Thread: Common Ancestor Questions

Couple of goofy questions on my mind. Hope this makes some sense or if you can figure out what I'm trying to ask....

If all life on Earth share a common ancestor(CA) and this includes everything, flora and fauna, then does it mean that the CA was a one of a kind happening? What I mean is, did the CA only occur once and survive to multiply or could many of them have come into being at the same time and be the only living things inhabiting an area of the planet before the evolutionary wheels started turning? Obviously at some point the CA started to evolve.

The other thing I wonder about is whether the split into plant and animal life occurred because one benefitted the other. IOW's did the animal side benefit the plants or vice versa? Was the split an evolutionary adaptation? If so then the CA adapted to what?

The last universal ancestor is commonly considered to be a species or population, rather than a single organism. At even earlier times, rampant horizonatal gene transfer was likely the order of the day; so back then, the idea of a common ancestor starts to become awkward. It does appear, however, that today all life shares a common ancestor that lived around 3.8 billion years ago.


The last common ancestor of plants and animals is estimated to have lived 1.6 billion years ago. Plants and animals, as we would recognise them today, are late comers on the scene - appearing around 400-550 million years ago. Prior to that, the ancestors of today's plants, fungi, and animals would have all been single-celled organisms. Single-celled organisms are still what evolution loves to this day.

Organisms living in the same area tend to have complex relationships with one another. It would likely have been no different in the remote past.

Originally Posted by Zwirko

The last universal ancestor is commonly considered to be a species or population, rather than a single organism.

Is it more likely that only one organism was spawned from the primordial soup and managed to replicate itself or did a number of similar organisms all arrive at the same time under the same conditions? How fast would a replicating mechanism evolve for a simple first organism? Not sure if the first organism could do this right away and maybe it took a whole colony of similar life forms that survived over time to evolve this trait. If it is the latter then did the first life forms live a long time or was their arrival an occurrence that continued on for years or at least until one evolved to reproduce?

Here's the thing: I see the first organism as being one of a multitude of similar organisms that all emerged from wherever at the same time. The process of the creation of life would be something that went on for several years, as long as conditions were right. During this time life did not replicate but depended on the process. I know one of the characteristics of a life form is to reproduce, so that being said, what then emerged from the creation pool was not a life form by definition but an organism that could only eat and shit for all I know. However I don't think a colony would all develop reproduction at the same time so one organism got the ball rolling and since it did not have a parent, then it would be the common ancestor to us all. That organism's ancestor would be a puddle of amino acids or something along that line.

From what I understand there are six kingdoms of life. Are animals, plants, one celled creatures (name escapes me at the moment), bacteria, archaea and fungi the only kingdoms that ever existed on Earth? The creatures within each group evolve to a variety of forms yet do the kingdoms themselves evolve? Does one kingdom evolve into another? Is it possible that the six life kingdoms all originated at the same time or do we know exactly how each one came about and in what order? I mean did they evolve from one another or are they naturally created when certain conditions exist?

there's 2 possibilities, one being that there was only one transition from non-life to life, or the other one being that it happened at least twice but one got the upperhand by being more efficient in converting raw materials into the next generation - in this case you could almost state that natural selection may already have been at work at this early stage (and maybe even at the pre-biotic stage)

Originally Posted by marnixR

there's 2 possibilities, one being that there was only one transition from non-life to life, or the other one being that it happened at least twice but one got the upperhand by being more efficient in converting raw materials into the next generation - in this case you could almost state that natural selection may already have been at work at this early stage (and maybe even at the pre-biotic stage)

Just want to get this next question out. Whether it has anything to do with the topic is debatable but I don't want to forget about it. Here goes.....

If life is created in a lab someday, do you think it will represent one of the known animal kingdoms or does the possibility exist that it could have its own category? To truly be a new life form (organism) will it be required to be part of a new life kingdom, or at least one we've never seen before?

for it to qualify as creating life that is totally different would require at least something that uses structural elements that differ substantially from the current DNA/RNA set-up - how different that had to be i'm not sure

still, the greater the difference from life as we know it, the harder it will be for those developing it to produce something that exhibits reproduction with modification and does so successfully over sizeable amounts of time

Originally Posted by marnixR

for it to qualify as creating life that is totally different would require at least something that uses structural elements that differ substantially from the current DNA/RNA set-up - how different that had to be i'm not sure

still, the greater the difference from life as we know it, the harder it will be for those developing it to produce something that exhibits reproduction with modification and does so successfully over sizeable amounts of time

Would new life even be recognizable if it is like nothing we've encountered. I wonder if some scientist somewhere has flushed one down the can.

there's 2 possibilities, one being that there was only one transition from non-life to life, or the other one being that it happened at least twice but one got the upperhand by being more efficient in converting raw materials into the next generation - in this case you could almost state that natural selection may already have been at work at this early stage (and maybe even at the pre-biotic stage)

You're saying that at the pre-biotic stage, natural selection almost had something to do with what material, method or process would be used to create new life? Wouldn't favorable conditions for specific chemicals be consider such? When you say twice do you mean two or more separate first organisms formed in the same time period. Is there any thought as to what the right conditions are for life? We can do many things in a lab but why is the recreation of the right conditions for life proving to be so hard to simulate? I mean they can practically create a mini black hole at the Hadron Collider but recreating conditions for life to form seems far off.

Originally Posted by zinjanthropos

You're saying that at the pre-biotic stage, natural selection almost had something to do with what material, method or process would be used to create new life? Wouldn't favorable conditions for specific chemicals be consider such? When you say twice do you mean two or more separate first organisms formed in the same time period.

no, what i'm saying is that organic chemistry being what it is, it would happen if the conditions were favourable for certain compounds to form
there could have been a multitude of possible building blocks, and not all of them would have been as effective or fast at building what ultimately would end up as life as we know it
my opinion is that natural selection happens when certain building blocks are better at building more copies of themselves than other building blocks, and thereby sequester the lion's share of resources for themselves
the less effective competing chemicals would have been starved of their raw material to make copies of themselves

presumably precursors to life on earth can't have been THAT different from one another in what materials they used, otherwise they each would have found a niche where competition was less sever and we would have ended up with life that has a clear signature of having a multiple origin - the fact that we don't means that the initial conditions were already sufficiently constrained that the pre-biotic materials were in competition with one another for the same materials

Originally Posted by zinjanthropos

From what I understand there are six kingdoms of life. Are animals, plants, one celled creatures (name escapes me at the moment), bacteria, archaea and fungi the only kingdoms that ever existed on Earth? The creatures within each group evolve to a variety of forms yet do the kingdoms themselves evolve? Does one kingdom evolve into another? Is it possible that the six life kingdoms all originated at the same time or do we know exactly how each one came about and in what order? I mean did they evolve from one another or are they naturally created when certain conditions exist?

Currently the in vogue method of classification is the so-called three-domain system or hypothesis, put forward by Carl Woese in the late seventies. This system, which is not without controversy and its detractors, divides live into three great grouping or domains: Archaea, Bacteria and Eukaryota. Archaea and Bacteria are bacteria-like organisms, while the Eukaryota comprise organisms with more complex cells.


Sub-classification of the Eukaryota is always in a state of flux and there are dozens of systems in use. The top-level grouping within this domain are often called Kingdoms, or sometimes called super-groups. How many there are is undecided, but six is perhaps the most common count. The six kingdom system includes: Excavata, Amoebozoa, Opisthokonta, Rhizaria, Chromalveolata and Archaeplastida. Humans, crabs, mushrooms and pretty much most of what you can see and think of as being a "critter" all belong to the Opisthokonta group. Archaeplastida contains land plants and green algae. All the others are single-celled "protists". Another six kingdom system has: Bacteria, Protozoa, Chromista, Plantae, Fungi and Animalia. There are also 4-kingdom, 8-kingdom and 5-kingdom systems. All very confusing - as soon as you learn one system it becomes obsolete next week. What I've said above is probably obsolete already as well.


These groups are all very ancient. Since the classification is a phylogenetic one, then all its members share common ancestry, so they didn't arise independently from one another. They didn't all appear at once either: Archaea and Bacteria are more ancient, for example - perhaps by as much as a billion years or even more. Eukaryotes seem to have diverged out of the Archaea group (although there are other hypotheses). Each group of Eukaryota wouldn't have arisen simultaneously, but rather as a series of divergences through time in the same way that languages evolve over time. The creation of a new group, like the "Klingonese" language, out of thin air is not something that is seen in the biological world. There is always an ancestral group. If life was created in the lab it would be interesting to see how it was classified, since I'm not sure it would make any sense to put it on the "tree of life".


In the image below you can see the major groupings and how they are related, which group diverged from where and which is older.

If there was a Like button I'd be hitting it for both you guys.

The very first life form, is there a possibility that it is not the common ancestor of all life on Earth? What I mean is, could it have died out and another form that appeared shortly after or during the same period when conditions were right been the CA? I'm thinking that in the initial stages of life grabbing a foothold on the planet that there may have been several new life forms that just couldn't cut it. Instead of those first organisms evolving could one of them have been lucky enough to be the best equipped to survive whatever nature or the environment at the time threw at them? More or less Nature performing trial and error but once established the CA took over?

Probably was a one off event. I suppose it is possible that there was a community of very different "lifes" at the very earliest stages - likely not cellular or bacterial life as we would recognise it though. The key point is that they have left no descendants, so I don't think it would ever be possible to determine such a thing because geological processes have destroyed all the evidence a thousand times over. Such an idea would always remain speculative and likely unanswerable. If it could be determined somehow that some "biology" got blasted off the earth by an impact event and made its way to Mars or something then perhaps that question could be answered. Currently, all life on this planet is known to share a common ancestor; nothing else made it through the great filters of time and chance.


Interestingly, there is a hypothesised "dark domain of life" (I've totally forgotten what the correct name for this is, so I'm calling it the "dark domain" for now). This life might be so different that we don't recognise it as being life as yet; it (if it exists) is imagined to be unrelated to the life we know, existing on its own evolutionary tree. It may be ancient or modern. A few folks are looking for such things (without success).


EDIT: the tern I was struggling to remember was "shadow biosphere".

Originally Posted by Zwirko

Interestingly, there is a hypothesised "dark domain of life" (I've totally forgotten what the correct name for this is, so I'm calling it the "dark domain" for now). This life might be so different that we don't recognise it as being life as yet; it (if it exists) is imagined to be unrelated to the life we know, existing on its own evolutionary tree. It may be ancient or modern. A few folks are looking for such things (without success).


EDIT: the tern I was struggling to remember was "shadow biosphere".

Checked it out quickly. One article mentioned something called desert varnish as a candidate. From Wiki : an article about desert varnish. No where does it mention it as a potential ancient life form but I like the idea.

One of the great "hopes" is to find some bizarre form of microbial life, perhaps even in our own backyards. Since most life is microbial - the vast majority of which is unsampled and unculturable - there is speculation (some might call it wishful thinking) that some of it may be unrelated to the life that we currently know, with a radically different biology and biochemistry. It's all speculation however, with no supporting evidence. Worth looking for and thinking about, perhaps.

The fossil record, as in this article, indicates that microbes existed as early as 1 billion years after Earth formed. Would that mean the CA predated that mark or could it be an imprint on the very ancient rock pictured in that story? The likelihood for life to form at the surface or above ground, is that the popular theory of modern day science? Or is it more likely the CA developed underground or deep in the ocean? I'm sure they work on it constantly but to know exactly what the conditions were at that point in time must be a daunting task. What do scientist believe are the right conditions? We hear so much of that term so I thought we should get a scientific perspective on it.

Originally Posted by Zwirko

The last common ancestor of plants and animals is estimated to have lived 1.6 billion years ago. Plants and animals, as we would recognise them today, are late comers on the scene - appearing around 400-550 million years ago. Prior to that, the ancestors of today's plants, fungi, and animals would have all been single-celled organisms. Single-celled organisms are still what evolution loves to this day.

I think you mean "most recent common ancestor." The earliest common ancestor was far, far before that.

Originally Posted by billvon

Originally Posted by Zwirko

The last common ancestor of plants and animals is estimated to have lived 1.6 billion years ago. Plants and animals, as we would recognise them today, are late comers on the scene - appearing around 400-550 million years ago. Prior to that, the ancestors of today's plants, fungi, and animals would have all been single-celled organisms. Single-celled organisms are still what evolution loves to this day.

I think you mean "most recent common ancestor." The earliest common ancestor was far, far before that.

Zwirko did say 3.8 billion years in post #2. However I was trying to determine if there was a chance something akin to life, a forerunner of sorts, or an actual living organism existed prior to the first life form revealed in the fossil record.

I wonder if, at first, the world's combined oceans was the "cytoplasm" (so to speak) of the one original organism. Why not? No other living entity would exist.

Originally Posted by billvon

I think you mean "most recent common ancestor." The earliest common ancestor was far, far before that.

I should probably reword that sentence to something like: the time of divergence between plants, animals and fungi is estimated to be around 1.6 billion years ago.

Originally Posted by Zwirko

I should probably reword that sentence to something like: the time of divergence between plants, animals and fungi is estimated to be around 1.6 billion years ago.

Agreed; the most recent common ancestor of plants and animals lived about 1.6 billion years ago.

Originally Posted by zinjanthropos

Zwirko did say 3.8 billion years in post #2. However I was trying to determine if there was a chance something akin to life, a forerunner of sorts, or an actual living organism existed prior to the first life form revealed in the fossil record.

just from the fact that probability tells us that it's more likely that the first fossilised are NOT those of the first life forms i'd have to answer your question in the positive - however, even the fossil record is unlikely to reveal how different at the molecular level the first life forms were from one another

Originally Posted by marnixR

Originally Posted by zinjanthropos

Zwirko did say 3.8 billion years in post #2. However I was trying to determine if there was a chance something akin to life, a forerunner of sorts, or an actual living organism existed prior to the first life form revealed in the fossil record.

just from the fact that probability tells us that it's more likely that the first fossilised are NOT those of the first life forms i'd have to answer your question in the positive - however, even the fossil record is unlikely to reveal how different at the molecular level the first life forms were from one another

The logic of those two times baffles me. If living organisms started 3.8 billion years ago, it would seem so unlikely there was only one species of it that hung around to 1.6 billion years ago to become the common ancestor! Wouldn't there be some sort of specialization right from the beginning?

Originally Posted by Robittybob1

The logic of those two times baffles me. If living organisms started 3.8 billion years ago, it would seem so unlikely there was only one species of it that hung around to 1.6 billion years ago to become the common ancestor! Wouldn't there be some sort of specialization right from the beginning?

I think you've confused two different things here. The first date (3.8 bya) is an estimate of the time of the last universal common ancestor (LUCA) - the most recent common ancestor of all life on Earth. The second date (1.6 bya) is an estimate of the time of the evolutionary split between what would eventually become modern plants and animals. In between those two dates (and since then) there were all sorts of other major evolutionary events and trends going on, with countless species present. If you look at the diagram I posted several posts above you can see that plants and animals are just two little twigs on that tree.

Originally Posted by Zwirko

Originally Posted by Robittybob1

The logic of those two times baffles me. If living organisms started 3.8 billion years ago, it would seem so unlikely there was only one species of it that hung around to 1.6 billion years ago to become the common ancestor! Wouldn't there be some sort of specialization right from the beginning?

I think you've confused two different things here. The first date (3.8 bya) is an estimate of the time of the last universal common ancestor (LUCA) - the most recent common ancestor of all life on Earth. The second date (1.6 bya) is an estimate of the time of the evolutionary split between what would eventually become modern plants and animals. In between those two dates (and since then) there were all sorts of other major evolutionary events and trends going on, with countless species present. If you look at the diagram I posted several posts above you can see that plants and animals are just two little twigs on that tree.

Thanks for that explanation. I'll have another look at it.

Originally Posted by Zwirko

Originally Posted by Robittybob1

The logic of those two times baffles me. If living organisms started 3.8 billion years ago, it would seem so unlikely there was only one species of it that hung around to 1.6 billion years ago to become the common ancestor! Wouldn't there be some sort of specialization right from the beginning?

I think you've confused two different things here. The first date (3.8 bya) is an estimate of the time of the last universal common ancestor (LUCA) - the most recent common ancestor of all life on Earth. The second date (1.6 bya) is an estimate of the time of the evolutionary split between what would eventually become modern plants and animals. In between those two dates (and since then) there were all sorts of other major evolutionary events and trends going on, with countless species present. If you look at the diagram I posted several posts above you can see that plants and animals are just two little twigs on that tree.

So do you mean all life today shares the LUCA? Before that is anybody's guess? If there was only one life formed prior to the LUCA then that would be the ancestor to all life that ever lived? If however there were multiple organisms formed in the time period prior to the LUCA then there is no way of telling? There are evolutionary dead ends, zinjanthropos itself is said to be one, so is it possible that multiple first organisms may have evolved so? If so then isn't it quite possible that not all life that ever lived on Earth shared a common ancestor, some may have shared other CA's but their branch on the evolutionary tree snapped off at some point?

the problem with LUCA is that is based out of necessity on the genetic code (fossils either not being available or not being very informative), and it can't tell you anything about anything that happened outside the confines of the limits set by the LUCA or prior to LUCA

so until we find a living organism that clearly does not fit in the current genetic framework, the LUCA information only tells us what we already know, which is that all life has one origin

it does not mean that that there was only one origin, but that all surviving lineages come from one ancestor

Originally Posted by marnixR

the problem with LUCA is that is based out of necessity on the genetic code (fossils either not being available or not being very informative), and it can't tell you anything about anything that happened outside the confines of the limits set by the LUCA or prior to LUCA

so until we find a living organism that clearly does not fit in the current genetic framework, the LUCA information only tells us what we already know, which is that all life has one origin

it does not mean that that there was only one origin, but that all surviving lineages come from one ancestor

That's what I was getting at, thanks for straightening that out. I don't know where I read the line, it might have been one of Dawkins' books, but I had to think when it said there was one common ancestor for everything that ever lived. Just one individual life form as CA, but what if there was more than one first organism(s), then any one of them could have been the ancestor of things we don't even know existed that have long since died out. MAybe the author got a little ahead of himself, I was just wondering if they knew something no one else did.