The OLDEST Common Ancestor of All Living Things?

(George Brooks) #1

“For the first time, scientists have put together a picture of what it might have looked like genetically. But not everyone is convinced. The portrait comes from new research published July 25, in which scientists sorted through 6 million genes to settle on 355 they think Luca may have carried.”

" Genes change in a predictable way over time, which means that comparing the DNA sequences of living organisms lets scientists make hypotheses about organisms we have no other way of studying. So the scientists, led by William Martin at Heinrich Heine University in Germany, looked at genes from bacteria and archaea: the two large umbrella groups of single-celled life. Genes that could be found in at least two groups of bacteria and two groups of archaea were considered likely to have belonged to Luca."

“The 355 genes the researchers picked out suggest Luca survived without oxygen, pulling energy from carbon dioxide and hydrogen instead, that it could survive very high temperatures, and that it required the presence of metals.”


I don’t normally keep up with this field of science—but I saw Luca discussed in my morning New York Times email briefing and found this quite exciting.

I’ve heard about the H2S vent organisms for years now but never ever paused to consider that they might be a L.U.C.A. leftover. Absolutely mind-blowing!

Frankly, the progress of fields like paleomicrobiology and genomics (and even areas like cloning) have progressed far beyond what I ever dreamed that I would see in my own lifetime----based on the science magazines I was reading in the 1950’s and 1960’s. Yet, we STILL have people still stuck in 1962-level Gish-Morris-Whitcomb Young Earth Creationist “creation science” denial of evolution! That’s mind-boggling too!

(sy_garte) #3


George, You might want to change the title of this post, since the article is about LUCA, not the first living thing on Earth. If the RNA world is correct (as is the consensus) there were at least one (and most likely a lot more) earlier forms of life before LUCA (with DNA and proteins and a genetic code) arrived on the scene.


I assume that he chose “The First Living Thing on Earth?” for the title because the scientists behind the story had also discussed the positively that vent organisms which lived off H2S—that is, the type of biological life that LUCA is yet another example—were also the very first life on earth.

At least in the New York Times article about this story, both LUCA and original H2S organisms were discussed and they speculated that all other lifeforms on earth came from that hydrogen sulfide type of ancestor.

However, I only scanned the story. Did I misunderstand it?

(George Brooks) #5

I’ll leave the question mark on the thread… I’m not sure it’s life without DNA … I’ll read some more about Luca before I make any more changes…

(sy_garte) #6

That’s right, in the original paper, they do speculate on that possibility, but the actual evidence presented is related to LUCA (which makes sense, since at this point, we cannot really go back further than that, in terms of the biochemistry involved.) And of course, the vents with H2S as energy source is a well known theory for first life. I dont really know if this paper supports that or not.

(George Brooks) #7


I think you are right.

And I found this economical paragraph which supports what you say:

“The last universal ancestor (LUA), also called the last universal common ancestor (LUCA), cenancestor, or progenote, is the most recent organism from which all organisms now living on Earth have a common descent. Thus, it is the most recent common ancestor (MRCA) of all current life on Earth.”

" As such, it should not be assumed to be the first living organism. "

“The LUA is estimated to have lived some 3.5 to 3.8 billion years ago (sometime in the Paleoarchean era). The earliest evidence for life on Earth is biogenic graphite found in 3.7 billion-year-old metamorphized sedimentary rocks discovered in Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.”

"A study in 2015 found potentially biogenic carbon from 4.1 billion years ago in ancient rocks in Western Australia. Such findings would indicate the existence of different conditions on Earth during that period than what is generally assumed today and point to an earlier origination of life. "

(system) #8

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