Definition Of Life Discussion

Somebody rudely deleted the following from DefinitionOfLife without explanation or permission:

Maybe "lifeness" is not Boolean. Mentally, one has a kind of multi-factor "score card" in their head when then are deciding to label something as "alive". It is the typical polynomial type of ranking system. A sterile guy cannot reproduce. However, we still consider him "alive". Contrast him with a biological virus, which barely has any kind of "metabolism", yet can reproduce and evolve.

Re: "A sterile guy cannot reproduce. However, we still consider him "alive"."

Note: his wife might not think so. :-)

{That's a very interesting point. Not so much because it suggests a non-boolean definition, but because it points out that there are multiple aspects (factors) of life. Maybe we should concentrate on defining the constituent factors. Then we can identify (e.g., by cluster analysis) what different common usages of the word 'life' amount to if broken down to these constituent parts.}

Here's a first draft at a multi-factored ruler:

An item must score at least 15 points to qualify and have at least one of the first two properties (natural selection or adaptability). The various criteria may also get partial scores if they only partially qualify.

The reason that at least one of the first two are needed is that life cannot be "static". If it's static, it's merely a machine. It must somehow change based on circumstances. A race of robots that simply makes exact copies of themselves forever is not "life" because the group does not adapt. However, if they re-engineer themselves based on circumstances, they then qualify.

A tricky borderline case would be cloning Einstein's brain and emulating it electronically. Such brain(s) will stay the same brain forever. However, brains can learn and adapt. Thus, it qualifies at least partially on the 2nd. Adaptability is matter of degree. Trilobites ultimately failed to adapt, but were "alive" for a good while.

Note that I am attempting to model general human perception of the concept of "life" rather than strive for a simple definition or simple formula. And, doubt there is a simple definition that would be satisfactory anyhow. Until it comes along, a multi-factor ranking system may be the best tool.

And my estimation of what most people "perceive" to be life-like characteristics is based on personal experience and a "gut guess", not any rigorous surveys. If you disagree with the weightings used, in terms of "common notions", please feel free to provide an alternative rank profile.

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This kind of model could be empirically tested by coming up with bunches of scenarios similar to those found in DefinitionOfLife (robots, prions, etc.) and have regular people and/or scientists score each one from say 0 to 10 or F to A+. Those scores can then be compared to the above model for each scenario.

In fact, maybe there is a "definition regression" technique whereby the weights/rules are assigned based on such a survey. It's the opposite of testing a definition: you form one based on survey responses. Just something to think about. -t

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