developed into a planned part of buildings with a specific function. Gould argues that many evolutionary developments are of this kind -- some feature arises as an accidental side-effect of another change, but then turns out to be useful and comes to be itself shaped by selective pressures.

This spandrel theory is not inconsistent with other accounts of the selective pressures for language development.

What were the steps in the process?

On any account of the selective pressures leading to human genetic specialization for spoken language, we may still owe a separate explanation of where the basic behaviors came from. Thus ears are for hearing, and their selective advantages presumably have to do with gaining information about the environment from sound; as a separate matter, it happens to be true that the bones of the mammalian inner ear developed from parts of the reptilian jaw.

For example, we can cite the theory that speech developed out of song. On this view, song-like vocal displays came first, perhaps with a function in sexual selection. Like music, they involved complex patterns but had no meaning. Certain "motifs" or bits of vocal pattern came to have referential value, for instance in naming individuals. Unlike bones, however, behaviors leave little evidence in the fossil record. Since no other species has developed a symbolic communication system like human language, we are not in a good position to make generalizations, except about the many cases where symbolic language did not develop. Therefore, it is difficult to make a strong case for or against the various theories of the evolutionary precursors and selective advantages of human language.






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