The Evolution of Intelligence

Renato M.E. Sabbatini, PhD
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Despite all differences that separate humans from other animals, especially non-human primates, it is the capacity for symbolic language that truly set us uniquely apart. Many differences we have in respect to other primates are relatively small, and  incremental in nature, but there is nothing like our ability for language, in all its forms. According to authors Terrence Deacon (in "The Symbolic Species") and Ian Tattersal (in "Becoming Humans"), our brains must have a fundamental difference in respect to other primate's brains, because although they seem to have some capacity for use of symbols and for communication using signs and vocalizations, there are enormous differences in the complexity of human symbolic language and it cannot be explained by a simple increase in volume of neural tissue.

Language is so important that it is probable that conscience, thought, planning and many other higher cognitive functions in man are determined by our brain's unique capacity for symbolic representation. According to author Derek Bickerton, language is not only a mean of communication, but it is the essential basis of human consciousness.

By symbolic representation, we mean that certain sounds (and later some graphical elements) are associated by the brain to elements of the physical world. For example:
The complex sound "ball"  is associated to an object we learn to recognize as a 
Neural networks (even simple ones) are capable of powerful generalization. Thus, we are able to extract the commonalities of all these different things: and  and still call them "" ball".

Many animals can do that. Dogs do it all the time, of course, and certain apes have been trained to recognize spoken words for dozens of objects and situations.

The next level of complexity, however,  is to learn words for things that do not have a physical counterpart, such as feelings, abstractions, etc. (example: "love", "future"), or even concepts that do not exist at all, except in our brain (e.g., mathematical operations). This, no animal except Homo sapiens sapiens can do in any significant way, although it is claimed by some scientists who have trained chimpanzees in the use of symbolic language that some mental constructs that we tend to think that are uniquely human, are also mastered by some apes, who also are able to use them for practical purposes.

The uppermost and most complex aspects of language, which are meaning and grammar, seem to be uniquely human. They are closely related to each other, and use vocabulary as it basis. Several authors, starting with the famed American  linguist Noam Chomsky, have proposed that, contrarywise to other primates, human beings have an innate capacity, or a hardwired brain, for acquiring languages. This conclusion was reached by Chomsky when he studied the way all human languages are intrinsically organized, and which led to a theoretical model of the so-called "transformational generative grammar". Despite the enormous variation among thousands of languages and dialects which are present in the human races, Chomsky and other linguists have been able to detect common elements which could be ascribed to this basic brain capabilities. The scientific evidence, so far, gives credence to their hypothesis, because infants are able to learn to speak and to understand very early in life, always in the same manner, and virtually any language which is present in their development milieu, be it natural or artificial.

So, there is a number of puzzling questions about the origins of language and its relation to human intelligence, which so far have not been completely answered:

• When hominids first developed language?
• What were the driving factors for this acquisition?
• What were the primitive functions of language?
• How language and the brain co-evolved?
• Why human language is so different from other forms of animal communication?

Evolution and Language

Were early hominids capable of speech? We do not know for certain, because fossiles do not preserve soft tissues that could give us a clue, such as the larynx, vocal cords, the tongue, the brain structures which we know that are responsible for the articulation of speech (the so-called Broca's area, in the third inferior frontal convolution), etc. However, modern human skulls have a very characteristic aspect, which is a flexion of the base of the skull to respect to the spinal cord, which has the function of creating a larger capacity in the neck for the anatomical structures responsible for articulated speech or the "voice box". Non-human primates have a flat skull structure in this area, showing no signs of flexion, so their vocal apparatus is incapable of the subtle modulations required by speech. Earlier hominids, such as the several Australopithecus species also do not show the flexion feature, so it is highly probable that they do not have speech. Starting with Homo erectus, however (the evidence for its antecessor, Homo habilis, is not clear from the fossil record), there are early signs of flexion. So probably this species and its sucessors (Homo ergaster, ancient Homo sapiens and Homo sapiens neanderthalensis) had some primitive forms of speech.

Another evidence is provided by brain endocasts (negative impressions left by cortex gyri upon the internal surface of the skull bones). Although results are inconclusive, Homo erectus, for instance, shows signs that it had well developed cortical areas responsible for commanding speech. This is not shown, again, in other earlier hominid species.

One intriguing theory proposes that symbolic language started with hand gestures. The first step in mankind's evolution was bipedalism, i.e., walking in the erect posture most of the time. This was probably caused by a dramatic shift in the environment and climate of proto-hominids. As we have seen, "Lucy" (the nickname given to a fossil of Australopithecus afarensis, which lived in Africa more than 2.5 million years ago) had a skeleton similar to modern's man as related to walking. This released the hands for carrying, manipulating and other useful tasks, and the hominids developed startling dexterity (thus coming to the fabrication of tools). The next step was then, speculate some scientists, the use of hands for a number of communicative gestures, and the first symbolic representations. They were used probably for communication among hunters and between men and women, which by then were highly differentiated regarding their roles in the social organization of hominids. All this slowly enlarged the brain, and eventually, the vocal apparatus started to be used for symbolic representation. Pure manual gestures were combined with facial expressions and then to vocalizations. Brain and glottal anatomical structure evolved along time to permit agility and complexity of coordination, because this kind of communication provided enormous adaptive and survival advantage for those hominids who, by virtue of mutations, displayed better skills at it.

Hominid's hands contrast starkly with those of other apes. Its joints and muscle actions make it highly adaptable for tool manufacturing, delicate handling and also for expressive gestures (we still use them today for this: see how a person gesticulates even when he/she is speaking at the phone!). For example, human hands are the only to have an opposable thumb (the thumb is a large finger, and folds completely in direction of the palm) and this is a fundamental evolutive "invention". The characteristic laterality of functions both in human language and dexterity (Broca's area and the dominant side of dexterity both occur at the same side of the brain, namely the left one for right-handed people) also give support for a common origin of the gestural and the speech channels. This degree of assymetry is apparent in hominid skull endocasts, already.

According to Corballis (1999), the time frame of symbolic communication in humans might have happened according to the following scheme:
 

6-7 million years ago Proto-hominids	Simple hand gestures. Vocalizations of alarm, emotions, etc.
4-5 million years ago Australopithecine hominids	Advent of bipedalism: appearance of more sophisticated hand signalling
1-2 million years ago Homo habilis and Homo erectus	Hand gestures become fully syntactical, vocalizations start to become symbolical, stark increase in brain size
100,000 years ago Homo sapiens	Homo uses vocal language, zenith of brain development, hand gestures play secondary role

Brain and language co-evolved, one boosting the efficiency and complexity of the other. Bickerton says that humans became intelligent because they they developed the capacity for speech. Mental representations of the world and of ourselves developed as a result (someone described thinking as a kind of "internal language"... In other words, the language skill is also a thinking skill)

Neurophysiologist William Calvin and linguist Derek Bickerton, again, speculate in their new book "Lingua Ex Machina", that language evolved in two phases, subjected to a "social calculus" pressure. In the first phase, humans used individual words (phonetic representations of objects), but with a very rudimentary syntax (the way words are used together to express structure and meaning). The second phase witnessed the development of more complex syntactical structures, permiting the formation of sentences and expressing many abstract concepts (including lies!) and the establishment of logic. Many neural adaptations have evolved to allow for the appearance of structured language. We still don't know what they are and how they work in the brain, but almost certainly we will be soon able to read the code for this in our genome.

The Functions of Language

However, it is still a mistery what were the primitive functions of language: why it appeared and what was its use in early Homo societies. One thing is absolutely clear: language was (and still largely is) a "social device", a unique capability that has sense only when related to man's social organization and its relation to the environment for survival.

One interesting theory proposes that language first developed as a mean of communication between infants and their mothers. Another one sees language as an all-important communication tool between hunters (for planning the hunt and coordination among hunters, for example), between warriors, and between members of the human family. In the arid and unforgiving African savanna, so the hypothesis goes, men left their home habitats for long lenghts of time, to hunt, to scavenger and to provide women and children, who were left behind. The communication of needs, planning, results of forays, etc, provided the requirements for the appearance of symbolic language. Finally, cultural transmission of important knowledge for survival, how to manufacture tools, weapons, shelters and clothes, to give names to objects and features of the world, etc.

But probably we will never know the exact reason or reasons, because all surviving humans are modern Homo sapiens, with the innate capability of language.

The "Symbolic Explosion"

For the first time, we could speak about the development of a real culture, with the beginning of all the elements of our own. There is little doubt that the development of full structured language is responsible for that, and why it appeared in one Homo subspecies and not in other, is still largely a mistery.
 

References

"The Evolution of Intelligence" Renato M.E. Sabbatini, PhD Brain & Mind Magazine, February/April 2001

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