[extropy-chat] Human Evolution

Fri Nov 21 11:57:32 UTC 2003

Brett Paatsch <bpaatsch at bigpond.net.au> wrote: 
Interesting. In your view then what is "life" ?

     I will start out by assuming that you know what the textbooks say about life. Scroedinger's whole concept of an open thermodynamic system lying far from equilibrium that decreases its own entropy by increasing the entropy of its surroundings has been the mainstay of molecular biologists and biochemists for some time now. It satisfied a certain need that they had to reduce complex phenomena into simple mechanistic terms. I too BELIEVED this to be the case until only a few years ago. What opened my eyes was taking several courses on Bioinformatics which, in case you are unfamiliar with it, is the application of Information theory to Biology. This was a great experience for me because it was a brand new field composed of mathemeticians and computer programmers trying to understand biology. I however had the advantage of already being a biologist who just happened to be good at math and computer savvy to boot (no pun intended).

     What I found out was that there is another type of entropy called Shannon's entropy or informational entropy which is distinct from, although somewhat related to, Boltzman's or thermodynamic entropy. In essense, both are related to the degree of randomness inherent either in a system of particles/molecules or a signal/message. Life is characterized by being remarkably low in thermodynamic entropy which is equivelent to saying that it is matter in a highly ordered state although it is not the static order of a crystal (although some chemists will say that life is a liquid crystal) but rather a dynamic ordered state that I prefer to call organized. Life is also low in Shannon's entropy which is a measure of ignorance or meaninglessness. This is equivalent to saying that life is high in information content. The best definition of information I ever heard was by somebody, I forget who, that said "information is a difference that makes a difference." To give you a simplified example
 of how informational entropy is different than thermodynamic entropy, take into consideration the following 6 RNA sequences: GUA, GAU, UGA, UAG, AGU, AUG. 

      Now since all 6 are composed of the very same nucleotides, they would all have equivalent thermodynamic entropy. Yet they have very different informational entropy because by themselves none of them mean anything to a ribosome (or for that matter a computer algorithm designed to find genes in the morass of sequence data generated by the Genome Project) except the very last one AUG. This is because AUG, in a addition to being the codon for methionine, is the start codon and its presence says, "all the nucleotide triplets that come after me are part of a gene and code for amino acids to be assembled into a protein". In other words, in the above context AUG has a lower informational entropy and therefore a higher informational content than the others.

      I will give one more example that is a bit more easily understood by a layperson. A library shelf with lets say 50 books in it has a certain entropy content. Work must be perfomed by a librarian to keep the books on the shelf since many visitors to the library are lazy and don't like to put the books back the way they find them. Now thermodynamically speaking any arrangement of the same 50 books on the shelf takes the same amount of work and would therefore have the same Boltzman entropy value associated with it. Now information theory however would say that because arranging the books in alphabetical order increases the shelf's information content, an alphabetical arrangement of the books on the shelf would have a lower Shannon entropy value than a random ordering of those same books on the shelf although any arrangement of the books on the shelf would have less entropy than having the books strewn randomly about the room.

     Now that I have explained the relationship between thermodynamic and informational entropy, I can now answer your question Brett. The "old school" definition of life relied on a thermodynamic definition involving coupled chemical reactions that built up an ordered state of matter by lowering the system's thermodynamic entropy. This lowering of a system's Boltzman entropy supposedly allowed for all the phenonemena normally associated with life such as homeostasis, growth, and reproduction. Yet this, if you think about it, is a fallacy. 

      Two systems composed of the very same chemical constituents and having the very same thermodynamic entropy content can have two very different biological states. One system can be alive and the other system can be dead and a simple chemical analysis will not allow you to determine one state from the other. If you put a living mouse in a blender and pass the slurry through a gas chromatograph you will get the very same readout that you would if you killed it before you put it in the blender. The difference between the live mouse and the dead mouse is not in its thermodynamic entropy content but in its information content. The living mouse has a higher information content and consequently lower Shannon entropy value than the dead mouse despite the fact that both the live mouse and dead mouse have the same Boltzman entropy value.

      In this regard one can say that information content supercedes chemical considerations in determining whether something is alive or not.  Indeed one can use a system with a high information content to spontaneously organize the system by lowering its thermodynamic entropy. It is precisely this phenomenon that allows two single strands of DNA with complementary sequences to lower their thermodynamic entropy spontaneously by hybridizing to one another to form double stranded DNA. If the second strand has the very same number of A's, T's, C's, and G's as the complementary strand but not the proper sequence, the two strands will not anneal to one another despite the fact that they are thermodynamically equivalent. 

      Another excellent example of how information can superceed thermodynamics comes from the fevered mind of a 19th century physicist named James Clerk Maxwell, unquestionably a genius far ahead of his time. In a thought experiment, Maxwell envisioned two chambers filled with a gas separated by a tiny hole just big enough for a single gas molecule to pass through at any given time. Now if left alone, the gas in both chambers would reach equilibrium such that the temperature of the gas in both chambers would be the same and consequently the Boltzman entropy of the gas would be at a maximum.

      He next envisioned a critter called Maxwell's demon. This demon is a tiny little fellow who is incredibly small (about  the size of a single gas molecule) and incredibly weak. In fact, he has only the strength to step into or out of the tiny doorway between the chambers and to fend off a gas molecule of his choice from entering through the tiny hole kind of like a minuture bouncer. But this puny demon has one thing going for him, he is also rather astute in that he can instantly determine the speed of any gas molecule that is headed toward the hole.

      Maxwell reasoned that if the demon allowed only fast moving gas molecules to pass through the hole in one direction and only slow moving molecules to pass through the hole in the other direction, then the gas in one chamber would get very warm and the gas in the other chamber would get very cold. In other words, simply by utilizing the information regarding the speeds of the individual molecules, the weak demon was able to perform a lot of work and lower the thermodynamic entropy of the system considerably. In many regards living cells behave as if they are manned by a huge crew of these little demons. In fact proton pumps and ion channels in cell membranes are conceptually very similar to Maxwell's demon. 

      Thus I hope that I have made clear my view of what constitutes a living thing and how a living thing is different than a non-living or a dead thing. It is simply a system using information to organize itself. Carbon chemistry has nothing to do with it because carbon is superfluous to information. If the information is present than any form of matter will serve provided that it can somehow store and process information. In this regard, chemistry itself is irrelevant to my definition of life. 

      Thus a computer program can be be just as alive as any carbon based lifeform. Indeed the latest generation of computer viruses seem as eerily alive as any carbon based virus I have studied. Who knows perhaps the singularity won't happen on purpose, perhaps it is already evolving in what the programmers at Symantec (the company that makes Norton's Antivirus) call the Wild where viruses are replicating, competing with one another for limited resources, and mutating through chance or design. Perhaps several different computer viruses will form an unintended symbiosis with one another and form a "computer bacterium" or something similiar and evolution will take its course while AI programmers are still wracking their brains over programming something that will pass the Turing test.    

      As you can clearly see by my definition of life, social entities and other highly organized systems like corporations, religions, clubs, governments, economies, cities, countries, cultures, ecosystems, and the biosphere are all alive forming something I call metaorganisms.

      Indeed, I don't see why nuclear reactions could not take the place of chemical reactions. Who knows maybe the stars themselves are alive since I hear astronomers talk all the time about the birth, death, and evolution of stars. I would go so far to wonder whether matter itself is essential to life. It is not beyond the realm of possibility that patterns of pure energy, like light or other forms of electromagnetic radiation, which can carry information,  might be able to form a living system. Perhaps this what the ancients reffered to as a soul or spirit.   

perhaps more easily, are things that don't die in the ordinary or expected 

course not alive? 

      If I understand you correctly, Brett, you are asking if something cannot die, is it alive to begin with? Well if you mean die in any fashion whatsoever, I would say no. Since information, no matter how redundant, can with enough effort be corrupted or erased, by my definition of life anything alive can be killed. Obviously some things are harder to kill than others.

      If you however you mean something that cannot die of old age or senescence because that is "nature's way" or some such rubbish, I would say yes. Nature is full of examples of organisms that don't die of old age. Indeed out of the five kingdoms of life on earth, two don't age at all, one ages but does not die, and only two die of old age. Monerae (bacteria and archaea) and protistae (algae and protozoans like ameobae or parameciums) don't age at all will live and reproduce indefinately so long as they have proper nutrients and aren't killed. Fungi (like yeast and bread mold) eventually undergo senescence but that just means they don't reproduce anymore, they will still live so long as they are not killed. Only metaphyta and metazoa (plants and animals) actually die of old age. As far as the history of life on our planet, the property of dying of old age has only been evolved by organisms in the last 2.5 billion years of the 3.8 billion years that life has been on our planet. Not
 coincidently senescence only seems to be a problem for the more complex multicellular life forms. This ties into recent theories of ageing I won't go into here, because I have said quite enough already.

Does the distinction between "life" and

"non-life" matter to you? Why?

       Yes . . . because I am a biologist. They pay me to know the difference. :)

P.S.  I apologize for the length of this post but Brett asked a good question for which there is no meaningful short answer. For those of you that that are still reading I would like to leave you on a humorous note that between Maxwell's demon and Schroedinger's undead cat, perhaps we do live in a "spooky" world after all. BOO! :)

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