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hello my name is teddy harriman i'm a

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first year grad student in the chemistry

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and biochemistry department at montana

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state university

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today i will be discussing the

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comparative complexity of cells in

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particular the complexity of microbes

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so that is the difference between

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prokaryotes archaea and bacteria versus

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eukaryotes but more specifically in this

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case protists the single celled version

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now i would argue that the goals of

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measuring complexity or comparing it

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between cells are at least two faceted

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the first component would be to

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constrain phylogenys

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at the moment there are three to four

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phylogenys that are cited the difference

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between these phylogenys are not just

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their results but the methodologies that

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they use for instance many use amino

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acid sequence comparisons some compare

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protein folds

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other compare information content so on

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and so forth the issue that they all

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seem to have is how to appropriately

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quote unquote root the tree

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which is to say which uh where do cells

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line up in terms of being in relation to

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a last universal cellular ancestor and

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how are they specifically related to

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each other evolutionarily

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on top of this there's an issue of

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adding viruses into the domains and

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figuring out where they fit

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within the tree of life the big issue

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here of course is viral genomes are so

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small that even if you're comparing

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amino acids or protein folds there's not

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a great way to compare them to the much

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larger genomes of cells

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now the second one which is especially

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important for origins of life is to

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constrain identity and properties of the

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progenites versus the last

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universal cellular ancestor

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which is to say can we say something

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about the simplicity and or complexity

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of luca and identify which biological

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features are quote unquote simple and or

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complex and therefore should be expected

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as the first form of life

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with this in mind i want to discuss some

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assumptions of biological complexity

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that are either implicitly or explicitly

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stated within the literature

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the first and foremost which is very key

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to origins of life in astrobiology is

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the idea that complexity increases over

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time which is to say we assume that the

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ancestral biosphere

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is less complex in a measurable way than

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the present biosphere and that ancestral

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organisms are also less complex than

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present day organisms

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with some numeric value of complexity

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assigned

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the second component is that life is

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complex so we assume traditionally that

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non-life is less complex than life and

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that this is a key identifier of what is

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as i alluded to it's important to have

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an exact mathematical definition for

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what you mean when you say complex

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in this case i'm going to be using what

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i call temporal information density or

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tid which is the amount of shannon

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information

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it takes to describe an object whether

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that's a biological object like a cell

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or other inanimate object divided by

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that object's overall mass

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times the amount of time you are

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actually looking at that object

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now the units for that would be number

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of bits per gram

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second

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for simplicity's sake bits you can think

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of how much

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uh space it would take to describe that

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object

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on a hard drive divided by its actual

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physical size

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so implicit in this

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derivation

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is the idea that size is just size and

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something can be big and simply big and

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not necessarily complex so for instance

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if i were comparing computers

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i would be first curious to know how

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much information it would take to

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describe that computer and then i would

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want to divide it by the computer's

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overall size which is to say the

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smallest computer that can

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produces the same functionality

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with the same amount of information to

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describe it

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now to understand the difference between

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prokaryote and protist complexity it is

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important to understand the history and

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the context of where claims come from i

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would argue the first

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statement of prokaryotes being simpler

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than protists began with edward chattan

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in 1925 when he first coined the terms

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prokaryote and eukaryote in those terms

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prokaryote

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is greek for essentially before the

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nucleus and protis means true nucleus

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and that he established one became

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before the other

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and also implicitly and to a certain

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degree explicitly implied that this was

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because prokaryotes were simpler which

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based on his microscopy made a lot of

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since that time

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a number of other measurements have been

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used to claim protus higher complexity

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among them are larger genomes slash more

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proteins

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the issue of course is known today that

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if we were to assume that this is the

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case you'll have many logical fallacies

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such as human beings would be less

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somewhat more recently information

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content has been used to claim

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complexity

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in at least two examples with sample

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sizes under

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two authors have claimed that total

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information content can be used to

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measure something's complexity however i

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will mention that even kunin in his

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paper along these lines mentioned that

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prokaryotes appeared admittedly better

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the third

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way that people claim complexity that

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i've at least found is that it's because

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eukaryotes have organelles whereas

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prokaryotes do not

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this today we know not to be true

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prokaryotes do in fact have organelles

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it seems the large difference between

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the types of organelles they have is

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that protein uh prokaryotes tend to have

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protein-based organization whereas

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eukaryotes depend heavily on their

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lipid-based organization

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and finally and

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is the idea that you can associate

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eukaryotic multi-cellularity to protist

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complexity in the sense that protists

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could have the potential to evolve into

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multicellular organisms whereas

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prokaryotes can only superficially do so

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this last point should be addressed

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further and can be addressed from a

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simple thought experiment which is could

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multicellularity evolve in the absence

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of prokaryotes the answer is no

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at least from an ecosystem in biospheric

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perspective multicellular eukaryotes are

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two component machines

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this has been addressed by the idea that

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if we were to eliminate all the

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prokaryotes on earth today

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biogeochemical cycles nitrogen fixation

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uh and

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many of the phages that we have that

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regulate our ecosystems would disappear

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and

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in particular with the loss of nitrogen

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fixation you could expect photosynthesis

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to die out within a year

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on top of this there's an even older

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idea which is the energy pyramid

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sometimes known as the trophic energy

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pyramid which is to say that

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multicellularity is regulated from the

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bottom up

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if we were to take prokaryotes out of

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the picture and be left entirely with

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protists as well addressed a bit more on

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the next slide there would not be enough

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energy for multicellularity to both

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now there are in fact some reasons to

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assume that the dogma of

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prokaryotes simplicity in comparison to

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protists might actually be incorrect

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first and foremost is that protist

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adaptability is not as good as

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prokaryotes ability to adapt

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how this could be measured is by the

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number of niches that protists occupy in

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comparison to prokaryotes

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what do i mean by niche i mean the

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number of environments they inhabit and

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also the metabolisms that they are

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actually capable of

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so for instance prokaryotes are abundant

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within deep sea hydrothermal vents

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whereas at least single-celled

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eukaryotes are unable to live in that

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such environments

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in addition while protists only have

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access to respiration and photosynthesis

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as far as we know prokaryotes have many

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other forms of metabolisms that allow

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them to access other environmental

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niches

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as a side comparison to this as well it

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is pretty uh well accepted that

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prokaryotes are more adaptable in the

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sense that we can also throw them into

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say the vacuum of space and they will be

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able to adapt at least to a certain

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extent

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the second point is that protis

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metabolic speed is less than prokaryotic

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metabolic speed

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and this is true for both respiration

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and photosynthesis by mass

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now if you are to accept that

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dissipation of energy as many do within

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the astrobiological community is

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fundamental to life

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then it would seem odd that the species

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that is slower at dissipating energy

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would be determined as being more

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complex

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in total with both of these we could

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almost assume that adaptability and

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dissipation of energy are not actually

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very much fundamental to biology and or

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they're not fundamental biological

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indicators of evolution

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last but not least that uh protist bio

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chemical tid is potentially lower than

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prokaryotic biochemical tid tid of

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course being the measurement of

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complexity i presented earlier

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i can gauge this by the lower proportion

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of lipids and lipid organization within

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prokaryotes

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lipids by even bochner were entirely

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left out of his mathematical formulation

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because they were considered to

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entropically

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in conclusion complexity deserves to not

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just be an abstraction but a numerical

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value that we can use to compare

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biological entities as well as

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non-biological entities

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and so doing so we might be able to have

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a better understanding of how life

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evolves and potentially what life

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evolved from

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as it stands there's a darth of

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literature in regards to biological

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complexity there's even less literature

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that actively compares living organisms

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at the moment there also appears to be

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some indicators of fundamental

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biological ideas that indicate that it

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is possible that prokaryotes are in fact

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just as complex if not more complex than

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protists

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i thank you for your time if you have

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any information regarding complexity

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context i might have missed and or would

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like to discuss prokaryotic complexity