Posted on 06/17/2002 4:40:34 PM PDT by Nebullis
CHAMPAIGN, Ill. — Life did not begin with one primordial cell. Instead, there were initially at least three simple types of loosely constructed cellular organizations. They swam in a pool of genes, evolving in a communal way that aided one another in bootstrapping into the three distinct types of cells by sharing their evolutionary inventions.
The driving force in evolving cellular life on Earth, says Carl Woese, a microbiologist at the University of Illinois at Urbana-Champaign, has been horizontal gene transfer, in which the acquisition of alien cellular components, including genes and proteins, work to promote the evolution of recipient cellular entities.
Woese presents his theory of cellular evolution, which challenges long-held traditions and beliefs of biologists, in the June 18 issue of the Proceedings of the National Academy of Sciences.
Cellular evolution, he argues, began in a communal environment in which the loosely organized cells took shape through extensive horizontal gene transfer. Such a transfer previously had been recognized as having a minor role in evolution, but the arrival of microbial genomics, Woese says, is shedding a more accurate light. Horizontal gene transfer, he argues, has the capacity to rework entire genomes. With simple primitive entities this process can "completely erase an organismal genealogical trace."
His theory challenges the longstanding Darwinian assumption known as the Doctrine of Common Descent – that all life on Earth has descended from one original primordial form.
"We cannot expect to explain cellular evolution if we stay locked in the classical Darwinian mode of thinking," Woese said. "The time has come for biology to go beyond the Doctrine of Common Descent."
"Neither it nor any variation of it can capture the tenor, the dynamic, the essence of the evolutionary process that spawned cellular organization," Woese wrote in his paper.
Going against traditional thinking is not new to Woese, a recipient of the National Medal of Science (2000), and holder of the Stanley O. Ikenberry Endowed Chair at Illinois.
In the late 1970s Woese identified the Archaea, a group of microorganisms that thrive primarily in extremely harsh environments, as a separate life form from the planet’s two long-accepted lines – the typical bacteria and the eukaryotes (creatures like animals, plants, fungi and certain unicellular organisms, whose cells have a visible nucleus). His discovery eventually led to a revision of biology books around the world.
The three primary divisions of life now comprise the familiar bacteria and eukaryotes, along with the Archaea. Woese argues that these three life forms evolved separately but exchanged genes, which he refers to as inventions, along the way. He rejects the widely held notion that endosymbiosis (which led to chloroplasts and mitochondria) was the driving force in the evolution of the eukaryotic cell itself or that it was a determining factor in cellular evolution, because that approach assumes a beginning with fully evolved cells.
His theory follows years of analysis of the Archaea and a comparison with bacterial and eukaryote cell lines.
"The individual cell designs that evolved in this way are nevertheless fundamentally distinct, because the initial conditions in each case are somewhat different," Woese wrote in his introduction. "As a cell design becomes more complex and interconnected a critical point is reached where a more integrated cellular organization emerges, and vertically generated novelty can and does assume greater importance."
Woese calls this critical point in a cell’s evolutionary course the Darwinian Threshold, a time when a genealogical trail, or the origin of a species, begins. From this point forward, only relatively minor changes can occur in the evolution of the organization of a given type of cell.
To understand cellular evolution, one must go back beyond the Darwinian Threshold, Woese said.
His argument is built around evidence "from the three main cellular information processing systems" – translation, transcription and replication – and he suggests that cellular evolution progressed in that order, with translation leading the way.
The pivotal development in the evolution of modern protein-based cells, Woese said, was the invention of symbolic representation on the molecular level – that is, the capacity to "translate" nucleic acid sequence into amino acid sequence.
Human language is another example of the evolutionary potential of symbolic representation, he argues. "It has set Homo sapiens entirely apart from its (otherwise very close) primitive relatives, and it is bringing forth a new level of biological organization," Woese wrote.
The advent of translation, he said, caused various archaic nucleic-based entities to begin changing into proteinaceous ones, emerging as forerunners of modern cells as genes and other individual components were exchanged among them. The three modern types of cellular organization represent a mosaic of relationships: In some ways one pair of them will appear highly similar; in others a different pair will.
This, Woese said, is exactly what would be expected had they individually begun as distinct entities, but during their subsequent evolutions they had engaged in genetic cross-talk – they had indulged in a commerce of genes.
I believe the gist of that discussion was that the early world was an RNA replicating type world from which cellular organization later developed. Maybe you anticipated Woese's direction in thought? I had a conversation before that with Godel regarding the "shape" of the universal tree. On a later thread (you see, I never save any of this stuff--this is my time off), a thread about parity violation, if I remember correctly, I mentioned my views about life originating multiple times.
I said Darwinians not Darwin. What is being pushed now, I believe, is called Neo-Darwinism. Be that as it may, I still say -- what is needed for Darwinian evolution? The answer is, of course, replication with error in order to generate the information needed for an organism to evolve. If the information is generated prior to and without the assistance of replication, what is the necessity of the replication errors for evolution? And this is not abiogenesis specific as it is stated in the article --- and he suggests that cellular evolution progressed in that order, with translation leading the way. . Cellular evolution, I take it, means exactly that.
What reasonable person could believe that something so complex could happen by random occurrence?
A cell just popped up one day with the DNA structure built in giving it the ability to reproduce and survive on a world void of any organic matter.
Nice straw man, but no evolutionary scientist theorizes anything like that.
Their INTENTIONS?
RIGHT. . . sure is difficult to get away from the notion of a conscious design isn't it.
Well, well. A living example of copying with error.
Please submit your proof that "replication with error in order to generate the information needed for the organism to evolve." Is some sort of essential stumbling block to the natural origins of life. What Woese and Kauffman & etc. have been trying to point out is that the game before DNA arrived must have been radically different from the game after DNA, to which your prescription applies.
What appears to be the rock bottom necessity is some sort of self-sustaining, energy conserving chemical cycle. Replication may have been so crude and diffuse compared to what we know of now, that we might not regard it as replication at all. All else is bells and whistles for later, as the earth cools down.
Not me. I saw Woese's outside-the-box stuff on that thread and was awed.
Have you been napping in the Darwinian classes? You need variation to evolve. That is potential information formed by random mutations of the living organism. And the randomization has to be reproduced to present itself to the natural selector which imparts "realness" to the potential information. Or so say the Darwinians.
Akin to leaving a hamburger in the back of the fridge for several months,
waiting for it to evolve into a t-bone steak...
Same RNA world, different lines of descent to the point where Darwinian evolution becomes a viable way of resolving ancestry.
Woese presents what he calls "A theory for the evolution of cellular organization." The root of the universal tree does not begin at the origin of life, it "has no root in the classical sense", but rather at the Darwinian Threshold, the point at which a level of cellular organization emerges when horizontal gene transfer is no longer the predominant form of novelty generation. It is at this point that vertically generated novelty assumes greater importance and one can speak of Darwinian evolution.
The time-line between the RNA world and modern cellular organization is a long one and includes the evolution of translation. Crossing the threshold happened at different times for the separately evolved organisms. There is ample evidence for this from molecular data. Bacteria crossed this threshold first. "The bacterial versions of the central (universal) cellular systems respresent earlier ancestral versions of these systems than do their archael or eukaryotic counterparts." Darwinian evolution predicts that genes should be shared more as you move to the bottom of the universal tree until one can predict a common ancestor which contains all the genes. Instead, there are gene families not common to the various prokaryotic and eukaryotic cells.
Woese doesn't address the point, unfortunately [compatible lineages]. Nor does he explain here what his theory does better, or even differently. What are the consequences, the tests?
The consequenses are an explanation for the molecular problems at the root of the tree. This explanation goes a long way toward explaining cellular evolution and the origin of the known different lineages at the root of the universal tree.
Replication does have the honored position. Woese is talking about translation in the evolution of cellular organization.
I still like endosymbiosis for the origin of eukaryotes. There's the resemblance between mitochondria and bacteria and the very late appearance in the fossil record. (Cellulars, when they appeared, probably gobbled the RNA world right up.) Even so, that still leaves Woese's ideas looking good for the origins of archaea and bacteria.
Another point cleared up! Thanks.
Is the natualist hypothesis more likely than the ID hypothesis? No, if cells did not have a single common biologic ancestor ID is more likely. Two of the three cell types show up as soon as Earth cools down enough to allow them (after asteriod shower about 3.6 bya). The other may have been there, but not quite in its current form.
The crux of my point is this : If the mythical pre-biotic 'soup' naturalistically produced not one but three separate cells in a geologically insignificant amount of time, then why have origin of life experiments hit one brick way after another since Urey-Miller?
I am not asking you to 'see the light'. I am just asking you to acknowledge that the lack of common biologic origin despite interchangability of some parts and quick arrival time all make ID a little bit more likely. Are either of you willing to concede even that much?
I don't suppose you've come to the realization yet that whatever science turns up with empirical support would be slam-dunk evidence for ID.
Uh huh. The original Darwinian formula applies to DNA-bearing entities that leave fossils behind in a comparatively cool earth. Please submit your proof that nearly-exact copying of completely discrete entities is the only possible way evolution could have happened.
As I have been manfully trying to suggest thru several threads here, the story has to be radically different when the evolving entities are not altogether discrete, and temperatures are so high that finding means of conserving energy is a trivial task.
As the Woese article I pointed to back in that old thread suggests, the essential problems of loosely organized evolving entities in a planet sized hot soup of bubbly broth are not anything like the problems of entities familiar to Darwin, and us. For RNA world and before, the field of contention in which evolutionary selection can occur, is something like staying a federated entity, not gathering and utilizing resources--a requirement of a far cooler world.
A different basic problem calls for a different basic survival paradigm. And I'd really recommend the Woese article to you on this subject, as it is very clear about how massive distinctions in mean earth temperature have to require massive distinctions in basic survival problems.
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