Let’s start with what is called « Nasa’s working definition » : « life is a self-sustaining system capable of Darwinian evolution”.

Viruses (as a system) are not self-sustaining in the sense that they would not be able to self-replicate when left alone even in a propitious environment (in a restrictive way, with energy sources, information, etc., but without living entities). Viruses are self-sustaining in the sense that they are able to self-replicate when left alone in a propitious environment (in a non-restrictive way) : if they can penetrate into a living entity with the replicatory machinery  (cell, bacterium, …), they will divert it and multiply themselves. But are they capable of Darwinian evolution ?  It seems not. Animals (as a system) are also self-sustaining in the sense that they are able to self-replicate when left alone in a propitious environment (in a non-restrictive way) : they will find a mate and show capability of Darwinian evolution.

Bacteria, unicellular organisms (as a system) are well self-sustaining in the sense that they are able to self-replicate when left alone in a propitious environment (in a restrictive way, with energy sources, information etc., but without living entities). They are also capable of Darwinian evolution. In that sense, they are better (= more independent) than viruses and animals.

What then about extra-terrestrial entities (as a system) which are self-sustaining in the sense that they are able to self-replicate when left alone in a propitious environment (in a non-restrictive way), for instance on earth or elsewhere, but neither diverting any existing replicatory machinery from living entities, nor mating, nor using any other known capability like prokaryotic division etc…?  What if the system of self-sustaining is unknown, unthinkable ?

The question then becomes : in front of a number of these entities, how will we make the difference between considering the number to result from self-replication or because they are just there with that number ? With the corollary question : is the self-sustaining system capable of Darwinian evolution ? And, to start with : what could “capable” mean for such a system ? Or is there a possibility that it would reflect a non-Darwinian evolution ? Can we then imagine and/or decrypt that non-Darwinian evolution ?

The answers will certainly help us to develop a General Theory of Living Systems.

Guibert,

Thank you for your clarification about the difference between restrictive and non-restrictive viral replication, and for clarifying some of the issues relating to how we currently define life forms in relation to Darwinian evolution.

Thanks too, for enlarging the question in your final two paragraphs. I hadn't considered an extra-terrestrial entity where the 'system of self-sustaining is unknown, unthinkable'. I had only considered whether we could 'imagine and/or decrypt' a 'non-Darwinian evolution'.

Ales,

Interesting definition. But what about those - as individuals or within a system - not able to exploit opportunities in the environment (harmed for the struggle for life ...) etc. ? Would "capability" not be better, as carrying (in my view) the idea of "intrinsic ability" ? However it might just be a question of English terminology (native advice needed ....) !  

Ok with the Darwinian stage as a milestone to recognise extaterrestrial life !

Aleš,

You have pointed out that we would recognize extra-terrestrial life 'if it has developed to the Darwinian stage', but what if (as the question indicates) extra-terrestrial life had 'another way' of achieving the same ends 'other than Darwinian evolution'? Would we recognise such a life, and if so, how?

Beyond replication - darwinian or not - there is the issue of metabolism, which should be also discussed as an indicator of life. That is what the early Viking Mars missions aimed at with - to my view - relatively restricted approaches ...

I am at a loss here as to the exact nature of this question, there is the mention of Darwinian evolution and would we recognise life, with the parameter set that we are defining life on earth as 'life'. with this in mind i think it is fairly obvious, hence my confusion over the question.

according to Darwinian evolution, a different environment will yield a variation in life forms that develop, or the way life forms develop. we see this with the beak example, but also with extremophiles that we know exist in all temperatures. The debate over ALH 84001, we have what is considered by some as nanobes in the rock and signified as possible life as some say yes and some say no. So I think this signifies an easy answer to your question and that is dependent on the assessor of the life form.

The reason I think this may be something more is dependent on your theory of evolution of the universe, are you a big bang person, or....If you are a big bag, then we know that as the universe expanded that in some directions there  was an increase in concentration of certain elements and this would be similar in all directions, this is why the universe ahs so many different phenomena present at different points.

Now consider Darwinian evolution and with different compositions of elements in different nurseries then if life was to develop it will most likely be different to all that we currently understand. If we have trouble defining life in relation to the ALH 84001 meteorite, then how are we to be able to define what other life is. If we look at extremophiles and we can accept them as life then we will look in different zones for life other than just the habitable zone and then maybe we could be open to identifying life that is not as we know it (carbon based).

Would we recognize extra-terrestrial life if we found it(?)

The question as stated begs the question. The antecedent of "it" is "extraterrestial life" which, if we find "it" implies that we recognize "it" to be "extraterrestial life". This only illustrates the dificulty we have in determining "living" from "non-living". This question has been bandied about for centuries with many efforts to arrive at a cogent definition of what it means to be "alive". "I think therefore I am [alive]" probably does not apply to the average tree except, possibly, for Tolkien's Ents but there would seem to be something that distinguishes living matter (us) from non-living matter (your Pet Rock). Another dimension to add perpendicular to those of space and time? So how do we recognize "it" (life) if we see "it"? NASA's definition offers no help because it is way too narrow. I suppose that our best hope is that we will recognize the extraterrestial we encounter by its form, environment and behavior - that is, if it doesn't eat us first.

Troy,

I like the ALH 84001 meteorite example. But take care that extremophiles might not be an as good example : they show a splendid adaptation to very bad conditions but they are also our cousins (carbon based life).

Dwight,

I like the words "form, environment and behavior". Yes indeed we can observe local physical movement or matter displacement and local chemical reactions in rocks or in dead formerly alife entities. But no sensible behavior as a whole.

Concerning the fossil-like structures observed on ALH84001 meteorite, it seems that they could have been produced by Ramlibacter Tataouinensis a terrestrial beta-proteobacterium newly discovered on a meteorite in the desert near Tataouine in Tunisia, see Wikipedia article on this bacterium :  

https://en.wikipedia.org/wiki/Ramlibacter_tataouinensis

This bacterium was further isolated alife in the neighbouring sands of the Tataouine meteorite.

Since 2011, we know that the genome of this bacterium reveals a well-stocked toolbox for adaptation to a desert environment. During the night it transforms into desiccation sensitive motile rods capable of dissemination in a desert. This appears to be a novel adaptation for life in a hot and dry desert environment (see enclosed links).

http://www.ncbi.nlm.nih.gov/pubmed/21912644

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023784

The rods are very similar to the fossil-like structures observed on ALH84001. Moreover, certain magnetite particles present in ALH84001 have many of the features exhibited by the prismatic magnetites produced by magnetotactic bacteria such as Ramlibacter Tataouinensis. Polycyclic aromatic hydrocarbons (PAH) and amino-acids were also found on ALH84001 as a testimony of extraterrestrial life, but investigation of the Antarctic ice-fields neighbouring the place of discovery of the meteorite have afterwards shown the presence of PAH and amino-acids of terrestrial origin.      

The issue of extraterrestrial origin of signs of primitive life on ALH84001 is thus controversed.

Some say that these signs are a proof of life on Mars (where the meteorite is thought to originate from), see e.g. the NASA document of 2009 :

http://www.nasa.gov/centers/johnson/pdf/403099main_GCA_2009_final_corrected.pdf

Others think that the fossil-like structures found on ALH84001 are just the result of terrestrial contamination by Ramlibacter Tataouinensis when the meteorite is thought to have reached the Earth 13,000 years ago.   

It looks like the controversy is still unresolved.

https://en.wikipedia.org/wiki/Ramlibacter_tataouinensis

http://www.ncbi.nlm.nih.gov/pubmed/21912644

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023784

http://www.nasa.gov/centers/johnson/pdf/403099main_GCA_2009_final_corrected.pdf

Dear Richard, 

I advise you to pay attention to my together with Elena Kadyshevich paper published recently in the J. Molecular Evolution. I hope, you will find there the answer to your question. This paper contains a new approach to the solution of the species diversity problem. The paper is available at my page and at  Elena's page of the ResearchGate site. There, other our papers on the problem of living matter origination are also available. 

Regards. 

Victor,

Read your interesting paper about how life on Earth may have begun. Not sure how that relates to how we would recognixe extra-terrestrial life. Are you saying that the terrestrial way of life is the only way there is, and that extra-terrestrial life has to conform to what we already know about life on Earth?

Richard

Dear Richard, 

Just DNA is the basis for all living on the Earth. And there are no scientific grounds to believe that the phenomenon that is termed life could be formed on the basis of some other principles. Therewith, this statement doesn't mean that life based on DNAs couldn't be of some specific form; however, the possibilities of formation of principally specific forms are limited because the ambient conditions under which life develops on the Earth are very different, the Earth's history is rather long, and the field of new ambient conditions under which the molecules similar to DNAs could exist and develop is very narrow. Therefore, I advise you to diminish your hopes. There are such sciences as logic, chemistry, physics, thermodynamics, biology, geology etc but there are no science "fantasy." I think that the maximum that could be expected it is the world of J. Swift in his Travels by Gulliver. 

Regards. 

"there are no science "fantasy.""

That's true, but there are those with backgrounds in chemistry, physics, thermodynamics, biology, geology, etc., who have fantasized and asked, "What if ..."  If scientists only thought in terms of what was already known, then no scientific progress would ever have been made.

Surely, progress comes from fantasizing and imagining things that went against perceived wisdom, and then designing experiments to prove or disprove the fantasy.  Usually the fantasy is proved to be just fantasy, but very occasionally the fantasy is proven to be real.  

In the past such fantasists eventually proved the world was not flat, that the sun wasn't the center of the universe, and the universe consists of more than the Milky Way.  

Everything we now know, leads us to believe that DNA is necessary to life, and that certainly appears to be true as far as terrestrial life is concerned.  However, to make a leap of faith and say 'all life within the Universe has to have DNA' is no more logical than to make a leap of faith that says 'perhaps, somewhere in the Universe, there is a none DNA way of achieving the same end'.

Yes, perhaps Darwinian evolution is not absolutely necessary to qualify for life. Self-sustaining systems using a DNA-like molecule for it (or even an RNA-like molecule providing it is sufficiently “protected” to allow reliable replication to sustain life) could probably be classified among living systems. The problem is on which chemistry this DNA-like (or RNA-like) molecule would be based. On earth, life is carbon-based because carbon makes a good backbone. This is because carbon forms 4 bonds so it can form chains with branches in very varied ways. Its bonds with hydrogen are strong. In addition, it is very abundant on earth, but probably also in the universe. So chains of ribonucleosides (like DNA) can form without too much problem. They can then also become supports for information. Moreover the double-helix is very stable for a reliable preservation of the information (less the case for RNA).

There are very few elements able to combine all these features. In fact, it seems that carbon is the only one. Silicon has also 4 bonds, but it is less abundant and the bonds with hydrogen are weak. But it could work in a restricted way in higher temperature environment. Germanium and tin could also play a carbon-like role but they are much less abundant and heavier. Not to speak of their chemistry. Nitrogen has several bonds and is lighter. But, a backbone with nitrogen atoms would be chemically more active (charged) than carbon, so the chemistry would be different and less easy for self-sustaining, preserving of information and reproducing purposes.

So, if Darwinian evolution is not absolutely necessary, the NASA’s working definition could perhaps be changed into : “Life is a self-sustaining system based on a DNA-type molecule with ribonucleoside-type components as support of information”.

But, NASA people have probably already tried this kind of definition without reaching a consensus ….

And, as the chemistry of the universe seems to be unique and as the proportion of chemical elements and the physical environmental conditions seem to be similar about everywhere in the universe, probably the only extra-terrestrial life one could encounter once would be carbon-based …with a (little) chance that it is not strictly DNA-based ... 

I would suppose that in that primordial environment on earth there must have been a considerable amount of chemical activityand experimentation occurring by chance, not by design, that came upon the recipe for "life" out of which emerged our DNA/RNA based system. I presume that out of the many possible roads that could be taken ours was the one that survived this pre-biotic selection process. But how much latitude is allowed in the details of what can form a "living system" by way of fundamental differences in chain-molecular structure? Ours is helical DNA coupling with RNA, proteins and amino acids. Are there other viable arrangements?

Here we are exploring the chemical basis of life but the question at hand is a bit broader and asks if we stumble across an extraterrestial entity enjoying life how do we recognize it to be what it is? If we observe from afar I suggest our guides could be the form taken by the entity, the environment in which the entity lives and its behavior over time. So in short what does it look like (tendrils, leaves, wings?), what are its living conditions (boiling sulfuric acid?) and what does it do (grow, crawl, fly?)? If we get up close perhaps we can grab a blood sample, that may be the clincher!

Dear Richard, 

You are as if right in general, but, factually, you are mistaken in the partial. Always, there is a region of known and there is a region of unknown. Fantasies are possible and, on frequent occasions, are useful as applied to the region of unknown, however, fantasies are useless and, on frequent occasions, even destructive within the region  of well-known things. For example, the elementary arithmetic is, within definite limits, studied totally and nobody, even being at a fair, may prove that 6 x 7 = 48. Analogously there are some completely studied fields in chemistry, in physics and in other sciences. Within these fields, everything is known.

I am sorry to write you that, if both we term “life” just the phenomenon similar to that which is termed at the Earth by this term, no another such a phenomenon based on carbon as its main component exists in nature. As for such life as we know it at the Earth, namely, life based on DNA, such life is possible anywhere in Universe; however, it is impossible at the surface of any celestial object over the Solar System and is possible, though is of low probability, in the underground layers of Mars and nowhere else. Meanwhile, in order to search life on Mars with any hope to find it, it is necessary to find there, for the beginning, phosphorus, because it is a necessary component of DNA and because this element isn’t found at Mars up to now.

Regards.    

Thank you Aleš for your very nice explanation.

Dear Ales Kralj,

You pass the desirable for reality.

Phosphorus was detected at the Mars by no space mission.

It is possible that phosphorus occurs there.

However, no real information about its occurrence exists. As for the paper by T. Adcock and E.M. Hausrath, these authors write only that the occurrence of phosphorus on the Martian surface was possible in the past and, maybe, it is there at present. These authors write that it is likely that phosphorus was at the Mars, because the Martian rocks are similar, in their opinion, to the Wishstone-class rocks.

This paper is of significance in the period of preparation of the Martian mission, but the authors don’t state that phosphorus occurs there and are not responsible for its presence there.

In this paper, it is noted correctly that phosphorus is necessary for existence of living matter; meanwhile, it is only one condition for the phenomenon of life and other conditions are also necessary.

Dear Aleš Kralj, 

The so-called "marsianian" meteorites, this is else not the Mars. There is only an assumption that they fly from the Mars, however, science should be constructed from proves but not from assumptions. 

Victor,

"Analogously there are some completely studied fields in chemistry, in physics and in other sciences. Within these fields, everything is known".

Not sure there is any single field in chemistry or in physics where we could be absolutely confident that everything is known.

Dear Richard, 

Yes, such fields exist, undoubtedly, not only in arithmetic. Especially, this statement  relates to chemistry and, meanwhile, the origin of life was governed by chemical and physicochemical laws. I know that you wrote some our works on the origin of life; this is physical chemistry and logic and nobody reproached us for alogisms. Look at our explanation of the phenomena of formation of monochirality and of the slowness of racemization. I think that these are unconditional explanations. I  am sorry, I don't know your specialization; I could present you a multitude of exact scientific conclusions.

Regards/  

Dear Richard Underwood,

You believe in the extraterrestrial life!

The belief – it is beautiful.

One Russian poet wrote approximately, the following:

“Believer is blessed,

He is warmed from within.”

You don’t know even, in what life you believe.

You wrote that this life can be somewhat another than our Earth’s life, you also think that it can be with no DNA and you don’t know what is instead of DNA in this life.

But, nevertheless, you believe that the extraterrestrial life is possible, and you ask, how we could recognize this life if anybody of us meets it.

Indeed, the belief is beautiful.

But, I am sorry, this your question is no more than a wild-goose chase and has scarcely any relation to science. 

Richard. The extraterrestrial subject is a sensitive issue within the scientific establiment, this is because it was connected with the Unidentified Flying Objects (UFOs), the negative recommendation of Condon report and nobody believes such vast space could be covere by any spaceship, hence our limit had been restricted .

Your question is about if it's found, but what if it's already here?

I am among those who claimed to have seen UFO, which initiate my current studies in theoretical physics, but I wrote a paper title "Scientific Study of UFOs," if you or anyone interested to read our view about this can check at:

http://www.exmfpropulsions.com/New_Physics/New_Energy/Propulsion/UFOs_Science/Scientific.htm

http://www.exmfpropulsions.com/New_Physics/New_Energy/Propulsion/UFOs_Science/Scientific.htm

Mahmoud,

I have read your papers and viewed your website and similar information, but I am not persuaded by your hypothesis.  To take just one example, if something like Roswell happened today, the person finding the wreckage would immediately post a picture of it on social media.  The second thing they would do almost immediately is to inform a media outlet and sell their story.  As far as I know, there is nobody who has done this where the evidence has been available to outside scientific scrutiny.   

Richard

Victor,

I don't believe I have said anywhere that I believe in extraterrestrial life, and I am sorry you feel my question has scarcely any relation to science.

My question is 'Would we recognize extra-terrestrial life if we found it".

The relevance of the question is actually unrelated to belief or otherwise as to whether extraterrestrial life actually exists as given the size of the Universe the answer to that question is probably unknowable.

The relevance of the question relates to my current research into 'definitions of life' and the quantifiable differences between animate and inanimate objects. To ask the question another way, "Given that our experience of life is completely limited to the life that has developed upon Earth, could we envisage any type of life that could develop somewhere that is not Earth like."  That is not to say such life actually exists, but is a means of building a scientific theory.

Some have looked at my question and have used their scientific knowledge and experience to claim, "such life CAN NOT exist, and this is why ...".  Others have looked at the same question and used their scientific knowledge and experience to claim, "such life MAY POSSIBLY exist, and this is why ...". Both type of answers are helpful for my own research and in time I will read all references or papers referred to by either type of answer.

What I am not expecting of course, is for anyone to answer "such life DOES exist", and I have never claimed to have done so myself.

Richard

Dear Richard,

The definition of the term “life” is considered in our paper printed primarily in Russian in the most prestigious Russian physical journal and translated then into English not by its authors under the title “Generalized hypothesis of the origin of the living-matter simplest elements, transformation of the Archean atmosphere, and the formation of methane-hydrate deposits” in Physics-Uspekhi, 50 (2007) 175-196. This paper is available by the address: https://www.researchgate.net/publication/235351966_Generalized_hypothesis_of_the_origin_of_the_living-matter_simplest_elements_transformation_of_the_Archean_atmosphere_and_the_formation_of_methane_-_Hydrate_deposits

There, we consider different opinions on the term “life” definition and present our relation to this problem.

Article Generalized hypothesis of the origin of the living-matter si...

Victor,

Had a quick scan through your paper and it looks helpful for my current project, the first part of which considers current definitions of life and definitions of death, current evidence of how life was first created, and the different ways in which life is reproduced.

Will obviously need more in-depth reading than my initial scan but I've downloaded it so I can look at it properly tomorrow onward.

Thank you for your helpful comments and for pointing me towards your paper.

Richard

Dear Aleš,

Very nice account on a difficult subject ! And yes the sum of entropy and information is a constant. A gain (loss) of information is always balanced by an equal loss (gain) of entropy (see e.g. : D. Layzer. The arrow of time. Scientific American, 12 :56-69, 1975).

Aleš,  Thanks for your information about loss of information and degredation into thermal noise.

Guibert, Thanks for info about 'The arrow of time' (available at https://www.scientificamerican.com/media/pdf/2008-05-21_1975-carroll-story.pdf ) Interesting 'Evolution of the Universe' model in which the initial state of universe is assumed to be devoid of all information.

.... and of entropy : "It is only for this brief initial phase in the evolution of the universe that local thermodynamic equilibrium can be assumed, but from that assumption it follows that the expansion of the universe has generated both macroscopic information and entropy" (p. 68, mid 3rd column). 

Dear Richard,

If you are interested in not only living matter origination and transformation but also in the Universe history, beginning from its origination up to today and even the future of our Sun and Earth, I could acknowledge you with our PFO-CFO Theory of Solar System formation. We proved the erroneousness of the General Relativity and inconsistency of the notion of big bang and proposed a new theory of Universe origination, which starts from the eternal and endless Space of mass/energy of a low potential and origination of Universe within this endless Space. I could give you the corresponding references if these problems are within the sphere of your interests. 

I think it dificult to describe the state of things at the beginning of the Universe because the words that we use to descibe what is heappening today may not apply to the very early Universe. That being said, we can imagine a Universe in its moment of becoming as a therodynamic system in equilibrium in which entropy is unchanging. Then something irreversible happens to destabilize the system (inflation?) that results in an evolving entropy-producing expanding system. Expansion could only occur if entropy were increasing but to increase entropy an irreversible change must occur and a change requires a before and after and hence there must be "time". But within this system there can be local regions in which entropy decreases here with an entropy increase there with the recognition that entropy is not conserved but overall must be increasing. This allows stars to form and life to live. We have, in a sense, an analogue to a Universe filled with virtual partcles that come and go because they are allowed to do so by Heisenberg's "uncertainty principle."

So where does "information" fit into this picture? Was the Universe devoid of information at the beginning? Or was there a store of information awaiting release? Is information a product of the evolving Universe that is additve and accumulative? It would seem that a DNA molecule harbors much information that is maintained while the DNA is a "living" molecule under continual repair but upon dying doesthe information evaporates unretrievably in a burst of entropy?

Dear Dwight Hoxie, 

The problems about what you wrire absent in the cosmological portion of our PFO-CFO Theory of Solar System Formation and transformation. We can imagine a Universe in the initial step of its origination as a therodynamic system. I don't sure that it is appropriate to write here on cosmological problems. You can read our consideration of this problem in my or Elena Kadyshevich publications which are available in our pages of the ResearchGate site, in my answers to different questions, and here in numerous discussions . The Space is eternal and the principal natural laws are eternal as well. Big bang is no more than a groundless fantasy. 

Dear Aleš Kralj, 

For Science, is of no consequence, either you concur with Richard, Guibert and Hoxie or you don't concur with them. For Science, it is important, when some hypothesis is under development, to use scientific principles for its solution. I am sorry, but your issues don't bear evidence for your deep understanding of the problem. The occurrence of carbon is by no means sufficient either for life origination or for life development. A number of other conditions should be fulfilled for these processes. I advise you to read our papers published in "Life" and in "Molecular Evolution" . You can agree with our conclusions or not agree with our conclusions if you find some mistakes in our reference positions or in our scientific logic, but I secure that, after reading these papers, you will understand the problem under consideration deeper and wider. These papers are available in my and Elena Kadyshevich pages at the ResearchGate site.   

We may have seemed to have strayed off the subject of whether we would 'recognise extra-terrestrial life if we found it', but we haven't really left the subject as we have now moved on to what happens to the genetic information of living things after they cease to be living. Understanding this also helps us understand about 'life'.

Dwight has suggested that 'a DNA molecule harbors much information that is maintained while the DNA is a "living" molecule under continual repair' and he asks 'upon dying does the information evaporate unretrievably in a burst of entropy'?

Aleš suggested that the information is indeed lost in the form of thermal noise during an increase of entropy at the end of life, and Guibert has stated the universe started with no information and no entropy, and that the sum of entropy and information is a constant.

Is that a fair summary?

It is a fair summary of our ignorance, yes. A minor point: Even if the Universe  began with whatever amount of entropy, entropy is additive and accumulative so we can subtract out "primordial entropy" so that the Universe always begins with zero entropy.

Indeed we should not diverge from the subject of extra-terrestrial life. There are other RG threads on entropy. My allusion to entropy was just to bind loose ends for coherence ….

Aleš noted that entropy and information were correlated in opposite manner in connection with death and life. This made me think of the « constant sum » rule recalled by David Lazer in an article on the arrow of time. His thinking put this author back to the origin of the universe. And John found it interesting that the article concluded to zero information in those remote times !

But of course the status of entropy at the beginning of the universe has nothing to do with the subject of this thread.

Sorry Richard (not John ...), I mixed with another thread ! It is sometimes difficult to follow all these threads in due time :( 

Dear Richard Underwood 

Thanks, its very important question toward exploration of Universe and entities in it. Its not only the matter of extra terrestrial life and its recognizances....but its linked with origin of cosmos and the expression of energy etc into different forms as well.

Hope following link might helping.

Regards,

https://www.researchgate.net/post/Bio-Phonons_Expected_Science_behind_None-Biological_Life

This question "Would we recognize extra-terrestrial life if we found it", is seeking (and has had) some very helpful qualitative answers.

On the same subject of 'defining life' I have also asked a question seeking more qualitative answers. It provides a list of things and asks for an intuitive 'yes' or 'no' answers as to whether you intuitively believe they are living.

That question can be found at "Is intuition enough to define living things".

https://www.researchgate.net/post/Defining_Life-Is_intuition_enough_to_define_living_things_Yes_or_No2

Thanks for the hint, Richard !

Thanks for the hint, Richard !

Thanks for the hint, Richard !

Dear All, 

It is known that there are researchers who search for living issues on other celestial bodies but Earth and there are researchers who try to synthesize living issues or their precursors from minerals; there are no doubts that such attempts will be made repeatedly hereafter. In this connection, I would like to express some my opinions relative to possible directions of such works. These opinions are based on the works of prime importance performed by R. Crick, R. Franklin, and J. Watson, on our works, and on the general condition in this field of knowledge.

(1)     No other searches or tries of synthesizing of a living matter but searches or tries of synthesizing of the living matter based on transformations of DNAs existing in that chemical composition and in that structure in which DNAs exist on the Earth have scientific ground and practical sense because we know no other life but the life based on DNA and any searches of some other life would be the searches of something unknown.

In other words, we should be based on the knowledge that life is the natural phenomenon based on the existence and transformations of DNAs.

(2)     The necessary conditions for natural formation of DNAs within some volume are the occurrence in this volume of water, hydrocarbons (CH4, C2H6, or C3H8), nitrates, phosphates (just N+5 and P+5 are necessary), and, possibly, S-2.

(3)     The temperature should allow formation of gas-hydrate structures.

 Without performance of these conditions, origination of living matter is impossible.

 As for the maintenance and development of life by wise organisms, the occurrence of the elements H, O, C, P, N, and, possibly, S in any valence form and the occurrence of any source of energy are necessary and sufficient.

Victor's 'Definition of Life'.

"life is the natural phenomenon based on the existence and transformations of DNAs"

The above definition immediately excludes self-replicating machines and computer viruses, so it complies with the Schejter and Agassi (1994) suggestion that any definition of life should not exclude anything you intuitively know is living, and not include anything you intuitively know is not living.

Reference:

Schejter, A. and Agassi, J. (1994) ‘On the definition of life’, Journal for General Philosophy of Science, 25(1), pp. 97–106. doi: 10.1007/BF00769279.

Dear Aleš,

Permit me to elaborate a bit further on your set of “necessary conditions” for life

“So, life must have (but not limited to):

1. Ability to explore (and optionally exploit);

2. Ability to get killed (deleted) in the selection process;

3. Ability to grow complexity (to evolve further) and to develop functions.”

I suggested in a previous comment that were we to encounter extraterrestrial life without being able to dissect it, we might recognize it through a combination of its appearance (form), e.g., leaves, flowers, legs, wings, eyes, tail, etc.; its environment, i.e., the chemistry and other aspects of the conditions in which, if alive, it was living; and its behavior, i.e., does it move, eat, reproduce, die, etc.

I think that we are largely in accord except for item 3 which would require generally an extended time of observation and I was thinking of an instant, for example, of “walking around a corner” and finding this entity there in front of us and trying to determine what it was without a laboratory or much time to arrive at a determination.

I also have a bit of a problem with item 2 in that I’m unclear what is meant by “selection process” but dying certainly is “behavioral” as is the ability to “explore.”

Would we recognize extra-terrestrial life if we found it - ResearchGate. Available from: https://www.researchgate.net/post/Would_we_recognize_extra-terrestrial_life_if_we_found_it#view=57a389a33d7f4b24e53a5e41 [accessed Aug 25, 2016].