What's going on with your lists of names?

We have been asked several times,

Why do the lists of names on your classification pages look like an indented outline? Is that on purpose? Not to mention, that there are far more levels of hierarchy in the chain than just the simplistic kingdom, phylum, class, order with which I (the layperson) am familiar...

Yes, these are intentional nestings based on our current understanding of evolutionary branching patterns. So, let's consider, for example Vertebrata. We currently believe that there are two groups of tetrapods that are "sister" to each other, the amphibians (Lissamphibia) and the amniotes (which in turn can be broken down into two sister groups of reptiles and mammals, and reptiles get further broken down . . . and so on). You'll notice that for the most part, there are pairs of sister groups. That's because we know the branching patterns pretty well (or think we do), so for three closely related groups of organisms we know which branched off before the other two.

Name that branch

This is where the overabundance of names comes in.

These days, wherever the tree branches, biologists tend to give a name to both branches. This is because it's handy to be able to use the name to refer to everything on that branch. But that means we now have a very large number of named branches, too many for the rank categories from the original, Linnaean system of classification (Kingdom, Phylum, Class, Order, Family, Genus, Species).

Ranks amuck

One thing people have done to handle this abundance of named groups is to add "super," "sub," "infra-," etc. to Phylum, Class, etc. , so that they can indicate the relative rank of the name. So you've got subclasses, infraorders, superfamilies, whatnot. But that gets pretty confusing too. The Animal Diversity Web prefers to use a "rank-free" classification system, so we don't bother to label the rank except where it will remind people where they are in the hierarchy (like using a familiar landmark to navigate). So, for example, if you click on Squamata you'll see we call it an Order. The name of the rank is less important than the name of the group and the organisms that are included in that group. So when we say "Vertebrata" people generally know what branch of the tree (and which organisms) we are talking about.

We have found that non-scientists appreciate ranks, even as biologists question their utility. Ranks help you know how far down in the tree of life you are. Certain ranks allow you to usefully lump groups of organisms together. We find that the rank of "Class" (Class Aves, Class Mammalia, Class Insecta etc.) is convenient; many books and college courses tend to focus on groups with these ranks. For the time being we'll continue to use both systems, because of the distinct benefits of each.

Serial numbers . . .

Given that names and ranks can change and be confusing, some biologists have proposed assigning numbers to organisms or changing the way we assign or track names. Name, Rank, and Serial Number Part 2 addresses these ideas.