Plan du site Aide Abonnement Nous Contacter


Actualité
Editorial
Interviews
Démocratie
Visites virtuelles
Art. Imaginaire
Du côté des labos
Le feuilleton
Manifestations
Biblionet
CD Rom
Echanges
Liens Utiles

 

Accueil > Biblionet
Automates Intelligents utilise le logiciel Alexandria.
Double-cliquez sur chaque mot de cette page et s'afficheront alors définitions, synonymes et expressions constituées de ce mot. Une fenêtre déroulante permet aussi d'accéder à la définition du mot dans une autre langue.
 
Archives

Gravity's Engines

Phi, a voyage from the brain to the soul

A propos du livre Mindful Universe

La médecine personnalisée

7 novembre 2002
Article, par John Stoyles

Up from Dragons
- how neural plasticity changes our understanding of our evolution - and symbolic culture

Couverture du livre : "Up From Dragons"Le Dr. John R. Skoyles est un scientifique à la carrière originale, qui s'efforce de remettre en cause les idées reçues, notamment dans les sciences de l'évolution et les neurosciences. Son dernier livre Up from Dragons, écrit avec Dorion Sagan (le fils du regretté Carl Sagan) refuse la primauté des gènes dans l'évolution et rassemble les différents facteurs ayant contribué à l'apparition de l'intelligence et des comportements culturels associés. John Skoyles est aussi Visiting Fellow pour le Centre for Philosophy of Natural and Social Science de la London School of Economics,

 Pour en savoir plus
Le site du livre qui en présente de larges extraits : http://www.upfromdragons.com/
Steven Pinker. The Blank Slate : http://www.mit.edu/~pinker/slate.html de la fiabilité des représentations culturelles.

The completion of the human genome project - the reading of the very DNA which programs the creation of each us including our brains from a single fertilized cell - suggests - indeed tempts us to believe that the answer to who and what we are lies in our genes. What I shall propose here is that genes are only half the story. The discovery of neural plasticity suggests genes play a different role in us than in other animals. Human evolution specialized us to transmit through culture what in other animals is transmitted through genes. That extragenetic information - passed through symbols - works by exploiting neural plasticity to modify - reprogram - earlier evolved functions into new ones. The genome does not make the humanities irrelevant to understanding ourselves but paradoxically even more important.

Genes and their evolution I should stress are central. When we look in the mirror, we see the products of genes - our face with the rest of our bodies - is a wonderful creation of a gene orchestrated dance of embryological development choreographed by natural selection. But what of our brains? Though created by genes and natural selection, is understand these enough to know what happens to create our thoughts, minds, emotions, and sense of being very much alive? Is evolution and genetics the single factor -- as with our bodies -- in making us who we are? Or it is only a factor with there being more to tell?

Adaptation and neurological evolutionary psychologies

Two quite different stories - adaptational and neurological - are emerging as to how human evolution and our genes link to the science of our minds. First, and presently, the most popular one - adaptational evolutionary psychology - argues that our brains are like the organs of body in that their functions - mental faculties -- are the products of natural selection. When we look at our hearts or other organs, what we see in effect are marvelous pieces of evolutionary engineering. Evolution did not exactly design them - evolution lacks intent. But we can read back from the utility of their design, that certain advantages for their survival caused them to be selected. Adaptational evolutionary psychology claims that the faculties of our minds like the organs of our bodies are in this way "designed". The human brain in this view is made up of a wide variety of cognitive "gadgets" - complex mental adaptations - whose engineering was selected during the Pleistocene - roughly one and half million years until 10,000 years ago.

Adaptation evolutionary psychology leaves little room for culture or the humanities: the core essence of what makes us human, according to it, lies instead in the evolution of complex mental adaptations during the Pleistocene.

Neurological evolutionary psychology also claims that when we look in the mirror we see the product of genes and evolution. But it sees this evolution stretching far back prior to the Pleistocene to the origins of early reptiles and even earlier - hence the title of the book explaining this approach: Up from Dragons (McGraw-Hill, 2002, Skoyles, J. R. and Sagan, D). Neurological evolutionary psychology, in contrast, to adaptational evolutionary psychology does not propose, however, that human evolution carried on this adaptation a stage further by creating the cognitive gadgets of our minds - at least not directly. Instead it argues that human evolution initiated non-genetic adaptation by opening this earlier evolution in the human brain to be refashioned by the extragenetic transmission. Human evolution created a brain specialized at creating itself through inherited culture not inherited genes. Thus, in this view, the human brain, rather than being full of evolved cognitive gadgets, as claimed by the adaptationists, consists of the equivalent of cogs, screws, and other components out of which culturally transmitted learning can create such cognitive gadgets. Culture is not something that happens on top of minds - it is a programmer that creates minds.

Neurological evolutionary psychology synthesizes neurology - the discovery of neural plasticity - and cultural studies - the role of symbols.

Neural plasticity

Neural plasticity - the flexibility of neurons to take on functions for which they were not evolved - is one of the great discoveries of recent neuroscience. It does not deny that evolution optimized much of the brain to carry out particular functions: what it observes is such optimization did not determine that cerebral and other brain circuits should also be limited in function by such specialization -- and so remain open if appropriated trained to do quite different things.

We know this due to Louis Braille. In those born blind, the part of the brain that natural selection has for nearly 200 million years in mammals being fine tuning them to see takes on a radically different function - that of reading Braille. Further evidence for neural plasticity is that if visual inputs from the retina in ferret embryos are redirected to the auditory or somatosensory cortex rather than go to the visual cortex, the circuits in this normally nonvisual part of the adult ferret brain develop sight. No adaptational evolutionary psychologist predicted a brain that could do this. Braille, after all, as a tactile skill that from an evolutionary viewpoint should be done in the somatosensory areas specialized for feeling with the fingertips not those evolved for vision. What neural plasticity reveals is that the circuits that make up the brain, while they might be fated, are not determined by evolution to do a particular function. It is a discovery with profound implications for understanding human evolution.

Steven Pinker, an adaptational evolutionary psychologist, has recently argued (Blank slate, 2002) that neural plasticity is "metaphor" if applied to those brain areas that process higher cognition. He is wrong: it is due to neural plasticity in these areas that our minds are robust against the effects of age, dementia, and small brain injuries. Brain tumors can grow to the size of small plums - in doing so they destroy brain tissue; however because their growth is so slow, the functions in these areas migrate to circuits nearby leaving an individual cognitively intact. Due to such evidence of the existence of neural plasticity, our understanding of aging and the process of dementia has shifted dramatically in recent years -functional imaging of the brain shows that the aging or dementing brain goes through a process of adaptation with new areas taking over functions previously done elsewhere in the brain - this process minimizes the impact of brain deterioration. Of course, this process can only go on until the "reserve" that enables such compensation is exhausted and the effects of brain deterioration can no longer be masked. Nonetheless, it is evidence that neural circuits are flexible throughout the brain including those most recently expanded in our evolution.

Neural plasticity and human evolution

Neural plasticity tells us that neural circuits evolved for one function can, if appropriately trained, do functions that no brain was evolved to do - cerebral circuits for sight, for example, can turn into cerebral circuits for Braille reading. Human evolution specialized the human brain to take advantage of this neural plasticity.

· First, it freed itself of the constraint of having insufficient neural circuits available to take on new nonevolved functions by expanding the cerebral cortex three fold.

· Second, it expanded the part of the brain best able to train novel functions upon the brain - the prefrontal cortex. The prefrontal cortex is central to learning. Very briefly, what has been found about the prefrontal cortex argues it has skills for making arbitrary linkages between processes elsewhere by holding together them - a skill needed to make the stand-in relationship of symbols - in "working memory".

· Third, the brain developed a powerful means for communicating skills - language. At present, it is not clear how far this involved speech rather than gestures - some have argued speech is a secondary development that followed the earlier development of vocal skills for singing. The details here are uncertain - what is clear is that humans evolved a specialization that enabled our species to communicate learning efficiently between generations.

Symbolization and the "stand-in" extension of old functions

Neural plasticity enabled a fundamental revision of the capabilities of the brain by reprogramming the old functions carried out by neural circuits to new ends by means of symbols. Basically, symbols make one thing stand-in cognitively for another. An already evolved process "X" that processes inputs "Y" can process - when rewired by neural plasticity - inputs "Z". The inputs "Z" act as stand-ins for the inputs "Y" in the process "X". This can revolutionize what the process "X" does since unlike inputs "Y", inputs "Z" might be in a different modality, nontransient, or able to combine into complex systems - things that might greatly extend or alter what process "X" can do.

For example, take process "X" to be the process by which we recognize spoken words, input "Y" to be the speech sounds - vowels and consonants, and "Z" to be visual patterns such as A, B or C. These visual patterns - letters - act as stand-ins for speech sounds, and thus enable an alternative means by which the word recognition process can identify words. Speech sounds are transient, and at least before audio recording, not easily reproduced. Visual patterns, in contrast, can be permanent, and readily copied even with primitive technologies. Thus, a completely new cognitive skill could be created upon an old one by the use of alphabetic symbol stand-ins for speech sounds - reading and writing. Note, that alphabet letters as stand-ins have a completely arbitrary linkage with what they take the place of - the letter B has no obvious link to the sound of the consonant /b/ for which it is a symbol.

Neural plasticity by allowing one thing to stand-in in the brain for another can profoundly change prior evolved adaptations - in this case an ability to recognize an image, and the ability to make or recognize a spoken word, can be combined to create the skills of reading and writing. An already evolved intelligence - the ability to recognize words - could through symbols become an artificial one - literacy - generated afresh in each generation through the neural programming offered by symbols - writing - from previous ones.

Symbols are not only important in extending cognitions: they also enable the novel sociability of the human species - and this played a critical role in the evolution of our human brain. The two aspects of sociability that mark out humans from our closest ape relatives are (1) the existence of communal defined relationships such as in-laws; and (2) long-term and separation resilient attachments, particularly those between biological parents. These innovations were profoundly important since long-term partnerships between parents enable humans to provide the substantial and reliable resources needed for child rearing, and in-laws and other socially defined relationships enable humans to be parts of intricate kinship networks that further aid this provision through complex forms of group cooperation. There is a feedback here: these bonds since they increase the resources for raising children enable the prolonged period of immaturity needed to develop and then educate brains with extragenetic transmitted learning.

Such communally defined and long-term robust attachments were made possible by symbolization. Consider the wedding ring - it is not merely a piece of metal but a device by which the limbic brain - the part of the brain responsible for attachments - can keep bonds robust against the physical separation of individuals by time and place. Emotional attachment normally requires that brains constantly affirm their relationship with physical contact and sensory cues with an attached partner. Without the daily contact that provides this input into the limbic systems, the emotions of attachment fade. But a symbol - such as a ring on the finger - can take the place of these daily contact emotions by standing-in for these limbic processes for the physical and sensory contact that does not happen. A wife or husband, for instance, may not see or hear each other (particularly in the pre-telecommunication age if away at sea or war) but they are still present to each other through that piece of metal. Due to neural plasticity, attachment processes in the limbic system can gain input from this (and other arbitrary stand-ins) in addition to transient sensory cues provided by the partner's actual presence. This lets it respond to a new kind of relationship affirmation: one that is permanent and does not require the presence of the other partner. That profoundly changes the endurability of that attachment.

Wedding rings, further, show another aspect of symbols: the limbic process that once enabled attachment was private between two individuals. But due to its symbolization such attachment could be made public and definable by the community. The wedding ring is thus usually part of a complex symbolic system "marriage" that puts people in different families into in-law relationships, for example. What had been personal now could be cultural.

This illustrates how neural plasticity enables completely novel sociability - one based upon long term and culturally defined bonds. The circuits in the limbic system did not need to change for this - what was needed was evolution to give an opportunity for neural plasticity to allow inputs into the limbic system to be reprogrammed by symbols.

Here we can see how neuroscience, and evolutionary theory can together radically change our view of culture. Human evolution did not select genes to build complex cognitions; it selected them to make culture that could transmit them. That required human evolution to specialize the brain to acquire symbols that could rewrite earlier evolved skills to acquire not only new skills but through them, new and unnatural - because made by symbols - cultural ways of living. Such new ways of life, of course, feedback enabling the support needed for the enlarged human brain.

The revolution of symbols

The brain's discovery that it could extend itself with symbolism was a revolution. Arguably, it was a watershed as momentous for the rise of the mind as catalysts were for the rise of life.

First, consider the power of arbitrary links to change what the brain did. Symbols allow new cognitions. Not only did this vastly increase processing power, but also it did this without needing any new evolution of special brain circuits.

But this was only the start of the brain-upgrade story -- symbols are much more than arbitrary associations. Arbitrary associations could exist only as a kind of private software that each brain learns in isolation. But because they are learnt, the human brain could copy the links discovered and used by other brains. That was a revolution: brains could select the best from other brains - programming could itself evolve. That turbocharged what brains could acquire. Again this would happen without the rest of the brain needing to change.

This even still was only the beginning: brains could combine symbols into complex information carrying systems, and use such systems of symbols to organize the rest of the brain -- including the ability to learn and pass on such learning. Moreover, here was a tool that it could pick up direct from other brains. The brain catalyst of symbolism would start catalyzing itself in new directions.

Brains could, for example, with complex symbol systems, go on to invent worlds that only existed due to them: mathematics, literature and science. Indeed, one philosopher, Sir Karl Popper, suggested that they make up a different kind of world: World 3. According to him, World 3 exists autonomously of the real one in which we physically live (World 1), and the subjective one of our inner thoughts (World 2). World 3 is the world of symbols we communicate and store-from the works of Euclid and of Shakespeare to Google and Internet.

Symbols give us the possibility of mindware - an extragenetic inheritance that creates our minds upon our brains as software does upon hardware. Not of a single kind, but of a nearly infinite number of varieties, limited only by human imagination. Our brains had contained many ape skills that were ripe to be changed in what they did. With the right symbolism they could be upgraded to do things and live forms of life that no other ape could - and with great diversity.

Here is the importance of neural plasticity. Neural plasticity argues that our brain is not functionally fixed. Evolution had created a biocomputer with a wide range of mental skills that were ready, without further evolution, due to it and the possibilities offered by symbols, to do totally novel things. Symbols, moreover, gave brains the ability to be different and pass that difference on. Neural change could thus undergo, independent of its genes, an evolution of its own.

Signified and signifiers

These ideas suggest an urgent need for dialogue between anthropologists and neuroscientists. Cultural anthropologists such as Levi Strauss, talk of "signifiers" and "signified." What people do with symbols must involve some underlying processes. Given the brain's role in making our experience, it would be reasonable to suggest the processing carried out by neurons. Neurological evolutionary psychology contends, that when anthropologists talk of signifiers, they are talking of symbols; and when they talk of the signified, they are in general talking of the social, attachment and other processing done in the limbic system.

We can only tentatively sketch rough outlines of how this might happen. The social life of all people is full of social "don'ts," taboos and rituals. One conjecture is that symbol signifiers extended signified processes in the orbital prefrontal cortex. In apes, they underlie behavioral "don'ts." Symbolized, they may have made possible the human experience of morals and etiquette. The experience of nonwestern and many western people is full of things to fear and be wary of-magic, pollutants, unlucky numbers, evil eyes, sacred places, ritual ceremonies and superstitions. Fears and anxieties are created in the amygdala - might processes in this part of the brain have become signified through symbols? We wear rings and powder and paint ourselves. Are processes in the insular or the somatosensory cortex - which links emotions to our bodies - being signified?

Neurological evolutionary psychology challenges present anthropology by suggesting that below the symbols of culture hides a brain story. Social culture, it argues, is the direct result of a skill we did not realize we had-the ability to symbolize earlier evolved processes in our brains. We live in cultures -and at the same time mentally exist due to our brains: they must link. Thus to understand ourselves requires both the humanities - the nature of these symbols - and science - the neurology of the original processes that they extend and modify.

Neurological evolutionary psychology argues that symbolic culture is a kind of artificial intelligence added on to the natural one transmitted in our genes. With this artificing of the brain came a vast leap in what brains could accomplish. With shared symbols, the human brain retooled its mind to make all manner of new bonds, new selves, new societies-and indeed-if we include the sacred and Popper's World 3-new worlds.

This liberated the human brain. No longer was the brain-as it had been-merely a skull-encased organ programmed with instincts to survive and reproduce genes. Brains could now go beyond such needs-symbols freed our brains to experience new things in life. With mindware humans put themselves apart from other animals and the rest of nature. Modern people now can see their our brains in action and soon with technological advances will be able to actively enhance their development even more than in the past. Neurons with symbols had started a new journey, one of which is far from finished.


Automates Intelligents © 2002

 




 

 

 

Qui sommes nous ? Partenaires Abonnement Nous Contacter

© Association Automates Intelligents
Mention légale CNIL : 1134148