Golomb, Solomon W.

Name not available

WHEN IS 
EXTRA-TERRESTRIAL 
LIFE 
INTERESTING? 
In order to discuss extra-terrestrial life intelli- 
gently, we must first have some working concept 
in our mind of what is life. The point of view 
that I would like to take is that life is basically 
a systems concept, and that the particular com- 
ponents used to realize this concept may be quite 
different from planet to planet. The systems con- 
cept itself involves growth and replication. Of 
these two, it is the replication aspect which is 
most characteristic of life. In other words, we 
are talking about structures, or machines, or de- 
vices, or organisms which are capable of making 
copies of themselves from the raw materials at 
hand in their environment, and we will regard 
such structures as life. 
There is every reason to assume that many dif- 
ferent components could be used to embody this 
systems concept. In fact, a prevalent view among 
biologists who think about such matters is that 
the conditions needed for life to evolve are quite 
simple. First of all we require soup, by which is 
meant any good random mixture of chemical ele- 
ments or con~pounds such as the oceans on earth 
have ideally provided for the origin and evolu- 
tion of earth life. Next, we need free energy, such 
as solar radiant energy, to bring about interactions 
between the ingredients in the soup, plus suffi- 
cient time for something to happen. You may 
recall Thomas Huxley's analogy that if you let 
the monkeys type on the keyboard long enough, 
sooner or later they will type out a meaningful 
word or sentence, or ultimately perhaps even a 
volume. 
Presun~ably, the richer the soup and the more 
abundant the free energy in the environment, the 
less time will be required for the appearance and 
the subsequent evolution of living forms. Con- 
versely, where the soup is a very thin broth and 
the free energy is meager, perhaps a much great- 
er length of time would be required for the 
emergence of living forms. But the basic view 
b y  Solomon W. Golomb 
here is that ultimately life forms will emerge 
wherever these conditions are at all present. 
Several decades ago, the late mathematician 
John von Neumann wrote an article about self- 
replicating machines. This was a mechanistic ap- 
proach to the problem of devices which will 
replicate themselves, and it described a method 
of building a self-replicating machine or of de- 
signing one. The device was basically a control 
computer which had the instructions for making 
a complete copy of itself, which it did step by 
step from the raw materials at hand. If anyone 
tried to realize this model of von Nenmann's 
today, he probably would have to enrich the en- 
vironment by having some finely-machined parts 
lying around in the vicinity of the machine, but 
the hypothetical machine must at least be able 
to look around for the parts it needs and build 
a copy of itself. Finally, the instructions for doing 
all this are on some kind of punched paper tape 
which contains all the coded instructions for 
building a duplicate machine, and of course the 
final step in the replication of the machine is 
simply to make a copy of this punched paper 
tape. 
Von Neumann didn't really know it at the 
time, but this is exactly what nature does on 
earth with all terrestrial organisms. Every earth 
organism, from the simplest virus to the most 
complicated animal and plant, has a punched tape 
consisting of long molecules of nucleic acid. Di- 
rectly encoded in these molecules of nucleic acid 
are the complete instructions for making each of 
the enzymes and other proteins and substances 
which the organism will need. Thus, the struc- 
tural parts are the proteins, which are actually 
built and assembled from the environmental ma- 
terials on the basis of these instructions. This is 
the basic growth and replication mechanism of 
all earth organisms. 
It is a very singular fact that earth life always 
uses nucleic acid for the genetic coding. In some 
organisms only ribonucleic acid (RNA) is used, 
while in most earth organisms deoxyribonucleic 
acid (DNA) is used as a permanent or long-term 
storage and ribonucleic acid serves the function 
of short-term working blueprints, from which the 
actual structures are built. But there is a fantastic 
February 1963 
amount of fundamental similarity in the basic 
life process of all earth organisms. 
If we find life on another planet, we should 
ask first of all, "Does it use the von Neumann 
model of replication?" If it does not, it must 
replicate by some different or more complicated 
model that would certainly be quite interesting 
in itself. If it uses too much of a short cut we 
might even wonder if it is sufficiently elaborate 
to be life, even in a very general sense of the 
word. For example, we don't regard crystal 
growth as biological replication. But certainly the 
question of what systems concept is used for rep- 
lication is, from my point of view, the most basic 
one we can ask. Beyond that we can start looking 
for similarities with our own forms of life. 'For 
example, we would ask if the chemistry of these 
organisms is based on carbon, or whether, as vari- 
ous science fiction stories have suggested from 
time to time, a silicon life, or a boron life, or an 
iron oxide life is involved. 
In terms of the processes of life we can certainly 
expect a great deal of variation. For example, we 
might ask whether it uses oxygen or fluorine or, 
as in the case of some earth bacteria, sulfur, as the 
oxydizing agent in its metabolism. Even here on 
earth we have more than one chemical element 
used as the oxydizer. When we start looking for 
really close similarities to earth life, we can ask 
if it uses the scheme universally prevalent on 
earth of nucleic acid for the genetic code and 
protein as the structural substance. Any nucleic 
acid-protein life would, of course, look extremely 
earth-like. 
Structure and adaptation to  environment 
There are other interesting questions which in 
this context are somewhat less basic. These are 
questions concerning structure, and adaptation to 
the environment. Does the planet have animals 
and plants in a recognizable sense? Are there 
analogies with terrestrial forms as far as adapta- 
tion to particular kinds of environment? These 
will be very interesting from the point of view 
of classical biology, whereas the kind of questions 
I have been asking are the ones the microbiol- 
ogists, or "modern" biologists, would certainly be 
more interested in. With these ideas as a basis, we 
can classify extra-terrestrial life forms according to 
the following scheme. A major category would be 
von Neumann life. As a subcategory of this, we 
would have carbon-based von Neumann life. A 
subcategory of that would be nucleic acid-protein 
life, and here we could even have the further 
subcategory of nucleic acid-protein life using the 
genetic code universally employed by all earth 
organisms from nucleic acid to protein. 
Crick-Watson life 
I would propose to call this narrowest category 
Crick-Watson life, in honor of the 1962 Nobel 
Prize winners in medicine and physiology, who 
discovered the structure of DNA; and I would 
tend to believe that any nearby planet on which 
we find Crick-Watson life has a physical link with 
earth life. This would certainly be true if the 
planet in question were Venus or Mars, where 
we could invoke the "cosmic spore" theory, which 
asserts that tiny spores, driven by radiation pres- 
sure, or Brownian motion, can effect the transfer- 
ence of life from one planet to another close by. 
On the other hand, if the code were different- 
and, a fortiori, if it were not nucleic acid-protein 
life, even if it were carbon life-1 would certainly 
suspect that the entire evolutionary system on 
that planet was quite independent of the system 
on earth. That is, I would postulate a separate 
Book of Genesis to account for all the life that 
we would find on such a planet. 
A question which has appealed very much to 
the Sunday supplement publications on the sub- 
ject of extra-terrestrial life is whether or not it 
is intelligent. Here too, my approach would be to 
look at intelligence as a systems concept in the 
sense of memory and processing, and then the 
question that I would ask about extra-terrestrial 
intelligence, whether it were in a simple organ- 
ism or a complex organism, would be whether 
the computer organization of this intelligence was 
similar to what we have found in earth life. For 
example, does the alien information processing 
involve something which is functionally similar 
to neurons, rather than something with elements 
structurally similar to neurons. 
I feel it is more likely in the near future to 
learn interesting things by asking this kind of 
question than by asking, "Well, what do they 
know that we don't know?" and, "What have they 
figured out about nuclear weapons and rocketry, 
or disease control, or immortality, or some of the 
other technological topics that we have been in- 
terested in?" I suspect it will be a frightfully long 
time, if ever, before we find a life form that is 
more advanced than ourselves in worrying about 
precisely those questions that have been of par- 
ticular interest to the  human race. I would be 
quite surprised, at  the very least, to find such life 
forms in the solar system. 
Engineering, and Science 
Considerable attention has been given recently 
to concern over the possibility that space probes 
launched from the earth and landing on the moon 
and other planets might cause biological contam- 
ination of those planets, and, of course, this is a 
legitimate cause for scientific worry. However, 
there is a much more basic problem that we are 
faced with when we start talking about the inter- 
action of possibly quite alien life systems. At the 
extreme of high organization and intelligence, we 
have the problem of facing the aliens who are 
smarter than we are, and who are similarly given 
over to aggressive militaristic passions and would 
therefore destroy us militarily. 
I don't lose any sleep over that one at all. It 
is not the sort of thing that I am worried about 
as a possibility within our solar system or within 
my lifetime. I t  becomes a possibility when we 
start fooling around with contacting people in 
different parts of the galaxy. If they're bright 
enough to be contactable, they might be form- 
idable opponents. The history of our species has 
been that whenever human beings have encount- 
ered a very similar life form with comparable 
intelligence-other tribes, other races, or other 
nations-their instinctive reaction is to have a 
military showdown first, and compare notes on 
the niceties of civilization afterwards. But, as I 
have said, this is not my immediate concern. 
An assortment of dangers 
The science fiction writers have in fact done 
a fine job of describing intergalactic warfare, and 
I couldn't hope to add anything to that. H. G. 
Wells described another menace which is also 
reasonably obvious; namely, that the diseases of 
one planet may be far more severe for the in- 
habitants of other planets who haven't built up 
an immunity against them. This was certainly the 
history of the European explorers in the New 
World, and has been one of the great problems 
whenever cultures on earth have interacted. The 
transfer of disease has been quite violent and 
virulent. This worries me somewhat in its impli- 
cations for exploration even within the solar sys- 
tem, but I think that rather routine quarantine 
procedures could be developed which would 
handle this problem without too much difficulty, 
as long as the problem is recognized in advance. 
I am reasonably hopeful that it would be. 
The thing that concerns me most is the com- 
petition that could go on, and sometimes inevi- 
tably would go on, between truly alien systems 
of life at the microscopic, almost at the molecular 
level, when it comes to competing for the basic 
raw material out of which they make replicas. 
This would involve competition as to which is the 
more efficient energy conversion system. The fact 
that there is only one mechanism on earth for 
replication is not necessarily the result of only 
one system having evolved. In fact, our present 
system is not likely to be the original form in 
which a replicating mechanism evolved. Appar- 
ently there is a "zero-one-law" of survival among 
replicating mechanisms leading to the survival of 
one system and the extinction of all others. After 
the first one has appeared, and it may have taken 
it millions of years to emerge, then there is sud- 
denly a strong competition among slight variants 
of this replicating mechanism as to which one 
can make replicas faster. That is, the one that is 
most efficient at it is using up all the raw ma- 
terials from the environment, and the others are 
starved out. 
The most efficient replicating mechanism 
What we have on earth is apparently the result 
of just such a situation as this, where the nucleic 
acid-protein mechanism turned out to be more 
efficient than any of its competitors, and took 
over. I t  is certainly conceivable that there is a 
mechanism on Mars or on Venus that is inherent- 
ly more efficient than the earth mechanism, and 
if we were to introduce some spores or some 
microorganisms of that type on earth, it is just 
possible that gradually, over a period of decades, 
or generations, or centuries, these microorgan- 
isms might take over the ecology of the oceans 
or of the soil on earth. Then, at the most basic 
level of the food cycle, they might make the 
oceans incapable of supporting the usual kinds 
of fish and other seafood, or they might make 
the soil incapable of supporting grass or animal 
life. At such a point, without anybody ever hav- 
ing fired a shot, we would have lost the entire 
battle of survival. 
I prefer to believe that life which is very well 
adapted to Mars, even if we say that Mars is 
a more hostile and inhospitable environment than 
earth, would not as a consequence be all the 
more hearty and successful when it came down 
to compete with the soft, coddled life on earth, 
just as desert plants do notoriously poorly when 
brought into lush tropical regions. However, the 
consequences of guessing wrong on this point 
are unspeakably disastrous, and I think we should 
pay a great deal of attention to this particular 
danger. 
February 1963 


When Is Extra-Terrestrial Life Interesting?

http://calteches.library.caltech.edu/2209/1/golomb.pdf

When Is Extra-Terrestrial Life Interesting?

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