The First Living Thing

Note that this is NOT the same thing as LUCA, the Latest Universal Common Ancestor; but the approaches are much the same: trying to read backward from living organisms.

The obvious way to approach this question of the first living thing is to look at very simple cells, and figure out which is the most primitivečthat is, which has the potential for being the original first cell that was the ultimate ancestor of all life on Earth. The main line of research has been genetic, looking at ribosomal RNA. If there was an RNA world, and a naked gene was the first organism, what is the closest living cell to that organism?

As geneticists have become better and better at analyzing genes, the problem has become murkier and murkier. The same researchers who confirmed the great split between Bacteria, Archaea, and Eukarya hoped to settle once and for all which group was ancestral to the others. Instead, it is clear that prokaryotic cells have undergone "gene transfer"čin which, for example, a gene for making a protein may have been transferred from a member of the Bacteria to a member of the Archaea, or vice versa. It seems that such gene transfer happened so many times among early cells that we will never be able to sort out their genetic lineages. Indeed, the leading researcher in the field, Carl Woese, has pointed out that if there was a great deal of gene transfer, the whole question becomes meaningless. He sees "the universal ancestor" as not one cell, but a kind of cellular mist, in which genes transfer from one droplet to the other like molecules of water vapor (my analogy, not his).

However, at the moment, the answer to the original question is: We do not know, and we may never know, because there may have been no single ancestor, but a mess of gene-swapping early cells. It's not a comfortable answer, but it may very well be right!

Further Reading

LUCA, the Latest Universal Common Ancestor of Life on Earth

There must have been a First Living Thing, but it is very difficult to reconstruct what it was. It is theoretically easier to determine what LUCA was: the Last Universal Common Ancestor of all the living things still surviving on Earth. However, there are serious difficulties in reconstructing LUCA too.

IN 1997, Carinne Blank identified the most primitive sequence of DNA so far discovered. It came from a bacterium in a hot pool called Octopus Spring in Yellowstone National Park, but the bacterium itself has not been identified yet.

By 2000, we could rationalize the thought that we might never be able to identify the universal ancestor. As genes were read from the most "primitive" Archaea, it became clear that gene transfer between very different bacteria was common. Concise summary article from the New York Times, June 13, 2000.

In fact, there is enormous variation in bacterial genomes because of this "lateral gene transfer". News article in The Scientist, 28 September 2005 (free registration required).

Here is a fine essay on the status of research on LUCA in 2002. It's fairly long, but (if you care about LUCA) well worth reading to understand the main points. None of the fundamental questions that Poole raises have been answered as far as I know (in August 2004), but that doesn't mean they can't be.

Last updated September 29, 2005.

Links last checked September 29, 2005.

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