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SETI
NEWS |
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Chief
Seattle once said, "Mankind would die of a great loneliness if all
the animals disappeared." Could it be that they have something to
share with us? Do animals communicate and will we ever really be able to
tell what they are saying to each other—and perhaps to us?If
one is willing to admit that all animals communicate (in some way or
another) then the next question might simply be to ask how complex their
communication systems are. A mathematical tool for actually calculating
the complexity of a communication system was invented in the late 1940s
by Claude Shannon of Bell Labs (who, incidentally, thanked our own
Barney Oliver for helpful discussions in the acknowledgements of this
seminal paper). The new field was dubbed "Information Theory,"
and has since been used to calculate the amount of information to be
sent along, for example, computer lines. But we were the first to apply
it to dolphin whistles.I
got interested in dolphin whistles years ago when I thought that some of
the signal detection techniques I'd learned for astronomical
applications (planet detection, for example) might have application to
the identification and classification of dolphin whistle-vocalizations.
Little did I know, when a colleague of mine, Jon Jenkins, and I visited
Dr. Brenda McCowan and Sean Hanser at Marine World in Vallejo one
afternoon, what we would be getting into! |
| Many
people have, of course, intuited that dolphins are very bright
"folks." Their trainability, learning, and playfulness all
attest to this. Many scientists have embarrassed themselves by initially
underestimating dolphins' intelligence. (It is a well-known fact that
dolphins also have to think the experiment is fun or they won't do it.)
But, we asked ourselves, would it ever be possible to measure the
complexity of their whistle communication system? We wondered if one
could put a number, so to speak, on just how much communication
intelligence (really the meaning of the Drake's Equation term Fi) they
express.That
day at Marine World the dolphins had had their fun with me by tossing a
ball to one side of the pool, where I ran around and got it, and after
tossing it back they tossed it to the other side, where I ran around to
get it, and they kept this up until I caught on to the notion that I was
being run around on purpose. Looking up at the natural smile on the
profile of the dolphin who had been throwing the ball, it was difficult
not to think that I had just fallen for a dolphin practical joke.Heading
back into the analysis room where Brenda, Sean, and Jon where discussing
signals, I remember that Jon pointed out that there had recently been an
article that discussed the "linguistic properties" of junk
DNA, and how this result had been pretty controversial. In this paper
the genetic scientists had made some plot of the frequency of occurrence
of so-called "junk" DNA and had been able somehow to show that
this distribution might imply linguistic properties. This was my
introduction to information theory. |
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| In
the late 1940s a linguist named George Zipf had had graduate students
count all the letters in some typical English texts—Ulysses, for
example (before word processors!). He plotted the frequency of
occurrence, FO, (actually the logarithm of FO) of the letters in
decreasing (also log) order. The letter "e" for example,
occurred the most frequently (10.1% of the time), followed by the letter
"t" (about 8% of the time), followed by the letter
"a" and so on down to the letter "q" (0.1% of the
time). Drawing a line through these values gave a slope of -1, that is,
a 45-degree line from top left to bottom right pretty much went through
all the points on the graph.He
tried the same for Chinese letters and also got a -1 slope. The same for
Russian phonemes, Arabic letters, and English words, and many other
human languages, all giving this -1 slope line. However, when the same
plot was done of baby babbling sounds the slope was much less steep,
that is, the plot of baby babbling sounds gave a closer to horizontal
line. This meant that the sounds babies were making were more random
than adult language. (Babies make all sorts of sounds that humans can
make before they start to specialize in one language—but the sounds
don't have a distribution of FO that indicates communication
complexity.)A
plot of adolescent baby talk, however, showed a line even more vertical
than the -1 slope line. This also made sense since adolescents learning
a specific language repeat a few sounds a lot (especially, in English,
for example, "Mama"). As vocabulary is added—adolescents to
adult speech, the Zipf plot approaches the -1 slope of adult languages
in every case.Armed
with this idea, we decided to plot adult dolphin whistles, since Brenda
and Sean had measured enough whistles to know their frequency of
occurrence. It was indeed quite a surprise to find that the distribution
of their signals gave a -1 slope—the same as human languages! It was
decided next to record baby dolphins—less than one month old—and the
plot of the FO of their whistles fell exactly on that of human infants!
Next, the distribution of adolescent dolphin whistles showed more
redundancy in a manner similar to adolescent human language learning (a
more vertical slope), before approaching the mature language -1 slope
again, just as in humans. |
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| From
this work we really had to conclude that dolphins learn their whistles,
and statistically do so in a way similar to the way humans learn their
languages. Also, this was mathematical proof that the dolphin
whistle-vocalization system of communication contains a substantial
degree of complexity. How complex is it? We don't know yet, but we know
the way to begin finding out.Human
languages have syntax—we rely on the juxtaposition of certain words,
for example, to other words for meaning (i.e. context). Human languages,
for example, apply context to strings of up to about 8 words in a row.
However, there is not much relationship of a given word to words more
than 8 words farther away in typical spoken English; that is, we tend to
lose the context after a string of about 8 words. In information theory
we would say that English word does not have any additional complexity
after the 8th-order Shannon entropy. (Mathematically we would say that
the conditional probability of a given word more than 8 words away from
a previous word is zero.)For
dolphins we have found that they have at least 2nd-order context to
their signals and quite possibly 3rd or 4th-order as well (we are
analyzing the data now). I wonder how many dolphins would be allowed to
be caught in a fishing net if we find they have, for example, a very
complex "language"? In addition, we have also applied these
methods to Squirrel Monkeys, Humpback Whales, Elephant Seals, and we
soon hope to be able to include Elephants, Hippos, Parrots, Bees (their
waggle dance) and perhaps some of the simpler "critters"
(those where we expect only a first-order entropy communication system)
for comparison. |
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Someone
asked me recently if we were taking the first steps toward a "Star
Trek-type universal translator". I don't know. So far we can only
quantify the complexity of the signaling system of other species; we may
be quite a few steps away from "translation" yet. But if we do
get a SETI signal some day, and can record the modulation and classify
individual signals, we should be able to use the general rules of what
we have learned about the communication systems of our fellow
inhabitants of this planet, to at least tell the communication
complexity of this extraterrestrial transmission. We should be able to
tell immediately if it is consistent with a communication system, for
example.But
what if such a SETI signal turns out to have 15th-order entropic
complexity? That is, what if it turns out to be far more complex than
any possible human communication system to date? If communications were
ever to ensue, we might hope that they would look upon us with more
respect than perhaps we have looked upon most other species of this
planet to date. They may just consider an 8th-order entropic
communicating species as approaching the level of intelligence necessary
to recognize the necessity of taking care of every species on its planet
- intelligent enough to avoid the great loneliness. I hope so. |
SETI Newsletter - Fourth Quarter 2001 Volume 10, Number 3 |
