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[WHAT IS TODAY'S MOST IMPORTANT UNREPORTED STORY?]

MIRROR NEURONS and imitation learning as the driving force behind
"the great leap forward" in human evolution

By V.S. Ramachandran

Introduction by
John Brockman

In 1995, to an audience of 6,000 scientists, V.S. Ramachandran (known to
friends and colleagues as "Rama") delivered the inaugural "Decade of the
Brain" lecture at the Silver Jubilee meeting of the Society for
Neuroscience, this country's leading organization for brain research. His
talk, laced with wit and humor, received a standing ovation. Ramachandran
also delivered the "Decade of the Brain" lecture to the Library of
congress and the NIH. Her received invitations to give The Dorcus Cumming
Plenary Lecture at Cold Spring Harbor, and the Weissman Memorial Lecture
at the Weissman Institute, Israel. He is in great demand as a speaker,
both for scientific and lay audiences.

Rama is on the editorial boards of several international journals and has
published over 110 scientific papers, including three invited review
articles for Scientific American. He edited a four volume Encyclopedia of
Human Behavio that was cited by Library Journal as "the most outstanding
reference for 1994 in the behavioral sciences." In 1995 he was elected a
member of the Atheneum, the world's oldest scientific club, founded in
London by Michael Faraday and Humphrey Davy . He has appeared on numerous
television programs (PBS, BBC, German television) and his work has been
featured in The New York Times, Discover, National Geographic, Time and
Life.

Originally trained as a physician at Stanley Medical College, where he was
awarded gold medals in pathology and clinical medicine,Ramachandran went
on to earn a PhD in neurology from Trinity College at Cambridge
University. Before moving to La Jolla, he held appointments at Oxford
University and the California Institute of Technology. In 1998 he received
a Gold medal from the Australian national university and in "99 the Ariens
Kappers Medal by the Royal Netherlands Academy of Sciences for landmark
achievements in neurosciences. In the same year he was elected a fellow of
All Souls College Oxford. and Newsweek named him a member of the "Century
Club" - one of hundred people to watch as America enters the next century.
Today he works exclusively with human neurological patients and one of his
main interests is in the neurological basis of art. He has been lecturing
widely on this subject not only to scientists, but to art galleries and
museums.

JB

V.S. RAMACHANDRAN is professor of Neuroscience and Psychology
and Director of Center for Brain and Cognition at the University of
California at San Diego. He also holds joint appointments at the Salk
Institute in La Jolla and with the Cognitive Sciences Program at UCSD. He
is also a physician. A dynamic speaker who rolls his r's and flourishes
vowels, Dr. Ramachandran gives scientific talks the world over. His book
Phantoms In The Brain (with Sandra Blakeslee) was selected as one of the
best books of 1998 by The Economist and was a finalist for the Los Angeles
Times Book Prize. It was on the "Editors Choice" list in Scientific
American, Discover Magazine and The American Scientist.

MIRROR NEURONS and imitation learning as the driving force behind
"the great leap forward" in human evolution
By V.S. Ramachandran

The discovery of mirror neurons in the frontal lobes of monkeys, and their
potential relevance to human brain evolution - which I speculate on in
this essay - is the single most important "unreported" (or at least,
unpublicized) story of the decade. I predict that mirror neurons will do
for psychology what DNA did for biology: they will provide a unifying
framework and help explain a host of mental abilities that have hitherto
remained mysterious and inaccessible to experiments.

There are many puzzling questions about the evolution of the human mind
and brain:

1) The hominid brain reached almost its present size - and perhaps even
its present intellectual capacity about 250,000 years ago . Yet many of
the attributes we regard as uniquely human appeared only much later. Why?
What was the brain doing during the long "incubation "period? Why did it
have all this latent potential for tool use, fire, art music and perhaps
even language- that blossomed only considerably later? How did these
latent abilities emerge, given that natural selection can only select
expressed abilities, not latent ones? I shall call this "Wallace's
problem", after the Victorian naturalist Alfred Russell Wallace who first
proposed it.

2) Crude "Oldawan" tools - made by just a few blows to a core stone to
create an irregular edge - emerged 2.4 million ago and were probably made
by Homo Habilis whose brain size was half way (700cc) between modern
humans (1300) and chimps (400). After another million years of
evolutionary stasis aesthetically pleasing "symmetrical" tools began to
appear associated with a standardization of production technique and
artifact form. These required switching from a hard hammer to a soft
(wooden?) hammer while the tool was being made, in order to ensure a
smooth rather than jagged, irregular edge. And lastly, the invention of
stereotyped "assembly line" tools (sophisticated symmetrical bifacial
tools) that were hafted to a handle, took place only 200,000 years ago.
Why was the evolution of the human mind "punctuated" by these relatively
sudden upheavals of technological change?

3) Why the sudden explosion (often called the "great leap" ) in
technological sophistication, widespread cave art, clothes, stereotyped
dwellings, etc. around 40 thousand years ago, even though the brain had
achieved its present "modern" size almost a million years earlier?

4) Did language appear completely out of the blue as suggested by
Chomsky? Or did it evolve from a more primitive gestural language that was
already in place?

5) Humans are often called the "Machiavellian Primate" referring to our
ability to "read minds" in order to predict other peoples' behavior and
outsmart them. Why are apes and humans so good at reading other
individuals' intentions? Do higher primates have a specialized brain
center or module for generating a "theory of other minds" as proposed by
Nick Humphrey and Simon Baron-Cohen? If so, where is this circuit and how
and when did it evolve?

The solution to many of these riddles comes from an unlikely source.. the
study of single neurons in the brains of monkeys. I suggest that the
questions become less puzzling when you consider Giaccamo Rizzollati's
recent discovery of "mirror neurons' in the ventral premotor area of
monkeys. This cluster of neurons, I argue, holds the key to understanding
many enigmatic aspects of human evolution. Rizzollati and Arbib have
already pointed out the relevance of their discovery to language
evolution. But I believe the significance of their findings for
understanding other equally important aspects of human evolution has been
largely overlooked. This, in my view, is the most important unreported
"story" in the last decade.

THE EMERGENCE OF LANGUAGE

Unlike many other human traits such as humor, art, dancing or music the
survival value of language is obvious - it helps us communicate our
thoughts and intentions. But the question of how such an extraordinary
ability might have actually evolved has puzzled biologists, psychologists
and philosophers at least since the time of Charles Darwin. The problem is
that the human vocal apparatus is vastly more sophisticated than that of
any ape but without the correspondingly sophisticated language areas in
the brain the vocal equipment alone would be useless. So how did these two
mechanisms with so many sophisticated interlocking parts evolve in tandem?
Following Darwin's lead I suggest that our vocal equipment and our
remarkable ability to modulate voice evolved mainly for producing
emotional calls and musical sounds during courtship ("croonin a toon.").
Once that evolved then the brain - especially the left hemisphere - could
evolve language.

But a bigger puzzle remains. Is language mediated by a sophisticated and
highly specialized "language organ" that is unique to humans and emerged
completely out of the blue as suggested by Chomsky? Or was there a more
primitive gestural communication system already in place that provided a
scaffolding for the emergence of vocal language?

Rizzolatti's discovery can help us solve this age-old puzzle. He recorded
from the ventral premotor area of the frontal lobes of monkeys and found
that certain cells will fire when a monkey performs a single, highly
specific action with its hand: pulling, pushing, tugging, grasping,
picking up and putting a peanut in the mouth etc. different neurons fire
in response to different actions. One might be tempted to think that these
are motor "command" neurons, making muscles do certain things; however,
the astonishing truth is that any given mirror neuron will also fire when
the monkey in question observes another monkey (or even the experimenter)
performing the same action, e.g. tasting a peanut! With knowledge of these
neurons, you have the basis for understanding a host of very enigmatic
aspects of the human mind: "mind reading" empathy, imitation learning, and
even the evolution of language. Anytime you watch someone else doing
something (or even starting to do something), the corresponding mirror
neuron might fire in your brain, thereby allowing you to "read" and
understand another's intentions, and thus to develop a sophisticated
"theory of other minds." (I suggest, also, that a loss of these mirror
neurons may explain autism - a cruel disease that afflicts children.
Without these neurons the child can no longer understand or empathize with
other people emotionally and therefore completely withdraws from the world
socially.)

Mirror neurons can also enable you to imitate the movements of others
thereby setting the stage for the complex Lamarckian or cultural
inheritance that characterizes our species and liberates us from the
constraints of a purely gene based evolution. Moreover, as Rizzolati has
noted, these neurons may also enable you to mime - and possibly understand
- the lip and tongue movements of others which, in turn, could provide the
opportunity for language to evolve. (This is why, when you stick your
tongue out at a new born baby it will reciprocate! How ironic and poignant
that this little gesture encapsulates a half a million years of primate
brain evolution.) Once you have these two abilities in place the ability
to read someone's intentions and the ability to mime their vocalizations
then you have set in motion the evolution of language. You need no longer
speak of a unique language organ and the problem doesn't seem quite so
mysterious any more.

(Another important piece of the puzzle is Rizzolatti's observation that
the ventral premotor area may be a homologue of the "Broca's area" - a
brain center associated with the expressive and syntactic aspects of
language in humans).

These arguments do not in any way negate the idea that there are
specialized brain areas for language in humans. We are dealing, here, with
the question of how such areas may have evolved, not whether they exist or
not.

Mirror neurons were discovered in monkeys but how do we know they
exist in the human brain? To find out we studied patients with a strange
disorder called anosognosia. Most patients with a right hemisphere stroke
have complete paralysis of the left side of their body and will complain
about it, as expected. But about 5% of them will vehemently deny their
paralysis even though they are mentally otherwise lucid and intelligent.
This is the so called "denial" syndrome or anosognosia. To our amazement,
we found that some of these patients not only denied their own paralysis,
but also denied the paralysis of another patient whose inability to move
his arm was clearly visible to them and to others. Denying ones one
paralysis is odd enough but why would a patient deny another patient's
paralysis? We suggest that this bizarre observation is best understood in
term of damage to Rizzolatti's mirror neurons. It's as if anytime you want
to make a judgement about someone else's movements you have to run a VR
(virtual reality) simulation of the corresponding movements in your own
brain and without mirror neurons you cannot do this.

The second piece of evidence comes from studying brain waves (EEG) in
humans. When people move their hands a brain wave called the MU wave gets
blocked and disappears completely. Eric Altschuller, Jamie Pineda, and I
suggested at the Society for Neurosciences in 1998 that this suppression
was caused by Rizzolati's mirror neuron system. Consistent with this
theory we found that such a suppression also occurs when a person watches
someone else moving his hand but not if he watches a similar movement by
an inanimate object. (We predict that children with autism should show
suppression if they move their own hands but not if they watch some one
else. Our lab now has preliminary hints from one highly functioning
autistic child that this might be true (Social Neuroscience Abstracts
2000).

THE BIG BANG OF HUMAN EVOLUTION

The hominid brain grew at an accelerating pace until it reached its
present
size of 1500cc about 200,000 years ago. Yet uniquely human abilities such
the invention of highly sophisticated "standardized" multi-part tools,
tailored clothes, art, religious belief and perhaps even language are
thought to have emerged quite rapidly around 40,000 years ago - a sudden
explosion of human mental abilities and culture that is sometimes called
the "big bang." If the brain reached its full human potential - or at
least size - 200,000 years ago why did it remain idle for 150,000 years?
Most scholars are convinced that the big bang occurred because of some
unknown genetic change in brain structure. For instance, the archeologist
Steve Mithen has just written a book in which he claims that before the
big bang there were three different brain modules in the human brain that
were specialized for "social or machiavellian intelligence", for
"mechanical intelligence" or tool use, and for "natural history" (a
propensity to classify). These three modules remained isolated from each
other but around 50,000 years ago some genetic change in the brain
suddenly allowed them to communicate with each other, resulting in the
enormous flexibility and versatility of human consciousness.

I disagree with Mithen ingenious suggestion and offer a very different
solution to the problem. (This is not incompatible with Mithen's view but
its a different idea). I suggest that the so-called big bang occurred
because certain critical environmental triggers acted on a brain that had
already become big for some other reason and was therefore "pre-adapted"
for those cultural innovations that make us uniquely human. (One of the
key pre adaptations being mirror neurons.) Inventions like tool use, art,
math and even aspects of language may have been invented "accidentally" in
one place and then spread very quickly given the human brain's amazing
capacity for imitation learning and mind reading using mirror neurons.
Perhaps ANY major "innovation" happens because of a fortuitous coincidence
of environmental circumstances - usually at a single place and time. But
given our species' remarkable propensity for miming, such an invention
would tend to spread very quickly through the population - once it
emerged.

Mirror neurons obviously cannot be the only answer to all these riddles of
evolution. After all rhesus monkeys and apes have them, yet they lack the
cultural sophistication of humans (although it has recently been shown
that chimps at least DO have the rudiments of culture, even in the wild).
I would argue, though, that mirror neurons are Necessary but not
sufficient: their emergence and further development in hominids was a
decisive step. The reason is that once you have a certain minimum amount
of "imitation learning" and "culture" in place, this culture can, in turn,
exert the selection pressure for developing those additional mental traits
that make us human. And once this starts happening you have set in motion
the auto- catalytic process that culminated in modern human consciousness.

A second problem with my suggestion is that it doesn't explain why the
many human innovations that constitute the big bang occurred during a
relatively short period. If its simply a matter of chance discoveries
spreading rapidly,why would all of them have occurred at the same time?
There are three answers to this objection. First,the evidence that it all
took place at the same time is tenuous. The invention of music,
shelters,hafted tools, tailored clothing, writing, speech, etc. may have
been spread out between 100K and 5k and the so-called great leap may be a
sampling artifact of archeological excavation. Second, any given
innovation (e.g. speech or writing or tools) may have served as a catalyst
for the others and may have therefore accelerated the pace of culture as a
whole. And third, there may indeed have been a genetic change,b ut it may
not have been an increase in the ability to innovate (nor a breakdown of
barriers between modules as suggested by Mithen) but an increase in the
sophistication of the mirror neuron system and therefore in
"learnability." The resulting increase in ability to imitate and learn
(and teach) would then explain the explosion of cultural change that we
call the "great leap forward" or the "big bang" in human evolution. This
argument implies that the whole "nature-nurture debate" is largely
meaningless as far as human are concerned. Without the genetically
specified learnability that characterizes the human brain Homo sapiens
wouldn't deserve the title "sapiens" (wise) but without being immersed in
a culture that can take advantage of this learnability, the title would be
equally inappropriate. In this sense human culture and human brain have
co-evolved into obligatory mutual parasites - without either the result
would not be a human being. (No more than you can have a cell without its
parasitic mitochondria).

THE SECOND BIG BANG

My suggestion that these neurons provided the initial impetus for
"runaway" brain/ culture co-evolution in humans, isn't quite as bizarre as
it sounds. Imagine a martian anthropologist was studying human evolution a
million years from now. He would be puzzled (like Wallace was) by the
relatively sudden emergence of certain mental traits like sophisticated
tool use, use of fire, art and "culture" and would try to correlate them
(as many anthropologists now do) with purported changes in brain size and
anatomy caused by mutations. But unlike them he would also be puzzled by
the enormous upheavals and changes that occurred after (say) 19th century
- what we call the scientific/industrial revolution. This revolution is,
in many ways, much more dramatic (e.g. the sudden emergence of nuclear
power, automobiles, air travel, and space travel) than the "great leap
forward" that happened 40,000 years ago!!

He might be tempted to argue that there must have been a genetic change
and corresponding change in brain anatomy and behavior to account for this
second leap forward. (Just as many anthropologists today seek a genetic
explanation for the first one.) Yet we know that present one occurred
exclusively because of fortuitous environmental circumstances, because
Galileo invented the "experimental method," that, together with royal
patronage and the invention of the printing press, kicked off the
scientific revolution. His experiments and the earlier invention of a
sophisticated new language called mathematics in India in the first
millennium AD (based on place value notation, zero and the decimal
system), set the stage for Newtonian mechanics and the calculus and "the
rest is history" as we say.

Now the thing to bear in mind is that none of this need have happened. It
certainly did not happen because of a genetic change in the human brains
during the renaissance. It happened at least partly because of imitation
learning and rapid "cultural" transmission of knowledge. (Indeed one could
almost argue that there was a greater behavioral/cognitive difference
between pre-18th century and post 20th century humans than between Homo
Erectus and archaic Homo Sapiens. Unless he knew better our Martian
ethologist may conclude that there was a bigger genetic difference between
the first two groups than the latter two species!)

Based on this analogy I suggest, further, that even the first great leap
forward was made possible largely by imitation and emulation. Wallace's
question was perfectly sensible; it is very puzzling how a set of
extraordinary abilities seemed to emerge "out of the blue". But his
solution was wrong...the apparently sudden emergence of things like art or
sophisticated tools was not because of God or "divine intervention". I
would argue instead that just as a single invention (or two) by Galileo
and Gutenberg quickly spread and transformed the surface of the globe
(although there was no preceding genetic change), inventions like fire,
tailored clothes, "symmetrical tools", and art, etc. may have fortuitously
emerged in a single place and then spread very quickly. Such inventions
may have been made by earlier hominids too (even chimps and orangs are
remarkably inventive...who knows how inventive Homo Erectus or Neandertals
were) but early hominids simply may not have had an advanced enough mirror
neuron system to allow a rapid transmission and dissemination of ideas. So
the ideas quickly drop out of the "meme pool". This system of cells, once
it became sophisticated enough to be harnessed for "training" in tool use
and for reading other hominids minds, may have played the same pivotal
role in the emergence of human consciousness (and replacement of
Neandertals by Homo Sapiens) as the asteroid impact did in the triumph of
mammals over reptiles.

So it makes no more sense to ask "Why did sophisticated tool use and art
emerge only 40,000 years ago even though the brain had all the required
latent ability 100,000 years earlier?" - than to ask "Why did space travel
occur only a few decades ago, even though our brains were preadapted for
space travel at least as far back Cro Magnons?". The question ignores the
important role of contingency or plain old luck in human evolutionary
history.

Thus I regard Rizzolati's discovery - and my purely speculative
conjectures on their key role in our evolution - as the most important
unreported story of the last decade.



POWRÓT