Couldn’t have put it better myself - the categories of species and genus are still not crisply defined because they are being moulded by the breeding activities of living organisms, but once the categories crystallise as ancestral divergences, they’re there for good.
and
Yes. I realise that I haven’t made that clear enough. Organisms living today fall into natural categories hewn out by ancestral divergences. Some of the more recent subdivisions (or sub-sub, etc) of those categories are not yet sharply defined.
But for many categories, won’t there be organisms on the edge of the classification for one reason or another such that they could be reasonably placed in one of 2 categories depending on an arbitrary weighting of attributes? I’m not saying I can think of one, but knowing the complexity of life and how things rarely are arranged in neat boxes, it seems like this would be a problem.
But you’re still going to find questions at many of the boundaries. Why is the hagfish, for instance, classified as a vertebrate when it has no vertebrae?
As I said before, caldistics (which is what you are talking about) solves some problems, but every time you select a branch point, you are doing so arbitrarily. Ultimately, you end up only with the individual. And I’m not sure you can even define “individual” all that well, since each of us has countless micro-organisms living inside us.
There shouldn’t be, for categories arising from very ancient divergences.
It may be that it needs its own category and trying to force it into one or the other existing one is simply a false venture. I totally understand the point about continua of intermediate forms - we see these today expressed as ring species, where there is divergence without separation. The nature of life on our planet, including frequent extinction, makes it unlikely that such broad divergence without separation would persist forever - and when a sufficiently large gap opens in the middle of the continuum, the break is irreversible.
Anyway, even if parts of the system are a bit wooly, these are still natural categories - I don’t see why we have to consider it an all-or-nothing question.
No. Every category is arbitrary, not natural. There is no reason to pick a category that contains A, B, C, and D species instead of two categories-- one that contains A and B and one that contains C and D (or other combinations). Why is “vertebrate” a category in the first place?
So ‘birds’ and ‘mammals’ are arbitrary categories? You can cite examples of organisms that we would like to place almost in one, but actually, partly in the other?
Well, why don’t you tell us what is “natural” about them? Why not classify the two groups as egg laying vs non-egg laying?
What’s natural about them is that they represent divergent evolutionary trees of descent; there was a point, somewhere back in time, at which the ancestors of birds and the ancestors of mammals no longer interbred.
This discussion is going nowhere and we’re just repeating ourselves. You may have the last word if you wish.
OK, but why did you pick those particular groups? Let’s say that all birds trace their ancestries back “X” million years and all mammals trace their ancestry back “Y” million years. Why did you determine that “X” and “Y” were natural, as opposed to some other numbers, especially since X ≠ Y?
I’m fine stopping if you want to.
I really didn’t intend to come back to this, because I think this particular issue could kill Sapo’s thread, but you asked a question…
Why do you think it matters that all of the categories into which organisms may be grouped did not arise at the same time. I don’t think it matters; the categories still exist, and even if there are parts of the domain that cannot be adequately or accurately categorised; some parts can be. I’m not claiming that everything in the natural world falls cleanly into one of a fixed set of categories, only that some distinct categories do in fact exist.
True, categories exist. The problem is, there is virtually an infinite number of categories that can be defined, and there isn’t any reason to call one “natural”. They’re all arbitrary.
Excuse me for insisting, would the elements be a natural classification? Different mentalities might deal with isotopes differently but there are no grey cases really between hydrogen and helium (or any other pair of consecutive elements). Am I missing something?
Black holes? Are there any gray cases (no pun intended)?
I think you need to refine your question. Do you mean “all civilizations” or “all scientists”? I think most of us have been trying to address the latter, while your OP asks about the former. At any rate, I indicated that elements would be a good, if not perfect, classification scheme in post #2 of this thread. The only problem is that there are lots of different quantum states that an element’s atoms can be in, and the properties of that element will change as a consequence. Is liquid gold in the same “category” as solid gold? I guess it depends on what the purpose of the category is.
I think “all civilizations” would be more to the point. Imagine meeting a truly alien but technological race and comparing notes (once we manage to recognize them as sentients and establish communication). What could we reasonably expect to see match in our sciences? Basic math I think is a given. After that, it gets really iffy.
Thinking about stars, I can see any definition getting really dicey in an environment like those star nurseries where it would be hard “cutting” a star from its environment.
Your point about gold is valid but I imagine that any civilization that can count nucleons would get to the same observations. Then again, I am making a huge assumption that they will consider nucleons at all and not just see quarks or strings and see nucleons as just an accident of those, if at all.
That’s different from what I was thinking. In that case, the elements might a better starting point. Who knows if they would have discovered quarks. The Voyager Golden Record (carried by the Voyager spacecraft) contains a diagram illustrating the two lowest states of the H atom. It was thought this would be some type of universal known quantity.
The phsycial constants would be another thing we’d expect to match up (speed of light, Plank’s constant, etc.). In fact, most of physics and chemistry should “match”, although it’s unclear how much biology would match.
Well, I have no doubt that the physics themselves (and chemistry for that matter) would be the same. That’s what holds our universe together. The question is if their description of them would match ours. Most of our physics and chemistry are models that describe (approximate, really) a more complex reality. Who says the corners we are cutting are the corners any other possible civilization would cut?
Although I wasn’t going anywhere when I started this thread, I am begining to see a match to my previous thread about things being unique or undistinguishable.
It seems that, once we go above atoms, groupings get iffy and everything starts to become unique cases. That doesn’t mean there can’t be science above the atomic levels, of course. It is just that we enter the realm of models and aproximations.