Slimebeast said:
hsrob said:
I would like to address some flawed assumptions regarding Slimebeast's problem of why we don't have multicellular prokaryotic organisms. (Skip to the end if you don't want to read the wall of text.)
Firstly there seems to be an assumption that somehow multicellular organisms are the pinnacle of evolution and therefore prokaryotic organisms in time should, due to selective pressure evolve into this 'higher' multicellular form. The design of evolution, if we can state it this way, is survival, not specialisation, complexity or diversity per se. The fact that bacteria accounts for more of the earth's biomass than all eukaryotes suggest that perhaps their form, i.e. unicellular is in fact the superior life form in the eyes of evolution.
Secondly we are ignoring a very simple fact regarding prokaryotic cell respiration. Regardless of the huge scope of the bacterial genome it is still bound by the laws of physics. Prokaryotic cell respiration occurs in the cytoplasm and across the plasma membrane, thus it is constrained by the cells surface area to volume ratio. If cells group together, as is the case with some forms of prokaryotes which demonstrate some degree of specialisation, you are still constrained by how efficiently the external cells can respire across a limited cell surface area. Now perhaps bacteria can evolve to increase the concentration of respiratory chain proteins expressed on the cell surface but ultimately that still has it's limits. Perhaps a folded cell membrane could evolve but maybe that makes the bacteria more susceptible to other environmental pressures. If there is indeed a constraint on prokaryotic multicellularity due to simple physical principles then that in turn would account for lack of variation within prokaryotes as there is limited number of changes that could occur within such a simple individual cell that are compatible with survival. Multicellularity allows a greater degree of diversity as cells can specialise and change to a much larger degree without necessarily adversely affecting survival of the organism.
So you question evolution based on the assumption of inevitable multicellularity, which you assume imparts survival benefit, while ignoring the fundamental constraints placed on prokaryotes by their method of respiration. This is not a strong basis on which to question a theory which has held up remarkably well over 150 years.
|
Your first objection is an extremely flawed objection. You think i havent thought about this basic thing? Of course bacteria can be regarded as superior to eukaryotes or the pinnacle of evolution. I agree. But that doesnt stop some of them to evolve into multicellular organisms at all. Because you know, it only needs one line of bacteria to evolve into multicellular (u dont think should be advantegous under no circumstances?) - the rest of the gazillions of bacteria can still remain single cellular and remain just as prosperous as they are!
To open your mind:
Just think "Spore" (the game). When people play it, or describe it, they tend to think (even scientists) that 'life' is destined to take all these ways eventually, including becoming multicellular (IMO that's a pretty basic thing), getting all these traits and organs and eventually evolve eyes and all these other traits that can be seen as 'inventions' by evolution, intelligence etc.
Second:
Wouldnt the eukaryotic line of cells have had this same problem of respiration limitations visavi the laws of physics? But yet they overcame it 500 million years ago.
|
Thinking about something and having it occur to you are different things. As about 20 posters have already said SOME bacteria did evolve into multicellular organisms and that worked for them, yet other prokaryotes adaptive changes were different. You then tell me to open my mind by thinking about Spore and saying that it's a pretty basic thing that life forms will inevitably become multi-cellular. I mean, are you serious, this is your arguement? I would invite you to again read my previous post, open YOUR mind and then tell me why multicellularity is better and/or inevitable or even a likely evolutionary step based on evidence, not your opinion. Your assumption that multicellularity is inevitable underpins your entire objection to evolutionary theory so you can't just dismiss it with "in my opinion it's a pretty basic thing".
Another factor which you are totally failing to give appropriate weight to, despite the fact that it has been repeatedly stated, is that mutations are RANDOM and not all mutations are equally likely to occur. You say, why don't more bacteria overcome the annoying contraints imposed by unicellularity and respiring across the cell membrane rather in the cytoplasm, it's happened before. Yes it's happened before, once, ever, successfully in the entire history of the Earth. DNA studies have shown there is a single precursor mitochondria/symbiotic bacteria for all eukaryotes alive today. So we know that this particular evolutionary step, unlike the developement of wings for example, is very unlikely, or at least the successful completion of this symbiosis is unlikely.
In the end we are back at the starting point, your assumption that bacteria would 'need' to evolve passed their single-celled state, that it's inevitable. There is no 'need', the environment exerts pressure and the organisms that mutate or have appropriate capabilities survive. The nature of the mutation, minor or profound, doesn't matter, survival is the only thing that matters.
This will be my last post on this as having any kind of reasonable debate across a 9? hour time difference is fairly pointless.
