At Science Slashdot, there’s a discussion around “Should science rethink the definition of life?” Trouble is, some folk don’t seem to grasp the extent to which the definition of life is a this-planet problem:
When NASA says it wants to find out if Mars was ever suitable for life, they use a very circumscribed version of the word. They are looking for signs of liquid water, which all living things on Earth need. They are looking for organic carbon, which life on Earth produces and, in some cases, can feed on to survive. In other words, they’re looking on Mars for the sorts of conditions that support life on Earth. But there’s no good reason to assume that all life has to be like the life we’re familiar with. In 2007, a board of scientists appointed by the National Academies of Science decided they couldn’t rule out the possibility that life might be able to exist without water or carbon. If such weird life on Mars exists, Curiosity will probably miss it.”
Yes, but surely we just can let that be NASA’s problem for now. If NASA doesn’t find it, we won’t either.
This-planet problems that are right in our ballpark include:
1. Megaviruses and mimiviruses that behave like degraded cells. Where should we draw the line? Same with parasites that have grossly simplified their genome by outsourcing vital life functions. What considerations should rule?
2. Some life forms that are way off the standard have probably lived and died on this planet without ever coming to attention. Consider, for example,
“Researchers haven’t been able to decide whether the remains come from animals, bacteria or close relatives of animals that thrived at the dawn of animal evolution.” Some wonder if they are a fungus. “What isn’t widely appreciated is that the Doushantuo rock formation contains billions of microfossils, many of which have no traits that are diagnostic of any living group and contain features that are not of biological origin.” says one researcher.
Matt Kaplan, “Enigmatic fossils are neither animals nor bacteria,” Nature, 22 December 2011
Which raises an obvious question: If we can’t classify it, what makes us sure that it is life? Following that up might get us somewhere.
3. Too many sources fall back on the outmoded “It’s life if it is capable of undergoing Darwinian evolution.” Outmoded because many simple life forms are well known to make only limited use of Darwinian evolution when undergoing great changes – horizontal gene transfer rules among them.
One can always argue that natural selection plays a vital role in trimming those life forms that are unable to compete. But, quite honestly, that isn’t an important enough role to justify forming a definition of life. For all we know, the same thing happens among agglomerations of chemicals in outer space that we do not consider life or even on their way to becoming life.
Probably, a useful definition of life will be found in information theory, not Darwinism. Could it be pegged to a level of information, as measured? Thoughts welcome. Many of us are just beginning to think about it.
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