Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!raybed2!applicon!hdsvx1!hoffman From: hoffman@hdsvx1.UUCP (Richard Hoffman) Newsgroups: talk.origins,net.bio Subject: Re: What's this LIFE stuff? Message-ID: <812@hdsvx1.UUCP> Date: Thu, 2-Oct-86 08:38:51 EDT Article-I.D.: hdsvx1.812 Posted: Thu Oct 2 08:38:51 1986 Date-Received: Fri, 3-Oct-86 05:36:13 EDT References: <45500088@uiucdcs> <7670@tekecs.UUCP> Reply-To: hoffman@hdsvx1.UUCP (Richard hoffman) Organization: Schlumberger HDS, Houston Lines: 59 Xref: linus talk.origins:122 net.bio:494 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)