Taxonomy Standards

So it turns out that assigning taxonomic grouping (Kingdom, Phylum, Class, etc.) is somewhat contentious. Even assuming we use the traditional system as opposed to Cladistics (which makes sense since we're primarily discussing ecosystems and not evolution), there doesn't seem to be a consistently agreed-upon set of groups, especially as regards Kingdoms. This is all news to me, so professionals in the field of biology should help me out.

According to Wikipedia, there is some difference in how the Kingdoms are taught in the US as opposed to Europe (and the rest of the world's groups are not even discussed). My question is really how we want to divide the kingdoms (and whether to use Domains/Empires/Superkingdoms). While using the standard American system is likely easiest in the game sense, I personally would rather stick as close to modern biological standards as is practical. Maybe this has already been decided, given that many cards have already been created.

As a taxonomist by profession (if grad school counts as a profession...), I'm always a bit surprised at others' surprise that the taxonomic classification of many groups remains in flux. We're constantly discovering unexpected things about organisms' relationships with one another, especially with the genetic revolution.

Take, for example, the five groups of vertebrates you learned about in third grade: Fish, Amphibians, Reptiles, Birds, Mammals, right?

WRONG. Birds are very firmly embedded within the reptiles. You can't talk about "reptiles" as an evolutionarily coherent group unless you include all the birds with them. Having the class Aves equal in rank to the class Reptilia renders the Reptilia what we call "paraphyletic," a state that's generally frowned upon, because you're excluding some of the descendants of the ancestor reptile (the birds), but not all of the descendants (the traditional reptiles). Despite their warmbloodedness and complex heart anatomy, birds are more closely related to crocodiles than mammals. As it stands, Phylo is currently using the traditional five vertebrate classes. It bothers me, but there's no easy fix.

The original post makes an excellent point: Phylo is focusing on ecosystems and not evolutionary lineages. It's easy to see why the old stand-by of "five groups of vertebrate animals" is the classic grouping system. It's intuitive to group birds with birds, separate from lizards. But we also want to teach that diversity also means diverse paths within the same evolutionary branch, right? Just look at the sharks: predatory great whites versus filter-feeding whale sharks.

On the whole, the sad fact is that these difficulties won't be resolved any time soon because things don't evolve in discrete units (apart from unique individual organisms, a generalization which in itself has the exception of bacterial lines, oy vey!). As scientists and as humans, we seek to classify the similar and related things together. So, we want a word for all the animals with backbones. But wait! That doesn't include some of the things with spinal cords but no backbones - why don't we make another term that's slightly more inclusive than the first? What about organisms with spinal cords and backbones but no jaws? A new group is proposed, slightly smaller than the other two. This is how we wind up with sub-genera and tribes and infra-orders and super-orders and all sorts of strange names for groups, because humans instinctually want to nest things into a hierarchy with discrete steps that don't exist. If you try to compare one "species" of plant to one "species" of bacteria to one "species" of reptile, you're going to get radically different groups of organisms, not just in terms of the organisms themselves but in terms of how closely related the individuals have to be to one another to be called the same species. Various species concepts exist and have been subject to much debate and has been for several decades. Even an ornithologist and a herpetologist are likely to disagree whether a given color morph represents a distinct species or not.

Comparing groups at higher levels is even hairier. We try to make the "level" of two genera roughly comparable, but really, there's no way to compare them, despite what our instincts say. In Phylo, we've tried to par it down to just a few levels of classification, which is a good idea in terms of avoiding information overload, but will introduce some artificial inflexibility.

Many of the broadest strokes are well understood and are unlikely to change. For example, if we're including prokaryotes with the eukaryotes, then there exists general agreement on the existence of three domains: Archaebacteria, (Eu)Bacteria, and Eukarya. I've seen a few virus/bacteriophage cards floating around. I don't believe those would fit in any of these kingdoms, but my microbiology foo is weak.

Not to be a downer, but "stick[ing] as close to modern biological standards as is practical" will be difficult because things are changing. Yet, so long as we accept that classifications will change - Poison Ivy is no longer Rhus radicans, it's Toxicodendron radicans - then I think doing our best to educate kids about (current) taxonomic classification is a noble and worthwhile effort. I wouldn't be in this line of work if I didn't believe that 100%.

Man, I miss those days when animals are grouped based on anatomy. Those days when Nemathods, Platyhelminthes, and Annelida were still classified as one: Vermes (worms).