The Evolution of Outer Space Aliens

[Geronimo]

Originally posted by Q Cubed


Precisely. Here we are, talking about the difference between prokaryotes and eukaryotes, or between insects and mammals and sizes, seemingly without considering that different evolutionary pressures on a different planet may have made things develop in an utterly alien fashion.

See how I worked "alien" in there? There's a reason for that.

You're absolutely correct!

I go off on these tangents that assume a world of prokaryotes and eukaryotes not because I believe these classifications would likely be meaningful on other worlds but because I am addressing specific objections from people who assume that all life has to use variations on what is found here on earth! I mean to show specifically in this case that even if we confine ourselves to earth-based biological building blocks there is nothing precluding brains much smaller than the human brain having as much intelligence than the human brain.

Earlier I did try to explain that physics allows for functional equivalents of brains much smaller than the human brain. I only went further to try to demonstrate that even familiar biology could be adapted to achieve the same end.

[DaShi]

Originally posted by Geronimo


Bold claims.

What? Are you reading what you write? My whole point is that your claims are too bold.

E-coli already comfortably fits a genome of about 4×10^6 bp whereas the entire human genome is about 3×10^9 bp

About 98% of human the human genome is non-coding or effectively non-coding DNA (introns and transposons and possible chromosomal structural elements) so lets call it 6 x 10^7 bp for the entire human genome.

Only a fraction of the genome is expressed in any given somatic cell. If you want to insist that the prokaryotic sized "neurons" use the same proteins as human neurons and also contain all of the coding genome expressed in human neurons while containing no more DNA than E-coli this could be achieved by a 'gene winnowing' process similar to that used in gene rearrangement in human b-cell precursors. Instead of retaining all coding DNA in all cells it would be retained only in (possibly much larger) germ line cells and snipped out at various stages of differentiation as the cells commit to fates where those genes will not be expressed. The resulting cells would contain all of the genes expressed in a human neuron while having roughly the same DNA content as an E coli.

Entire organelles are not necessary to modify any proteins. Instead particular chaperone proteins or similarly sized binding sites on other macromolecules participate in modifying the proteins.

This has all been generously assuming that you can only have the functional equivalent of a human neuron if it contains functional equivalents for all of the proteins present in a human neuron AND assuming that you require as much genomic material as human neurons use to accomplish this AND assuming that prokaryotic sized cells can't accomodate a longer genome than e coli can.

I don't see why we should hold such assumptions when speculating about alien life forms.

I've just been assuming that the cells have the basic functions of a neuron. That they can carry an electrochemical pulse and send and receive chemical signals. Just the pulse is difficult for bacteria based on size. How far can you stretch those little guys? Then there are the problems of creating the membrane proteins (cell walls?, vacuole formation?, 2 membranes?). Energy is another issue. Something's got to run those pumps to restore the action potential. There's no way that something as small as a bacteria could fill those roles.

Making assumptions and speculation about how alien intelligence could form is fun and all, but there's also realistic concerns to take into account.

You could say that something as small as bacteria could form an intelligent network, but you'd have to redesign the entire process. But if you're not even going to use realistic models, you could say that aliens are made of cheese. Gorganzola can form the central intelligence network. Parmesan the respiratory system. Feta can serve as the circulatory system. And Brie is just there for aeshtetics.

[Geronimo]

Originally posted by Kuciwalker


As far as makes sense

In the case of bacteria, there are so many of them and they've had so much time to evolve such traits that it is unthinkable that they didn't if they could. Thus they can't.

Just like there cannot be $20 on the street, because if there were, someone would have picked it up



The grounds for that argument are weaker than the grounds for mine.

First let's remember that multicellular prokaryotic life with specialized cells has been observed on earth. So we can dismiss any notion that prokaryotes are just too small and simple to specialize as part of a multicellular organism.

Furthermore, check out this paper that discusses the evolution of multicellular prokaryotes:

However, the evolution of multicellularity in bacteria is possible, since multicellularity has independently arisen among bacteria several times in actinomycetes, cyanobacteria and myxobacteria (Bonner, 2001Down). Moreover, experimental microbial evolution demonstrates that cooperative behaviour can readily evolve in bacteria (Rainey & Rainey, 2003Down; Velicer & Yu, 2003Down). The work of Pfeiffer et al. argues that the combination of multicellular organization and economical use of resources (e.g. respiration) could represent a major fitness advantage that does not require cell differentiation and thus benefits the simplest multicellular organism derived from respiring cells as soon as it arises. Why, then, have biofilm bacteria not evolved into multicellular organisms?

One possible reason that could impair the evolution of multicellularity in bacteria is that multicellularity may create a ‘feeding problem’. The solution of the feeding problem typical for eukaryotes is ‘eating’: the ingestion and exclusive digestion of large food items. While the structure of eukaryotic cells with a cytoskeleton-driven phagocytosis mechanism may have facilitated the evolution of eating, the bacterial cell structure with a rigid mesh wall and lack of a phagocytosis mechanism could have constrained evolution, not allowing the feeding problem to be solved efficiently. The best solution possible for bacteria is the ‘wolf-pack feeding’ of myxobacteria (Bonner, 2001Down); arguably, such external digestion by a cooperatively produced cocktail of exoenzymes is intrinsically less efficient due to the diffusive loss of enzymes and degradation products. (Note that such a feeding problem does not exist for phototrophic organisms, and cyanobacteria are indeed one of the three groups of multicellular prokaryotes.) Another reason is that the trade-off in heterotrophic resource use is most pronounced when comparing the yield of fermentation versus respiration. Thus, the benefit of cooperative resource use may have been sufficiently large only after oxygen levels reached a sufficient level, which could explain why the evolutionary transition to multicellularity in heterotrophic eukaryotes appears to have taken so long. Identifying the ecological and evolutionary factors that promote the evolution of multicellularity rather than complex microbial ecosystems such as biofilms remains a challenging problem for future research on competition in microbial communities.

Multicellularity appears to arise only long after eukaryotes had already established a hetertrophic niche based on 'eating' other organisms whole (phagocytosis) rather than absorbing the externally digested broken down components. During this unicellular era multicellurity would have been maladaptive for all of the hetertrophs, (mainly due to low oxygen levels).

When conditions later favor a multicellular approach the heterotrophic eukaryotes are already adapted to using the feeding approach that it will require to pay off.

A biological niche can be a bit like the $20 in your example. If you want it you either have to get there first or you have to wrestle it away from the lucky sob who got there first.

It is one thing to say an organism occupies a niche because it's history of adaptation favored it's exploitation of that niche when it first became available. It's quite another thing to claim that lack of occupation of that niche by a particular clade means it could never have adapted to fill the niche.

Suppose that oxygen enrichment of the atmosphere had occured much earlier in earths history. Perhaps the oxygen-sinks were far less extensive. In that instance conditions conducive to a multicellular organization could have arisen prior or concurrent to the specialization of a clade of phagocytizing heterotrophs. In that case it would be possible for multicellularity to be developed to facilitate the consuming of entire organisms rather than increasing the size of single celled organisms. In that case both niches would be empty at once and could be occupied together by a smaller organism that evolved into multicellular organism with small cells.

You insist that because we don't see multicellular organisms with tiny cells that we can assume such organisms are impossible. How do you exclude the possibility that instead these organisms are not seen simply because the opportunity for them to arise did not present itself?

[Geronimo]

Originally posted by DaShi


What? Are you reading what you write? My whole point is that your claims are too bold.

Perhaps we are simply misunderstanding each other?

My claim: There is nothing that rules out the alien evolution of a brain with functional equivalents to neurons that are much smaller than human neurons. We can't even rule out bacterial sized "neurons" in alien brains.

My understanding of your claim: Science has shown us that brains cannot have functional equivalents of the neuron substantially smaller than human neurons especially not bacterial sized "neurons".

You are making a claim much harder to defend. ie "bold" if that understanding is correct.

Originally posted by DaShi
I've just been assuming that the cells have the basic functions of a neuron. That they can carry an electrochemical pulse and send and receive chemical signals. Just the pulse is difficult for bacteria based on size. How far can you stretch those little guys?

Human neurons "stretch" meters. neurons in an ant sized alien will only need to "stretch" millimeters

Originally posted by DaShi
Then there are the problems of creating the membrane proteins (cell walls?, vacuole formation?, 2 membranes?). Energy is another issue. Something's got to run those pumps to restore the action potential. There's no way that something as small as a bacteria could fill those roles.

Those pumps are tiny Bacteria already use pumps of such size to create proton gradients to drive oxidative respiration. The smaller the bacteria the less surface over which such potentials are maintained and the less energy is required. Where's the problem?.

Originally posted by DaShi
Making assumptions and speculation about how alien intelligence could form is fun and all, but there's also realistic concerns to take into account.

You could say that something as small as bacteria could form an intelligent network, but you'd have to redesign the entire process. But if you're not even going to use realistic models, you could say that aliens are made of cheese. Gorganzola can form the central intelligence network. Parmesan the respiratory system. Feta can serve as the circulatory system. And Brie is just there for aeshtetics.

I guess you're trolling? saying that a functional equivalent of a neuron could be as small as a bacteria cannot somehow be equated to postulating organisms whose tissue differentiation is based on different varieties of cheese

[Kuciwalker]

Originally posted by Geronimo
First let's remember that multicellular prokaryotic life with specialized cells has been observed on earth. So we can dismiss any notion that prokaryotes are just too small and simple to specialize as part of a multicellular organism.

I'm familiar with examples of prokaryotic "multicellular" life. In every instance it is a primitive form of multicellular eukaryotes. The benefits of the more complex structures of eukaryotes are more complex abilities. They wouldn't pay the energy cost of this complexity if it wasn't necessarily to do the tasks they do effectively. It's too easy for prokaryotes to jump in.

[Kuciwalker]

Originally posted by Geronimo
You insist that because we don't see multicellular organisms with tiny cells that we can assume such organisms are impossible. How do you exclude the possibility that instead these organisms are not seen simply because the opportunity for them to arise did not present itself?

Because there is half a billion square kilometers of opportunity and it hasn't shown up except in primitive forms of multicellular eukaryotes.

[DaShi]

Originally posted by Geronimo
Human neurons "stretch" meters. neurons in an ant sized alien will only need to "stretch" millimeters

If you're stretching the cells, how thin can you get them to so that they can still carry the potential between the membranes? If you're not, then you lose speed when the pulse needs to travel from one cell to the next, which it will have to do more often with bacterial sized cells.

You're assuming that a creature so small could form an intelligence with such a small brain. However, not enough is known about brains to guess how large they need to be in order to support intelligence. If it's about the capacity of each cell's performance, then bacterial sized cells would be a poor choice. If it's soley about the interaction among cells, small cells may be able to perform the task by having more interactions.

I guess your trolling? saying that a functional equivalent of a neuron could be as small as a bacteria cannot somehow be equated to postulating organisms whose tissue differentiation is based on different varieties of cheese

What? Me troll? Never!