Although I realize most of our classification schemes for most everthing are artificial constructs of our minds with gaps, overlaps and exceptions (from numbers to subatomic particles to taxonomy to music types), I wonder if there are true natural categories out there that all civilizations would agree to.
First example that comes to mind are atoms. No matter what type, they all share the same basic characteristics and number of protons as a classification system makes infinitely more sense than any other. Even so, H+ breaks the model a little bit in that it is [indistinguishable from] a single proton, a subatomic particle (don’t flame my ignorance of basic atomic physics, please).
Stars also come to mind. Space objects are either big balls that sustain fusion or they are not. Are there exceptions or special cases?
Beyond those two, I am drawing a blank. States of the matter, life, forces, etc, they all are very iffy as universal classifications.
So, are there any natural categories or is it all constructs of our need to put things in little boxes? If there are, is there a name for them?
(I am posting here instead of on GQ as I can reasonably expect irreconciliable opinions appearing)
Protons aren’t fundamental particles like electrons. Protons are composed of 3 quarks. And stars are not so clearly defined. There isn’t much difference between a gas giant like Jupiter, and dwarf star. We arbitrarily set the definition.
I think the only real “natural classification” scheme would be fundamental particles, and we never really know when we’ve gotten to the bottom of that well. But the periodic table is pretty darn close, too. We can include isotopes as categories, and in that case H+ isn’t unique in any meaningful way.
I would say that taxonomy does more or less represent natural categories, it’s just that there are cases where the edges are a little fuzzy. Gaps, overlaps and exceptions don’t stop the natural categories existing - they just make them harder to describe (impossible to describe in absolute, discrete terms). For example, the categories of phylum, class, perhaps even genus are pretty much set solid, because they represent divergence events that happened a long time ago.
There is a lot of fuzziness, especially if we consider the fossil record. All life that has ever lived on earth forms one continuum. Arguing otherwise is a creationist position. And taxonomists argue among themselves all the time.
There is fuzziness at the species level, because divergence is still in progress there, in a lot of cases. There is fuzziness in the fossil record through simple difficulty of identification/classification, and also because some of the speciation fuzziness was preserved in the fossil record as it happened, but once a divergence event falls far enough back into history, descendants are forever in their category.
This is why the creationist argument to the effect ‘if evolution were true, we should see changes occurring at higher levels than species - we should see things changing phyla and genus too’ - is false, because it ignores the fact that these categories represent changes that have already happened - watershed events - an organism can no more change phylum than you or I can suddenly become the descendant of new/different grandparents.
taxonomy’s fuzzines is exactly what i am talking about. Take a quick glance at taxonomy and it looks great. Stop for a minute to look at it and it is a nightmare. The perfect example of trying to draw lines to separate what is ultimately a continuum. We can agree to certain conventions to make it workable (and it really works great) but they are just that, conventions. Agreed upon arbitrariness to make something workable. I would be extremely surprised if Klingon taxonomy matched ours, even loosely.
Tell me about Jupiter, though. It is clearly not a star as it is not massive enough to start fusion and turn into a ball of plasma. Are there any intermediate objects between gas giants and stars? Can a space object be somewhere in between being a ball of gas and being a ball of plasma? Start but don’t go all the way? Could Klingons classify as stars something we do not (or viceversa)?
As it stands right now, a star is not all that well defined. The energy production mechanisms inside a star are not as simple as “fusion” or “not fusion.” Most astronomers define a gas cloud in hydrostatic equilibrium that is fusing hydrogen to helium in its core as a main sequence star. As a star ages the first property stays mostly the same (though not in all cases) and the second property changes radically. Some stars fuse helium in their core, some stars fuse other elements there, some fuse nothing in their core and hydrogen in a shell surrounding it.
It is not obvious to me that classifying space objects according to the method by which they produce energy is “natural” or otherwise intuitive. The reason we do so is because such a classification gives us information about the object. The purpose of classification is utility, not adherence to a universal sense of order.
For example, stars that are still in the process of forming, not yet in equilibrium and not yet undergoing fusion, can be larger and more luminous than the sun. I can’t see a reason a priori why such an object could not be considered a star according to some other system of classification (perhaps “big bright objects in space”). We classify them as “pre-main sequence” stars because such those characteristics (equilibrium and fusion) tell us something about a star’s age and that’s something we’re interested in. If we did not care about the age of stars and only viewed them as, I don’t know, lanterns of the universe, I imagine that anything big and bright would be lumped into the “star” category regardless of its other characteristics.
Divergence is still in progress at every level of the chain. The species category is arbitrary and very fuzzy. Inter-species breeding is common. Hell, inter-genus breeding isn’t that uncommon. Furthermore, categories above the species level are not sanctioned by any governing body, so you are going to get lots of disagreements.
No, descendants aren’t “forever in their category”. The fuzziness is that you can’t draw a clear line between one species and another. Taxonomists are forever arguing about this. Cladistics introduces some objective order, but even still scientists disagree about classification schemes all the time.
Procyon, thanks a very informative response (wiki’s entry in star is very vague in defining one). What would be a definition that included all starts, including those outside the main sequence?. I certainly do not expect a “natural” classification of stars, but I can imagine forming (and dying) stars all including some characteristics enough to make them a coherent group (I could just as easily be wrong, of course).
In general, I would expect “natural” definitions to be very simple and depend only in the most basic physical principles. A small collection of binary conditions that lead to an inequivocal state. Yes or no.
Again, and excuse me if it is a stupid question, is there something between a Jupiter-style gas giant and a star that someone would hesitate whether it is a star or not?
Is it just gravity that “starts” a star? Is there any other source of energy for a star other than fusion? What are they gray cases?
Are atoms then a good natural class? The periodic table?
But where do you draw the lines for your “categories”. You’re saying you can put us and our ancestors from X millions years ago in two categories, and I’m saying so what-- what do you with everyone inbetween? Any place you draw the line is going to be arbitrary.
In between what? - you’re a Chordate, vertebrate, tetrapod, mammal, primate. You don’t have the option of leaving any of those categories, neither is there a continuum of organisms in between you and other organisms in other categories - the divergence between, say, mammals and avians is complete - the categories are completely and unambiguously divided.
Sure, it isn’t the case with categories that are the result of more recent divergences (mostly those that result in categories species and genus), but that doesn’t stop the other categories being quite distinct.
You’re only considering species alive today. But even then, there are disagreements at the borders.
In your scheme, I’m also a human. Was my ancestor from .5M yeas ago a human? How about 2M years ago? 2M years is about where we arbitrarily draw the line between the genus *Homo *and whatever came before. You can play that game with every one of your categories, and find species that may or may not fit, depending on your arbitrary definitions. If it weren’t so, the creationists would be correct.
There certainly is a coninuum from modern man all the way back to the common ancestor of all vetebrates and then, turning around, from there to modern fish. Or birds. Or any other veterbrate.
Perhaps you meant only life that is doing its living today?
As Dawkins points out, our current methods of classifying living things would utterly fail if we had anything close to approaching perfect knowledge. We couldn’t use discrete boxes or circles like we attempt to today. We’d need a sliding graph and long reference numbers for generations and mutations or something else as esoteric.
The point is, living things are probably the antithesis of “natural categories.”
There was a time when the difference between those were as vague as the species of today because they were still speciating from a common ancestor and only later they would branch out themselves.
The taxonomists of a billion years in the future will look at the speciation of wolves and dogs as the moment where the Lupata and the Cannata phyla separated.
There is no principled difference between a Jupiter-style gas giant, the super-Jovian extrasolar planets, a brown dwarf, a red dwarf star, and a regular star. They are all just balls of mostly hydrogen, the difference is the amount of hydrogen. At very small masses you’ve got a planet, at very large masses you’ve got a star. The difference is that the larger the mass, the higher the gravity, and the greater the amount of fusion. Really high-mass stars will burn out in only a few million years, low mass stars might last for hundreds of billions.
I think you are left only with elementary particles, as I said in my first post. Subject, of course, to further a further breaking down of those particles at some future point.
I suppose you could add “quantum state” to that, but I’m not sure if you’re interested in processes or just “things”.