Living Machines..

[Radical Edward]

viruses are awkward yeap, plus if you accept that they are alive, you have to accept that alot of other things are alive too, for example computer viruses and so on, or even computer programs that are designed to be reproductive and so on (for example some life simulations) - or would you say that the stuff they are made of has to be "matter" ?

[JaKiri]

Originally posted by Radical Edward

I thought she was accused of this before she was beheaded.

 

She was accused of it before she married him.

 

She was beheaded because she didn't give Henry a son, and he tired of her.

[Glider]

Originally posted by Radical Edward

are sterile people not alive then?

 

People reproduce; i.e. the 'generic human' is capable of reproduction. People who for some reason (trauma, pathology, congenital condition) cannot reproduce are exceptions to the species-universal rule.

 

In fact, there's only one thing I can think of that fulfills these (admittedly imperfect) criteria for life, and yet isn't alive, and that's fire. It requires fuel and leaves waste (ash). It needs oxygen and produces carbon dioxide. If provided with these, it grows, and when the conditions are right, it reproduces (via airborne sparks).

 

Viruses don't fulfill any. They are viable, but not alive. They don't respire, they don't ingest, they don't excrete and they don't reproduce (they need host-cells to do it for them).

[blike]

What happens when a machine fits all the criteria for life?

 

"(Ingestion, excretion, respiration, growth and reproduction)."

 

A machine could be built to perform all those functions, but when do we call it alive? What is the line that seperates living things from nonliving things?

 

(but yes, sentient would have been better suited)

[Radical Edward]

Originally posted by blike

What happens when a machine fits all the criteria for life?

 

"(Ingestion, excretion, respiration, growth and reproduction)."

 

A machine could be built to perform all those functions, but when do we call it alive? What is the line that seperates living things from nonliving things?

 

(but yes, sentient would have been better suited)

 

then it is alive. However, like fire, unless it was well designed, it would have two flaws in that it wasn't capable of mutation and (hence) adapting to cope in different environments.

[T_FLeX]

Originally posted by blike

 

"(Ingestion, excretion, respiration, growth and reproduction)."

 

A machine could be built to perform all those functions, but when do we call it alive? What is the line that seperates living things from nonliving things?

 

(but yes, sentient would have been better suited)

 

have they built a machine that can create an exact duplicate of itself?

[Glider]

Originally posted by blike

What happens when a machine fits all the criteria for life?

 

"(Ingestion, excretion, respiration, growth and reproduction)."

 

A machine could be built to perform all those functions, but when do we call it alive?

I'd say when it doesn't need to be built to to perform these functions, but performs these functions as a function of being.

What is the line that seperates living things from nonliving things?

It's a tricky question. Admittedly, the criteria above are quite broad, and there is at least one arguable exception. However, each of those criteria are more complex than they initially appear. For example, ingestion (is not just taking on fuel, but invoves invoves altering the substance ingested and changing it from whatever it was, to a part of yourself, literally and on a chemical level), reproduction (is not just producing an identical 'self', but producing a thing which conforms to the species 'blueprint', and yet is different from every other member of the species (at least on a genetic level (fire fails this one)), growth (is not just not just an increase in physical size, but a process of development and adaptation to the environment in which growth takes place (fire fails this one too)).

 

 

I think the answer is subtle, but simple (like most things in nature). I'd say you'd have to look at all living things, and identify the thing(s) they have in common, which are absent in non-living things.

 

You could end up with just a logical argument along the lines of "A circle is that in which the ratio of circumference to diameter = Pi". Therefore, anything which does not show this is not a circle, i.e. life is anything that posesses characteristics x, y and z. Therefore anything which does not show x, y and z is not alive. The trick is providing definitions for x, y and z.

[Skye]

My problem with the viruses is that seem to have been left out simply because they make defining life too difficult. People look out into the world and for some reason say some things are life and some things aren't. Once we have some idea of the scope of what we consider life is, then we start trying to define it. I might be wrong but I think alot of people would consider viruses life, at least as far as they would consider any microbe life. Scientists study them as part of life sciences or biology. Aside from life then...what are they?

 

Maybe it's good to look at what makes us think something is living in the first place. I can think of a few but they don't really seperate the living from the dead. On that, death is perhaps something that defines life, all living things die. Hmm maybe not, maybe the opposite. Maybe life could be defined by the ability to continue replicating itself indefinately. Ah well, it's been a long day and I'm starting to ramble.

[Glider]

As far as I'm aware, the general consensus (at least according to the virologists I know) is that viruses are not alive. Virology is studied usually to investigate the effects of viral infection on living things, modes of transmission, mutation etc. and how to protect against them.

 

Aside from life then...what are they? They are considered 'viable'.

 

A virus (in essence) is just a strand of RNA in a protein coat. It takes nothing in, and excretes nothing. There are no internal processes and no metabolism. Their action is a function of chemical attraction. Viruses bind to cell membranes and inject their RNA into the cell, but this is a product of mutually attractive binding sites on the viral coat and the cell membrane...there is no 'behaviour'. The mechanisms are the same as those which cause antibodies to bind to non-self particles (antibodies are not alive either).

 

Not being alive, viruses don't die. They can be destroyed (denatured), but not killed. This being the case, in a stable environment, they can exist in a viable state indefinitely. Viruses can't self-replicate either.