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When does intraspecific variation cross the line into interspecific variation? Or to put it in plain English, how different is different enough to justify calling something a new species?

[I'm intentionally going to be controversial in order to stimulate debate, so be forewarned.]

To my mind, this is a bogus question, because the concept of "species" is a bogus concept. If the best minds in biology cannot even agree on how to define a "species", how can we even begin to talk about differentiating between species? The concept is an archaic artifact of the human need to classify and name. Just as "ice", "water" and "steam" are three discrete terms that describe a CONTINUUM of physical properties of H2O under continuously varying conditions, so too a "species" is a continuum of diverse characteristics which human beings arbitrarily demarcate into discrete units. The "species" concept certainly has heuristic significance (i.e., it is useful as a common sense means of naming and talking about things, just like words such as "catfish" and "cichlid" are), but it has no "natural" counterpart (it exists only in our minds).

The taxonomic debate on the virtues of "lumping" (lumping diverse characteristics under one species name) vs. splitting (splitting small variations in characteristics into new species names) is as silly as asking "how many real numbers are there?". Let's catalog diversity by all means, but let's not confuse continuous processes with discrete ones.

Dinyar

It's all a matter of personal perception.
Guess Science sometimes isn't as objective as we would like it to be, huh?

Hi,
I think, there will never be a final conclusion for this problems.
First of all scientists are also "only men", with all their faults like oversized ambition and seeking for approval, who wants to "loose" species described by himself?
And I guess you know the saying "If two scientists are in agreement, one of them is no scientist" ;)
And finally its probably really not possible to fix a limit for what´s a species and what´s only a variety.

The taxonomic debate on the virtues of "lumping" (lumping diverse characteristics under one species name) vs. splitting (splitting small variations in characteristics into new species names) is as silly as asking "how many real numbers are there?". Let's catalog diversity by all means, but let's not confuse continuous processes with discrete ones.

Its far from silly. You said "lets catalog diversity by all means". Ok. I agree. But with whose oppinion about systematics? As long as there are humans, there are different opinions. Whose oppinion should we chose to classify species? When you discover a animal/population... that does not fit in the system you have to decide first if it is a new "species" or just a "variation". And there the discussion between lumpers and splitterers is again. If you want to stop discussing about lumping and splitting you have to nominate one person that does all the work. I am pretty happy that we have this discussion, because it inspires us to think about species concepts and the "essence of species" which does not handicap research but impels it.
Nevertheless one always has to keep in mind that the binominal system is just a try to press a complex case (a constant flux, i agree with you there) into a simple sceme. Much better than that simple system would be to differentiate by specifying percentual differences between populations. Best would be to base that on the complete Basecode of each individual. First we determine the differences between individuals of one population. Then we monitor individuals that overlap with other populations and determine their percentual difference. Then we go on monitoring other populations, determinating the percentual Basepair deviants. And so on. So we then have species 123765547312389876478390234638 which differenciates 85% from 12873673467236487 and 60% from 298364728346287364 and... . Unfortunatly thats a little bit impracticable ;) So we have to stick with good old simplifying and thus highly discussable binominal nomenklature. The discussion will never come to an end, because there is no solution/consensus with this system. And i am pretty happy about that because it keeps us in mind that the system we use is just a highly simplified help to be able to name "species" and it keeps the discussion and the occupation with the "species" that surround us running. There is nothing more important in science than dicussion and criticism.
Well at least thats my opinion.

Achim (Lumperer

Actually, Achim, I agree with everything you said. My main point was there there are no sharp delineations between species, and the concept of a "species" is heuristically useful but does not have an "objective" basis. I read your post as agreeing with both those two points. Please correct me if I misread you.

Dinyar

Dinyar,

you are right that i agree with most of your points. I just don't think the discussion about lumping and splitting is silly

Achim

I largely agree with you on that point too! I was just trying to stir some debate and phrase my opinion in a way that would get people motivated to respond.

But we ARE saying that the present system (let's call it "the binomial system") may be the best we've got, but it's far from an ideal system. If, hypotehetically, biologists were in future to advance to a different system (say quantitatively based, with each population described as a cluster in n-space, with axes defined by genome, meristics, etc.), they may very well look back on this one, and the ensuing debate on lumping vs. splitting, as "silly" -- more metaphysics than science.

Dinyar

I largely agree with you on that point too! I was just trying to stir some debate and phrase my opinion in a way that would get people motivated to respond.

well ok, i misunderstood you then. Im not that familiar with the subtleties of the english language

let's call it "the binomial system"

correct me if there is a better english term. I just translated it 1:1 from german.

But we ARE saying that the present system (let's call it "the binomial system") may be the best we've got, but it's far from an ideal system.

No question about that. full ack.

Achim

because the concept of "species" is a bogus concept

Systematists like to think that the species is a natural entity, each with its own separate (evolutionary) history.
Whether we can empirically prove this is true 100% of the time is another story.

Great topic Dinyar and one that I have given much thought to. To my mind, the greatest, perhaps fatal, flaw in Linnaeus' system is the idea that every species known to science must be represented by single holotype that "defines" what it means to be this spp. We do not have to look far to see how crazy that idea is. Who should be the holotype for our own species, Homo sapiens? A tall fair Nordic, a member of the Yanomami, or a Kalahari bushman? Why do we capture one single fish from one single location and say that it represents a species? It represents only one single fish from one single location. If you were an alien and took specimens of the three human types above back to your planet you would describe three spp of the genus Homo. However, if you looked all over the planet at the entire human race you would easily come to the conclusion that what you really have is ONE variable spp. adapted to different environments.
In the future we need to study habitats as systems. You can not travel to Colombia, catch a few fish in a river, and go back to the US to describe them as new spp. You must start at the headwaters and collect samples throughout the river system over time and space. Only then with a good sample base can you sit down, make good comparisons, and talk about spp. This would also solve most of the lumper vs splitter debate which mostly exists (to my mind) because single individuals have been used to base what it means to be a certain spp. When a sp. is finally described you can show a continuum of the changes in that sp. over distance throughout the system it inhabits. Perhaps the animal will eventually become two separate spp. over its range as the system changes. For example, in the mountains and piedmont in cool fast flowing water you find Corydoras venezuelanus. Reaching the llanos, in the same system, you encounter C. venezuelanus "black." The two fish do not very different in much but coloration, but to my mind they are different spp. because there is a clear demarkation in habitat and environment. C. venezuelanus dies at the high water temps C. venezuelanus "black" enjoys and C. venezuelanus "black" dies at the cool temperatures C. venezuelanus thrives in. This is just one fish that I know well because I spent two years surveying the streams and llanos. Any taxonomist who just stopped by the side of the road and grabbed a few specimens could never understand this dynamic when describing his new finds.
I do believe that the current system is workable if we throw out the holotype concept. How many fishes (Corys esp.) have been described from aquarium imports? How can anyone say something is or is not a new spp. when they do not even know what river it came from? Not that past taxonomists were better. The holotype location for Hypostomus plecostomus is India! I believe that the ICZN could do more to improve our understanding of the natural world by throwing out most of the "taxonomy" that was done inthe 19th and early 20th centuries. We need a clean slate more than we need to waste our time trying to figure out what was Gronow's Mystus or Linnaeus' Hypostomus. I sometimes think that the ICZN tries harder to protect the namesakes of long dead scientists than promote an understanding of the diversity of the natural world.
OK, off the soap box lads!
-Shane

To my mind, the greatest, perhaps fatal, flaw in Linnaeus' system is the idea that every species known to science must be represented by single holotype that "defines" what it means to be this spp.

That is unfortunately not true. The system as originally conceived by Linnaeus did not include the concepts of types as we understand them today. The "types" that Linnaeus had in mind were closer to the Aristotelian concept of archetypes in which it was believed that it was possible to capture the "form" or the "essence" of a species in as a sort of idealized being. The recognition of type specimens came long after Linnaeus' time and even then, the concept of a holotype is a relatively recent one.

To my mind, the greatest, perhaps fatal, flaw in Linnaeus' system is the idea that every species known to science must be represented by single holotype that "defines" what it means to be this spp.

The concept of the holotype arose out of a need for stability in zoological nomenclature. A single individual is the smallest unit possible in which (almost) all of the characteristics of the species are embodied. Given that theat the degree of biological variation varies as much between different species as individuals within a species can vary, who is to say how many is a good number to represent variation in a species. Ten? Fifty? One million?

Only then with a good sample base can you sit down, make good comparisons, and talk about spp.

A noble ideal, but alas fatally flawed practically. Scientists have had to work under extreme limits placed on time and funding. Would it be good to sample as thoroughly as possible? Sure. Can we do it on limited time and money? No. If I had to choose between sampling one habitat comprehensively and doing ten less so, I would pick ten any day. The loss in our diversity is probably faster than we can ever hope to document, and I don't see sampling one habitat as being a cost-effective in terms of time, money and effort spent.

I do believe that the current system is workable if we throw out the holotype concept.

And what would you replace it with, bearing in mind that the need for stability in nomenclature is the prime directive?

The holotype location for <i>Hypostomus plecostomus</i> is India!

Unfortunately, this is the baggage that the current system has to carry from the failings of past workers. Bearing in mind that stability is always the main issue, there is nothing one can do, short of petitioning the Commission.

I believe that the ICZN could do more to improve our understanding of the natural world by throwing out most of the "taxonomy" that was done inthe 19th and early 20th centuries. We need a clean slate more than we need to waste our time trying to figure out what was Gronow's Mystus or Linnaeus' Hypostomus. I sometimes think that the ICZN tries harder to protect the namesakes of long dead scientists than promote an understanding of the diversity of the natural world.

You're not the first to suggest doing away with the Linnaean system. People have been trying it for decades, and it has gotten us nowhere. Current debate on the Phylocode (touted as a replacement for the Linnaean system) places it on the losing side. It's not that we don't want to replace the Linnaean system, but none of the alternatives offered so far are any better (most are worse) than it is.

Sorry for the long rant, but nothing raises my ire more than complaints by people not fully cognizant of the limitations we work under. Sure it's easy to fault the system, but scientists have been brainstorming for decades now, and have come up with zilch. I am not defending the system because I like it, but because there has been no viable alternative that scientists can agree upon so far.

'Tis always easier to criticize than to suggest viable alternatives.

I said at the outset (actually, I think it was at the end of another thread that spawned this one) that my purpose was not to find solutions but to generate debate. I fear you are rushing too eagerly to the defense of the status quo, Silurus. There are many systems -- democracy, in Winston Churchill's famous phrasee -- that are horribly flawed but may still be the best alternative available. That doesn't mean we shouldn't have a full debate on the costs and benefits of democracy -- or the Linnaen system. We learn by debating, and what could be better for democracy or the Linnaen system than an informed public?

Moreover, no model -- political or "scientific" -- lasts for ever. Yes, our grandchildren will certainly live in a world with less biodiversity, but the taxonomic system they use will equally certainly be quite different from the one we use today. So let's look forward rather than backward. Hennig was a radical too, even if his views represent the emerging orthodoxy today.

And finally, to the extent that biodiversity concerns any of us, political action should concern us too. Just "describing species" is merely fiddling while the world burns. What good does a "described species" in a bottle in a museum do anyone, except perhaps the person who described it? Rather than reading the card catalog of the library of Alexandria, I'd rather save the books and burn the catalog!

Dinyar

As I have mentioned before, I am not defending the system. I am just too cynical to believe that a solution is going to be on the horizon, given the fractious lot that scientists are (read some of the taxacom posts, and you will see what I mean).
I am still waiting for some revolutionary to show us the way, but I doubt we will ever get one (at least not in my lifetime) because we are not doing sexy science and the number of recruits is a dwindling business.

And finally, to the extent that biodiversity concerns any of us, political action should concern us too. Just "describing species" is merely fiddling while the world burns. What good does a "described species" in a bottle in a museum do anyone, except perhaps the person who described it? Rather than reading the card catalog of the library of Alexandria, I'd rather save the books and burn the catalog!

The bottle in a musem may be all that's left for posterity of the species given the current state of events. Not much, but better than nothing. People are always stomping on taxonomists. Yeah yeah yeah, they're nothing but stamp collectors and all that jazz. The work they do is certainly unsexy (certainly nothing like cloning sheep), but it forms the cornerstone for other areas of research in biology and the environmental sciences.
I have seen the library analogy very aptly applied to ecosystems and their species (books). This is not the time or place to debate the merits of saving selected tomes from all of the library vs. saving selected sections of the library. What is unquestioned, however, is that time and money are severe constraints when it comes to saving ecosystems.
What good is saving the library if you don't even know what's in there (and consequently whether it's worth saving in the first place)?

'Tis always easier to criticize than to suggest viable alternatives.

I thought I was suggesting an alternative for (what I see) as the main fault in the current system. We do away with the idea of a single holotype and replace it with a series of the species in question from throughout its range encompassing various growth stages and both sexes. What is so crazy about this? I completely understand the limitations for research scientists with regards to funding and time. What I am talking about is an expandable system of type material that could be added to over time. Example: You collect a new Ancistrus from Lake Valencia and describe it. Your type material may consist of 10-30 individuals at various growth stages and of both sexes. Latter I collect groups from the Rio Tuy and Rio Guapo. I realize they are the same sp. you have described and deposit a group from each river that represents various sizes and sexes. That material, say 20 from one river and 25 from another, them is added to the continuum of the type series. Now the type material is much more comprehensive because it consists of 55-85 individuals from three river systems. We can now begin to look at the species' evolutionary history and where it fits into the big picture because over time we have collected a broad sample of the sp. in question from different environments.

Given that theat the degree of biological variation varies as much between different species as individuals within a species can vary, who is to say how many is a good number to represent variation in a species. Ten? Fifty? One million?

In answer to this, I can only say that it depends. For a killie known from a single mudhole perhaps a dozen is enough. For a Corydoras known from a single small river perhaps you can get away with five specimens from five locations along the river. The idea is to do the best you can and have a system with the flexibility to change and be added to over time. This in turn will bring more stability. Instead of saying "So and so's material is a synonym of such and such spp" you just move so and so's material over and attach it to the type material for the described spp. Far less messy synonyms this way as well. Flexibility brings stability but rigidity (the idea of a single holotype) forces constant change and mistakes.

The loss in our diversity is probably faster than we can ever hope to document, and I don't see sampling one habitat as being a cost-effective in terms of time, money and effort spent. If I had to choose between sampling one habitat comprehensively and doing ten less so, I would pick ten any day.

We do not completely disagree very often but on this I believe the opposite. Understanding one system, be it river, lake, or sinkhole is far more valuable than simply collecting a few specimens at ten different locations. Running out and grabbing a few random fish, to me, seems to be the definition of "stamp collecting." A solid understanding of all the spp. in one environment speaks to diversity, interrelationships, microhabitats, prey-prdator relations etc, etc. A few random fish from a few random locations tells us nothing about the big picture. If taxonomy is "the science concerned with naming and classifying the diverse forms of life" then collecting random fish only speaks to the naming half of the science because you can not classify the species if you have no context of where it fits in the big picture of its environment.

Sorry for the long rant, but nothing raises my ire more than complaints by people not fully cognizant of the limitations we work under.

I am sorry that you consider me one of these people my friend as for many years I have had a very keen interest in your work (Infact, I may be your biggest admirer) and I do understand that taxonomy is not "sexy" enough to get the kind of funding or attention that it deserves, but we can not fault taxonomists for this.
-Shane

The alternative type system you propose has an inherent fatal flaw, which has to do with the theme that started this all, i.e. lumping vs. splitting.

Using your hypothetical <i>Ancistrus</i> as an example, will all scientists ever agree that the populations from Rio Tuy and Rio Guapo are conspecific? I don't think so, given the existence of lumpers and splitters. One man's population is another man's species. By creating a type series that may contain two or more species to some members of the scientific community is cause for more confusion, not more stability. At least with a single holotype, you cannot argue about its identity (it is either species A or species B but cannot be both).

People have proposed doing away with the holotype system, but most of the schemes involve complete abolishment (i.e. names that are no longer associated with a physical specimen). I certainly don't see your alternative as being very viable.

Understanding one system, be it river, lake, or sinkhole is far more valuable than simply collecting a few specimens at ten different locations.

I have no beef about trying to understand a river system this way. Practical diffculties have always forced us to sample any given system very spottily. What we are doing is akin to trying to guess at the entire contents of a library (here comes the library aphorism again) by grabbing an armful of books while being blindfolded.
For limited time and money, we have to spread out all the geographical coverage and get more bang for our buck. Ideally, we would like to do all systems in great detail, but we don't live in an ideal world.

I am sorry that you consider me one of these people my friend as for many years I have had a very keen interest in your work

I got a little testy, and I apologize for that. This is a forum, and debates are an integral part of it. However, as I have told Dinyar, what is said here, stays here. I do not and will not consider you any less a good friend and supporter for anything you say in here.

Perhaps this needn't be said, but let me say it anyway: this is a forum for discussion and debate. We may disagree at times, even sharply, but intellectual differences should not damage the fabric of our mutual respect and friendship. As for me, the people I like the most are the ones I argue with the most often!

Dinyar