Evolution theories with no universal common ancestor

[Jim]

Now I want to review what I’’m thinking, and I’d like to know all the reasons that anyone might have for thinking that it can’t be true. The idea is that life could have started in many different places with the same chemistry that that is common to all life today. I’m not denying that life could have also started in many other ways, without any of the life that came from that continuing long enough to leave any traces that we’ve found. I’m saying that no matter how other life started, it could still have started in many places with the same chemistry that is common to all life today.. That’s one way that all life today could have some chemistry in common without all having any ancestor in common.

 

[Jim]

One argument that I’ve seen for a universal common ancestor is that if there were many trees of life, and if all life today did not come from the same root, we would see some that did not use all the same chemistry that is common to all life today. I’d like to know all the reasons that anyone might have for thinking that there was only ever one place and time where life started with the same chemistry that is common to all life today.

 

[Skwim]

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

Which researchers? My suspicion is that they're not even scientists much less scientists in a biological field.

So let's have some names here.

.

 

[Jim]

Which researchers? My suspicion is that they're not even scientists much less scientists in a biological field.

So let's have some names here.

See this post in this thread.

 

[Jim]

(edited to insert something I left out, about life chemistry in my view)
What I’m proposing now is that there might be many trees of life that began separately, and have always evolved separately, without any species in one tree having any common ancestor with any species in any other tree. All of the similarities that are used as reasons for imagining a universal a universal common ancestor, including any chemistry that is common to all life, could be a result of convergent evolution. A multitude of trees evolving separately could have all started with the same chemistry that is common to all life today.

If anyone thinks that can’t be true, I would like to know their reasons for thinking that it can’t be true.

One reason that I’ve seen for thinking that life today can’t be from more than one tree is that some of the chemistry of life is the same for all life today. if life today were from more than one tree, then there would be some of it that does not use that same chemistry. For example, in some life some of the amino acids used in building proteins would be different, or there would be more of them, or fewer.

Does anyone have any other reasons for thinking that what I’m thinking about many trees of life can’t be true?

 

[sayak83]

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.”

I have read some of what you posted here. I think you should read a reasonably good college level textbook on evolutionary biology to begin with. That would help you understand what are reasonable models and what are unreasonable ones given the data.

 

[LuisDantas]

What I’m proposing now is that there might be many trees of life that began separately, and have always evolved separately, without any species in one tree having any common ancestor with any species in any other tree. All of the similarities that are used as reasons for imagining a universal a universal common ancestor, including any chemistry that is common to all life, could be a result of convergent evolution.

If anyone thinks that can’t be true, I would like to know their reasons for thinking that it can’t be true.

One reason that I’ve seen for thinking that life today can’t be from more than one tree is that some of the chemistry of life is the same for all life today. if life today were from more than one tree, then there would be some of it that does not use that same chemistry. For example, in some life some of the amino acids used in building proteins would be different, or there would be more of them, or fewer.

Does anyone have any other reasons for thinking that what I’m thinking about many trees of life can’t be true?

I posted a version of this in another thread, but the short of it is that there is a lot of evidence of the lifeforms that we know to exist and none for a separate strain.

Essentially, those hypothetical lifeforms would either be very rare (and as a result also presumably either extinct or near-immortal), active competitors for resources with known lifeforms within their ecological niches (which would make the absence of evidence of their existence inexplicable), or capable of interbreeding with known lifeforms (and therefore not a separate strand after all).

If none of those three rather exotic situations apply, you could probably still propose their existence, but calling them lifeforms would ultimately be an arbitrary choice. They would be very unusual indeed and presumably even non-physical.

 

[Jim]

I’m asking for any reasons that anyone might have for thinking that that life could not have started in many places with the same chemistry that is common to all life today. I don’t know if that has a name or not. I’ll call it “Universal Life Chemistry and abbreviate it “ULC.” One example is that out of about 500 amino acids that occur naturally, all life uses the same 22 of them to build proteins.

I’m trying to imagine how it could be true, that life could not have started in more than one place with that same chemistry. First of all, it would have to be possible for life to exist without that chemistry. Some researchers are questioning that, but for discussion purposes let’s say that it’s possible. That is not a reason to say that life could not possibly have started with the ULC in more than one place. Maybe people are thinking that the probability of that is very low, for simplicity let’s say 1%. In order to calculate that probability, we would need to know the probability p of life starting with the ULC in any one place, and the number of places n where it started. Then the probability that it started with ULC in only one place is (1-p)^(n-1). As an example, let’s say that p is .00001. Then n would need to be less than 461,000. That is, life would have to have started in less than 461,000 places to have a probability that it started in only one place with the ULC.

 

[Jim]

No more thoughts about this?

 

[Jim]

I’m planning to look more deeply into some tree and web diagrams of relationships between species, and discuss here what I’ve been learning. In this post I’ll describe an idea that I’m considering, of how there could be more than one tree of life. Life could have started in many places, and many times in the same place. Maybe thousands or even millions. A smaller number, but still possibly thousands, could have started with whatever chemistry would be needed to evolve into one or more of today’s species.

In case anyone is wondering, I haven’t seen this idea being discussed in any evolution research.

 

[Jim]

I’m posting this here for later reference.

Here, I argue an alternative point of view, in which a “tree with reticulations” is a network, and that therefore a network will be a better-metaphor, model, and heuristic for phylogenetics, in the sense that it will be more inclusive and more powerful. ... The tree metaphor/model/heuristic pre-supposes tree-like data, whereas the network allows the data to determine the tree-likeness of the metaphor/model/heuristic—some networks are more tree-like than are others. So, the network view does not deny the importance of the ToL, but simply makes it a special case of something much more general.

- Is the Tree of Life the Best Metaphor, Model, or Heuristic for Phylogenetics?

 

[Jim]

NOTE: Because of the political environment I want to say that I’m not endorsing any version of ID or Creationism, and I don’t see “God says” or “scripture says” as reasons for believing anything.

I’ll try to explain as well as I can what I’m aiming for here as far as I can see now. It’s to discuss some possibilities that I see for there to be more than one tree of life. I’m looking for any reasons that anyone might have have for thinking that can’t be true. I don’t think that probabilities are relevant to whether it can be true or not, but I have no objection to discussing them if anyone wants to.

I want to discuss this now from a different angle: what trees of life are used for and how a model with more than one tree might be better for some of those purposes. I could use some help with examples of what tree models are used for. I’ve found some examples, which I will be discussing, but I would like to see more.

What I mean by a model with more than one tree is that the branches don’t all merge into one single root or trunk at the bottom. I’ll be discussing how that could be better for some of the purposes that a tree of life is used for. Then I’ll discuss some possibilities that I see that life could have started in many places and at different times, branching out into trees that have evolved separately from each other into our time.

Again, for anyone who wants to know, I haven’t seen that idea being discussed by any researchers.

 

[Jim]

Plants and animals have been classified and grouped together in different ways, for different purposes. For some of those purposes they are grouped together by similarities in their appearances and other features that are easy to find. Sometimes there have been major revisions in the groupings for various reasons which I’ll discuss after I learn more about them. As I understand it, one of the advantages of grouping them according to ancestry has been to reduce the need for major revisions in classification systems based on appearance and structure. I’ll say more about that after I learn more about it myself. This is a kind of preview of what I might discuss in this thread.

For some time ancestry was partly or even mostly guesswork, and sometimes the guesswork turned out to be obviously wrong. When possibilities opened up for comparing gene sequences, that looked like a foolproof way of grouping by ancestry. As it turns out, it hasn’t been foolproof, but it has been very useful in some ways.

For classification purposes, I don’t see what purpose a universal common ancestor can serve, and I haven’t been able to find any examples of it being used for any practical purpose. It looks to me like a useless appendage for any practical purposes. I can see its value for research purposes, because it has motivated and inspired some valuable research with beneficial applications.

 

[Jim]

I want to discuss some significance that I see in the choice of words in “natural selection,” and some possible misconceptions about survival of the fittest.

One way that people have created new kinds of plants and animals has been by selecting individual ones from a stock that most resemble tge kind of plant or animal we want, and having those reproduce with each other to produce a new generation. That’s done repeatedly. “Natural selection” is a process of selection that happens naturally. “Naturally” is not the same thing as “randomly.” Part of the changes from one generation to the next might be from random mutations, but the individuals that reproduce the most are selected by the environment.

Sometimes when people think of survival of the fittest, they might picture a fight to the death between two wild animals, and think of fights to the death between species the same way, but that has little or nothing to do with natural selection. It’s more about what happens within a species than what happens between them, and even there it isn’t only, or even mostly, about some of them being eliminated in fights with the others or from competition for resources. It’s about some of the individuals within a species being better equipped to survive in the environment around them and to reproduce.

Species don’t survive by eliminating other species. Any species that would completely exterminate species that it feeds on would be weakening its chances of survival. Any species that would exterminate other species by competing with them for resources would be changing the environmental conditions that have bred the species, weakening its chances of survival. The vast variety of species in the world shows that species survive in cooperating with each other more than by competing against each other, no matter how much killing there is between one species and another.

 

[Jim]

Indeed, I too think that “LUCA was a population,” but I argue that this in fact means that there actually was no LUCA.

- Doolittle WF (2005) If the Tree of Life fell, would we recognize the sound? In: Sapp J, Microbial phylogeny and evolution: concepts and controversies. Oxford University Press, Oxford, pp 119–133

I’m not sure that Doolittle is the only researcher who thinks that, but he’s the only one I know of who has said so publicly, and even he hasn’t proposed what I’m proposing, that trees of life that started in many different places could have continued into our time. I’ve seen one researcher who might be thinking that, or at least not discounting it:

UCA does not demand that the last universal common ancestor was a single organism in accord with the traditional evolutionary view that common ancestors of species are groups, not individuals. Rather, the last universal common ancestor may have comprised a population of organisms with different genotypes that lived in different places at different times

- Theobald DL (2010) A formal test of the theory of universal common ancestry. Nature 465:219–222

I want to discuss the views of Doolittle, Theobald and another researcher who pictures LUCA as a population in his research. Then I’ll discuss my ideas some more, about many trees of life.

 

[Jim]

I’ll explain my understanding of why some researchers have been discussing other models besides a tree model, for the history of life on earth. Part of it is that sometimes genes are transferred from one species to another, and become part of its ancestry. That’s represent by horizontal lines between branches. Another reason might be because according to some theories, none of the fossils of the earliest life could be from the last universal common ancestor. That means that if we draw a trunk with the earliest known life forms branching up from it, that trunk doesn’t represent any known life form. It doesn’t serve any practical purpose to include that trunk at the bottom if the tree, so why do we keep doing it? In some theories two or three of the earliest life forms have no common ancestor in any kind of living cells or anything composed of living cells.

 

[Jim]

I’m studying this now, to get as recent a view as I can of Doolittle’s view, in his own words: What Is the Tree of Life?

 

[Jim]

Here’s how it looks to me now. Ancestry seems like a natural way to organize a list of plants or animals. Comparing gene sequences looked like a sure way of doing that. Then it didn’t.

Sometimes two species merge into one. That can happen with actual trees, too, but it happens so much in the lower part of the tree of life that it looks more like a network than like a tree. That’s a separate question from whether the branches all merge together into one at the bottom. According to some theories the first two or three species began separately from different parts of a self-perpetuating cloud of molecules producing proteins without any living cells. I don’t see any researchers denying that it all started in one place at one time. All the discussion is about whether to call the diagram a tree or a network, and whether or not to include that original cloud of molecules in the diagram.

 

[Jim]

It still seems more likely to me that life started in many different places, and that the life that started in some of those places continued into our time without ever merging together.

 

[Jim]

Maybe the reason that researchers are ignoring the possibility that I’m seeing of more than one tree is because for research purposes it doesn’t matter how many trees there are.

UCA does not demand that the last universal common ancestor was a single organism, in accord with the traditional evolutionary view that common ancestors of species are groups, not individuals. Rather, the last universal common ancestor may have comprised a population of organisms with different genotypes that lived in different places at different times.

On universal common ancestry, sequence similarity, and phylogenetic structure: the sins of P-values and the virtues of Bayesian evidence