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Phenotypic Plasticity and Speciation


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Dog breeders have produced a broad range of morphological variation within the species variety Canis lupus familiaris . See attached chart from American Kennel Club.

But no one, so far as I know, is claiming that selective breeding has produced a new species within the genus Canis.

 

No natural environment would pull as much phenotypic plasticity out of a species genome as is shown in this chart. And yet, nature is credited with producing all the various species of creatures, despite nature's ability to produce only a much narrower range of phenotypic variability from a given species genome, If dog breeders haven't yet produced a new species (or if they have, please comment) then how does nature do it, given its much feebler ability to produce morphological variability from a genome?

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But no one, so far as I know, is claiming that selective breeding has produced a new species within the genus Canis.

 

I have seen arguments that, for example, Chihuahuas and Great Danes should be considered separate species because they are reproductively isolated. It is probably mainly a matter of convenience that they are still considered one species.

 

 

how does nature do it

 

In a variety of ways: http://www.talkorigins.org/faqs/faq-speciation.html

(That page also has a good discussion of the difficulties of defining species.)

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I have seen arguments that, for example, Chihuahuas and Great Danes should be considered separate species because they are reproductively isolated. It is probably mainly a matter of convenience that they are still considered one species.

Probably a cruel idea, but it would be interesting to see the outcome of artificial insemination -- testing the boundaries of phenotypic plasticity. If such an experiment produced fertile, viable offspring would we have to concede that the parents were of the same species?

 

In a variety of ways: http://www.talkorigins.org/faqs/faq-speciation.html

(That page also has a good discussion of the difficulties of defining species.)

 

"Niche" has the same problem.

 

The pattern seems to be that we get an idea (based on our preconceptions, biases and limited knowledge), then we coin a term for the idea, then we go looking around in nature for a target on which to pin the term.

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Probably a cruel idea, but it would be interesting to see the outcome of artificial insemination -- testing the boundaries of phenotypic plasticity. If such an experiment produced fertile, viable offspring would we have to concede that the parents were of the same species?

 

Not really. There are plenty of examples where two species can succesfully interbreed with suitable intervention. After all, reproductive isolation could just be caused bya mountain.

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I have seen arguments that, for example, Chihuahuas and Great Danes should be considered separate species because they are reproductively isolated. It is probably mainly a matter of convenience that they are still considered one species.

 

 

In a variety of ways: http://www.talkorigins.org/faqs/faq-speciation.html

(That page also has a good discussion of the difficulties of defining species.)

But if breeders of Great Danes started selecting ones that were chihuahua like and Chihuahua breeders started selecting for larger features could they unify the two "dog species" again? It might take another 1000 years but it would happen.

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If dog breeders haven't yet produced a new species (or if they have, please comment) then how does nature do it, given its much feebler ability to produce morphological variability from a genome?

 

Neither nature nor dog breeders are trying to produce a new species, but the dog breeders are probably more interested in the traits that would keep a dog a dog, within the same breed. They go out of their way to enhance dog qualities. Nature, on the other hand, doesn't consider any of those traits unless they make the dog more successful at passing his genes along.

 

The pattern seems to be that we get an idea (based on our preconceptions, biases and limited knowledge), then we coin a term for the idea, then we go looking around in nature for a target on which to pin the term.

 

Actually, most ideas come from observation, and I really wouldn't call that preconceived or biased. This is just labeling, and is an important part of the process. We have to worry about biases, limited knowledge, and preconceptions after we've labeled something.

 

We labeled the Earth "flat" because that's what we observed. Then our observations got better, and we realized it wasn't flat after all. We didn't change our definition of flat, we didn't let our flat bias influence us once we realized what we were seeing.

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Neither nature nor dog breeders are trying to produce a new species, but the dog breeders are probably more interested in the traits that would keep a dog a dog, within the same breed. They go out of their way to enhance dog qualities. Nature, on the other hand, doesn't consider any of those traits unless they make the dog more successful at passing his genes along.

 

I can't imagine a dog breeder thinking, "Hmmm, I'd better be careful. My breeding project might produce a non-dog."

 

A dog breeder wouldn't last long as a breeder if she produced dogs that were not successful at passing their genes along. Whether breeders select or nature selects, both will factor in prospects for reproductive success. If natural selection produces new species by working on the variation in a population, then, with all the variation among dog morphologies, why yet has no non-dog been bred? The link in post #5, above, goes to a web page that makes clear the ambiguity of the term "species."

 

And I like your anthropomorphizing of nature as an agent who "considers" before she "selects."

 

 

Actually, most ideas come from observation, and I really wouldn't call that preconceived or biased. This is just labeling, and is an important part of the process. We have to worry about biases, limited knowledge, and preconceptions after we've labeled something.

 

We labeled the Earth "flat" because that's what we observed. Then our observations got better, and we realized it wasn't flat after all. We didn't change our definition of flat, we didn't let our flat bias influence us once we realized what we were seeing.

 

My comment referred to category names, like "species" and "niche". I suppose you could say that those terms are like "flat" in your example, insofar as they ought to be retired or superceded.

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The breeders aren't going "I'd better not breed something that isn't a dog" but they do breed for specific traits, which means that once a specific breed has been established, most of the breeding effort goes into keeping it static.

 

Which is part of why there are so many breeds of dog, because humans do their best to preserve all of the variations that crop up that we happen to like and prevent them from melding back into the general dog population or developing even further off on some tangent and becoming even less "dog-like."

 

And then there is the aforememtioned argument that chihuahuas and Great Danes may no longer be the same species. Certainly, if we found them in wild in their current state rather than having bred them ourselves we would almost certainly classify them as separate species that had diverged relatively recently.

 

Which then, though, is the "non-dog?" There may be, and probably will be, frankly, a point where it is even more readily apparent that various branches of the dog tree are no longer a single species, but defining the precise moment where they diverged won't be particularly easy and picking which one is the real dog and which one isn't is going to seem just as silly as picking whether it is Great Danes or Chihuahuas that aren't really dogs.

 

And this is beside the point that dogs have already speciated. Humans put a selection pressure on wolves until we got something that was a "non-wolf" and then named the new species we bred "dog."

 

I can't imagine a dog breeder thinking, "Hmmm, I'd better be careful. My breeding project might produce a non-dog."

 

A dog breeder wouldn't last long as a breeder if she produced dogs that were not successful at passing their genes along. Whether breeders select or nature selects, both will factor in prospects for reproductive success. If natural selection produces new species by working on the variation in a population, then, with all the variation among dog morphologies, why yet has no non-dog been bred? The link in post #5, above, goes to a web page that makes clear the ambiguity of the term "species."

 

And I like your anthropomorphizing of nature as an agent who "considers" before she "selects."

 

 

 

My comment referred to category names, like "species" and "niche". I suppose you could say that those terms are like "flat" in your example, insofar as they ought to be retired or superceded.

Nobody who knows anything about biology thinks "species" is an objectively extant category. It's a useful convention for keeping track of the relatedness and breeding status of populations. It's not the equivalent of calling the Earth "flat." It's the equivalent of calling Earth a "sphere." It's not a sphere. Even the more accurate "spheroid" isn't strictly accurate if you want to get into the really fine topology of the planet like the mountains and valleys going up and down all over the place. The Earth is approximately spherical and that'll do for keeping track of its shape without inventing a new "Earth-shape" that exactly matches every contour of the planet's surface and helps precisely no one understand what shape the Earth actually is.

 

If we want to impose the same strictly accurate categories onto evolutionary biology and only discuss distinct categories that actually exist and don't have any fuzzy edges or blur into each other, we'd be reduced to talking solely about individual organisms as entirely separate entities which, again, helps precisely no one understand how individuals are related or their interbreeding status.

 

We don't retire ideas in science because they are imperfect (that is generally assumed), we retire them because we have come up with something better for the purpose at hand. So yes, if you can point us to something as or more useful than the concept of categorizing by species that is more accurate, you'll gladly pull in some converts to your new system. Until then, this is what we've got.

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The pattern seems to be that we get an idea (based on our preconceptions, biases and limited knowledge), then we coin a term for the idea, then we go looking around in nature for a target on which to pin the term
Backwards, in this case (and in science generally).

 

The usual sequence in these biological matters is the opposite: we see a pattern in nature, we coin a term for it so we can talk about it, and then over years of research and discussion we develop a concept of what is actually going on. The concepts of a "species" or a "niche" (or a "phylum" or a "biome") illustrate this process well - the observations of the natural patterns predate the terms by thousands of years, and the terms predate the concepts or ideas of what's actually happening by decades or even centuries.

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And then there is the aforementioned argument that chihuahuas and Great Danes may no longer be the same species. Certainly, if we found them in wild in their current state rather than having bred them ourselves we would almost certainly classify them as separate species that had diverged relatively recently.

 

Why would it matter to their taxonomic status whether their current state is the result of natural or artificial selection?

 

If a person wanted to create a new species from a founding population of dogs (without manipulating genes in a laboratory), that person would do what dog breeders have done -- namely, divide the founding population into inbreeding subgroups that are reproductively isolated from one another and breed within each group selectively for morphologies that diverge from those of the other groups. Normal evolution theory says that this, effectively, is what nature does, but with much less capacity to render morphological variation from a given species genome -- that is, generating much less variability in a population for selection to work on, as compared to dog breeders.

 

The dog breeder's chart included in the OP can be read as a depiction of dog morphospace, and it's pretty well filled up, but still no new species. (If you want people to take seriously an assertion that Great Danes and Chihuahuas are distinct species, I think you'll have an uphill battle.) (I don't suppose there's much interbreeding between Eskimos and Tutsis, but would anyone say that these ethnicities represent different species? Have biologists quantified how much interbreeding would have to go on before two groups of whatever would be designated as the same or distinct species?)

 

On your characterization of "species" as being a useful, if fuzzy, convention for tracking relatedness and breeding status of populations ---- all kinds of scientific terms are fuzzy (e.g., do the planets include Pluto or not?), so I don't pick on biology in particular. But one can find references to speciation events, and it seems to be a standard term. But given the fuzz around "species," such events would seen to consist of a panel of judges (whoever they are) deciding that some critical number of criteria are met. But it seems pretty arbitrary which criteria are considered, how much they are weighted relative to one another, and what the thresholds are for deciding species or nonspecies in any particular case.

 

As an exercise in truth-in-advertising maybe we need to rename Darwin's book, "On the Origin of Pragmatically Useful but Admittedly Only Loosely Defined Categories"

 

Again, my point in the OP is that dog phenotypes vary much more than would be found in any natural population of some given species. And phenotypic diversity is supposed to be fertile ground for speciation, yet we find no non-dogs resulting from dog breeding. (& who gets to decide dog/non-dog? The American Kennel Club? {!} )

Edited by starlarvae
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Can all those dogs interbreed? Can you get a viable offspring from a Chihuaha and a Great Dane?

 

Nature can produce clines wherein there is still gene flow despite the opposite ends being incompatible.

https://en.wikipedia.org/wiki/Cline_%28biology%29


addendum:

 

I have seen arguments that, for example, Chihuahuas and Great Danes should be considered separate species because they are reproductively isolated. It is probably mainly a matter of convenience that they are still considered one species.

 

We picked the same dogs! :eek:

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Again, my point in the OP is that dog phenotypes vary much more than would be found in any natural population of some given species. And phenotypic diversity is supposed to be fertile ground for speciation, yet we find no non-dogs resulting from dog breeding.

There hasn't been a selection event yet, or any other ecological separation, so there's no need.

 

Kill all the dogs except Brazilian mastiffs and pomeranians, put them on different continents, and you'd have two species of dog.

 

 

 

 

But one can find references to speciation events, and it seems to be a standard term. But given the fuzz around "species," such events would seen to consist of a panel of judges (whoever they are) deciding that some critical number of criteria are met. But it seems pretty arbitrary which criteria are considered, how much they are weighted relative to one another, and what the thresholds are for deciding species or nonspecies in any particular case.

They're panels of taxonomists, specialists in the given type of organism, and they fight endlessly over just such matters as you describe. What's your point?

 

 

As an exercise in truth-in-advertising maybe we need to rename Darwin's book, "On the Origin of Pragmatically Useful but Admittedly Only Loosely Defined Categories"

That's what it's named already. Why would be have to use some long-winded definition rather than the perfectly good noun?

Edited by overtone
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Kill all the dogs except Brazilian mastiffs and pomeranians, put them on different continents, and you'd have two species of dog.

 

I've wondered whether larger populations evolve more quickly, and whether evolution might accelerate when periods of amplified reproduction and diversity are puncuated by bottlenecks, as opposed to a stable but small population.

 

Regardless, starlarvae may be hastily generalizing / inducting. Although it's uncommon (how uncommon?), a hybrid zone is an overlap between the territories of two diverging or recently diverged populations, and it shows that nature can produce sufficient variation for speciation. However, because these hybrids may have reduced viability or no viability, individuals who prefer members of their own population may be more successful. Hence reproductive isolation may be a natural, negative-feedback response to hybrid zones.

Edited by MonDie
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Although it's uncommon (how uncommon?), a hybrid zone is an overlap between the territories of two diverging or recently diverged populations,
Hybrids are very common in plants - afaik every oak species in North America has associated hybrids with one or more other oak species.

 

 

I've wondered whether larger populations evolve more quickly, Larger populations generate more variation, smaller ones are more sensitive to selection pressure, the combination is what establishes an evolutionary step - for any given species and landscape and set of circumstances there is probably a sweet spot combination regime of maximal evolutionary rate.

 

Most Darwinian pressure maintains, rather than altering, any given successful species. Darwinian selection prevents evolution, most of the time.

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There hasn't been a selection event yet, or any other ecological separation, so there's no need.

 

Kill all the dogs except Brazilian mastiffs and pomeranians, put them on different continents, and you'd have two species of dog.

 

They're panels of taxonomists, specialists in the given type of organism, and they fight endlessly over just such matters as you describe. What's your point?

 

That's what it's named already. Why would be have to use some long-winded definition rather than the perfectly good noun?

 

Right. "Species" does not name a natural kind. It's just a convention of terminology. If the taxonomic panel perceives a lack of family resemblance, then two species. So, the actual origin of species does not take place in nature or at the kennel club, but in the tally of votes among the panelists.

 

Makes sense to me.

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Perhaps the problem is that, although Canis lupus has enough variation to speciate, we can't know whether it will ultimately end up speciating or converging back together. Just as a hybrid zone may lead to further reproductive isolation, or to a repooling of gene pools.

 

Starlarvae, it's not clear (to me) that the scenario for Canis lupus would ever occur in the wild. Reproductive isolation is often naturally selected, so it may not happen for a domesticated species, especially one that is intentionally bred for greater variety.

Edited by MonDie
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Right. "Species" does not name a natural kind. It's just a convention of terminology. If the taxonomic panel perceives a lack of family resemblance, then two species. So, the actual origin of species does not take place in nature or at the kennel club, but in the tally of votes among the panelists.

 

Makes sense to me.

There's no such thing as a "natural kind" so I would have to agree that a species is not one.
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Right. "Species" does not name a natural kind. It's just a convention of terminology.

It's the name of a biologically and ecologically and taxonomically significant category of organisms. All terminology is conventional.

 

Do you have a point? What are you trying to say - that the scientific naming of things is an arbitrary and capricious triviality? That the pros in their fields have no good reason for their arguments and classifications?

 

 

 

 

So, the actual origin of species does not take place in nature or at the kennel club, but in the tally of votes among the panelists.
You are confusing the name with the thing. The naming of a species is the naming of an observed category of organism - when they are named, the name is attached to a formal description of the features collectively distinguishing that group of organisms from all others. The name originates in the proposal of a taxonomist or discoverer of that group of organisms, and is approved - not originated - in the tally of panelist votes.

 

The organisms themselves originate in nature (or possibly in a kennel), and are observed in nature to belong to a group, be and act in certain ways as members of a common entity, have certain significant features in common. Human beings name such common entities "species", at least in English.

Edited by overtone
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Perhaps the problem is that, although Canis lupus has enough variation to speciate, . . . .

 

How do we know how much variation is enough? We have to wait for the panel of taxonomists to declare a new species, I guess.

It's hard (impossible?) to imagine a species producing as much variability in nature as the breeders have been able to pull out of the dog genome -- and reproductively isolate.

 

Starlarvae, it's not clear (to me) that the scenario for Canis lupus would ever occur in the wild. Reproductive isolation is often naturally selected, so it may not happen for a domesticated species, especially one that is intentionally bred for greater variety.

No, I cannot imagine that it would occur in the wild. I think it's fair to say that the specialized breeds ARE reproductively isolated. The breeders make sure of it.

There's no such thing as a "natural kind" so I would have to agree that a species is not one.

 

Then I guess that the origin of species occurs when the taxonomists decree that a new species has originated. Speciation events occur at meetings of taxonomists, not in the wild. That seems to be the implication of what you guys are saying.

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Then I guess that the origin of species occurs when the taxonomists decree that a new species has originated. Speciation events occur at meetings of taxonomists, not in the wild. That seems to be the implication of what you guys are saying.

 

Although the species concept can be rather fuzzy and hard to define, there are also cases where no (reasonable) person would disagree that a new species had been created. Many such events have been recorded..

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Then I guess that the origin of species occurs when the taxonomists decree that a new species has originated. Speciation events occur at meetings of taxonomists, not in the wild. That seems to be the implication of what you guys are saying.

No. Whether something qualifies as a species is decided by taxonomists. While there is a level of arbitrariness to categorization in this many, it's not completely arbitrary, and is based upon on reproductively isolated two populations are. Based on that reproductive isolation, taxonomistss decide whether a population qualifies as a separate species, but the "speciation event" is whatever lead to the population becoming reproductively isolated in the first place, which is something that actually happened in nature rather than the moment a labelled was applied.

 

Whether an event counts as a speciation event or not certainly depends upon how taxonomiats have decided to classify the populations involved, but it's still an event that took place regardless of how it is classified.

 

It's like having a name for the formation of a planet "the planet formation event" and saying that, since taxonomiats of a sort vote on whether something is a planet, if the decision on Pluto ever got overturned and it is reinstated as a planet, that would be the real "planet formation event."

 

That's nonsense. Pluto's formation happened regardless of whether it qualifies as a planet or not, and if it does, that is a "planet formation event." Similarly, whatever event lead to the traits which lead taxonomiats to classify a population as a species happened regardless of whether the label is applied. If it is applied, that is the speciation event. If it does not get applied, that would still be an event that happened, it just wouldn't count as a "speciation event" because it didn't lead to enough reproductive isolation for taxonomiats to classify the result as a new species.

 

In no circumstance is the application of the label the "real" event.

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It's like having a name for the formation of a planet "the planet formation event" and saying that, since taxonomiats of a sort vote on whether something is a planet, if the decision on Pluto ever got overturned and it is reinstated as a planet, that would be the real "planet formation event."

 

That hunk of rock [Pluto] originated whenever and however it did. At some point it was deemed to be a planet. Then not. It became a planet only when it was granted planethood, and ceased to be one when the definition of "planet" was changed. If the definition of "rock" gets changed, then the object might cease to be a hunk of rock.

 

Point is, anyone can look up the definition of planet and see if Pluto qualifies.

 

It's not clear that anyone can look up the definition of species and see if Great Dane qualifies.

 

 

Whether an event counts as a speciation event or not certainly depends upon how taxonomiats have decided to classify the populations involved, but it's still an event that took place regardless of how it is classified.

 

You want to have it both ways. You wants speciation events to occur in nature and you want taxonomists to decide what counts as such an event.

 

SO, prior to the taxonomists' verdict being rendered, how do you know whether or not any of those events out there in nature are speciation events?

Do you have a point? What are you trying to say - that the scientific naming of things is an arbitrary and capricious triviality? That the pros in their fields have no good reason for their arguments and classifications?

 

You are confusing the name with the thing. The naming of a species is the naming of an observed category of organism - when they are named, the name is attached to a formal description of the features collectively distinguishing that group of organisms from all others. The name originates in the proposal of a taxonomist or discoverer of that group of organisms, and is approved - not originated - in the tally of panelist votes.

 

The organisms themselves originate in nature (or possibly in a kennel), and are observed in nature to belong to a group, be and act in certain ways as members of a common entity, have certain significant features in common. Human beings name such common entities "species", at least in English.

 

If the pros in their fields have specific thresholds of, say, reproductive isolation, or phenotypic (or genotypic) variability, or other parameters that determine whether two critters are of the same or distinct species, then what are those parameters and what are the thresholds?

 

I would like to see (and it might shut me up if I did) the formal description of the features collectively that distinguish some group of organisms as a species, distinct from all others.

 

If such parameters with their thresholds and attendant formal descriptions of features are not to be had, then I suppose that an accusation of "arbitrary and capricious" is to a degree justified.

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It's not clear that anyone can look up the definition of species and see if Great Dane qualifies

 

Actually, you can. There are different species definitions used in various (evolutionary) contexts. Thus, one has to define what concept one is using and for what purpose. You may want to check out wikipedia for starters: http://en.wikipedia.org/wiki/Species#Definitions_of_species

 

For different type of research question the use and definition may differ. It is true that one has to have some knowledge of the literature to be certain what is used and what for, but that only highlights the complexity we see in nature and the fact that one need quite some effort to make sense of it.

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I would like to see (and it might shut me up if I did) the formal description of the features collectively that distinguish some group of organisms as a species, distinct from all others

They vary by field and purpose.

 

Here is a semi-formal (readable in English, without the botanist's technical vocabulary) description of a group of organisms that has been taxonomically classified as Quercus rubra, a species of oak, for more than 250 years (originally by a creationist, a century or more before the standard theory of evolution was developed): http://www.gbif.org/species/2880539 If you want to dig into it, and you know enough Latin and Greek, follow the links on the page.

 

Clearly few or none of those features would apply to an equivalent description of a group of organisms taxonomically classified as a species of vole. There is no such thing as a collective set of features that distinguishes any species of anything from any species of anything else.

 

So there's nothing there to shut you up, if you wish to persist in your ignorance and unfamiliarity. But if you try to sell a lumberman or firewood cutter the logging rights to an acre of mature, healthy, well grown woods dominated by this species: https://gobotany.newenglandwild.org/species/quercus/ilicifolia/ for the price of an acre of equivalently mature, healthy, well grown Quercus rubra, they will laugh at you. People with money on the line do not regard species distinctions as capricious and arbitrary whatsoever.

Edited by overtone
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There are different species definitions used in various (evolutionary) contexts. Thus, one has to define what concept one is using and for what purpose. You may want to check out wikipedia for starters: http://en.wikipedia.org/wiki/Species#Definitions_of_species

 

For different type of research question the use and definition may differ. It is true that one has to have some knowledge of the literature to be certain what is used and what for, but that only highlights the complexity we see in nature and the fact that one need quite some effort to make sense of it.

 

Pick & choose from among a menu of definitions according to my purposes? That's weird science.

 

This link: http://en.wikipedia.org/wiki/Species#Definitions_of_species really is an eye opener. Is there any term outside of the biological sciences that is so problematic, any term whose definition is so wildly elastic?

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