An occasional e-zine by Robert Muratore
In May 1987, The Firm had a hit single called "Star Trekkin'" in which an ersatz Spock utters the words making up the title of this column. How could we recognize life if it's not as we know it? Not the producer's popular humanoids with a remarkable ability to speak fluent English, but the tough cases? In order to recognize something as alive, it must be a little bit like that which we already know to be alive. From what we know of living things, the more generally (abstractly or theoretically) we can define life, the easier it will be to recognize in novel forms.
So here it is: how to define life from a theoretical point of view - based in part on a course I taught at Cold Spring Harbor Laboratory, Summer 1995.
1. Why is the definition of life important in Star Trek?
Within the world of Star Trek, there are at least these two broad reasons to define life:
2. Why is the definition of life important today?
I will not be addressing big issues such as the meaning of life, or the nature of human intelligence. But within this snug philosophical boundary, I will describe how we come to look at sand on a planet such as Earth (or Ceti Alpha V) and say "not alive", and look at little things burrowing in the sand and say "alive".
If we understand this, then when new complex phenomena are encountered, we will be in a position to decide whether they are living.
The opportunity to make this decision will present itself frequently with:
3. A method that would appeal to Spock
There is a progression of abstracted beings on Star Trek who embody the ideals of logic:
One can judge a new phenomenon, whatever its nature, by comparing it to previous experiences. If these experiences are well understood, then the new experience can often be quickly analyzed. The scientific-technology enterprise proceeds largely in this manner (and less by force of rotten vegetables).
To apply this to the most basic biology, we would distill our sense of what makes various living things alive into a short list of essentials, and then test a newly discovered phenomenon against this list. The essentials are called rules or axioms.
The rules can be based on a widely varying set of ideas, from very specific to very abstract. Carl Sagan, in The Cosmic Connection, describes this spectrum of ideas as a spectrum of chauvinisms, each of which can be imagined to be broken.
I find it difficult to break this chauvinism with its ideas of change and cycles and still say something more interesting than "everything is alive in its own way". If you have any ideas along this line, please write to me, and I will post your ruminations.
4. The three axioms of life
The abstraction of life is central to the discussion of theoretical biology, much of which is carried on in the Web in a spirited manner (an artificial life site is a good starting place). Among the more popular definitions of life is a set of three abstract axioms:
Living systems, in creating pattern or structure, produce order from disorder. For example, a baby in growing produces organized bones and flesh from uniform white milk.
The production of order requires a metabolism, or use of energy of some sort. Metabolic wastes are a telltale sign of life.
The structures that are produced must be stubborn. That is, the momentary swirl pattern in coffee with milk stirred in is not a sign that the coffee is living. One means of understanding the stubbornness is R. B. Fuller's "rope trick". Imagine a long rope put together from various pieces: a cotton length connected to a hemp length connected to a polypropylene length etc. Tie a loose knot near one end of the rope. Move the rope through the knot. At one time or another, the substance forming the rope will be cotton or hemp or polypropylene. Thus, the structure (the knot) is more stubborn than the substrate (the rope material). Another example: growing muscle depends more upon what exercises I perform and less upon what cereal I eat.
I tuck my rope into my backpack, and decide to exercise by hiking in a quarry. I notice some shale, and in it see little spiral patterns. I immediately sense that I am looking at a fossil because of the intricacy of the structure, a structure that is stubborn, and has outlasted its original material to be replaced by stone.
Axiom 2 is about reproduction. For many creatures, this means sex.
Furthermore, the system must reproduce reproducible copies of itself. That is, the offspring, as copies of parents, must be of high enough resolution to include the reproductive apparatus.
This axiom, like the others, focuses on the system rather than the individual. Therefore, it is untroubled when confronted with a mule, the sterile offspring of a donkey and a horse (and the protagonist of Isaac Asimov's Foundation).
Here are some sweeping issues. The third axiom means that living things "don't always breed true". The randomness in the reproductive processes opens the door to selection based upon environmental factors. This allows evolution to proceed.
New computer experiments reveal that a system without parasites evolves slowly, and a system with parasites evolves hundreds of times more quickly. (You can download many of these.)
In the sense that evolution is faster in species that reproduce more rapidly, "evolution loves death more than it loves you or me" (Annie Dillard, Pilgrim at Tinker Creek, NY: Harper's Magazine Press, 1974, p. 176).
So, axiom 3, beloved by some biologists as the most important of the three axioms, is all about randomness, parasites and death.
To recap, an attempt can be made to define life with three axioms. A living system exhibits:
5. An encounter with aliens
The point of assembling the axioms is to guide the construction of a set of "tools" with which to decide whether or not an observed system is living. The sort of tools to be constructed are:
Success of the application will depend on the relative scales of both time and space between the observed lifeform and the observing lifeform. In fact, the problem with axioms 2 and 3 is that many individuals take longer to reproduce than a simple scan of the sensor array would voyeuristically reveal. How can Spock make his pronouncement? He must rely on axiom 1, leaving his pronouncement as a hypothesis to be tested later by the observation of axioms 2 and 3.
As expected, the axiomatic method correctly declares that life as we do know it is alive.
Crystals form an interesting case. First, the formation of a crystal is clearly the formation of a structure. Second, a crystal reproduces: it grows, the pattern is reproduced, small pieces branch off, and pieces can break away to serve as nucleating sites for new crystals. Third, randomness yields irregularities in the crystal, which can be manifested in a Darwinian way by their greater or lesser ability to accrete new ions. So we even have natural selection of a sort. So are crystals alive? The correct interpretation of axiom 1 shows that although structures are produced, the structures are not robust in the sense that they can respond to external stresses. Furthermore, the crystals are not FORMING pattern, they ARE pattern. There is no mechanism that must fight against the tide of the universe to carve out a niche.
You might say that this is so much hand waving, and you are right. Crystals are ambiguous when looked at axiomatically. In fact, this very ambiguity is the reason that science fiction often introduces "crystal entities".
The axioms also work for viruses. However, as with crystals, viruses do not contain the mechanism for forming order; rather, they contain instructions that cause other creatures to form order for them. Viruses can also crystallize. Once, when the chauvinism of life force hadn't yet been broken, it was debated hotly whether viruses are living. Although it seems that almost everyone now accepts them has living, the debate still smolders.
Various androids have appeared in the Star Trek universe, and in many instances they were accepted as alive, or the plot hinged on whether they were alive. Mr. Data can use our rule-based process to determine that he himself is alive. He creates order and pattern around him as well as any human. He can also reroute certain circuits inside of himself as a form of healing. So he fulfills axiom 1. In "Offspring", he reproduces, fulfilling axiom 2. And since his daughter Lal differs from him, he fulfills axiom 3 as well.
Although the missing name of Voyager's holographic Doctor recalls Dr. Who, the debate over the living state of holograms goes back to Dr. Moriarity in "Ships in Bottles". And although Janeway often forgets the Doctor while preserving the lives of her crew, Picard came to accept the living state of Moriarity. Picard's determination hinged mostly on the persistence of the hologram during the program shutdown, and the growth in knowledge and sophistication of the hologram during that period. That is, he relied upon axiom 1. Does Moriarity reproduce? If you can describe how his female companion came to be, write to me.
Suppose that the Universe itself were alive after a fashion, spawning little baby Universes in the form of black holes. What would evolution amount to? Watch out for Lee Smolin who is tackling these ideas.
6. For further reading