Evolution: common ancestor?

[Dizredux]

Dizredux

It was probably not a single individual but more likely a surviving population as Armoured and DogmaHunter mentioned. With horizontal gene transfer it could have been a mix of more than one population. We just don't know yet.

And I believe some biologists have said they'll never know*, which is what makes this so confusing. If it was a population and not an individual, how much can really be said to be "common" and how is it a "universal" ancestor?

* I don't have the paper I was thinking of at my fingertips, but this reference mentions the issue in the "Outstanding questions" box.

http://www-bac.esi.umontreal.ca/~db...erts-horizontaux/HGT_genome_Olga_TIG_2004.pdf

Interesting questions. Let me take a stab at it.

On populations. Let me do a hypothetical. Say your family is descended from an Englishman who came over several hundreds of years ago, married several times and had children from each wife. He would be the last common ancestor for all descended from him. If you look before him at England there are thousands of ancestors in the English population that are related to him. You cannot point to any one of these and call him to be the LCA but you can refer to them as the ancestral population.

To elaborate a little, say life was able to get started a number of times. Many of these did not survive for one reason or another. The ones that did may have transferred genes between them. Somewhere in there is a population(s) that all life descended from. Now due to common genetics we know that, at least so far, all known life is related but most in the field seem to consider that descent from a single individual doesn't work all that well but from an ancestral population(s) it works quite well.

You asked about universal and common ancestor. What is known is that all of life that we know of shares the same genetic basis so it is reasonable to feel that they all came from, in some manner, a common ancestor be it individual, group, or groups. Actually, I think the LCA to be more statistical than anything else.

It is just too far back to tell much.

Thanks for the link. I have seen this discussed before but had not see the original article. So thanks for posting it.

This is my view on the subject so take it for what it is, a layman's thoughts.

Dizredux

 

[Loudmouth]

I'm not desperate; I'm just curious what evolutionists believe was *the* common ancestor that kicked things off.

It is highly unlikely that there was a single organism or species that all life descended from. It is much more likely that the common ancestor was a pool of organisms and species that swapped and traded genetic and metabolic systems.

In that pool of organisms we would have found, at a minimum, the biological systems that all life shares. This includes, but not limited to, common codon usage, tRNA's, ribosomes, metabolic pathways like the TCA cycle, and DNA replication. In case it isn't too obvious, the common ancestors would have been single celled and probably didn't have organelles.

 

[Loudmouth]

And I believe some biologists have said they'll never know*, which is what makes this so confusing. If it was a population and not an individual, how much can really be said to be "common" and how is it a "universal" ancestor?

It is common and universal because all life carries features from those ancestors.

 

[Loudmouth]

An interesting fiction is that the planet was one very complex organism. This would explain increasing entropy leading up to man.

What is it with creationists needing to be wrong about thermodynamics? According to their logic, embryonic development is impossible.

 

[Resha Caner]

On populations. Let me do a hypothetical. Say your family is descended from an Englishman who came over several hundreds of years ago, married several times and had children from each wife. He would be the last common ancestor for all descended from him. If you look before him at England there are thousands of ancestors in the English population that are related to him. You cannot point to any one of these and call him to be the LCA but you can refer to them as the ancestral population.

Sure, but what establishes the line of descent? Is it the paper trail of birth certificates or the observed traits that establishes them as descended from Englishmen? If it's the traits, then there must be some test that demonstrates Englishmen ... otherwise this becomes something like a "no true Scotsman" fallacy (which is oddly convoluted given that your example was about Englishmen).

For example, what if there were a hypothesis that a group of people descended from Englishmen because of their tea culture. Hmm. Well, China also has a tea culture, so why couldn't they be descended from the Chinese rather than the English? Now we have to separate English tea culture from Chinese tea culture, which becomes very difficult (I actually did a paper on this for a history class).

I realize we're talking DNA here, but the problem is similar. That's why the thread on a synthetically larger alphabet is interesting. One argument for a common ancestor might be the possibilities for other alphabets (or other amino acids, etc.). Well, maybe. It would first need to be demonstrated that these other alphabets or amino acids would actually form naturally and produce sustainable life. Difficult to do. Or, it would need to be shown that other branches of life based on our 4-letter alphabet and 20-some amino acids have developed and then died out without contributing anything to the pool that continues on. Again, very difficult to do.

To elaborate a little, say life was able to get started a number of times. Many of these did not survive for one reason or another. The ones that did may have transferred genes between them. Somewhere in there is a population(s) that all life descended from.

Uh, yeah (above emphasis mine). As you move from individual to population to populations, at what point does it stop being LCA - stop being an idea with explanatory power - and become a statement that all life is descended from prior life. Duh.

You asked about universal and common ancestor. What is known is that all of life that we know of shares the same genetic basis so it is reasonable to feel that they all came from, in some manner, a common ancestor be it individual, group, or groups. Actually, I think the LCA to be more statistical than anything else.

Very interesting. If LCA is just a statistical statement, that is something very different from how people seem to use LCA as a referant. It is something I could probably agree to.

I have no doubt all life stems from common processes. It's the part about a common ancestor that leaves me befuddled.

It is just too far back to tell much.

Yeah, my opinion too. But I'm also a layman.

 

[Loudmouth]

Sure, but what establishes the line of descent? Is it the paper trail of birth certificates or the observed traits that establishes them as descended from Englishmen? If it's the traits, then there must be some test that demonstrates Englishmen ... otherwise this becomes something like a "no true Scotsman" fallacy (which is oddly convoluted given that your example was about Englishmen).

A good example is tRNA's. Here is a picture of one.

The list of features:

Tertiary structure of tRNA. CCA tail in yellow, Acceptor stem in purple, Variable loop in orange, D arm in red, Anticodon arm in blue with Anticodon in black, T arm in green
Transfer RNA - Wikipedia, the free encyclopedia

All of those different parts of the tRNA can be different, and are different between tRNA's. There is no physical law that says an UAC anticodon at the bottom of a tRNA molecule (the black bit at the bottom) has to match up with a methionine amino acid at the top (the yellow bit at the top). None. We would expect separate origin events to produce different tRNA's, or even different genetic systems altogether. The only reasonable conclusion for seeing the same tRNA's in all life is that there was a single origin of life, and that all modern life inherited those tRNA's from their common ancestor.

For example, what if there were a hypothesis that a group of people descended from Englishmen because of their tea culture. Hmm. Well, China also has a tea culture, so why couldn't they be descended from the Chinese rather than the English? Now we have to separate English tea culture from Chinese tea culture, which becomes very difficult (I actually did a paper on this for a history class).

If you found that both Americans and Englishmen spoke nearly the same language, which would be the most reasonable conclusion?

1. Americans and Englishmen share a common ancestry and a common ancestral language.

2. American and English cultures and their ancestors had never met, and they just both happened to stumble onto the same language and pronunciation by accident.

One argument for a common ancestor might be the possibilities for other alphabets (or other amino acids, etc.).

That would be an argument for separate origin events.

It would first need to be demonstrated that these other alphabets or amino acids would actually form naturally and produce sustainable life.

Do we have to demonstrate that bacteria came about through abiogenesis before we can conclude that they produce naturally occuring infections?

Or, it would need to be shown that other branches of life based on our 4-letter alphabet and 20-some amino acids have developed and then died out without contributing anything to the pool that continues on.

I don't understand this requirement.

Uh, yeah (above emphasis mine). As you move from individual to population to populations, at what point does it stop being LCA - stop being an idea with explanatory power - and become a statement that all life is descended from prior life. Duh.

It stops being common ancestry when different types of life no longer have common features.

I have no doubt all life stems from common processes. It's the part about a common ancestor that leaves me befuddled.

What is befuddling about it? Do you and your siblings look similar because of common ancestry or common processes?

 

[dysert]

I'm getting a bit confused, and I haven't even asked my next question yet. Some say the ancestor was probably a single celled organism, some say it was probably a population of single celled organisms. Obviously, we don't know for sure. At first glance, though, it seems that for evolutionists to say we have a common ancestor is a bit disingenuous if we really came from a common population. That would likely produce multiple "trees of life", wouldn't it?

Anyway, regardless of those details, my next question is, what was the ancestor of the common ancestor (or common population)? Does anything honestly think that these living organisms were alive in the pre-Big-Bang singularity?

 

[Resha Caner]

The only reasonable conclusion for seeing the same tRNA's in all life is that there was a single origin of life, and that all modern life inherited those tRNA's from their common ancestor.

Are you saying this is the only tRNA structure or is there more than one?

That we can speculate about other structures proves nothing. We would need evidence that evolution has experimented with these other structures and rejected them. Otherwise, it would seem very likely there is some law that prevents using other structures. That was my point in all those examples.

If abiogenesis produced many of these different possibilities, and then they died out for some reason unrelated to those different structures, I would consider LCA well-founded. So, proof that life once existed with a different structure would be strong evidence for LCA. Otherwise, it seems a strong possibility that any and all abiogenesis events produce the same structure and that they eventually all mixed together into one pool.

If you found that both Americans and Englishmen spoke nearly the same language, which would be the most reasonable conclusion?

No, no. At this level your example is analogous to asking if Poodles and Beagles have the same origin. To make it analogous to all life having the same origin you must determine if all human speech is composed of the same elements. IOW, is it possible that an English baby is born incapable of speaking the sounds that make up the Chinese language? If an English baby can learn perfect Chinese should we conclude that all languages share a common source? Oooh. Did we just prove the Tower of Babel?

It stops being common ancestry when different types of life no longer have common features.

We can't pick common features where it's hard to distinguish them and say that's proof of common ancestry (hair on mammals), and then pick common features where it's easy to distinguish them and say that's proof of separate ancestry (wings in birds and bats). Rather, you would need to show that those common features claimed for common descent couldn't have had separate origins.

What is befuddling about it? Do you and your siblings look similar because of common ancestry or common processes?

The converse of a true proposition is not necessarily true. So, yes, things with similar origins look similar, but looking similar doesn't prove similar origins. I've had the freaky experience of meeting someone who looked very much like me, but who was not related AFAIK. Isn't that the whole allure of body doubles for celebrities - the weirdness of someone who looks so similar but isn't related?

 

[Resha Caner]

At first glance, though, it seems that for evolutionists to say we have a common ancestor is a bit disingenuous if we really came from a common population.

It does appear that way. I don't think there is any real intent to deceive, but I do think biology is in a very difficult pickle. As I would understand it, the original term did mean a specific organism (or at least a specific set of DNA). However, as time went on biologists realized that wasn't the case and the idea developed. So, there is a level of common understanding amongst biologists as to what LCA is that doesn't really match with the literal interpretation of the term.

However, I think there is a fear of conceding that to layman because some polemicists would grab it and run with a headline that biologists are admitting evolution is false - which is not what they would be admitting.

 

[Loudmouth]

At first glance, though, it seems that for evolutionists to say we have a common ancestor is a bit disingenuous if we really came from a common population.

That is what common ancestor has always meant. When we say that humans and chimps share a common ancestor we mean that we share a common ancestral population, not a single individual.

That would likely produce multiple "trees of life", wouldn't it?

Most biologists refer to it as the root ball of the tree of life.

what was the ancestor of the common ancestor (or common population)?

It was a population of single celled organisms with the characteristics that all life shares, at a minimum. They may have also had features that were later selected against and did not make it into more distant populations.

Does anything honestly think that these living organisms were alive in the pre-Big-Bang singularity?

Of course not. Why would we think that?

 

[Vaccine]

All life (on earth) has decended genetically from the very first life form, which was probably a prokaryote, such as Cyanobacteria and bacteria.

That is a statement of faith, not fact. Fine if people want to believe it but it is just a hypothesis.

 

[Loudmouth]

It does appear that way. I don't think there is any real intent to deceive, but I do think biology is in a very difficult pickle. As I would understand it, the original term did mean a specific organism (or at least a specific set of DNA).

It never meant that. At it's most exclusive, it meant a single species with many individuals. At it's most inclusive, it refers to many species that participated in horizontal genetic transfer.

However, I think there is a fear of conceding that to layman because some polemicists would grab it and run with a headline that biologists are admitting evolution is false - which is not what they would be admitting.

I have always been upfront with it.

 

[Loudmouth]

That is a statement of faith, not fact.

It is a theory backed by mountains of evidence. That is not faith.

Fine if people want to believe it but it is just a hypothesis.

Which is it? A supported hypothesis or faith?

 

[bhsmte]

That is a statement of faith, not fact. Fine if people want to believe it but it is just a hypothesis.

Oh, I think there may be a tad bit of evidence to support this that may have eluded you, or maybe, you just choose to ignore it.

 

[Resha Caner]

It never meant that. At it's most exclusive, it meant a single species with many individuals. At it's most inclusive, it refers to many species that participated in horizontal genetic transfer.

I originally used the term "species" rather than "set of DNA", but edited it out because species has also become a somewhat muddy term. Anyway, I'm not going to disagree with you on what LCA might have originally meant. My point was only that the term seems to take on a broader and broader context over time.

That's not something unusual to biology. It happens in all the sciences. And it's not something creationists can crow about - another point I tried to make. It just means one needs to spend some additional time trying to grasp how current scientists use their terms.

 

[Vaccine]

If I'm not mistaken the ToE says that all life ultimately came from one common ancestor. Going back in time, what do you think was that common ancestor? Thanks.

The ToE simply stated is species adapt or change to their environment over time. Which few object to, I certainly don't.
It's when people extrapolate changes within a species proves the complete transformation from one species into another is where the objections are.


UCA - universal common ancestor is a hypothetical life form which all life evolved.
LCA - last common ancestor. The Extrapolated intersection between two species in the past, or the point where they diverged. Depending on the history, This may be a known or unknown species.

Anyway, that's what I was taught. I was an atheist until I was 26 and believed all that, now I know it's all inferred not known. Read what Koonin said.

 

[Loudmouth]

My point was only that the term seems to take on a broader and broader context over time.

Our understanding of HGT and its possible impact on LUCA grew over time which is why the theory changed over time. Also, the original hypotheses were made before we had fully sequenced a single genome.

It just means one needs to spend some additional time trying to grasp how current scientists use their terms.

Very true. The same could probably be said for jargon in any field or profession. The word "bridge" can mean two very different things to a civil engineer and a dentist.

 

[Loudmouth]

It's when people extrapolate changes within a species proves the complete transformation from one species into another is where the objections are.

Since we have the endpoints of that process, it is actually interpolation, and not extrapolation. Also, we can compare genomes of different species to determine if the differences are consistent with the processes that cause change from generation to generation within species. This is called hypothesis testing, and it is a central part of the scientific method.

 

[DogmaHunter]

These are all very interesting statements. I'm curious if this is just intuition or if some research has been done on these points. While the common ancestor concepts are straight-forward enough, whenever I delve into the details I always leave wondering exactly what biologists can say on the matter.

The first thing to remember is that abiogenesis is a hypothesis. Nevertheless, evolution theory does make a predictions about "first life". It makes no claims or predictions about the processes of origins though.

What it predicts is that it was something very simple. Since it's evolution that makes things more complex. We also know that at some point, multi-cellular life did not exist. So the progression from "simple" to "complex" is quite obvious.

From this, logically follows that the closer we get to "first life", the simpler it will become.

Now, when we talk about the process that gave rise to life, we assume it was a natural process. Why? Well, because we only have evidence of natural processes taking place. We have no evidence of unnatural processes or agents anywhere. In fact, 100% of the claims of supernatural causation that have been investigated, turned out to have natural causations 100% of the time.

So it's a reasonable assumption.

(borrowing some Neil deGrass Tyson here... - I just like the formulation)
Next, we can look at the elements that life is made of.
Hydrogen, Oxygen, Carbon, Nitrogen and "other stuff"
The most common elements in the universe:
Hydrogen, Oxygen, Carbon, Nitrogen and "other stuff"

The relative composition of our bodies matches the make-up of the universe.
Hydrogen: most common element in the universe.
Hydrogen: most common element in our body.
etc

So we're not even made of exotic things. Creationists might have a case if we would have been build from some extremely rare isotope, or even one that doesn't actually exist naturally. But we aren't. Instead, we are made of the most common materials available.

Carbon, furthermore, is the most interesting element in the universe. You can make more molecules with carbon then you can make with all other elements combined. So, idd, it's not a surprise that life is carbon based. It's exactly what we would expect if life is "just" an extreme manifestation of complex chemistry.

People talk sometimes about the possibility life based on elements other then carbon.... It's surely interesting, but I think it's not necessary to engage in that exercise. Carbon is a common element in the universe and if we would encounter alien life, I'ld bet on it being carbon based for sure.

So we have good reason to assume that first "life" came about through some chemical process. The big question is how that process looks like. And that's what Abiogenesis investigates.

So to get to my main point (lol, sorry)...
I don't see why a chemical reaction would produce just one self-replicating molecule. I'ld expect it to create a whole bunch of it.

 

[Vaccine]

Oh, I think there may be a tad bit of evidence to support this that may have eluded you, or maybe, you just choose to ignore it.

If you equate evidence with assumptions, then yes, there's plenty of that.