On the thread entitled “Species Kinds”, commenter phoodoo asks:
What’s the definition of a species?
A simple question but hard to answer. Talking of populations of interbreeding individuals immediately creates problems when looking at asexual organisms, especially the prokaryotes: bacteria and archaea. How to delineate a species temporally is also problematic. Allan Miller links to an excellent basic resource on defining a species and the Wikipedia entry does not shy away from the difficulties.
In case phoodoo thought his question was being ignored, I thought I’d open this thread to allow discussion without derailing the thread on “kinds”.
I’m saying that we as humans experience species as discrete entities, that is all.
When you get down to it this is simply another instance of the problem of the one and the many.
We don’t know when individual water droplets become a cloud but we know they do.
The wrong approach is to wave our hands and pretend that clouds don’t exist.
The common sense experience of humanity which is that species exist.
The aim should be to explain what we see not dismiss it as an illusion unless we have compelling evidence to do so.
peace
I disagree. Species is a category of convenience, and many species are somewhere in the process of dividing into two or more species, all the time.
I think this is a category error. Individual droplets remain individual even in groups, just as people retain their identities even when they are part of a group (like a congregation or a mob).
I don’t think anyone is doing this.
And that variations, sometimes LARGE variations, exist within species. Imagine the individuals of a species as forming a bell curve, with most individuals in the middle, and very few at the two extremes. Perhaps individuals at these opposite extremes are too different to interbreed. But they CAN interbreed from these extremes with most of the population, so they’re members of the same species. So does that make these two curve-tail-inhabiting individuals different species? Perhaps these individual represent a nascent fork in the branch, an indication of speciation in progress. So when during this splitting process (which might take thousands of years) do they become different species?
Instances in the middle of the curve are obvious. At the margin, ambiguous.
I’m not sure what you mean by “category of convenience” so you might need to expand on that one.
Humans don’t commonly observe species in the process of dividing. It’s only after the fact that division was deemed to have taken place
I agree but groups like mobs and species are real discrete things. They are not illusions or “categories of convenience” incorrectly placed on a reality that is actually a fuzzy amorphous continuum of individuals.
When the individual in question exemplifies the form of a different species. For the life of me I don’t see why this is so difficult for you all two grasp when it comes to biology.
You do this kind of thing every time you categorize any entity you encounter in everyday life. Why should it suddenly become hard when we are looking at organisms
It’s the same with any random pile of stones you come across but we humans have no trouble separating the stones into circular stones and non circular ones if we choose to.
It’s just what we do
peace
fifthmonarchyman,
Just basic biology, chum. A lineage cannot proceed, in an obligately sexual species, without it. This means that ‘a new species’ cannot exist in isolation. Descendants can only be produced by back-crosses with the ancestral population, except in rare instances of single-pregnant-individual isolation and sibling matings.
Otherwise, descendants are clearly not all ‘the new species’. By the second generation, they are only a quarter ‘the new species’. Unless and until you get some degree of inbreeding, ‘the new species’ is continually diluted by the old.
Give this a little more thought, huh? Maybe draw some diagrams of lineage. Try and keep the gametic contributions equal.
fifthmonarchyman,
The biological reality I talk of is that, in obligate outcrossing sexual populations, reproductive compatibility with something is essential for continuance of the line. I wasn’t talking of classification at all there.
Are you familiar with ‘the species problem’ … ?
fifthmonarchyman,
Are any of you familiar with that chapter?
Not me, no. And you aren’t exactly inspiring me to delve deeper.
Allan Miller,
I’m reminded of something that the late John A Davison used to say loudly and often. That sex prevents evolution. I guess he was partly correct in that sex prevents speciation.
fifthmonarchyman,
Oh, that’s all right then. As long as it doesn’t require future vision all the time …
fifthmonarchyman,
So you take that intuition, but then insist it still applies where we don’t experience discreteness. It makes no sense. ‘Circles and squares are distinct, therefore all intermediate shapes are also either one or the other’.
There are some taxonomic levels with clear cut divisions. Others, not so much. For some reason, you want to extend the fact that some divisions are clear cut, at a moment in time, to the entirety of nature, regardless what ridiculous notions that forces you to espouse, such as indistinguishable parent-child pairs being different species. ie, they don’t have the distinction that causes you to declare discreteness in the first place, but by golly they WILL conform!
Maybe it’s OCD. For goodness’ sake don’t buy a spork, your head will explode!
The variety of life on earth approximates the diversity of life possible.
Yes and similar ecological niches will support animals with similar phenotypes even if they are dissimilar in genotype.
peace
The topic of this thread is classification I don’t it’s helpful to introduce other stuff if we don’t have too. That is what got us in trouble in the first place
peace
not exactly
Every shape is either circular or not circular.
See the difference?
peace
Why is it all about the gonads for you? Why not just do classification like we do in every other realm and let the sex stuff take care of itself?
If I did not know better I would say you have an ulterior motive. 😉
peace
What, keeping god out of classification systems?
This classic image, which I’m sure most of you have seen, demonstrates the issue nicely:
fifthmonarchyman,
This is a transparent dodge. The title of the thread is merely ‘species’. All posts that pertain to the topic of ‘species’ are relevant.
You are claiming that an individual in a sexual lineage can reasonably be classified as the ‘first of a new species’, and not the same species as its parent. How can it not be relevant that that lineage must, by some means, continue? And therefore, one has to consider the role of reproduction, not in classification, but in the retention of that supposed species’s characteristics over the generations.
Your new species will be rapidly subsumed back into the old. That point is entirely relevant. Your supposed methodology breaks down at this point, so I can see why you would wish to sweep it under your lumpy carpet.
fifthmonarchyman,
I see the difference, but not the relevance. I know you think you can dichotomise everything. That does not need establishing by repetition.
eta – I’ll change my answer slightly. Everything is either ‘an elk’ or ‘not-an-elk’. But if it’s a ‘not-an-elk’ it must be ‘a-something-else’. So you haven’t really achieved much by the rewording.
fifthmonarchyman,
Yes, I note another attempt to rile me by some snide remark about sex. I hate to break it to your puritanical ears, but organisms reproduce. Obligate outcrossers reproduce by combining gametes (produced in metazoans in gonad-like structures, though not in plants, fungi or unicellular protists). That fact is relevant when one considers whether an individual, in a sexual species, can be reasonably considered the ‘first of a new species’, and whether its descendants are also of its species rather than the old one.
Why would we want to do that, especially? If it worked across the board, that’s what we’d do. But it doesn’t, hence the debate.
But you do know better, right? So why say it? What’s that about false witness? You can’t pretend it’s mud you didn’t sling, just because the wording was careful.
I have given you very detailed reasons why I take the approach I do. My motive is simply to discuss the why’s and wherefore’s of the issue of species in biology. It interests me.
I’m afraid you are missing the point. It’s easy to separate the red from the blue text. You just pick a spot to your liking, draw a line and declare everything above it red and everything below it blue.
IOW you make a choice. That is how categorization is done and we do it all the time.
In fact that is what categorization is
Why should it be different when it comes to biology?
peace
No, that isn’t what categorization is. It’s what categorization of continua is. For example, it’s exactly how igneous rocks are classified, by setting names to arbitrary divisions of a continuous space of mineral composition. But species (talking about organisms here, not Aristotelean categories) are not continua. The only reason we recognize species is that differences among organisms are clustered. Species aren’t arbitrary. Of course they would be if extended far enough in time and if our sampling of that time were good enough. But we generally don’t do that extension, and our sampling isn’t good enough. The number of ambiguous cases in the present is comparatively small, not because of any “essences” whatever they are, but because of divergence over evolutionary time, which requires (not necessarily complete) reproductive isolation. The biological species concept is operational and incorporates a major biological phenomenon that results in clusters of individuals. So what’s the problem?
John Harshman:
OK, I looked up the chickadee thing, and I remembered wrong. The bird I was trying to mention was the titmouse, a member of the chickadee family. Ornithologists had regarded the tufted titmouse and the black crested titmouse as different species. Then the two were lumped, and regarded as subspecies. Now I notice that have again been split into different species.
(Birders are always competing to have a longer life list, so they love splitters because it adds a bird to their list, and they hate lumpers, which cost them a species. The holy grail North American list is 600 species, which is very nearly every identified species found (sometimes accidentally) in North America. So a single lumping event knocks a whole bunch of competitive birders below 600.)
Flint,
I believe I’m currently at 503. But hey, I should add the black-crested titmouse. 504. Fortunately, we live in an age of splitting, heavily assisted by DNA and song playback.
I agree, That is why the red/blue letter exercise is a diversion and irrelevant to biology
agree again it’s about the resolution of our measurement. If our resolution were different our understanding of species would be different
AMEN brother. It seems like we are in perfect agreement so far. The interesting question is, why is it the case that species aren’t arbitrary. I wish more people would ponder that.
Here is where we disagree. Reproductive isolation is not required for divergence.
You are assuming Darwinism. Reproductive isolation can lead to divergence or not, so can other things. Things like purposeful design and Neo-Lamarckism
The problem is it takes a perfectly good common sense activity (categorization) and imports an arbitrary unnecessary add on (reproductive compatibility) only for the purpose of shoring up a philosophical/theological position.
This introduction muddies the waters unnecessarily causes confusion and introduces error. It’s the cause of the species problem. On the practical side it dooms the red wolf to extinction.
A much better approach would be to just leave the philosophical baggage out of it altogether and get on with the categorization.
peace
You are incorrect. Unless you can say what theological position and demonstrate support for that in biology/taxonomic literature or text books you are talking bollocks.
Says fifth, who is so soaked in essentialism that he’s dripping it all over the place.
Fixed that for you.
Why do you think it’s the case that species aren’t arbitrary?
Reproductive isolation inevitably leads to divergence, though not necessarily to morphological divergence. Not sure what you mean by “purposeful design” or how that could lead to divergence. If we’re talking about fiat creation, that isn’t divergence, just difference. If we’re talking about tweaking of genomes, that would require reproductive isolation to result in divergence. And the latter would also be the case with neo-Lamarckism, which at any rate isn’t actually a thing.
Categorization itself can be arbitrary, and frequently is, as in the example of igneous rocks. Recognition of biological species is not simple categorization of that sort, and there’s no reason to equate the two. Nor can you say current species concepts introduce error, as you have no criterion by which to judge errors or correctness. On what basis do you claim that the red wolf is a species, other than your personal preference that it be so? Are coy-dogs a species? Are collies a species?
I think it is because God is a God of order and pattern rather than disorder and randomness.
That is just me Why do you think that species are not arbitrary?
Is there a specific evolutionary benefit for the discrete logical pattern we see?
something like this
http://www.mrbigben.com/Petshop/great20dane20and20chihuahua20small1.jpg
or this
http://news.nationalgeographic.com/news/2014/07/140717-gene-drives-invasive-species-insects-disease-science-environment/
Do you think there is divergence between the wolf and the coyote?
I’m thinking about epogenetics and related mechanisms that don’t involve genetic change but would result in phenotypic divergence if the result is large enough.
Why not? Please be specific because this is important.
It seems to me that it’s precisely what separates Biological categorization from normal categorization that causes the difficulties with the enterprise.
1) Red wolfs have a different phenotype than either Wolfs or Coyotes.
2) Individual red wolfs have more genetically similarity with each other than they do with either wolfs or coyotes
3) Red wolfs occupy a different ecological niche than either Wolves or Coyotes
No but there is no reason that they couldn’t be in the correct circumstances.
peace
Your sense of order may not be God’s.
So you say that all order and pattern must arise directly from God? Wouldn’t common descent and speciation also produce order and pattern? I think you’re making post hoc rationalization: whatever there is, that’s what creation would look like. But you run into contradictions. If God likes discrete species, why is the visible spectrum continuous? Why are igneous rock types continuous? Likewise, one can find a fair amount of disorder and randomness in the world, the same world you claim God created.
There are a number of mechanisms, but the one we are considering here is speciation followed by divergence. That has the bonus feature of also explaining why there are examples of intermediate stages in speciation that you would find hard to fit into your created, discrete model.
Benefit for whom? Evolution, in so far as it’s about benefit, is about benefit to individuals. There is in fact a benefit to individuals in speeding up the later stages of speciation (see Reinforcement), but I doubt that’s what you’re asking about. Speciation is just a thing that happens, generally as an accidental consequence of geographic separation.
Your first example is of artificial selection. Do you think God makes new species by artificial selection? Your second example isn’t of divergence at all. Do you mean to imply that God does indeed tweak genomes? Please be clear. Neither can result in divergence without separation of populations, which will eventually also result in reproductive isolation.
Yes. It was once ecological and geographic isolation, at least partly. Hybridization is a recent phenomenon and probably transient.
Not only isn’t that neo-Lamarckian, it’s not a thing either.
First, simple categorization can happen in the absence of any clustering, as in the several examples so far of arbitrary division of a continuum. If we agree that species are real (I would say real-ish), that isn’t what we’re talking about. Second, the clustering of individuals results from clearly understood mechanisms, i.e. isolation and divergence, the sort of thing that requires special conditions not found in most things you might want to classify. I can think only of languages as an analog, but even those have too many intermediates to work as well as biological species. If you’re going to classify, you should pay attention to the mechanisms.
I’d say that we simply choose to ignore the greater difficulties in non-biological classification because we aren’t even trying to follow a real pattern of clustering there.
The first is probably true. I’m dubious about the second and the third.
So why aren’t coy-dogs and collies species? They have different phenotypes. If red wolves are genetically more similar to each other than to wolves and coyotes, the I expect coy-dogs to be the same, and collies certainly are. Collies also have an ecological niche different from that of other dogs. Don’t know about coy-dogs; probably not enough of a population to tell. I also note that the process you appeal to in creating species isn’t what led to red wolves.
Common descent and speciation would be impossible unless God was a God of order and pattern. But lets not go down that rabbit hole just now. It would derail an interesting discussion
Of course that is the case.
If we can see it it’s part of creation by definition, nothing post hoc about it.
I see not reason conclude that God likes things discrete or continuous. Just that he is a God of order
I think you know that I’m a Calvinist so you’d have a hard time convincing me that their is randomness in the world.
As for disorder it wouldn’t be called disorder if it did not seem some how out of place. That is something else I wish people would ponder.
peace
fifthmonarchyman,
I see nothing to respond to in your hermetically sealed worldview. So much for interesting discussion. If you start out by assuming that everything must by definition have been created, evidence is irrelevant. If order means “whatever we see”, then there can be no disorder, and again evidence is irrelevant. I would be glad to discuss theology another time.
Simple categorization can happen in the absence or presence of anything. That is not a bug it’s a feature in that there is no bias for or against clustering (or anything else) for that matter.
1) You are assuming isolation and divergence are the cause of clustering I’m not sure I would agree. I know I would not be dogmatic about it
2) Every thing we classify is different than every other thing. That why simple classification is so powerful it works on everything
I think this is mistaken usually in the real world we classify first and look at mechanism that produce the patterns we see.
It’s seems a little like question begging to begin with the mechanism and then classify
peace
I agree. lets not get into it now. Feel free to ignore my response to your theological question. I separated it for just that reason
peace
Of course there’s a bias for clustering. That’s what classification is. Even things that aren’t naturally clustered get clustered by classification schemes. Thus “red”, “orange”, “yellow”, or “granite”, “quartz monzonite”, “granodiorite”. That’s what makes biological species different.
Does not being dogmatic make you feel superior? I can’t see another purpose. Are you also not dogmatic about whether the moon is bigger than a pingpong ball? No, we aren’t assuming. We’re concluding on the basis of quite good evidence. And not just the historical explanation for divergence but the present explanation for continued separation.
Well, it sort of works. Works best on discrete groups, and species, courtesy of reproductive isolation and divergence, are more like discrete groups than most things. This discussion grows increasingly pointless and decreasingly interesting.
This is a telling statement.
We agree that there is clustering but IMO reproductive compatibility is not necessarily the cause. You are assuming what you need to prove.
There lots of things we categorize that cluster just fine with out abandoning common sense practice for example extra solar planets
Check it out
http://www.sciencemag.org/news/2016/07/forbidden-planets-understanding-alien-worlds-once-thought-impossible
peace
How so?
Ah, but there is good evidence for my “assumption”. You, on the other hand, claim to be assumption free, but whenever asked to justify your position on anything, you bring God into it. Now that’s a serious assumption.
We can classify anything. Doesn’t mean that classification is classifying real entities. I note that your intended example shows a continuum of distance and radius (the only characteristics considered); the clusters are artificial. Now there is apparently a difference between terrestrial planets and gas giants, but that difference might be an artifact of what we happen to see in our solar system. Super-earths would appear to grade into gas giants. So your example actually appears to argue against your claim.
Studies of opinion polling suggest that for most questions, either 3 (agree, disagree, no opinion) or 5 (excellent, good, fair, poor, terrible) are about as fine a granularity as opinions generally get.
Polls that have people grade on a scale of (let’s say) 1 to 100 find that most people select either 1 or 100, reducing the scale to two effective options.
And this illustrates the problem of reducing a continuum to discrete mutually exclusive selections — where clustering is not inherent, the human mind seems to want to fabricate pigeonholes, which then become “real” somehow. People like bright lines and clear choices, binary reduction whether it makes sense or not.
Not all I have lots of assumptions. Including the assumption that God exists. What I try to do. What I’d think we all try to do is not let our assumptions intrude where there is no legitimate reason for them to intrude. Like in our categorization methods
When I look at the chart I see at least two “real” clusters.
Do you think biological clusters are more pronounced than super earths and directly detected distant giants in the chart?
I would agree that clusters might be a artifact of our measurement efforts. Our categorization will always be just as good as our measurement resolution
Don’t you think that is true of species as well?
peace
PS
Thank you
I’ve enjoyed this conversation.
I think I am sensing a little bit of frustration on your part. I don’t want to be a source of unpleasantness for you
How about we just agree to disagree on this one and take it up another time?
Your assumptions are intruding whether you realize it or not. That’s why you don’t want my “assumptions” (quotes because there’s plenty of evidence for them) in the discussion: because they conflict with yours.
Yes, you see them. I don’t. I think you see what you want to see.
Definitely.
I would not agree. Did you think that’s what I was saying?
I don’t even think it’s true of planets.
Suit yourself. I’ve grown used to frustration in dealing with creationists.
That happens for all of us. It’s part of what it means to be human
So you would disagree with the folks who are arguing that the discreteness we see is an artifact and the edges of species are fuzzy and indistinct?
Not sure what you mean by creationist. It seems like an artificial category Perhaps you are seeing clusters where they don’t exist 😉
I will, give me a little bit to catch up on stuff and I’ll get back to you
peace
Flint,
Indeed. We love dichotomies, be they true or false.
sounds subjective
For most species, it isn’t an artifact. For some species, it is, and that’s because speciation is a gradual process. All species would be artifacts if we had a complete sample reaching way back in time. But, once again in case you haven’t noticed all the other times I’ve said it: most species in the present day form distinct clusters of individuals exactly because of speciation and divergence.
The fact that the biological world at the present moment is generally separatable into distinct types is not contested. But the naturalistic account of speciation is that it is not an instant process (it can’t be, in an outcrossing sexual species …). And hence, one expects to find circumstances where the observed general discreteness breaks down. And we do. Yet to accept this simple fact would be to open the door to conceding some tiny ground to the ‘Darwinists’. And that would never do. So one tries to ignore the process-based account, and simply … ‘categorise’. Meantime, the entire field of taxonomy has incorporated the process into its methodology. It’s not the 1700’s, still less Sometime BC.
It cannot be emphasised enough, speciation is not ‘one species turning into another’, but a parallel process in separated populations. There’s nothing ‘disordered’ about this process. Species cluster on characters simply because the present population is commonly descended from a few members of an ancestral population. When you look at a flock or a herd or a football crowd, you are looking at a bunch of relatives, at some remove. Of course they cluster.
Not if they are Millwall supporters. 😨
Alan Fox,
Perhaps they are even more related than the average …
That is generally not true. You’re perhaps thinking of founder effect speciation, which is probably rare compared to simple splitting by geographic barriers. Species cluster on characters because they’re a gene pool, free to diverge from other gene pools but constrained within by interbreeding, fixation of neutral alleles, and common selective environment.
John Harshman,
No, I’m not. I’m thinking of the fact that most individuals in a population of any size do not contribute any genetic material to the future population. Most do not even remain ancestors, and even those that do may contribute nothing. Or, looking backwards, the further back you go, the more the same individuals appear again and again at nodes. For a given genetic stretch, coalescence is ultimately upon an individual – even given recombination. It’s recombination that causes this integration.
Our phenotype is constructed from a mosaic of genetic stretches, but these stretches coalesce upon relatively few individuals, at a sufficient remove from any given population. Characters recombine into the mosaic genome (the ‘gene pool’) but they come from singular origins.
They would not cluster on a given character (thinking of a genetic locus, here) if they did not inherit it from the first individual to possess it (ignoring repeat mutation).