TAXONOMY: The name game

The killer whale is a ... dolphin?

Another good example that highlights the need for taxonomy is the many names for the North American cat known variously as the cougar, mountain lion, puma, Florida panther, red tiger, catamount, American lion to name but a few. It actually has over 40 different names in the English language, whereas taxonomically it is known only as Puma concolor. That makes a scientist's life much simpler. Having multiple names also leads to mistakes. For example, the killer whale is not a whale at all, it is actually the largest of the dolphin family. This is where the science of classification (known formally as taxonomy) is an invaluable addition to biological research. It has no variation in language, pronunciation, spelling or anything else, which therefore allows scientists to discuss and study organisms with no mistakes or misdirection, leading to greater understanding and overall better science.

Why classify?

The need for accurate classification is incredibly important for a variety of different reasons. If you consider that scientists have classified about 1.5 million species of living organisms, some kind of organized catalogue is essential. It is estimated that there are at least 10 million to 25 million or more different species of organisms on the planet. Accordingly, we have only discovered and named a small percentage of Earth's living creatures.

Research into species can also only develop if the organism has been properly classified and therefore it's relatedness to other species and its behavior can be properly understood.

Another reason to classify organisms is to identify those that are helpful to us, especially medicinal organisms, such as plants and certain fungi and bacteria. In contrast, it is also imperative that we understand harmful organisms such as venomous creatures, poisonous plants and fungi, and especially harmful viruses and bacteria.

What is classification?

Classification has a system hierarchy that shows relatedness between living things. Its structure is constantly under debate and changes as new species are discovered. Essentially there are two Domains - Prokaryote (organisms without a nucleus; i.e., simple bacteria) and Eukaryote (or ganisms with a nucleus).

The Domains are then split into five Kingdoms: Plants, Animals, Fungi, Monera (bacteria) and Protista (generally single-celled plant-like organisms). The Kingdoms are further broken down into Phyla, which are broken down into Class, then Order, then Family, Genus and finally Species. There are also sub-Phyla, sub-class, etc.

As organisms descend down the ranks, organisms in the same groups are more closely related. As you reach the species level, you finally narrow an organism down to just one type. Therefore, organisms with the same genus name are very closely related, whereas organisms with the same family name are fairly closely related and organisms who only share the same kingdom name are very distant relatives.

You are very distantly related to an earthworm at the kingdom level; are distantly related to a shark at the phylum level; are fairly closely related to an elephant at the Class level; and are very closely related to an Orangutan at the order level.

Binomial system of classification

In the 1700's, Carolus Linnaeus devised the internationally accepted definition of a species. Linnaeus, known after being nobilized as Carl von Linne, proclaimed himself to be the greatest scientist of his generation.

He proposed that all organisms be classified into species and given a binomial ("two-name") Latin name that describes the organism. The first part, the genus, always starts with a capital letter, and the second name, the descriptive species name, is written in all lower case. Both names must be italicized. He classified thousands of plants and animals and organized them into his book, Systema Naturae. This was a truly monumental feat and the majority of his classifications remain the same today.

We are scientifically known as Homo sapien. Your pet dog is Canis familiaris and food poisoning you may have contracted is a result of the bacterium Esrichia coli. A lion, Panthera leo is very closely related to a tiger Panthera tigris, as they have the same genus name and they are so close that they can interbreed, forming a tigon or a liger, depending on which is the male!

As they don't interbreed under normal circumstances in the wild, and as their resulting offspring is infertile, they are classified as a separate species, similar to the offspring of a horse and donkey, the infamous and infertile mule.

Organisms with the same species name, such as Falco peregrinus (the peregrine falcon), Pseudocheirus peregrinus (an Australian possum) and Typhlodromalus peregrinus (an insect) are obviously not closely related, so it is the genus name that indicates close relatedness and certainly not the species name.

Many organisms now have three names, such as Equus burchelli bohmi (zebra) and Giraffa camelopardis reticulata (giraffe), but this just indicates that the animal is a sub-species. Subspecies can almost certainly interbreed and produce fertile offspring, but they can also be slightly different in their physiology. They are often geographically separated and therefore never interbreed.

Taxonomy used to be based predominantly on physiology and behavior, yet with the ever increasing advancements in DNA analysis, the science of taxonomy is continually developing with some surprising results. The most remarkable is the elephant's closest living relative, the rock hyrax, which is a cat-sized, rodent-like, furry rock-dwelling animal. Before advances in DNA technology, it would have been almost impossible to class them as closely related. Species are also being reclassified due to DNA similarities, and there is talk of Pan troglodytes (chimpanzees) and Homo sapiens (humans) being reclassified in the same family or even genus, to represent their incredibly close relatedness.

Classification means that you are a monkey's uncle and a mushroom's grandparent somewhere down the line as all life is related somehow, and because all life has the same origin.

Knowledge you can use A mnemonic (memory) device is a simple tool used to help you to remember an otherwise unwieldly concept, such as the Linnaean system of classification, which is: kingdom, phylum, class, order, family, genus, species, form. How can one possibly remember the specific order of such abstract terms? Here's an easy solution. For the first letter of each entry (k, p, c, o, f, g, s, f), use a word that can be made into a simple sentence. An old one is:"King Peter came over from Germany seeking fortune." Here's one I made up: "Khao pat can only fatten Gik's smiling face." But you can create your own! ~ Editor

David Canavan has an MSc in Behavioral Ecology and teaches science, math and ICT at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind; the more dangerous the better. You may contact David at davidc@gardenbangkok.com .