Stealing this one from Moselio Schachter:
A guy walks at night on a beach in California and stubs his toe against an old bottle, which breaks and releases a genie. “I’ll grant you one wish, oh Master,” says the genie.
The man replies, “Well, I'd dearly love to go to Hawaii but I hate both airplanes and ships, so would you build me a highway from here to there?” The genie thinks for a moment, then replies, “Indeed, I said you could have one wish, but this one seems nearly impossible. Could you ask for something easier?"
The man, being a microbiological sort, says, “OK, can you then tell me what is a species?”
The genie pauses, then answers, “Do you want it two lanes or four?”
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HA!
Boy, I'm glad you brought this up again. I was just thinking about it. We have had several conversations on this topic.
It seems to me: all animals (ignore plants) are related to all other animals. Isn't that the essence of evolution? If no animal group had ever died out there would be a complete bush with continuous variation from the earliest creatures to the most recent. So, it is only because groups go out of existence, leaving gaps between other groups on both sides of them, that allows us to call those separated groups different species. This comes into play in cases that we have discussed here. I said that big dogs and little dogs should be considered different species. You said - put a complete range of dogs on an island, come back later, there will be a collection of medium sized dogs - they are interfertile. So, not different species. But, consider ring species: gulls, salamanders. At the ends of the ring, the adjacent animals are considered to be separate species because they cannot interbreed successfully. But, to use your counter argument from above: Put members from each step of the ring on an island and there will be a totality of intermediates created. So, again, the end groups that cannot interbreed should, nevertheless, be considered the same species.
I guess the only point I'm making is that there is inconsistency in the use of the term. It seems clear that in both cases, if the intermediates die out, then the end groups will be distinct species. But, until then. it is inconsistent to call all dogs one species, but not gulls.
And, of course, that is the point of your story.
It seems to me that folks will either get it or they won't. To my mind, evolution predicts that the concept of species will be a slippery one, that there's no definitive boundary, and sometimes, even when there seems to be, there may still be gene flow. The real world of biology can be a messy place. I suppose, ultimately, it's like any kind of categorization; there's a certain amount of arbitrariness, if for no other reason than it's a means of categorization. You have to draw a line somewhere, but you should always be aware that the line may very well be an artificial one.
But categorizations are not always messy. Parliamentarians (in sensible jurisdictions) sit in the upper house or the lower house). Spacetime intervals are spacelike, timelike or null. Fundamental particles are bosons or fermions. Even in biology, discounting just the odd pathologically idiosyncratic individual: extant mammals are monotremes or marsupials or placentals.
It's so much easier to speak in terms of "kinds," because this term is so utterly meaningless. Thus the "fish kind" includes whales, the "cud-chewing kind" includes bunny rabbits, but the "primate kind" does not include humans (because they are special). As some of the above have suggested, the difficulties in definition are an expected consequence of evolution.
People have already pointed out excellently that if you really think about evolution you realize that species is a pretty nebulous categorization method, but for metazoa the biological species concept works for the most part. There are exceptions (ring species were pointed out) and there sometimes are exceptions of rare gene flow, etc.
But to me, given that the joke specified the wishee was a microbiologist, is that for unicellular organisms, particularly bacteria, where LGT is rampant the species concept breaks down. Granted we use different ones for them then we do for the Metazoa but even then trying to define a bacterial species becomes a really difficult question.
What about these thoughts from Vienna Cardinal Schoenborn (I can't find them in english, hope you have them translated. If not, ask Massimo Pigliucci)?
Il primo esempio e' il concetto di "specie". Il celebre libro di Darwin s'intitola The origin of species. Ma esistono davvero, le specie? Il metodo meramente quantitativo riesce a comprenderle? Nella teoria dell'evoluzione c'e' posto per loro? Non e' forse vero che tutto cio' che chiamiamo specie non e' che un'istantanea nell'ampio flusso dell'evoluzione? I concetti di specie, genere, regno (regno animale e vegetale) non sono forse soltanto nomina nuda, senza una realta' corrispondente? A livello di misurabilita' e quantificabilita', species e genera sono parole vuote. Ma gli occhi dello spirito comprendono perfettamente che esiste la specie "gatto" (e proprio il Santo Padre Papa Benedetto, amante dei gatti, ne e' un sicuro testimone!). La differenziazione fra il cane e il gatto e' pertanto gia' di per se' non scientifica?
From: http://www.zenit.org/article-15006?l=italian
John, are you still there?
Marco
Wait a minute. I heard that the genie built the four-lane highway to Hawaii because the genie didn't want to help men understand women.
Marco, as best as Babelfish can work it out, Schönborn is saying something like - "species is a construct of the way we name things". This is an old claim, and not one that I think explains the facts of biology. Yes, they are hard to delineate in some cases, especially as Moselio says in microbiology, where lateral transfer is rife, but they are facts of the biological world in my opinion.
You surely remember Schönborn as the creationist cardinal who attacked evolution many times (especially in a New York Times article a couple of years ago). The excerpt above is inside a new long article on Osservatore romano (pope's newspaper) titled "Creazionismo ed evoluzionismo senza ideologie possono incontrarsi" (creationism and evolutionism can meet, without ideologies). It is a clear endorsement of creationism - of the most subtle kind, to tell the truth. And a pamphletist accusation of evolutionism as ideological, when it doesn't agree with end and means of religion. The cardinal quotes at length Newton, Jaki, Galileo etcetera, to "demonstrate" that nature cannot generate life and evolve all by itself. There's a pressing need for "final cause" (sensu Aristotle).
It is just to remind you english speaking people that the catholic church (at least this pope) is not at all against creationism.
I think most fish species are clearly bounded individuals. Much of my research focused on resolving questions of how many species of killifish do we have here. I used hybridization and behavioral studies, as well as morphology, including karyotypes, and more recently have collaborated with DNA workers. I think many of the "fuzzy species" situations reflect lack of study. There are some very interesting situations with ring species, persistant hybrid swarms, introgression, etc., as well as situations where speciation may be happening. But I think this is the uncommon rather than the common.