so what is species?

[acroyear]

Going back to a discussion javasaurus and I had a few months (more than a year?) back...

The Questionable Authority: How many species 2: What is a species, and Why does it matter?:

The reason that we have a hard time coming up with a definition of species that works for everything is that there isn't one. Different types of organism keep themselves sorted out in groups in different ways. Mayr's definition works (at least in theory) for organims that are sexually reproducing. It goes all to hell when confronted with asexual organisms, and it gets worse when you toss plants into the mix - they do the wierdist damn things as they evolve.(Go read John Wilkins' paper on the topic, since he does a much better job explaining this.) Because evolution is an active, ongoing process, you will also find - no matter what definition works best for your organisms - some groups that are pushing the boundaries between species.

[...]

It's a tired analogy, I know, but dealing with "species" really is a lot like dealing with the concepts of "child" and "adult." We know that there are differences between children and adults. It takes no real insight to look at the two and identify significant distinctions between the groups. The problem comes when you try to come up with definitions of "child" and "adult" that are capable of unequivocally distinguishing the two. It can't be done - there is no sharp distinction between the two there to identify.

Comments

[javasaurus.livejournal.com]

From the article that you cite: "Tigers and lions do not interbreed in the wild, are very different in appearance, and have very different behaviors. If they are not different species, the term becomes essentially meaningless."

The section that I quoted is talking about why lions and tigers are not the same species, despite the fact that they can, biologically, interbreed and produce fertile offspring. I must disagree with the notion that difference in appearance and behavior is sufficient or even important to distinguish species. Different breeds of dogs are much more diverse in behavior and appearance than lions and tigers, yet are considered the same species. But this is, again, a case of no definition of species being universal.

I believe, in the case of lions and tigers, the lack of naturally occurring interbreeding is the major point of speciation -- they'll never encounter each other in the wild.

As for why it's important...maybe it shouldn't be, but certain aspects of our society have chosen to make it so. For example, laws protecting endangered species depend on being able to identify a species. Additionally, some biologists base their careers on taxonomy and discovery of new species. Many medicines are plant-based, and may be available only from one or two species of plant, so being able to distinguish plant species can be important. There are about 30 species of mosquito in our area -- not all of which carry west nile, and none of which (yet) carry malaria. Being able to track the migration of mostquito species allows us to predict the spread of some species-specific diseases.

[acroyear70.livejournal.com]

his examples on other "kinds" (read his part 3) get even more complex, but the reality is that it shows that even something as basic as "each according to its kind" (from Genesis) no longer has any meaning once science gets involved.

That's the real point of the species discussion: we used to think that at least we could talk about species and know what we were dealing with (as opposed to our definitively arbitrary kingdom/phylum/class/family/order/genus measurements) - now we are definitely sure we can't even be definitive about species anymore.

What a "species" means is relative to other factors in the hierarchy, so even as the species defines the hierarchy, the hierarchy defines what species means. Science, its the efforts to achieve the perfection of classification that Linneus wanted, has shown that such perfection of classification and specification is impossible. Reality is never convenient.

In this, its finally philosophically "proven" that biology is just as complex as physics and chemistry - at any point we try to achieve perfection in precision (like General Relativity), we realize that such precision defies achievement (Quantum Mechanics). Statistical likelyhoods are all that can be known, and exceptions will always defy the odds.

Not to worry - you can always lie with statistics! ;-)

As for your other examples - it gets more complex than that when hybreds get involved. Only "one or two species" of plant might provide such-n-such, but at what point is a plant no longer of those "one or two" due to hybredization? If it is still of that species yet doesn't provide that attribute, though it provides all others, do we add subspecies? do we add a new classification for hybreds? do we just call it a new species, even though it can and does still reproduce with the originals in the wild thanks to pollinating insects?

then there's the whole naturally reproducing vs artificial reproducing (i.e., forced breeding by man in controlled environments) issue...

our classification mechanisms try to force us into a "pure-blood" model of biology, where the reality of biology is that no such model has ever existed. fortunately, this means that in spite of the handful of social darwinists (either socialists or robber-barons) still out there, biology could never support such racist claims of perfection or superiority.

the reality of *modern* biology (as it has changed from Linneus's and Darwin's models) is that of individual's features and some regionalized population groupings of individuals with those features. anything else is a force-fit of reality into a model for convenience, an abstraction that should be described like all abstractions man has ever invented: a leaky one. reality is never so abstract...