Taxonomy: The Real Poop

Taxonomy is an intimidating term associated with an area of biology which is generally considered tedious even by biology geeks. The reputation is not really deserved there's more to this than meets the eye.

The idea really isn't that mysterious. Taxonomy is simply the name for the practice of classifying organisms. We also happen to base our system of naming things (nomenclature) on our taxonomic system, though it certainly didn't have to turn out that way.

Humans classify compulsively. Consider the myriad ways we classify ourselves. There's the vast, complicated family classification system, then there are cultural class systems and socioeconomic systems and even the anachronistic racial systems. We classify by sexual preference, handedness, level of academic achievement — you name it, and somebody somewhere has used it to classify humans.

When the body of objects to be classified includes all living things, the classification problem is immense. There have been a lot of attempts to sort out and make sense of the dizzying diversity of life.

For example, Aristotle made one of the early attempts. We call his effort the "scala naturae," or the "ladder of life," or the "great chain of being." Your book discusses this idea. Aristotle's philosophy insisted that the world and the universe were ultimately perfect, so he envisioned the species of living things as a long, ascending line, with something like worms on the bottom and, of course, humans on the top. This line was continuously climbing, with each species occupying the metaphorical equivalent of a step in a huge staircase. Since the universe is, of course, perfect, there would be no empty stairsteps in this array.

Of course, this is a pretty inadequate classification system, and a lot of its assumptions and predictions break down if we look at them too closely. For instance, if all species are part of this staircase, then it automatically results that, for any two species, one must be "higher" than the other. We have no problem with this if the species in question are, for instance, humans and earthworms. It gets tougher if they are, say domestic cats and domestic dogs. You can incite a riot by getting a crowd of people started discussing this question.

The key taxonomic effort in our biological history took place in the 18th century. A man named Carolus Linnaeus (1707 - 1778) devised the familiar system with its kingdoms, families, genera and species. Your book discusses this briefly. Basically, Linnaeus took on a truly daunting task. He set out to examine, describe, classify and name every living species on Earth. This was obviously more than a life's worth of work, but he got pretty far. Many plant names today still end with the abbreviation "L." which means that the name we use was devised by Linnaeus.
*material*linnaeus.htm*endmaterial* (Read more about Linnaeus and language.)

Linnaeus's classification system turned out to be very important in the development of evolutionary ideas in the next century, but it is important to understand that he had no such idea in mind. His task was simply to make sense out of chaos — to devise an organizational system to sort out the confusion. He grouped species together into genera based upon physical similarities, and grouped genera into families based upon broader physical similarities, etc. He had no idea in mind that one species might actually be biologically related to another. That realization was a century in the future.

Of course, Linnaeus's task was huge, but it was fundamentally simpler than what today's taxonomists have to do. Besides the purely functional task of making a classification system that is well organized and relatively easy to understand, they have to consider the evolutionary relationships among species. Especially at the higher levels — kingdom and phylum, for instance — these relationships are not well understood, so there's a lot more going on in the world of taxonomy than most suspect.

Your book introduces you to the Whittaker five kingdom system of classification. This is the system most commonly taught in biology classes today. However, it is not as universally accepted as the book may lead you to believe. There are a number of problems with this system which are pretty much unresolvable. A number of groups of experts have suggested other systems as they try to sort out some of these difficulties.

For instance, in the Whittaker system, all bacteria are lumped together into one kingdom. Data accumulate every day suggesting that there are two very different and only distantly related groups of bacteria. Some suggest splitting that kingdom, thus having six instead of five. Some point out that the DNA evidence suggests that all of the other kingdoms — the plants, animals, fungi and protists (single celled organisms with elaborate cells) — are significantly more closely related to each other than these two groups of bacteria are. These people have suggested three kingdoms — two for the bacteria and one for the rest of us.

Then there's the problem with the Protists. This is a really diverse group of organisms which includes all of the algae (well, most taxonomists put all of the algae here — but that's yet another story), animal-like creatures like Amoeba, Paramecium, etc., and some really lovely organisms commonly called slime molds, all lumped together, in spite of their great differences. Some have suggested that this group should be split into at least two and probably four different groups.

The message here is that, though taxonomy has a reputation as a subject involving nothing except hours and hours of boring memorization, it's really a pretty dynamic subject. Will we ever know the "correct" classification system? Who knows if there actually is one. But the search is getting more fun all the time.

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Updated 25 September 2004