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Comment by Symmetry | Hacker News Reader

So, one the one hand all Earth life depends on proton gradients over membranes in some form or other for energy, as in the mitochondria powering us. But because prokaryotes and archea seem to share a common ancestor but use radically different cell membranes it looks like their common ancestor might not have generated its own membranes but used naturally occurring lipid membranes. And we'd probably want to call that common ancestor alive.

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One feature of living things is that, in a metaphysical sense, the whole precedes the parts (you might get away with calling them simultaneous in some simple cases, but it isn't the case with complex organisms). To call a collection of things incidentally arranged "living" is to either pass the buck and assign "life" status to the thing doing the "using", or to adopt a mechanistic view of reality that renders the notion of "life" meaningless.

True, but your parent comment isn’t there.

mechanistic view of reality that renders the notion of "life" meaningless.

Correct. All notions are tools constructed by and for human minds for their own purposes. It's possible to hypothesize a definition-breaking example for nearly everything that isn't a mathematical abstract. What counts is useful definitions. In the case of "life" we already have many examples of things that don't perfectly fit the definition, like viruses and prions.

Prokaryotes are archaea. The nature of the difference between their cell walls and other single cell organisms is not fully explored, and whether they formed from convergent evolution or not is still up for debate: https://en.m.wikipedia.org/wiki/Pseudopeptidoglycan

Archaea are prokaryotes, but not all prokaryotes are archaea.

Last I knew, they were considered two separate domains?

I don't doubt there is some relationship, but that isn't the definition of domain. Otherwise we'd have 1 domain.

Prokaryotes = Bacteria | Archaea

Again, there are three domains afaik: Prokaryotes, archaea, eukaryotes.

I'll cut this thread short and Google it for you:

> Archaea (/ɑːrˈkiːə/ (listen) ar-KEE-ə; SG: archaeon /ɑːrˈkiːən/ ar-KEE-ən) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes.

https://en.m.wikipedia.org/wiki/Archaea

There’s actually two ways of seeing this: the three-domain system and the two-domain system.

The three-domain system divides life in Archaea, Bacteria, and Eukarya. In this system, Archaea and Bacteria can be grouped together as prokaryotes.

In the two-domain system, the division is between Archaea and Bacteria. In this case, eukaryotes are seen as a subgroup of Archaea.

Hope to have cleared up some of the confusion.

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