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A blog by Leon Oudejans

Luca, our Last Universal Common Ancestor

27 July 2016

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For quite some time, I have been wondering about the possibilities of (human) gene dating. Genes are organic material. Radiocarbon dating of organic material usually allows for a maximum period of 50,000 years (Wiki). Finding ancient organic material requires specific circumstances, like deep frozen in the Arctic or Antarctic, or ancient fossils that contain organic material inside.

The ever expanding DNA database of the 3 main domains of the Tree of Life – being bacteria, archaea and the eukaryotes (eg, humans, animals and plants) – allows for a new kind of testing. This new kind of testing compares the DNA of various samples and then looks for common DNA. Common DNA implies a common ancestor. Also see my 23 April 2016 blog on the Tree of Life.

A 6 March 2013 New Scientist article mentions the remarkable discovery that modern mankind (ie, Homo sapiens) is twice as old as we formerly assumed: 340,000 years. This discovery resulted from the DNA testing of only 1 African American male. His DNA contained a unique Y chromosome that was unfamiliar in the DNA databases despite hundreds of thousands of DNA tests. Ultimately, researchers were able to track similarities in his DNA to a small village in Cameroon.

On 25 July 2016, a NYT article mentioned a stunning new discovery by Dr. William F. Martin and colleagues as reported in Nature Microbiology last Monday. Similar DNA comparisons between the 3 main domains in the Tree of Life revealed that the Last Universal Common Ancestor (LUCA) of all cells was a single-cell, bacterium-like organism which lived nearly 4 billion years ago when Earth was a mere 560 million years old.

NYT: “The 355 genes pointed quite precisely to an organism that lived in the conditions found in deep sea vents, the gassy, metal-laden, intensely hot plumes caused by seawater interacting with magma erupting through the ocean floor. Deep sea vents are surrounded by exotic life-forms and, with their extreme chemistry, have long seemed places where life might have originated.”

NYT: “Dr. Martin’s portrait of Luca seems likely to be widely admired. But he has taken a further step that has provoked considerable controversy. He argues that Luca is very close to the origin of life itself. The organism is missing so many genes necessary for life that it must still have been relying on chemical components from its environment. Hence it was only “half alive,” he writes.”

Half alive. These words bring back memories of another topic: viruses. Viruses are still not included in the Tree of Life because they lack compliance with the definition of life. Viruses can act dead for 30,000 years and then quickly return to life when they find a suitable host (source). DNA of such ancient viruses mostly (ie, 60%) does not resemble any known DNA on Earth (eg, PNAS, Telegraph). Viruses may well be older than any known life form on Earth, may even predate the origin of Earth itself, and may thus even have an extraterrestrial origin (source).

The research of Dr Martin and colleagues is a big jump in the search for the origin of all Life. I still wonder what a comparison between Luca and the DNA of viruses would tell. If Luca is also “half alive” then such a comparison would make perfect sense. I also can’t stop thinking about this famous line in movie history: “E.T. phone home” (1982, IMDb, video).

Suzanne Vega – Luka (1987) – artist, lyrics, video, Wiki-1, Wiki-2

My name is Luka

I live on the second floor

I live upstairs from you

Yes I think you’ve seen me before

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