Classification of Exobiota


If extraterrestrial organisms are discovered at some point in the future, how will they be classified? Will a tier of classification higher than “Kingdom” be required (ie, “Planet of Origin” or something similar)?

Has this issue been addressed at all by various space organisations? Scientific journals? Or at the very least, by science-fiction authors?

And let me just say that I realise that the best answer to this question may presently be “we’ll cross that bridge when we come to it.” Fair enough, but if that’s the case, what might be done?

Depends on what the lifeform is and where it appears to fit into the current life scheme.

If we discovered a Martian bacterium next week, and an analysis showed it had the same basic genetic sttructure as Earth bacteria then we would probbaly conclude either it came form Earth, or Earth life came from Mars. It would need some pretty hefty differences not to just be grouped in the existing kingdom Monera. Maybe if it had different bases in its DNA, or was entirely RNA based or if it used amino acids unknown on earth it would be considered to have diverged from Terran monera a long time ago and be assigned a new kingdom.

If we discovered an alien plant-like or animal-like organism on Mars then we would almost certainly need to asign it a new kingdom. It’s unlikely that complex life would survive the liftoff, vacuum and re-entry needed for unassisted interplanetary travel. Again this is based on some evidence of common ancestry, at the very least the use of DNA/RNA and proteins.

All we would do here is alter what we think we know about the common ancestor of all life. If Martian life were purely RNA based then it might give a boost to the original ancestor being RNA based. Or it might not. However it wouldn’t necesitate new kingdoms. As it stands kingdoms essentially divide up organisms whose ancestral relationships are open to speculation.

If we found a lifeform that had no obvious ties to Terran life then we still wouldn’t assign anything above kingdom. There is no need and we are comparing apples and oranges if they have no common ancestry. Taxonomy works on a basis of describing evolutionary realtionships. If there is none then it’s no more valid to assign a Beetlegeusian slug to a new kingdom than it is to assign a computer a new kingdom. They don’t compare in any way and placing them onto the same tree of life tells us nothing about them.

What we would do is just start a new tree for the new organisms.

You know, it’s likely that every place that has life will have it be wildly different. But I could imagine if we looked at life evolving on thousands of worlds, we might find some reasonable groupings. For instance, Life based on Water, Life based on Amino Acids, Life based on Heptane, things like that. That would justify a classification tree with a step or two above Kingdom.

“>>>>Life based on Water, Life based on Amino Acids, Life based on Heptane, things like that. That would justify a classification tree with a step or two above Kingdom”


Would such a classification tell us anything about the evolutionary relationships between these creatures? Would a heptane creature be considered ‘ancestral’ to an amino acid lifeform, or vice versa, and why?

The cladistic “tree of life” is supposed to be an evolutionary diagram isn’t it?

Why not put computer viruses on the tree we already have?

Well, yeah, but who says we have to stick with this scheme forever? If you have thousands of things, and there is some potential structure to their organization, you know scientists are going to employ it.

I don’t think so. Scientists don’t just use an organizational structure just because it exists. It has to deliver some meaningful information as well, and I really don’t see how adding more layers to the existing cladistic tree will tell anybody anything.

I don’t even think that broad classification wil dliver any information on their own. A ‘zarfrax’ based creature could have far more in common with an AA based creature than a heptane based creature behaviuorally, environmentally and structuraly despite being essentially heptane based. There is no reason to believe that organisms with the same broad structure but no evolutionary relationship would have more in common than they have differences.

Okay, well then, nevermind.

Well, some scientists DO have a grouping above a “Kingdom” (in the classical 5 or 6-kingdom sense); it’s called a Domain. Thus, bacteria and archae(bacteria) are in their own “domains”, while all eukaryotes are in their own domain; domains are further divided into “kingdoms”.

I would hazard a guess that, even if exobiota is discovered to be based on DNA/RNA, it would be different enough to warrant classification in another “domain”. If it was not based on DNA/RNA, it would most likely start its own tree.

It seems to me that classification systems develop from a need for them, and that the rubrics that are used pertain to some common characteristics. When that bridge is, indeed, crossed, the similarities and differences will determine if the current grouping systems are satisfactory to include them, or if there needs to be some modification. The types and numbers of these modifications must rest on the identifiable characteristics of the newly discovered life forms.