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Why Scientists Think Completely Unclassifiable and Undiscovered Life Forms Exist
An anonymous reader writes: In a new paper published in Science, researchers at the Department of Energy's Joint Genome Institute note that "there are reasons to believe that current approaches [to discovering life] may indeed miss taxa, particularly if they are very different from those that have so far been characterized." They believe life forms exist that don't fall into the established eukaryota, archaea, or bacteria kingdoms. They argue that there may be life out there that doesn't use the four DNA and RNA bases that we're used to; there may be life out there that has evolved completely separately from everything that we have ever known to exist; there may be life that lives in places we haven't even looked.
Historically, "Life" has been defined as being any phenomenon that possesses all 5 life processes:
#1 Food intake/ nutrition
#2 Respiration
#3 Excretion
#4 Growth & Repair
#5 Reproduction
However, this seems to have been expanded to 7:
#1 Movement
#2 Respiration
#3 Sensitivity
#4 Growth
#5 Excretion
#6 Reproduction
#7 Nutrition
This is for "Life" in the generalized sense, fully abstracted away from any specific mechanisms by which those processes may be achieved. It is perfectly sensible for an artificial lifeform to be constructed, as long as it is able to fully carry out those processes. It needn't have any organic components whatsoever.
Nowhere in the historical definition of "life" used by life science is there a requirement for specific mechanisms-- just processes.
What they mean by the term is "not fitting existing classifications" of course.
The original article is pure speculation. Can life exist that is so different from the stuff we know, so that we can't detect it with current molecular biology techniques?
Sure why not. What the article fails to mention is that we can find life in other ways. Even if we can't sequence the DNA in many cases we can culture microorganisms from environmental samples. We can also use microscopy to directly examine environmental samples. In fact both the microbial cultures and microscope have been done on large scale over many years. Not once have we seen an organism that does not conform to our current understanding of life on earth. Life can also be identified by the changes in the environment it create. Again nothing we have seen so far has suggested that there is a life form so unusual that we can't detect it with our current techniques.
Where authors of the original article fail most miserably is their solution: high throughput sequencing techniques. Huh? How would those techniques lead to the discovery of life that is fundamentally different if they are dependent on the standard properties of DNA and DNA replicating enzymes??
Not quite. They're suggesting that there's a good chance that there's an entirely different domain (or more) of life other than eukaryotes, bacteria, and archaea. That's a pretty radical proposition, ...
Um, not really. A bit of quick googling verified within a minute my memory that the "discovery" of the archaea only dates back to the 1970s. Before that, the few that were known were (mis)classified as bacteria. Then a few researchers looked into their details, and showed that they weren't bacteria at all. Biologists basically watched the discussions, and eventually recognized that those researchers were right, and since then we've had 3 "kingdoms" of Earthly life forms.
It's the idea that those 3 root classifications are all there is that's really radical. The default conjecture should really be that, if we discovered such a major root clade so recently, there are probably more waiting to be discovered. Assuming otherwise mostly just shows a lack of knowledge of the recent history of biological discovery.
In particular, someone else has already mentioned the fact that the various deep-drilling projects have found living things kilometers deep in the rocks, no matter where they've drilled. The folks working with this data have estimated that there's more biomass below the surface water+soil layer than there is above it. It's likely that the critters living their slow, warm lives down there are radically different from anything up here on the planet's thin skin. Learning about them is going to take time. (And we can hope that the rapid expansion of "fracking" won't cause a mass extinction due to the massive habitat destruction down there before we have a chance to study them. ;-)
Those who do study history are doomed to stand helplessly by while everyone else repeats it.