We might not be intimate the meaning of life , but a group of scientists working for NASA fall up with a definition for it that ’s just seven words long : “ Self - sustaining chemical organisation equal to of Darwinian evolution . ” But does this rightfully cover all life , include the types we have yet to discover ?
This definition of life was developed in 1994 by a commission of scientist to proffer NASA steering as it developed missions to find extraterrestrial life .
There are , of course , competing definitionsof what make up animation — including some scientists who debate that such a definitionisn’t even possible . And there are researchers who have seek to define animation by listing its basic characteristic . But a lean demand a theoretical framework . Otherwise , it ’s hard to make the case that these characteristics would be universal , found among life forms that we have n’t yet encountered .
So , the NASA committee sought not merely to offer a working definition of spirit , but a introductory theory of life history . The scientists choose their terms carefully , imbuing their seven - Scripture definition with a conceptual heft that belie its brevity .
The sum of its parts
permit ’s seem at this definition again and break it down , piece by piece : “ ego - sustaining chemical system up to of Darwinian development . ”
At first glance , the term self - sustaining does n’t make much sense . Life needs to eat . To develop and rise , living puppet need first to be consumers , since growth admit changing biomass , create new individuals and the shedding of waste . But , in this context of use , ego - sustaining means that life does n’t postulate uninterrupted intervention by an reasoning being — be it God , a alumna student or a gardener — to provide its keep . Given an environment with sufficient resources , it can survive on its own .
Next , we have chemic system . In part , this recognizes that life is the integration of multiple , interdependent metabolic processes . But , the term “ arrangement ” also distinguishes between “ life ” and “ livelihood , ” which are not of necessity one and the same . A pedigree cell in your body is living tissue paper , but , by itself , it is not life .
And now , the biggie : subject of Darwinian phylogeny . There ’s a lot packed into that phrase . When we verbalize about Darwinian evolution , we have-to doe with to the mechanism behind natural selection that allows living to survive and accommodate to change environments . In the wide sense , Darwinian evolution means that “ life ” must be capable of making gross copies of frail information during facts of life , and then passing that information to its offspring , across generations . In terrestrial life forms , that information is encoded within DNA .
This is especially critical in differentiating between an existent support organism and chemical substance mental process that can mimic life history . An oftentimes - cited example is crystals .
As molecular life scientist Steven Benner and physicist Paul Davies explicate inFrontiers of space biology :
A quartz of sodium chlorate can be powder and used to seed the growth of other sodium chlorate crystals . In this means , these crystals can be said to reproduce . Further , feature of speech of the crystal , such as whether its atom are set up in left - handed spirals or right - handed spirals….can be passed to its descendants .
However , the replication is imperfect ; a genuine lechatelierite take many defects . Indeed , to specify all of the defects in any decent - sized crystal would require an tremendous amount of information , easily exceed the 10 billion bits of entropy hold in in a human genome .
But the information in these flaw is not itself heritable : the defects in the parent crystal are not reproduce in the descendent crystals . Thus , the information held in the defect in the descendent crystal is entirely sovereign of the data held in the defects in the parent . Therefore , the crystal of sodium chlorate can not support Darwinian phylogenesis , meaning that a system of Na chlorate crystals does not qualify as life sentence .
finally , we have the parole capable of Darwinian phylogeny . Gerald Joyce , a famous professor and scientist at the Scripps Research Institute , who is credited with being the primary author of this definition , explains in an interview :
It ’s the population , or even the ecology , that get the living system . adequate to does n’t touch to one private entity ; that does n’t constitute a living system of rules . A single individual might seem to be capable of undergo Darwinian evolution , but may in fact be dead , or a fossil end , or about to kick the bucket , or unable to find a fellow . So it is the system that is said to be capable , not the individual .
And , Joyce add , this also bring us back to another aspect of life-time being a “ self - keep up chemical substance system”—which , in this context , refers to the information necessary to undergo Darwinian evolution :
Chemical information is the product of Darwinian evolution . So all of the information necessary for the system to undergo Darwinian evolution must be part of the scheme .
So then you derive back to : Why is Darwinian evolution put front and center in think about life ? Because it is a way for complex entity to keep themselves , not as an individual but as a system , in the face of a changing surroundings that is subject to unanticipated variety . A system of rules evolves to adapt to environmental change . It has to be able to invent new role because those environmental changes may be more than incremental .
When is life not life?
There are several conceivable example of different type of life that do not fit the NASA commission ’s definition . Benner and Sir Humphrey Davy flex to one of the most authoritative reservoir on this subject , Star Trek :
The crowd of Star Trek : The Next Generation come across nanites that infect the computer of the next - generation spaceship , the Enterprise , in Episode 50 ( “ Evolution ” ) . These were informational or , perhaps , electromechanical , but in any case not chemical ; their evolution was not tied to an informational molecule like DNA ( although they did postulate a chemic matrix to survive ) . Likewise , the Crystalline Entity of Episode 18 ( ” Home Soil ” ) appeared to be chemical , but not evidently Darwinian . The Calamarians from Episode 51 ( ” Déjà Q ” ) were made of “ pure energy ” ( whatever that mean ) , not chemicals . And in Episode 1 , Q himself ( ” Encounter at Farpoint ” ) appeared to be neither matter nor energy , move instead in and out of the so - holler Continuum without the plain pauperism of either .
If we were to run into Q , the Calamarians , or any of these other suppositious entities during a real , not conceptual , trek through the hotshot , we would be force to concede that they do represent support systems . We would also agree that they do not go down within the NASA definition of life . We would therefore be forced to agree that we need a new definition for life history .
We put in , however , that we do not change our definition of life now so as to reconcile Q … or other examples of “ unearthly ” life from Hollywood because most of us do not constructively conceive that this kind of life is possible .
Benner and Sir Humphrey Davy , however , do n’t refer to one Star Trek entity that seems increasingly plausible : Lt . Commander Data . Should an android , or any machine capable of artificial intelligence , be weigh life history ? It ’s tantalising to say so , but “ sentience ” and “ lifespan ” are two different concepts . Joyce mentions that , even 20 years ago , the NASA commission touched upon this subject :
Can you have life story that is just minute in the ether ? At that meter , stilted life-time in the electronic computer was a new thing . There ’s a statement in the written document about how studies of so - ring “ Alife , ” life in the estimator , should be encouraged to the extent that they cross - inform report of chemic life .
But NASA ’s not expecting to find a clustering of supercomputers on Mars or Titan . Or even PC or iPhones . So at least for NASA ’s purpose , we wanted to focalise on chemical aliveness .
For his part , Bennerbelievesthat the first organism we bump that will not fit this definition of spirit will be ourselves :
In a few yr , we may be able to distinguish DNA sequences that prospectively help our children survive , and gain the technology that allows these sequences to be placed into our germ lines to generate mutant children that are fitter by design . If this happens , then our specie will commence to break loose Darwinian mechanisms for amend our cistron .
The good news is that we will no longer require to see children give out of genic disease ; a large number of bad mutations is the Darwinian price of a few good ones . With gene therapy , we may imaginably be able-bodied to read the germ line for deleterious gene and take them .
But , Darwinian evolution does not allow prospective mutation . Through this technology , humans would be able to evolve in a more Lamarckian way … .So perhaps we should start thinking now about a better definition - theory of lifespan .
BiologyNASAScienceSpaceStar Trek
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