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hmm binding this topic to aliens, how aliens density would be? 

  is it possible that evolution in similar oxygen excess having planets creates similar density? I mean I wonder whether if aliens have pruning mechanism like mammalians? trying to imagine how neurocircuitory of aliens is :) talking of of course this type of nervous system model of central nervous system model. would they also have a specialized organ for neural functions. most possibly they would have. most possibly it would be also similar. or if it were not an oxygen dominated environment, their molecular systems would most possibly even unsimilar though still they might have similar central nervous system. 

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hmm now checked also myelin structure to see its consisting of water and lipids. hmm why does it crawls around I mean molecular shape wise why its liking to roll over axons like that:

Myelin - Wikipedia

hmm evolutionary wise its structure that its lipids/molecular structure should have had evolved to be such structure either in evoljution drift in creating complex systems direction or just functionalist approach. hmm then but this means that if another neuron structure might have been present another myelin form might had formed surely.

wov evolution creating a rolling over axon structure is quite interesting :) i mean this rolling sheet behavior of myelin, hmm thinking its not that hard to create behavior if shields attract each shield but still a fibre of molecule growing and creating this structure is interesting. 

it most possibly would always roll like that but just started with mutation that created such OPCs. interesting.  there might happent lots many other moleculer structures which might not roll like that. so such a cell presence in brain to have created such structure, wondering where when myelin first appeared in phylogenetic tree? might give insight in how much time such complexity evolves. some insight to evolution of such moleculer mechanism that rolls like that. we could one by one then have inferences of such molecular complexities around all to have insight of how evolution usually happens to create  mammalian branch. I mean in other planets. to get to know in how much time this moleculer form gets created would be giving a nice insight to time span of evolution happening in other planets imho. e.g. our evolution roughly happent in 2 billion years. up to this point. if we dont use any evolutionary architecture coming from proterozoic periods early begininngs. (I mean bfore oxidation event in planet history).  hmm how does it happens to create this OPC cell. to understand such similar evolution units. I wish I had a chance to track down history of these OPC cells (myelin) before from mammalian point to see where it first happent and its relation to the first neural systems to have ideas how much it could take to generate myelin. 

but in billions years scale, aliens must have myelin also if their neurons are working in similar principles to us. though if its a different elements compoisition place/planet, they might not even needed myelin if theirs neurons were not like ours.  if its not for instance a planet with phytoplanktons having created an oxygen rich atmosphere, it might be other elements there or other molecular factories inside their cells moleculer constructs. e.g. in unsimilar gravity, maybe their molecular machineries might be totally unsimilar. though hjow much gravity effects molecular forces, considering the nonsignificant mass factor, though the quantum forces there in such unsimilar gravity settings their molecules might have created very unsimilar lipid/protein structures? I need to check molecular engineering topics to have remmeber gravity force's impact to moleculer dynamics but as far as i think it might be very unsignificant taking in to account the mass factor and other force systems of charges related and quantum forces there might be more effective then gravity. otherwise we would not stay stable in space. b ut still gravity might have chance of high chance of effecting how evolution turns out to create which common architectures in which organization/arrangement. but still its curiosity creating to get to know in molecular level proteins level how their basic protein factories would be if they had evolved in a higher gravity or lesser gravigty setting or with an atmosphere with lots of oxygen or not much. (in case they had not had excess phytoplanktons that created excess oxygen of world if they lacked phystoplanktons somehow due to any reason of such molecular mechanisms, then they might lack excess oxygen in their atmosphere and they might have anaerobic respiration mechanisms surely either. but still the amino acids and other basis of molecular factories I wonder how unsimilar could they have been in other planets if all things samew similar to planet earth, its very possible they would also have similar bipedal humanoids like us with 2 eyes  2 arms 2 legs etc )