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Genes Hint that Life Originated in Hydrothermal Area
Science Magazine and the New York Times report on work published in Nature Microbiology (full article paywalled) (DOI: 10.1038/nmicrobiol.2016.116). Searching through databases, geneticists looked for genes shared among prokaryotes (bacteria and archaea). Their goal was to identify traits of the last universal common ancestor—an organism from which all cellular life is descended.
The genes that met their criteria suggest an organism that could incorporate nitrogen from molecular nitrogen and carbon from carbon dioxide into their cells—they were autotrophs rather than heterotrophs (they did not rely on other organisms as a source of carbon). Also suggested is that the organism was thermophilic, (thriving at high temperatures) and anaerobic (not using oxygen). The researchers think it had the Wood–Ljungdahl pathway, also known as the reductive acetyl-coenzyme A pathway, in which hydrogen is oxidised, carbon dioxide is reduced, organic molecules are synthesised, and chemical energy is made available to the organism.
They say that these characteristics support the idea that life originated in hydrothermal conditions. Such conditions exist today in hot springs, underground waters in volcanic areas, and deep-sea vents.
Meet Luca, the Ancestor of All Living Things
The New York Times published a story yesterday that demonstrates that with sweat and persistence, long lost relatives can be found:
A surprisingly specific genetic portrait of the ancestor of all living things has been generated by scientists who say that the likeness sheds considerable light on the mystery of how life first emerged on Earth.
This venerable ancestor was a single-cell, bacterium-like organism. But it has a grand name, or at least an acronym. It is known as Luca, the Last Universal Common Ancestor, and is estimated to have lived some four billion years ago, when Earth was a mere 560 million years old.
The new finding sharpens the debate between those who believe life began in some extreme environment, such as in deep sea vents or the flanks of volcanoes, and others who favor more normal settings, such as the "warm little pond" proposed by Darwin.
The article goes on to describe how this discovery was made, and concludes:
[The genetic analysis performed in the research] 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.
No doubt there is more to be revealed on this subject.
(Score: 5, Disagree) by TrumpetPower! on Tuesday July 26 2016, @04:14PM
The paleontological tree of life was strong enough in Darwin's time for him to conclude a very likely probability of a single universal common ancestor...and that conclusion has become overwhelming with the scientific advances of the past 150 years. The coffin was already nailed shut by the time of Watson and Crick, but modern DNA analysis has superglued it and then buried it under the Roosevelt Dam.
All life today is descended from a single ancestor a few billion years ago...but that ancestor would have been one of a sizable population. You're likely familiar with the exact same phenomenon on a much smaller scale with human families...you and all your cousins and what-not can trace your own ancestry back to a pair of great-great-great-grandparents, but there were many more people alive at the time than just that couple. And other people today trace their ancestry to different great-whatever-grandparents.
As should be plain from this article, the line between primordial chemistry and early life was especially fuzzy. Just as you're not going to be able to pick a wavelength in the spectrum that divides blue from green, yet we can all agree that 400 nm is violet and 700 nm is red...well, there would have been lots of chemistry at the time of the LUCA that wasn't all that different from the LUCA.
And, indeed, that same chemistry, whatever it actually was, is almost certainly still going on today. The difference is that, today, we've got some very sophisticated living beings that have a few billion years of evolution making them particularly adept at eating that sort of chemistry long before it can have the tens or hundreds of millions of years of undisturbed evolution just to get to the single-cell stage...but even said single-cell stage would be hopelessly outcompeted (and eaten) in the modern world.
A car analogy. Imagine a back-bush tribe that even today is so isolated that rumors of civilization are dismissed as lunatic ravings. (Not that any such still exist; just pretend.) Some bright kid there might draw inspiration from a story about a Jeep and thereby reinvent the wheel. That wheel is never going to go on the axle of a tractor-trailer rig hauling cargo at 65 MPH on a freeway in Denver; rather, it's going to wind up in the fireplace or eaten by termites.
Cheers,
b&
All but God can prove this sentence true.
(Score: 2) by VLM on Tuesday July 26 2016, @05:43PM
Why not something more extreme? A fossil record of something that lived separately awhile and died out. I mean if something grew here, why not there too?
A standard issue bad car analogy would be ever Ford manufactured (distinct from rebadged) car is a direct descendant of the model T. That doesn't mean the Pierce-Arrow Motor Car Company never existed, although it died out around the great depression. In fact there's still evidence in junkyards (well, more like museums) of the P-A motor car company.
Or extending your paragraph two, yo why no cousins? Or just neighbors in general?
(Score: 1) by curril on Tuesday July 26 2016, @07:59PM
...modern DNA analysis has superglued it and then buried it under the Roosevelt Dam.
This is a bit too strong. Modern DNA analysis can't identify the LUCA, only code that has become common across all cell lines. Consider starting with cell A that later has a descendent B with a mutation that dominates across all cell lines. After the fact , there is no sure way to determine which DNA code was in A and which was new in B. Now consider another mutation C that happens fairly often and comes to dominate across all cell lines. There is no sure way with DNA analysis to determine if C was inherited from a common ancestor or occurred as a mutation across multiple cell lines.
Once you get back to the really messy bits of abiogenesis where gene replication was very imperfect and genes were created, lost, and recreated all of the time, the concept of a LUCA tends to lose meaning. After genes get complex enough that, to use your metaphor, reinventing the wheel is unlikely to occur, then ancestry becomes more well defined. So the LUCA becomes something of an arbitrary dividing point between cells with well-defined ancestors and organic, self-replicating soup.
(Score: 2) by HiThere on Wednesday July 27 2016, @02:44AM
The problem with your assertion is that you assume inheritance is a branching tree, where that's not even true for modern bacteria, a lattice would be closer. Gene flow between previously unrelated organisms is common at the microbial level. And it's not clear that the first life even HAD a cell wall, in which case even the boundaries of the organism would be difficult to define.
So there may not be a LUCA for life, but only for certain features of life, i.e. particular chemical pathways. And then you need to consider the problem of convergent evolution. It's like the problem of copyright on interfaces. Having a common interface may be an independently decided response to external pressures, and the only optimal solution. That make it functional.
This kind of argument is easy to see at the gross level. Nobody thinks the dolphin descended from the ichthyosaur, even though they have many features in common. But it also happens at finer levels. It's probable that the strategy of pumping out antibiotics was developed by several strains of bacteria independently, but each strain then started spreading it to otherwise unrelated bacteria. And it was a successful change, so it kept spreading.
I suppose you could come up with a definition of Luca that would work in this environment, but it's certainly not clear what it would mean. (It might be after you create the exact definition, but not ahead of time. There's too many alternatives.)
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