mikes@tekecs.UUCP (Michael Sellers) (09/24/86)
> So, I challenge anyone who reads this notesfile to the following > challenge. The challenge is: > > What is LIFE? > > If we want to discuss the origin of life...we should know what this > `life' stuff is. Think conceptually and abstractly, in the sense that if > (a definite hypothetical example) we go (someday) to other planets both > in this and other solar systems, how will we recognize primitive life forms? > Some things are definitely alive (I am, and you presumably are if > you are reading this). But how do we definitely draw the line between life > and non-life? What properties does a system have to have to be A LIVING > ORGANISM? > What is LIFE? (Post all responses here) There are some general common to all those things we say are alive (though most if not all of them have a few notable exceptions): IT MUST METABOLIZE. All living things use material from their environment that, when broken down, is used for the maintenance of the thing itself (or for growth or reproduction, etc.). IT MUST REPRODUCE. All living things are able to reproduce others of their kind that are or will become fully functional, independent entities. IT MUST RESPOND TO ITS ENVIRONMENT. All living things have mechanisms for responding to the changes in the environment that are salient to them, as for avoidance, food location, life cycle staging, etc. IT MUST BE AN INDEPENDENT ENTITY, not bound up physically in the structure of another living thing. All living things are entities unto themselves, interdependent but not completely dependent on the structure of another. There may be more to this list, but I believe it is fairly complete. Now, many things are clearly life or non-life: I am alive (except before 10:00 am Monday :-), you are alive, your shoes (we hope) are not alive. There are at least two types of things that may or may not be alive, or may be right on the edge. The first are things such as viruses. Viruses can be crystallized, like a complex but non-living chemical compound, and kept in crystalline form indefinitely. Most of them have no metablic or reproductive functions, relying on their hosts for these functions, nor do they possess mechanisms for responding to the environment. However, they do seem to be independent entities, and they are able to reproduce after a fashion; they successfully pass their genetic code on, though only by usurping a target cell's machinery. So they possess some characteristics of things both living and non-living. No one ever said this was going to be clear-cut (in fact, a case could be made that evolutionary theory would predict such fence-sitters, since this is a viable niche to be filled, and since Life in general must have once passed through such a stage in going from non-living to living). The second group of things that may or may not be "alive" are things such as mitochondria (and possibly ribosomes) in eukaryotic cells. Mitochondria possess their own genetic code, reproduce themselves, have their own metabolic structures (in fact it is from these that the rest of the cell gets its power), and may have small structures and "procedures" for responding to the environ- ment. All animals have them in our cells; we could not live without them. They appear to be life, being almost identical to many prokaryotic (bacterial) cells that are definitely alive. (Their analogues in plants, chloroplasts, are much the same, being similar to bacterial cells containing photosynthetic material instead of or in addition to having a respiratory layer like other bacteria and mitochondria.) While these cell organelles show many of the aspects of Life, they are not normally thought to be alive because they are very highly specialized and not independent entities. One hypothesis of the origin of mitochondria says that they were (possibly parasitic or symbiotic) bacterial cells that became highly specialized for their niche inside of the eukaryotic cell, to the point that they became an integral part of it; another hypothesis (also with good evidence) states that they never were independent living things, but resulted from cell membrane invaginations, much like lysosomes and other structures (Golgi complex, vacoules). Either way, they show many of the aspects of living things, and yet we do not think of them as being so (even though the cell they are in and the body it is in may be alive). It is clear that simply enumerating a list of requirements is not enough to say whether something is alive; the various factors must be weighed according to non-obvious rules and heuristics. It is not that different from asking if something (say, Rich Rosen) is conscious or not. The thing may exhibit what we call conscious behavior in some cases and not in others, so our final decision will be a judgement call. This is one reason biologists are not a dying breed (:-), and also, as I'm sure you can see, one reason the abortion debate has gone on so long. -- Mike Sellers UUCP: {...your spinal column here...}!tektronix!tekecs!mikes INNING: 1 2 3 4 5 6 7 8 9 TOTAL IDEALISTS 0 0 0 0 0 0 0 0 0 1 REALISTS 1 1 0 4 3 1 2 0 2 0
steve@jplgodo.UUCP (Steve Schlaifer x43171 301/167) (09/29/86)
In article <7670@tekecs.UUCP>, mikes@tekecs.UUCP (Michael Sellers) writes: > There are some general common to all those things we say are alive (though > most if not all of them have a few notable exceptions): > > IT MUST METABOLIZE. All living things use material from their environment > that, when broken down, is used for the maintenance of the thing itself (or > for growth or reproduction, etc.). > IT MUST REPRODUCE. All living things are able to reproduce others of their > kind that are or will become fully functional, independent entities. > IT MUST RESPOND TO ITS ENVIRONMENT. All living things have mechanisms for > responding to the changes in the environment that are salient to them, as for > avoidance, food location, life cycle staging, etc. > IT MUST BE AN INDEPENDENT ENTITY, not bound up physically in the structure > of another living thing. All living things are entities unto themselves, > interdependent but not completely dependent on the structure of another. > > There may be more to this list, but I believe it is fairly complete. A problem I have had with definitions like this is there are many things we don't consider to be living that slip through and some we do consider living that fail to pass. For the most part, a mule doesn't reproduce (there are reports of rare exceptions). A solar powered refrigerator with automatic sun-tracking and a motorized carriage, on the other hand, satisfies the other three conditions above as well as the mule does. Seems to me that this is a VERY complicated question that cannot be simply defined. -- ...smeagol\ Steve Schlaifer ......wlbr->!jplgodo!steve Advance Projects Group, Jet Propulsion Labs ....logico/ 4800 Oak Grove Drive, M/S 301/165F Pasadena, California, 91109 +1 818 354 3171
lonetto@phri.UUCP (Michael Lonetto) (10/01/86)
> = Steve Schlaifer >> = Michael Sellers >>(quoting Steve) >> There are some general common to all those things we say are alive (though >> most if not all of them have a few notable exceptions): >> >> IT MUST METABOLIZE. All living things use material from their environment >> that, when broken down, is used for the maintenance of the thing itself (or >> for growth or reproduction, etc.). >> IT MUST REPRODUCE. >> IT MUST RESPOND TO ITS ENVIRONMENT. >> IT MUST BE AN INDEPENDENT ENTITY, >> There may be more to this list, but I believe it is fairly complete. > >A problem I have had with definitions like this is there are many things >we don't consider to be living that slip through and some we do consider >living that fail to pass. For the most part, a mule doesn't reproduce >(there are reports of rare exceptions). A solar powered refrigerator with >automatic sun-tracking and a motorized carriage, on the other hand, satisfies >the other three conditions above as well as the mule does. Seems to me that >this is a VERY complicated question that cannot be simply defined. It seems to me that part of the problem is that the definition is TOO complicated already. In order for something to be alive it need not be reproductively competent (my grandmother doesn't look at all dead yet, even though she's well past menopause). Obligate parasites are still considered alive (many protozoan parasites are only found outside their hosts under laboratory conditions). This leaves only metabolism and response to the environment. Broadly defined, metabolism and response to the environment overlap, and the important events from the viewpoint of life vs nonlife all fall under metabolism. The question thus becomes: What is this metabolism stuff?? Metabolism is a SELF SUSTAINING, SELF REGULATING network of chemical reactions capable of maintaining HOMEOSTASIS. Homeostasis is a "steady state", ie: changes in the rates and directions of the reactions are kept within limits, as is the overall chemical activity of the organism. This is not the same as stasis (the lack of change), but implies that the changes tend toward a specific rate. This is a process of considerable complexity. Metabolism is responsible for ASSIMILATION, which isthe conversion of environmentally obtained chemicals to substances which can be used as part of the organism, and their subsequent utilization. Note that the substances taken in from the environment are chemically distinct from the substances produced from them by the organism. This is in marked contrast to the growth of a crystal, where each molecule or ion which is added is identical to those already there, and no chemical change occurs (even in the case of doping semiconductors this second condition holds true). So while an organism may take in protein and DNA and make protein and DNA, the proteins and DNA taken in have different structures than those produced. In the case of proteins, even if identical proteins are available, the organism will digest them to amino acids before reutilizing them (I'll discuss exceptions for DNA if any interest is expressed). Metabolism is also responsible for ENERGY CONVERSION. In order to carry out assimilation energy is required (amongst other reasons is the never ending battle with entropy: life is entropically very unfavorable, and thus requires a great deal of energy for maintainance). Living beings convert chemical energy to different forms (e.g. burning sugar and converting the energy to high energy phospate bonds) and sometimes convert sunlight to chemical energy (photosynthesis converts C02 and water to sugar, sugar can be oxidized to produce energy). Unfortunately I can only give examples from life as we know it, but the principles of assimilation and energy conversion should hold for anything to be considered living. By this definition viruses are not living, though they are clearly borderline. Other parasites, with more complete metabolisms, would be considered living. Note that this discussion leaves out entirely the more complex issues which sometimes arise with complex organisms: is a brain dead person who's heart is still beating alive? By this criteria he is, though clearly the person we used to know is no longer with us. But that's all there is time for so till the next time I can't let something by. Michael Lonetto UUCP:(allegra!phri!lonetto) USMAIL: Public Health Research Institute, 455 1st Ave, NY, NY 10016
hoffman@hdsvx1.UUCP (Richard Hoffman) (10/02/86)
In an earlier posting, someone posed the question, "what is life?", with particular emphasis on how to recognize alien lifeforms as being alive. In article <7670@tekecs.UUCP> mikes@tekecs.UUCP (Michael Sellers) writes: >There are some general common to all those things we say are alive (though >most if not all of them have a few notable exceptions): > > IT MUST METABOLIZE. All living things use material from their environment >that, when broken down, is used for the maintenance of the thing itself (or >for growth or reproduction, etc.). Yes, but this is awfully easy to fake. There are many kinds of man-made systems that take material from their environment, process it, and then use the material for maintenance. (You might be able to make this defintion tight enough to exclude, say, an automobile, but I'm sure that someone could design and build an electo-chemical-mechanical system to duplicate almost any metabolic process you can come up with). > IT MUST REPRODUCE. All living things are able to reproduce others of their >kind that are or will become fully functional, independent entities. Nope. Mules do not reproduce. Furthermore, although a species may posess the ability to reproduce, it is possible for individual members of that species not to posess the ability, having lost it through congenital defect or later damage (e.g. sterilization). > IT MUST RESPOND TO ITS ENVIRONMENT. All living things have mechanisms for >responding to the changes in the environment that are salient to them, as for >avoidance, food location, life cycle staging, etc. Although I believe you are correct here, this is not always a very useful criterion for judgement. Lots of vegetation may not appear to respond to the environment, except when observed long and carefully. For example, moss, or evergreen trees, as long as they remain healthy. > IT MUST BE AN INDEPENDENT ENTITY, not bound up physically in the structure >of another living thing. All living things are entities unto themselves, >interdependent but not completely dependent on the structure of another. I think this one would be very hard to call for parasitic organisms, highly symbiotic organisms, and fetal organisms (even hard-core pro-abortionists might recognize that a non-viable fetus is still alive in some sense). All of which is to say that I don't think it is possible to tell the difference between something which is alive, and something which has been cunningly wrought to seem alive, nor between something which is dead and something which seems to be dead, without advance notice of the properties of the life-forms under consideration. But then, why does it matter? [This is reminds me of a biology course I took once where someone asked the professor how you could tell whether something was a mammal. The professor replied (essentially) "hair and milk." I said "you mean like a coconut?" The professor was not amused.] -- Richard Hoffman | "They sought it with thimbles, they sought it with care, Schlumberger WS | They pursued it with forks and hope; hdsvx1!hoffman | They threatened its life with a railway share, 713-928-4750 | They charmed it with smiles and soap." (L. CARROLL)
MIQ@PSUVMA.BITNET (10/04/86)
In article <812@hdsvx1.UUCP>, hoffman@hdsvx1.UUCP (Richard Hoffman) says: >[This is reminds me of a biology course I took once where someone asked >the professor how you could tell whether something was a mammal. The >professor replied (essentially) "hair and milk." I said "you mean like >a coconut?" The professor was not amused.] Which reminds me of the ancient school of philosophers who defined "man" as "a featherless biped." It worked great until someone plucked a chicken threw it over the wall into their school. They added the qualifier of having broad nails shortly after this-- of course, no one had seen a chimpanzee yet. In any event, could we bring DNA into the definition? Is it possible (theoretically, anyway) for life to exist without it? ------- --------------------------- James D. Maloy | THIS SPACE FOR RENT | The Pennsylvania State University | Call 555-2317 | --------------------------- Bitnet: MIQ@PSUECL UUCP : {akgua,allegra,cbosgd,ihnp4}!psuvax1!psuvma.bitnet!miq "I am pleased to see we have differences. May we together become greater than the sum of both of us." -- Surak of Vulcan
mikes@tekecs.UUCP (10/04/86)
> In an earlier posting, someone posed the question, "what is life?", with > particular emphasis on how to recognize alien lifeforms as being alive. > > In article <7670@tekecs.UUCP> mikes@tekecs.UUCP (Michael Sellers) writes: > >There are some general common to all those things we say are alive (though > >most if not all of them have a few notable exceptions): I realized when posting my original response that the criteria I suggested were, in some cases, almost too general to be of value; and that they are easily (at face value) confounded, as in the solar-refrigerator-on-wheels scenario. I originally had a more narrow set of criteria, but broadened them to include what might have to be considered in looking for/at extraterrestrial life. > > IT MUST METABOLIZE. All living things use material from their environment > >that, when broken down, is used for the maintenance of the thing itself (or > >for growth or reproduction, etc.). > > Yes, but this is awfully easy to fake. There are many kinds of man-made > systems that take material from their environment, process it, and then > use the material for maintenance. (You might be able to make this defintion > tight enough to exclude, say, an automobile, but I'm sure that someone could > design and build an electo-chemical-mechanical system to duplicate almost > any metabolic process you can come up with). I would lean toward saying that the metabolic process must happen on a micro scale, such as with individual or small sets of carbon chains being broken down for their bond energy in a cell rather than en mass in a car engine. This might not hold for ET life, though. Also, it has been recently suggested (no refs here, sorry) that our classical view of the cell as a very small test tube is essentially flawed; given that, for example, muscle cells have calcium thresholds at concentrations of 1x10-7 to 1x10-9 (-7 and -9 are superscripts), that viewing them as very small test tubes operating only by using the vagaries of diffusion and osmosis (and using active transport only when necessary) is infeasable. In this view, every single chemical reaction and gradient (upwards of 10,000 per minute per cell) is maintained by active guidance of proteins and controller molecules. There is much evidence for this, the muscle cell (above), paramecia contractile vacoule, Golgi complex activity, and ribosomal protein synthesis rates in response to various factors being the few pieces that I can remember. This would seem to be a hallmark of life; it is not so crude as a gasoline engine, and makes use of chemical properties in a directed fashion on a micro scale. What happens when we find life that uses atomic forces instead of chemical? I don't know; with luck I'll be dead by then :-). And, when someone manages to build a molecular machine that uses chemicals in its environment for its continual upkeep, will that be life? If not, then it is awfully, awfully close, and maybe only egotism would prevent us from saying that it was. > > IT MUST REPRODUCE. All living things are able to reproduce others of their > >kind that are or will become fully functional, independent entities. > > Nope. Mules do not reproduce. Furthermore, although a species may posess > the ability to reproduce, it is possible for individual members of that > species not to posess the ability, having lost it through congenital defect > or later damage (e.g. sterilization). True, mules do not reproduce, and yet you bring up the larger issue. They are descended from species that do. I think this requirement, amended, still stands: living things reproduce. Some living things do not, but they are the exception; if they became the rule, there would be no more life. > > IT MUST RESPOND TO ITS ENVIRONMENT. All living things have mechanisms for > >responding to the changes in the environment that are salient to them, as > >for avoidance, food location, life cycle staging, etc. > > Although I believe you are correct here, this is not always a very useful > criterion for judgement. Lots of vegetation may not appear to respond to > the environment, except when observed long and carefully. For example, > moss, or evergreen trees, as long as they remain healthy. On the contrary. All things that are without argument alive can be seen to respond to their environment with just a little observation. Mosses only reproduce if the temperature and humidity are just right; evergreens have a variety of responsive systems (chemical responses to parasites, for example). Some things that are not life also respond to the environment, which makes the puzzle more difficult (lead only agrees to melt if you set the temperature just so). In our experience, only those things that live are seen to responed coherently and with a wide range of activities to different conditions. This is doubtless why we are still startled by robots and intrigued by solar- tracking systems; they mimic life very well, and yet we don't want to believe that they are alive themselves. > > IT MUST BE AN INDEPENDENT ENTITY, not bound up physically in the structure > >of another living thing. All living things are entities unto themselves, > >interdependent but not completely dependent on the structure of another. > > I think this one would be very hard to call for parasitic organisms, highly > symbiotic organisms, and fetal organisms (even hard-core pro-abortionists > might recognize that a non-viable fetus is still alive in some sense). Agreed. I don't know that this invalidates the criterion though. It does become a judgement call as to why mitochondria are not alive by a bacterial parasite found only in humans is... > All of which is to say that I don't think it is possible to tell the > difference between something which is alive, and something which has been > cunningly wrought to seem alive, nor between something which is dead and > something which seems to be dead, without advance notice of the properties > of the life-forms under consideration. But then, why does it matter? Also agreed. I don't think that we are going to be able to find a litmus test that says "A" is alive, "B" is dead, and "C" is non-living. At best we can approximate the central distinguishing marks of life vs. non-life. > [This is reminds me of a biology course I took once where someone asked > the professor how you could tell whether something was a mammal. The > professor replied (essentially) "hair and milk." I said "you mean like > a coconut?" The professor was not amused.] Actually, I think that is an excellent example of the sorts of examples you can expect to encounter when dealing with something like this. I'll have to remember that one. > Richard Hoffman | "They sought it with thimbles, they sought it with care, -- Mike Sellers UUCP: {...your spinal column here...}!tektronix!tekecs!mikes INNING: 1 2 3 4 5 6 7 8 9 TOTAL IDEALISTS 0 0 0 0 0 0 0 0 0 1 REALISTS 1 1 0 4 3 1 2 0 2 0
michaelm@bcsaic.UUCP (10/06/86)
In article <2446@phri.UUCP> lonetto@phri.UUCP (Michael Lonetto) writes: [Lots of proposed definitions of 'life' and discussion thereof omitted] >The question thus becomes: What is this metabolism stuff?? > >Metabolism is a SELF SUSTAINING, SELF REGULATING network of chemical >reactions capable of maintaining HOMEOSTASIS. Homeostasis is a "steady >state", ie: changes in the rates and directions of the reactions are >kept within limits, as is the overall chemical activity of the organism. >This is not the same as stasis (the lack of change), but implies that >the changes tend toward a specific rate... >...Metabolism is responsible for ASSIMILATION, >which is the conversion of environmentally obtained chemicals to >substances which can be used as part of the organism, and their >subsequent utilization. Note that the substances taken in from the >environment are chemically distinct from the substances produced from >them by the organism.... Just to throw in a curve ball--if you omit the word 'chemical' in the above, then stars metabolize. A star converts H into He for most of its 'lifespan', using the H that it gathered from the environment during its 'birth'. The interaction between gravitational forces that would cause collapse, and thermal 'forces' that would cause expansion, results in a more or less steady state that lasts a large proportion of the star's lifetime (this steady state is referred to as the 'main sequence'. Most stars spend the majority of their lives in the main sequence.) Before you object that stars don't assimilate substances during their later lives, two answers: (1) There are certain insects that don't eat during their adult lives (i.e. after metamorphosis; one could argue that the point at which a star begins burning H is its metamorphosis). (2) Some stars, in binary systems, do assimilate gas from their environments. These are usually collapsed stars, and they strip gas from their noncollapsed sisters. Eventually this gas piles up on the collapsed star to a depth where fusion starts, which is the phenomena we call a 'nova' (not a supernova, which is quite different). Some stars even reproduce, in a certain sense. When a interstellar gas cloud collapses, some regions will collapse into stars long before others. The first stars produced are often very large, last a short time (10's of millions of years), then become supernova. The shock waves from the supernova propogate through the clouds, triggering local collapses of the cloud which then form--you guessed it--more stars. I wouldn't be surprised if there weren't certain cultures that considered stars to be living creatures. -- Mike Maxwell Boeing Advanced Technology Center ...uw-beaver!uw-june!bcsaic!michaelm
emigh@ecsvax.UUCP (Ted Emigh) (10/07/86)
In article <2446@phri.UUCP> lonetto@phri.UUCP (Michael Lonetto) writes: >In order for something to be alive it need not be >reproductively competent (my grandmother doesn't look at all dead yet, >even though she's well past menopause). ... >Unfortunately I can only give examples from life as we know it,... ... >Note that this >discussion leaves out entirely the more complex issues which sometimes >arise with complex organisms: is a brain dead person who's heart is >still beating alive? This discussion points up the problem of ALIVE vs LIFE. Alive is an attribute of an individual (it is alive, it is dead, it is not alive). Life is an attribute of a group (class, ...) of individuals. While a human individual may have Down's Syndrome, Turner's Syndrome, Triple X Syndrome, Testicular Feminization, etc, and not be able to reproduce INDIVIDUALLY, it is a member of a class of individuals (humans) that are able to reproduce. As a population geneticist, I tend to view LIFE in population terms. A quick (and very dirty) definition of life is something that is a member of a population (group) which can reproduce itself ALMOST EXACTLY. By almost exactly, I include the condition that difference (mistakes) in replication are passed on in successive generations. This excludes crystals, but does include viruses. The other conditions that have been mentioned simply are the various strategies (or the common Earth strategy) for doing this. -- Ted H. Emigh Genetics and Statistics, North Carolina State U, Raleigh NC USENET: {akgua decvax duke ihnp4 unc}!mcnc!ecsvax!emigh ARPA: decvax!mcnc!ecsvax!emigh@BERKELEY BITNET: NEMIGH@TUCC
roy@phri.UUCP (Roy Smith) (10/10/86)
In article <7706MIQ@PSUVMA> James D. Maloy writes: > [...] could we bring DNA into the definition? Is it possible > (theoretically, anyway) for life to exist without it? If you are willing to concede that viruses are alive, then the answer is yes. There are viruses that use RNA as their genetic material instead of DNA. Of course, this is really sort of nit-picking. RNA and DNA are both nucleic acids that differ only in some fairly minor chemical details (don't try telling that to a hard-core structure person, though). As far as information storage goes, there is a trivial one-to-one mapping between the two. I don't see why there is any reason why you can't have living things without nucleic acid heteropolymers (i.e. DNA or RNA) being used for genetic storage. Of course, it wouldn't be life as we know it, but you could speculate about auto-replicating polypeptides or polysacharides. Both of these systems would maintain one of the basic properties of nucleic acid base genetic material; you can store information by stringing together strings of similar, but differentiable, building blocks. All three types of building blocks have consistant inter-block interfaces to simplify polymer construction and various side-chains to provide information storage and processing. Sounds sort of like Ritchie's streams, doesn't it? :-) There is no reason to believe that these systems exist, and to make them work would require revamping most of the metabolism of the cell, but I suppose they are possible. To go out on the speculative limb even further, do we even need to store genetic information in heteropolymers at all? I suppose not, but I can't imagine how it would work. -- Roy Smith, {allegra,philabs}!phri!roy System Administrator, Public Health Research Institute 455 First Avenue, New York, NY 10016
mikes@tekecs.UUCP (10/11/86)
> In article <812@hdsvx1.UUCP>, hoffman@hdsvx1.UUCP (Richard Hoffman) says: > > >[This is reminds me of a biology course I took once where someone asked > >the professor how you could tell whether something was a mammal. The > >professor replied (essentially) "hair and milk." I said "you mean like > >a coconut?" The professor was not amused.] There's something profound (in a kind of perverse way) lurking somewhere deep in the above example... > In any event, could we bring DNA into the definition? Is it possible > (theoretically, anyway) for life to exist without it? > > James D. Maloy We've all agreed (or have we?) that LIFE --not merely that which is alive-- must reproduce. Does this equate to replication, though? I don't know. My parochial view of things tells me that reproduction of a kind is important, not just general reproduction. If this is correct, then some sort of rep- licator/controller entity (e.g. molecule) is necessary. If my feeling is not correct, then it is merely happenstance that life on earth reproduces by way of extension of the material that decides the characteristics of the surrounding organism. If it is true, and there are good reasons for it being so, that life is such a complex set of phenonmena that it requires a controlling entity containing "backup" information about the organism as a whole, rather than having the organism just grow and live willy-nilly; then if the LIFE is chemical in nature, the controller would almost certainly also be chemical. It would not necessarily be DNA, but would probably be some sort of analogue (though note that the purines and pyrimadines are cosmically "common" molecule formations, and might be expected to occur elsewhere as well). If reproduction as replication (or near-replication) is not necessary, then you could theoretically posit nearly anything as being alive -- one "generation" would have no relation to the next, and no organism would have any more relation to any one than to another, since there would be no controlling, moderating entity. While this is possible, I find it difficult to really envision. -- Mike Sellers UUCP: {...your spinal column here...}!tektronix!tekecs!mikes INNING: 1 2 3 4 5 6 7 8 9 TOTAL IDEALISTS 0 0 0 0 0 0 0 0 0 1 REALISTS 1 1 0 4 3 1 2 0 2 0