Over at my other weblog, Gene Expression "Classic", I addressed the polemics of one David Stove, author of Darwinian Fairytales. I won't go into the details of Stove and that book, but if you follow the comment thread you will see that sometimes shit can be a very good fertilizer and give rise to food for thought. The comment thread made more explicit in my mind a few issues I have in regards to evolution.
First, I hold to the scale independence of evolution, that is, there is no fundamental difference between microevolution and macroevolution. Macroevolution is in reality simply a posterior observation about the nature of microevolutionary dynamics framed by particular subjective criteria.
And those criteria relate to species. Not only do I believe in the scale independence of evolution, but I lean toward the continuity of the web of life and am skeptical of "rigorous" definitions of species. I am inclined to take a very instrumentalist view toward this issue and don't dismiss phenetics or cladistics. Certainly species have more of a reality than genera, but their utility is contingent upon the branch of the tree of life you are examining. Myself, I tend to think of species as populations which exhibit a tightly linked correlation of alleles across a broad swath of loci. In other words, there are no idealized Platonic species, they are simply working classifications which allow us to make sense of the genetic architecture of a population.
Just because I reject Platonic categories does not mean I neglect order or classification, rather, I believe that such things need to be expressed in a nuanced manner. Rejection of strict universals does not imply that all things are equally true and false and that the gates of Post Modernism should be thrown open, rather, statistics and probability can offer us a rough gauge of various distributions of likelihoods and offer us a way to characterize the more complex topology of some concepts. You saw this crop up in the race debate, I don't deny that races exhibit genetic and phenotypic continuity, but the inability to "objectively" offer up Platonically idealized types does not negate the reality of non-random structure.
Evolutionary biology is the science of exceptions to generalizations, but, the reason our generalizations are so prone to being violated is that we don't truly speak in the language of evolutionary biology, which is in discrete genomic packets. Species, individuals and gene loci are simply gestalt approximations that hold, more or less, but they all have their weaknesses. The utility of each level of organization and approximation is framed by the questions you ask and the answers you are seeking.
Finally, in regards to language I am beginning to think that it wasn't smart of me to simply concede semantics to evolutionary skeptics and play the rules of the popular game in regards to "species" and "macroevolution." As you can guess from above, I have serious issues with the idea of species as such, but nevertheless I am asked to "prove" speciation. My heart of hearts tells me that in many cases this is irrelevant or incoherent, but my reflexes born from debates in places like alt.atheism tells me that I should rise to the challenge and refute, refute, and refute. Similarly, arguments about macroevolution presuppose that I believe that such a thing as macroevolution is anything more than an extension on microevolution, which I don't, but coupled with the species question I have entertained this topic in rhetorical matches.
The reality is that evolutionary biology is beautiful, and the post-genomic era is upon us and we are gazing into the abyss of unimaginable riches. And yet Creationists and their ilk still speak the language of 1906, not 2006, and demand that we battle them on the traditional dueling grounds. But the future beckons, and they are soon going to be irrelevant.
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You may not like the concept of speciation, but the parts that make it up (reinforcement, geographic isolation, pre- and post-zygotic barriers, etc) are real. They are also worth studying, imo. In studying those factors, scientists are, for all intents and purposes, studying "speciation". And to study speciation, we must come up with a definition for what we consider species. Coyne and Orr argue that the best definition (in terms of practicality when studying speciation in sexual organisms) is the BSC. I like this line of thinking, and seems appropriate regardless of whether you think species are real or not.
yes, like i said, i'm an instrumentalist. my point is i get tired of getting into quasi-philosophical debates with creationists on the topic because the subject is too malleable. since the BSC is fuzzy that means the goal posts can always be changed. stuff like the various isolations you mention are not absolute of course. they are good enough for scientific discussion, but not rock-hard enough that i want to start system building or getting into a rhetorical war over them.
Thanks for the link to that paper on scale independence.
i've always had a kinda gut dissatisfaction with the idea that micro and macro are separate. Now I know how to articulate it instead of just saying "look damn you...its obvious" which was also my argument in support of an evo-devo-type look at the world (instead of strict modern synthesis).
good post, and it looks like we agree far more on classification than either of us thought months ago when I was bitching about the humans being chimps paper a few months ago.
As far as I can see the only difference I can see is that I do find genera and higher level taxonomic categories useful for talking about and understanding things at I guess a more naturalistic level of understanding (feeding ecology, gross morphological trends, behavioral trends, stuff like that). Although, like you, I try to understand and acknowledge that this is basically grouping things to make them more intelligible.
I'm really just a cladist who likes to use colored pencils.
There's a pretty famous picture of the 6 (or is it 8...i forget) baboon 'species' and hybrid zones. I could do one up for marmosets pretty quickly too.
Are they no longer species despite differences in appearance, behavior, and the fact that less than 1% of either population mates with the others?
What about something like the horse and donkey. Mules aren't fertile. But hinnies are.
There are a lot of examples out there that make the BSC, as Razib said, all too fuzzy.
The mechanisms of speciation are fascinating, but I don't know that we'll ever be able to define it beyond "look damn you...it's obvious"
I'm going to keep talking about Saguinus fuscicollis and Saguinus nigricollis as separate species, even though there's a fairly substantial hybrid zone, but I'll recognize that their separateness is kinda fuzzy. It's just useful since they each form mixed species groups with a different specie of 'large' tamarin (if 1lb is considered large)
Forgive me for maybe having a simple mind, but to me, not to creationists, it's almost as simple as this:
Broad phenotypic resemblance=broad genotypic resemblance(genotypic consistency), & that it *must be that way* -- i.e., that this relationship is not stochastic but very straightforward. Species members resemble each other broadly(phenotypic & genotypic continuity), which happens to be *no accident* & this makes it very useful, almost inevitable, to draw species boundries. I can hardly see anything fuzzy about it. These crazy creationists *don't* have any argument in their favor. Bio-Statistics doesn't support creationist assertions. I'm sure that there's more to it than this, but also that creationists have NO arguments in their favor. I've heard such nutty arguments as "since there in *considerable* genotypic variablity within species, concept species must then have *no validity* to it". This still doesn't mean that species members are more broadly dissimilar than they are similar. To me, there must be *genetic constants(broad consistency)* within all species members that cause them to look & behave alike. Breeding groups geno-phenotypically distinct.
As far as mirco-vs-macro, I believe that science(*right now*) is in the process of uncovering just how macro(speciation)happens. Now, I know about dogs, wolves, but c'mon here.
it's really simple. Take one population. micro is operating throughout the population.
take wall. plunk down in the middle of population, separating one half from the other half. micro is now operating on two separate populations. In subtly different ways. Even if there is no difference in habitat on either side of the wall, the quirks of sexual selection (See marmosets), neutral selection, etc. will result in population level differences in allele frequency between the two. furthermore, mutations that arise in one population can become fixed in that one, but can't even get to the other one. Should these mutations affect pre or post zygotic mechanisms, you now have two species.
To complicate matters (and make it more real-worldy), let's now turn one side of the wall into a savannah, and the other side into a rainforest, complete with ecosystems. Now selection pressures operating on each population are alos different. the process will be much more speedy.
all that happened was your basic micro evolution. It just happened in a population that was divided into two halves due to external factors.
"Should these mutations affect pre or post zygotic mechanisms, you now have two species. ..... ..."
IndianCowboy,
You've brought about as much clarity & elucidation to the subject as I suppose is possible. Anytime you encounter an evolution skeptic or a fool, give them your explanation. There's no way any rational mind could pick holes in what you've just said, I believe; it just makes sense and so elegantly simple too! Reading(& understanding) your explanation above was perfectly easy for me, so why/how do supposedly *educated* people have problems w/ grasping these concepts, I wonder? I don't even understand elementary arithmetic or algebra, so anyone understanding those things should certainly understand, & accept as true, what you have written, I believe.
btw, thanx for that explanation:)
glad to be of service
micro, macro evolution and species concepts. Kinda a synthesis of my comments here