How difficult is the transition to multi-cellular life?

[Avalancheon]

IMVHO, the abiogenesis of a protocell capable of reproducing and evolving is the Great Filter.

George Dvorsky has a good take on this over on his blog. His opinion is that the transition from prokaryote to eukaryote is so incredibly difficult that it could well be the great filter we've prophesised. If true, it would certainly remove a gigantic amount of potential biospheres from the race. I happen to agree that the filter has to make its appearance at an early stage. Otherwise, that would leave such a large number of intelligent species that some of them will get through based on sheer luck... Thus leaving the galaxy with multiple advanced civilisations, billions of years before humanity even appeared.

The question we have to ask is this: Could a filter that makes a late appearance have sufficient reliability to wipe out 99.9999% of all intelligent species? Unlikely. I can't say whether or not its impossible, since we're dealing with an unknown unknown. But based on the potential candidates we've speculated on (hostile superintelligence, nuclear war, resource depletion), late filters don't seem adequate.

[Avalancheon]

Re the Great Filter - why assume that there is only one?

It's been a while since I last checked, but IIRC there are easily a dozen or more ideas for why we don't see evidence of intelligent life all over the universe. The big issue with nearly all of them seems to be that it would have to work that way for all civilizations everywhere. But what if instead it's a case of all the various reasons all being in play at once?

You mean the non-exclusivity problem, right? If there are dozens of alien civilisations in the galaxy observing us from a safe distance, then it would take only one of them to break protocol and contact us. Thus invalidating the Fermi paradox.

Advanced life (beyond bacteria or simpler stuff) might be comparatively rare. Out of those, intelligent life might be comparatively rare. Out of those some number destroy themselves for one reason or another. Out of those that don't, some turn to pursuits that don't result in space travel. Out of those that do become spacefaring only some go to the stars. Out of those, only some decide to go in for activities that are visible across interstellar distances. Out of those, only some happen to be close enough to us in space and time to be engaged in anything we would recognize as a civilization or could detect. Out of those, only some have any interest in contacting non-spacefaring civs or in spreading far enough to get anywhere near us. And so on and so forth.

The upshot of all this is there could be millions of civilizations in the galaxy - but only a very tiny percentage occupy a range of types and activities and cultures that we could potentially detect or contact. And who knows how far away the nearest one could be from us?

Just some thoughts,

Todd

Thats right. Just because you have sapient aliens on some planet doesn't necessarily mean they will develop an advanced civilisation. And some of those that do may go on to destroy themselves. Those are things that George Dvorsky calls 'porous filters', which I think is a wonderful term.

However, I would disagree with you about spacefaring aliens not visiting the stars, and not being visible from interstellar distances. After all, a race of post-singularity beings wouldn't take long to colonise the milky way. If there are aliens in our galaxy that aren't visible to us, then that can only be because they are at a similar tech level. This is extremely unlikely to be the case.

If two sapient races happen to evolve in the galaxy, then theres going to be a time space between them. Tens of thousands of years, at the absolute minimum. And more likely to be millions of years.

[Avalancheon]

I've done some more reading on this topic, and it really does appear that the emergence of eukaryotic life was a unique event. I think its safe to say that such a transition is unlikely to be repeated in most biospheres. Heres a quote from William F Browns book. Perspectives: The Evolution of the Cosmos, Life, Humans, Culture and Religion.

"The evidence that the beginning of eukaryotic cells was a singular event with a common ancestor is twofold. First, eukaryotes share many strutural similarities not found in bacteria or archaea. Second, among the five major families derived from the common ancestral group of eukaryotic cells, their common heritage is spelled out in the many similarities in their genomes, especially for those genes that encode key eukarytic proteins.The big mystery surrounding the emergence of eukaryotes is why it took so long for a common eukaryotic ancestor to emerge. "

"After all, for close to two billion years the earth was populated by bacteria and archaea, and at no time during that long period or since then has either domain shown any evidence of evolving intermediate steps towards eukaryotes, such as the development of an enclosed nucleus or any of the membranous cytoplasmic inclusions so characteristic of all eukaryotic cells. Nick Lane suggests one reasons may be that bacteria and archaea possess some fundamental constraint which somehow blocked the development of further complexity - except once, when one, and only one common ancestral eukaryote possibly emerged in four billion years of life on earth."

[stevebowers]

As a rough guide for OA purposes, we might say that around one star in every four hundred has a life-bearing planet and about one life-bearing planet in every thousand has macroscopic life (including but not limited to 'eukarytoid' lifeforms) while the rest are microbial or protobiotic.

Of the planets with macroscopic life about one in fifty have developed a civilisation of some sort at some time in its history. There are about a billion stars in the Terragen Sphere, so that means about 50 unique instances of civilisation (not counting colonies). Currently we have about fifty extant and extinct xenosophonts in the setting, so we probably don't want to introduce any more.

I think we might already have a rough estimate of this kind somewhere on the site, and the details might be somewhat different to the ones given above- does anyone know if this is the case? If so we might need to adjust the estimate slightly- over time we have gradually added more xenos to the list, mostly extinct ones, and this means we need to change the estimates as well.

[Drashner1]

I have a vague memory of an EG article somewhere saying there are something like 256 garden worlds in the Terragen Bubble - but not sure if that article or statement still exists in the EG. Also not sure how that would or would not fit into the above guideline.

On a related note, we have never really said much about the number or frequency of non-terrestrial ecologies in the setting (e.g., gas giant ecosystems, Muuhome type ecosystems, T'oul'h type ecosystems, chlorine based ecosystems etc. We have mentions of specific worlds of these types (usually the homeworld of a xenosophont race) but don't provide any numbers on how common they are or whether or not they are included in the total number of garden worlds in the setting. We currently imply that the 'garden world' term applies only to Earth-like biospheres, which seems rather parochial really and might do with an update.

Todd

[Evil DoDo]

I have a vague memory of an EG article somewhere saying there are something like 256 garden worlds in the Terragen Bubble - but not sure if that article or statement still exists in the EG. Also not sure how that would or would not fit into the above guideline.

On a related note, we have never really said much about the number or frequency of non-terrestrial ecologies in the setting (e.g., gas giant ecosystems, Muuhome type ecosystems, T'oul'h type ecosystems, chlorine based ecosystems etc. We have mentions of specific worlds of these types (usually the homeworld of a xenosophont race) but don't provide any numbers on how common they are or whether or not they are included in the total number of garden worlds in the setting. We currently imply that the 'garden world' term applies only to Earth-like biospheres, which seems rather parochial really and might do with an update.

Todd

Eh, isn't Tohul Prime called "tohulian type garden world"? Sorry if I am wrong

[iancampbell]

I have a vague memory of an EG article somewhere saying there are something like 256 garden worlds in the Terragen Bubble - but not sure if that article or statement still exists in the EG. Also not sure how that would or would not fit into the above guideline.

On a related note, we have never really said much about the number or frequency of non-terrestrial ecologies in the setting (e.g., gas giant ecosystems, Muuhome type ecosystems, T'oul'h type ecosystems, chlorine based ecosystems etc. We have mentions of specific worlds of these types (usually the homeworld of a xenosophont race) but don't provide any numbers on how common they are or whether or not they are included in the total number of garden worlds in the setting. We currently imply that the 'garden world' term applies only to Earth-like biospheres, which seems rather parochial really and might do with an update.

Todd

Eh, isn't Tohul Prime called "tohulian type garden world"? Sorry if I am wrong

I think the parochiality is reasonably acceptable - given that the EG as "quoted" on our website is written for the use of Terragen bionts, who have a varying degree of common ancestry.

If one allows for different types of biology, then the term "garden world" needs to be qualified when using it. To take an extreme example, a garden world in the opinion of Hildemar's Knots would be instantly lethal to any bionts made of conventional matter.

[stevebowers]

I have a vague memory of an EG article somewhere saying there are something like 256 garden worlds in the Terragen Bubble - but not sure if that article or statement still exists in the EG. Also not sure how that would or would not fit into the above guideline.


Todd

256 garden worlds and 50 xenosophont species means that one in five garden worlds develops a civilisation, which seems a bit too high. However most of the xenosophonts we have described have not emerged on Earth-like worlds.

...we have never really said much about the number or frequency of non-terrestrial ecologies in the setting (e.g., gas giant ecosystems, Muuhome type ecosystems, T'oul'h type ecosystems, chlorine based ecosystems etc. We have mentions of specific worlds of these types (usually the homeworld of a xenosophont race) but don't provide any numbers on how common they are or whether or not they are included in the total number of garden worlds in the setting. We currently imply that the 'garden world' term applies only to Earth-like biospheres, which seems rather parochial really and might do with an update.

If we stick with the figure of 256 Earth-like garden worlds, but introduce my suggestion in post #14 that would mean ~2500 worlds with macroscopic life in total, that is to say 10 times as many (but only 1 in 10 are Earth-like). However the figure of 256 was established in the early years of the scenario, before we expanded the territory somewhat; it could easily be twice that now.

Eh, isn't Tohul Prime called "tohulian type garden world"?

Excellent point. We can classify the other worlds with macroscopic life by using their biosphere type as a descriptive marker (Tohulian, Halogenic, Jovian, Europan, Softoneian, Muuhian, Vitriolic, Neutronian and so on).

[JohnnyYesterday]

However, I would disagree with you about spacefaring aliens not visiting the stars, and not being visible from interstellar distances. After all, a race of post-singularity beings wouldn't take long to colonise the milky way. If there are aliens in our galaxy that aren't visible to us, then that can only be because they are at a similar tech level. This is extremely unlikely to be the case.

Or their tech is really advanced, and they're just not "showy" like in OA, building giant megastructures for the hell of it.

You're assuming that they'd colonize the galaxy. Maybe they don't want to? Maybe to them neutron stars are prime real estate, and the rest of the galaxy is like the Atacama Desert is to us? 

Another possibility, further "out there", but physically possible, is that they edit what we can sense. They could have come to Earth and other life-bearing worlds hundreds of millions of years ago and left self-replicating technology that infiltrates nervous systems and controls what the infected can see, hear, etc. If you were in a diminished-reality "Matrix", how could you ever know, unless they wanted you to?

[Drashner1]

256 garden worlds and 50 xenosophont species means that one in five garden worlds develops a civilisation, which seems a bit too high. However most of the xenosophonts we have described have not emerged on Earth-like worlds.

Couple of thoughts here:

a) This might be an argument for the idea that a 'garden world' is any planet with a complex, naturally evolved, biosphere - regardless of whether or not baseline humans would find it shirtsleeve habitable. Given the sheer environmental diversity that Y11k human descended beings enjoy, the definition of 'shirtsleeve habitable' being limited to humans like us feels a bit...odd.

b) Regarding the number of xenosophont races - are we counting only races currently extant or those that are currently extinct? Also, some of the currently extant xenosophonts are extremely old (the Muuh, the Soft Ones). If we are including extinct and/or ancient races in this count, would stellar drift and/or galactic rotation play a factor here? Basically, would it be inappropriate to include some of these races since they they originally evolved far from the Terragen Bubble and have only had their worlds or artifacts come into Terragen space relatively recently, cosmically speaking?

If we stick with the figure of 256 Earth-like garden worlds, but introduce my suggestion in post #14 that would mean ~2500 worlds with macroscopic life in total, that is to say 10 times as many (but only 1 in 10 are Earth-like).  However the figure of 256 was established in the early years of the scenario, before we expanded the territory somewhat; it could easily be twice that now.

True - although we could just as readily lower it if we found that to fit in better with our current take on things. Or we could could non-baseline human habitable, but possessed of a complex ecosystem worlds within that 256 number.

Not overly attached to the 256 number (not even totally sure I'm remembering that number accurately) but would like us to come to some sort of standard for the project in terms of both garden world numbers and what exactly is meant by that term.

Todd