Evolution theories with no universal common ancestor

Lake, again using the conditioned reconstruction algorithm, proposes a ring-like model in which species of all three domains—Archaea, Bacteria, and Eukarya—evolved from a single pool of gene-swapping prokaryotes.”

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In 1999, W. Ford Doolittle proposed a phylogenetic model that resembles a web or a network more than a tree. The hypothesis is that eukaryotes evolved not from a single prokaryotic ancestor, but from a pool of many species that were sharing genes by HGT mechanisms.

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Jim said:

I’ve been discussing this in the “Evolution vs Creationism” forum, but it has nothing to do with creationism, so I’ve decided to post about it here. According to some current theories, some of the first lines of ancestry of living cells evolved separately from a pool or some pools of primitive protein factories sharing genes with each other. Eventually they divided up into three groups, which eventually became the first species from which all other species evolved. There’s some disagreement between researchers about whether to call that pool or those pools an “ancestor.”

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The ancestor cannot have been a particular organism, a single organismal lineage. It was communal, a loosely knit, diverse conglomeration of primitive cells that evolved as a unit, and it eventually developed to a stage where it broke into several distinct communities, which in their turn become the three primary lines of descent.

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A genetic annealing model for the universal ancestor of all extant life is presented ... The scenario pictured starts when “genetic temperatures” were very high, cellular entities (progenotes) were very simple, and information processing systems were inaccurate. Initially, both mutation rate and lateral gene transfer levels were elevated. The latter was pandemic and pervasive to the extent that it, not vertical inheritance, defined the evolutionary dynamic. As increasingly complex and precise biological structures and processes evolved, both the mutation rate and the scope and level of lateral gene transfer, i.e., evolutionary temperature, dropped, and the evolutionary dynamic gradually became that characteristic of modern cells. The various subsystems of the cell “crystallized,” i.e., became refractory to lateral gene transfer, at different stages of “cooling,” with the translation apparatus probably crystallizing first. Organismal lineages, and so organisms as we know them, did not exist at these early stages. The universal phylogenetic tree, therefore, is not an organismal tree at its base but gradually becomes one as its peripheral branchings emerge. The universal ancestor is not a discrete entity. It is, rather, a diverse community of cells that survives and evolves as a biological unit. This communal ancestor has a physical history but not a genealogical one. Over time, this ancestor refined into a smaller number of increasingly complex cell types with the ancestors of the three primary groupings of organisms arising as a result.

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Long before cells had the advanced translation mechanisms of today, cells or pre-cellular entities of some type must have had a rudimentary translation apparatus that was less complex and more prone to error and unable to produce many of the modern, complex proteins. Woese and Fox (1977) coined the word “progenote” for such entities. ... The idea of the progenote and how it relates to common ancestry was then further developed in Woese (1983, 1987, 1998).
Not only are progenotes simple entities utilizing only relatively few small proteins, but because they lacked cell walls, their parts would freely move in and out between other progenotes in their immediate environment in a process which has similar results to lateral gene transfer. This means that individual progenotes are not really individuals in a biological sense at all. Rather, clusters of progenotes evolve together like overlapping communities without forming genealogical lineages. Woese argues that the process is analogous to a kind of physical annealing where the progenote world undergoes rapid evolutionary change until eventually we reach the emergence of cellular structures that are more stable. Once translation becomes accurate enough, communities make the transition across what Woese et al. call the “Darwinian threshold.” After this, the idea of genealogy makes sense and individual organism-like entities begin to form true lineages. While lateral gene transfer can still occur, vertical evolution is now in play, and the concept of a phylogenetic tree makes sense. What the progenote model of LUCA asserts is that this threshold was crossed independently at different times. Woese (1998) postulates that each of the three primary lines of descent (Bacteria, Archaea, and Eukaryotes) crossed the threshold independently.

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What would a truer model look like? At the top, treelike branching would continue to be apt for multicellular animals, plants and fungi. ... Deep in the realm of the prokaryotes and perhaps at the base of the eukaryotic domain, designation of any trunk as the main one would be arbitrary.

Though complicated, even this revised picture would actually be misleadingly simple ... The full picture would have to display simultaneously the super-imposed genealogical patterns of thousands of different families of genes ...

If there had never been any lateral transfer, all these individual gene trees would have the same topology ... But extensive transfer means ... gene trees will differ ... and there would never have been a single cell that could be called the last universal common ancestor.

In other words, early cells ... differed in many ways. By swapping genes freely, they shared various of their talents with their contemporaries. Eventually this collection of eclectic and changeable cells coalesced into the three basic domains known today.

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ChristineM said:

There are hypothetical ideas that life could have started multiple times but DNA show all life existing today had a common ancestor. So if life did start multiple times then all other strains of life have become extinct or none have been found to examine their DNA

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Jim said:

I’ve been discussing this in the “Evolution vs Creationism” forum, but it has nothing to do with creationism, so I’ve decided to post about it here. According to some current theories, some of the first lines of ancestry of living cells evolved separately from a pool or some pools of primitive protein factories sharing genes with each other. Eventually they divided up into three groups, which eventually became the first species from which all other species evolved. There’s some disagreement between researchers about whether to call that pool or those pools an “ancestor.”

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Jim said:

I’ve been discussing this in the “Evolution vs Creationism” forum, but it has nothing to do with creationism, so I’ve decided to post about it here. According to some current theories, some of the first lines of ancestry of living cells evolved separately from a pool or some pools of primitive protein factories sharing genes with each other. Eventually they divided up into three groups, which eventually became the first species from which all other species evolved. There’s some disagreement between researchers about whether to call that pool or those pools an “ancestor.”

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shunyadragon said:

The primary lineages of PreCambrian and Cambrian animals are the chordates from which later animals diversified and evolved.

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Jim said:

I’ve been discussing this in the “Evolution vs Creationism” forum, but it has nothing to do with creationism, so I’ve decided to post about it here. According to some current theories, some of the first lines of ancestry of living cells evolved separately from a pool or some pools of primitive protein factories sharing genes with each other. Eventually they divided up into three groups, which eventually became the first species from which all other species evolved. There’s some disagreement between researchers about whether to call that pool or those pools an “ancestor.”

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Evangelicalhumanist said:

I'll not pretend to be speaking with any authority, but it does certainly seem to me that if it's possible that if basic organic molecules could be assembled on earth based on prevailing conditions (moisture, available materials, source of energy, geological or meteorological and so on), then it isn't in the slightest unreasonable to suppose that this could have happened in many different ways around our planet. After all, conditions are different based not only on latitude, but local environments that include land masses, hills and valleys that make shade, or plains that give plenteous sunlight, and so on. So I don't really adhere to the idea that there was a single event, from which all other life forms evolved.

And I think it's reasonable to suppose that if there were, in fact, a variety of abiogenesis events, as seems probable to me, then that would go a long way to explaining the wonderful diversity we see today.

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beenherebeforeagain said:

I think you're forgetting many other kinds of animals besides chordates, such as arthropods, molluscs, etc., and those that are neither plant nor animal, fungi, for example...what survived the Cambrian and later extinctions and diversified also included plants as well...

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shunyadragon said:

clearly defined as originating from Chridata including arthropods.

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shunyadragon said:

I do not believe there are any strong disagreement of the known ancestors of modern animals. The primary lineages of PreCambrian and Cambrian animals are the chordates from which later animals diversified and evolved.

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beenherebeforeagain said:

Arthropods are not Chordates. There are many other phyla that exist, and are not descended from Chordates...

You said:

Your statement read as if ALL animals arose from the Chordates. I pointed out that there are other kinds of animals that are not Chordates. Wikipedia discusses the various phyla of which there are many...

Phylum - Wikipedia

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Jim said:

I’ve been discussing this in the “Evolution vs Creationism” forum, but it has nothing to do with creationism, so I’ve decided to post about it here. According to some current theories, some of the first lines of ancestry of living cells evolved separately from a pool or some pools of primitive protein factories sharing genes with each other. Eventually they divided up into three groups, which then evolved into the first species from which all other species evolved. There’s some disagreement between researchers about whether to call that pool or those pools an “ancestor.”

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Jim said:

Some researchers think that calling that pool or those pools an “ancestor” is stretching the word “ancestor” too far.

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Jim said:

Perspectives on the Phylogenetic Tree

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ChristineM said:

There are hypothetical ideas that life could have started multiple times but DNA show all life existing today had a common ancestor. So if life did start multiple times then all other strains of life have become extinct or none have been found to examine their DNA

Click to expand...