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  • Not really living, according to primates with limited knowledge, and arbitrary definitions.

    • We invented the word "living", we get to chose what it refers to. We are necessarily right, because this is a truth we create, not a transcendent one. If we collectively decide to change the definition of "living" to include viruses, we will still be right but it won't mean we were wrong before.

      • Our opinions are not homogeneous and they change in time too.

        • True, I guess several definitions of life may coexist with different implications and all of them are right in the right context as long as they don't contain a self-contradiction. But in the context of this debate, I think most would agree that the best definition would be the one that has the biggest consensus amongst biologists, and maybe more precisely microbiologists. And most such definitions you'd find would include "self-replication" as a necessary trait.

          • I disagree. At one time, consensus was the Earth was the center of the universe, that the world was just a few thousand years old, that life just sprung into being sometimes, that unwashed hands were perfectly fine to perform surgery with, that some peoples were much closer to other animals than some other peoples, that the universe was static, that light was continuous, and that Ceres was a planet.

            Consensus is nice, but usefulness is the gold standard. Is holding metabolism and a complex proteome as the limit of life --excluding viruses, preons, and mechanical reproducers-- useful to expanding our understanding of life and how it functions? Is taking replicators as the most important distinction a necessary step to understanding the origin of life and how we can engineer it ourselves? Will the ability to manipulate certain chemicals and not others help us describe the world? Are edge cases explained better with a genomic, proteomic, or metabolomic base?

            I do know that we have a lot left to learn, and I would be very surprised if our current definition of life is fully sufficient for the next century of life sciences.

            • But words have no utility aside from being understood, a word is good as long as there is a consensus as to what it means, and you can always create other words for things it doesn't describe.

              Light acting like a wave in some regards and like a particle in others is something we can see experimentally, not just a matter of semantics. It's a conclusion that experience lead us towards. Calling light "continuous" wouldn't work because there is already meaning assigned to that word, and that meaning clashes with observations. Unless we changed the whole word and redefined the continuity of everything, which would be absurd.

              That "operating with unclean tools would be fine" clashes with the observation that it can lead to infections, coupled with the axiom that inflicting bodily harm to someone is bad. The axiom could still be changed, but the problem with observations is that they're imposed by reality, they would still be true even if we didn't believe they were. You could also change the word "fine" tho. If you make a language almost identical to English safe that the word "fine" means "an unreasonably dangerous practice" the sentence "Practicing surgery without disinfecting your tools is fine!" is true in that language.

              Ceres not being a planet depends only on our definition of planet. It was considered a planet for a while, but what led people to reconsider that isn't just that it was smaller than believed, but also that there were many similar objects in the asteroid belt. Referring to all these objects as "planets" could've been an acceptable truth, but since that would've meant most planets known at the time are small and in the asteroid belt (the Kuiper belt and Port cloud weren't known yet, but now it's just mean most planets are in a belt), and if the likes of Pallas and Juno were included (as was the case once) it also would've meant that most planets weren't round.

              Since the previously known planets would've been outliers in several ways, a new word should've been coined for them. It seemed more simple to let them be the only planets and coin the word "asteroid" for the rest (and much later the intermediate category "dwarf planet").

              If a different choice had been made, asteroids could be planets, what we now call planets could be called "big planets" and dwarf planets would be called "intermediate planets". This would be an acceptable truth, it wouldn't contradict itself or observations. If it was the consensus, it would be true, but it isn't so it's false, it's as simple as that.

              If in the future we find a different definition of life more useful, that definition will be true then. But that won't change what definition is true now. Ceres was a planet. Now it isn't. Something can change category either because it itself changed or because the category changed, like how substances can go from being legal to illegal or vice-versa.

              • Sure, I agree with most of that. Dwarf planets not being planets feels intentionally confusing though, and the definition is basically Major/Minor planet anyway. A planet having hydrostatic equilibrium is such an elegant and applicable limit, yet the current definition specifically counts only bodies that clear orbits (how is poorly defined) around this star. It's a bad definition in several ways, and many astronomers have already complained about this. Many use planet anyway, particularly planetary scientists.

                It's all about how useful the word is, and putting the limit at our star and a vague idea being the biggest thing in one general area feels more like it's gatekeeping the word "planet" rather than facilitating understanding or discriminating something useful. Planets can change class simply by drifting closer or farther away from the sun, or even be temporarily demoted by a rogue planet.

                most would agree that the best definition would be the one that has the biggest consensus amongst biologists, and maybe more precisely microbiologists.

                This is precisely the part I disagree with. Consensus isn't truth, and better definitions are likely possible. Not that consensus even exists here, the specific definition of life is controversial and several definitions are used in different areas. Homeostatic reproducers, replicators, entropy pumps, chemical system that evolve; it's almost as bad as double-slit interpretations.

                And most such definitions you'd find would include "self-replication" as a necessary trait.

                Replication? Sure. Self-replication? That's either an incredibly arbitrary limit seeminly designed to specifically exclude viruses, or isn't applicable to anything except perhaps the entire tree of life as a whole. Where is the line of "self" drawn? As a human, you can't replicate yourself, you need other organisms to collect energy for you and to make some proteins for you, and a sexual partner. Tapeworms need their hosts to digest food for them; cuckoos need other birds to feed and raise their chicks; E.coli needs other organisms to feed them and maintain a suitable environment; clonally transmissible dogs need another dog for all nutrients, and protection; and viruses need cells to provide the replication hardware. Some viruses even have some of the genes necessary for DNA copying and protein synthesis, and can be infected by smaller viruses themselves.

    • You joke, but it's still a valid way of doing it.

      If we are going be inquisitive in a systematic manner, we have to measure things in comparison, and to start doing that we had to start somewhere, in every single different field. Eventually we got to the speed of light as a constant, figured out the 1/137 fine structure constant, the helical configuration of DNA and RNA, etc., all starting from arbitrary suppositions, getting honed and adjusted by laboratory and thought experiments.

51 comments