Mega-Organism fills the Oceans

Our Ancestor LUCA, The Mega-Organism

Can it be true that a single giant organism that once filled the oceans is our ancestor? 

LUCA sounds like a Star Trek character. I could hardly believe what I had just read in the Nov.-Dec. issue of New Scientist magazine. The article, Our Ancestor, the Mega- Organism by Michael Marshall was worth writing about in this blog.

Check it out yourself. Refer to Biology Direct: The Last Universal Common Ancestor. Warning! I struggled though most of this tedious (at least to me) paper and I understood little of what I read, except for general concepts.

I’ll try to translate with the help of Michael Marshall, the author of the article in New Scientist magazine. The following points are his. My comments are in italics.

LUCA, (Last Universal Common Ancestor) is a single organism that lived 3 billion years ago, from which all life evolved. It was enormous and filled the planet’s oceans. I am still tying to grasp the meaning of these first statements, as probably are you.

 LUCA was not the first life but was the common ancestor of all life thereafter. The oceans became a soup of genetic swapping. There was no recipe; just add what ever you have available into a pot of salt water, turn up the heat and stir. 

 For billions of years the trillions of ancient cells, desperate to survive on their own, swapped useful parts with each other. Eventually a global mega-organism was formed. This sounds like endosymbiosis as theorized by the late Lynn Margulis, the controversial ex-wife of  astronomer/educator Carl Sagan. Please see my blog on Endosymbiosis and Symbiogenesis at for further explanation.

 Endosymbiosis – When one organism engulfs or ingests another organism and uses its parts for its own metabolism and survival. Chloroplasts and mitochondria are thought to have been separate organisms until they were incorporated into other cells and used for energy production. Both structures have their own DNA. Digestive bacteria in the bodies of termites and humans are thought to have originated this way.

 Symbiogenesis – When two organisms join together and collaborate in order to improve their survival chances in a changing environment. Their combination in essence, creates a new organism that did not exist before. (Lichens are combinations of an algae and a fungus).

 LUCA split into several domains of life 3.9 billion years ago, bacteria and other simple one-celled organisms that swapped parts and cooperated together. I am leaving out many scientific terms in order to simplify my explanations. Basically, the internal structures (organelles) in living cells are remnants of other simple organisms whose ancestors were parts of LUCA.

 LUCA, in order to qualify as an organism had to have a membrane, as do all cells. It seems that LUCA did have a membrane, although it was thought to be diffuse and leaky. It also had an internal organelles. It is thought that LUCA reproduced with RNA not DNA, which came later in evolution. “LUCA was a clumsy guy trying to solve the complexities of living on primitive earth” say researchers. In order to cope, simple cell within LUCA had to share their genes and proteins with each other. New and useful molecules would have been passed from ancient cell to ancient cell without competition. Survival by cooperation was more important to survival than competition. These traits apparently qualify this primitive oceanic conglomerate as being the first mega-organism. It is not what you and I usually think of as being an organism, but it is fulfills the definition.

 Remnants of this gene swapping system are seen in communities of microorganisms today that can only survive in mixed communities (jellyfish). LUCA’s permeable membrane made it easier for cells to share and contain ingredients.

 Scientists are fascinated with the concept of LUCA but cannot be sure that it existed. It is a great theory that explains a lot but it may never be proven.

I agree, it sounds feasible and it’s a fascinating concept. The scientific community needs to take a more thorough and detailed look.

 Only when oxygen was introduced into the planet’s atmosphere and individual cells could produce their own energy did LUCA split asunder into several single cell organisms.

For clarity the author, Michael Marshal included the following time line.

4.5 billion years ago – Earth forms

3.8 bya – Earliest chemical evidence of life

3.4 bya – Earliest fossils of cells

2.9 bya – LUCA splits up into single celled organisms

0.9 bya – First multicellular life appears


I was fascinated with this science fiction like concept, so much so that I had to share it with those who might have missed it. “So what” you might say, and I agree, we can live without it. But it is amazing how the features of biology, including competition, cooperation, endosymbiosis, cell membranes, organelles, chloroplasts, mitochondria, RNA, DNA, natural selection, etc. all fluidly contribute to the concept of a primitive mega-organism, our ancestor, LUCA.

 We have asked ourselves where and how did the first life begin? What came before the first primitive cells? What was the environment that made the creation of ancient and modern cells possible, even inevitable?  Was a single minute ancient cell the precursor of all life? Or, were trillions of  ancient cells, swapping parts, responsible for the first mega-organism and ultimately to all life thereafter?  You know, I’m inclined to believe it.   


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About cgosling

I am a retired medical/scientific illustrator who has given up illustration to write about science, superstition, and secular humanism. I consider myself all of the following: atheist, agnostic, secular humanist, freethinker, skeptic, and nature lover. I have several published books but the mass of my writing is unpublished. I write children's fiction, poetry, essays, and several plays and radio theater shows, that are available as free downloads to be used on secular podcasts and meetings. They can be heard on Indy Freethought Radio. I hope some of my writings will be of interest to like minded freethinkers who I cordially invite to respond.
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