Science at a Distance

Classification
Prerequisties
CLAS What do you need?

Gathering Data A systematist gathers data. Any scientific approach to classification needs evidence and systematics is that branch of science that provides the data and evidence needed to justify decissions taken later. Organisms are examined from as many points of view as possible. All branches of science contribute. Once upon a time morphology (what the creature looks like) and anatomy were important contributors, but today evidence is gathered from genetic studies, field studies, laboratory tests, enzyme assays, metobolic patterns, DNA sequences, ecological patterns and much, mush more. Everyone has something to contribute.

Thousands of facts about each creature studied are assembled and amassed into data banks. A popular item of data these days are DNA electrophoretic patterns generated by cutting up the hereditary apparatus of an organism with special enzymes and then separating the fragments by length. These patterns can give a lot of data about the present and past state of the organims carrying them, and strong similarities in DNA patterns argue for a close relationship.

Human and Ape chromosomes Humans, for example, share 98.5% of their genes with chinpanzees and the differences identifed so far do not seem profound enough to give humans such a big advantage (in brain development, language, etc.). Such a close resemblence between the DNA of the two species suggests that humans and chimpanzees should occupy either the same, or very closely related groups in any classification scheme.

Other types of similarity, however, can be missleading. Many animals have evolved the ability to fly. Butterflies, bees, pteranodons, pigeons and bats all use (or used) adaptations of their physical form to propel them through the air. It might be tempting in classifying these forms, therefore, to consider flight as a strong characteristic that should be given a lot of weight. But there is a danger in this. The methods and forms evolved by insects to allow them to fly are profoundly different from the forms and type of flight evolved in the pteranodons, birds and the mammals. Close grouping together of butterflies and pigeons would be a big mistake despite the importance of flight as a characteristic.

One possible use of the data and relationships discovered in a systematic study would be to draw up long lists of characters and characteristics for each and every organism. Every item in this data bank would be given equal weight, and then the computer could be given any two creatures and aske to find out in how many ways these creatures resemble one another. For example, from a huge systematic data bank the computer might be asked to compare a butterfly and a bee, and a butterfly and a pigeon.

Hypothetically (no data bank I know of has this much data), the computer might respond that the butterfly and the bee share 2,734 characteristics, whereas the butterfly and the pigeon only have 956 points in common. Repeated comparisons of this kind should, in theory, give a picture of the relationships between whole sets of organisms, and a classification scheme could be built around groupings withing these relationships. This concept of commonality is, in fact, the basis of numerical phenetics, a method of classification that attempts to substitute unweighted data, rigor, repeatable proceedures and the iron logic of computers in the place of schemes that rely much more on subjective judgement.

This phenetic method has its attractions, but even its most ardent supporters recognise that unweighted data can give rise to some unacceptable results, particularly where convergent evolution has given rise to two organisms that have totally different origins, but now look alike because they utilize the same ecological habitat. The fact that dolphins and fish look somewhat similar is because swimming through water requires a certain 'look'. That 'look', out of context, is not the best way of establishing a classification relationship.

CLAS Nomenclature Giving it a name. What do we call it? All the thousands of human languages have thousands of names for all of the different living creatures enountered by their cultural users. Even lingusitic experts recognize considerable ambiguity in translating the name for any one creature between any two languages. A condition that is unacceptable in science.

Even within a given language common names for apparently common creatures have considerable lattitude. The word 'grass' is often a part of speach that has nothing to do with any recognize botanical reference, and the word 'rat' is frequently applied to creatures that are not rodents.

When giving a creature a scientific name, therefore, systematists wanted to use a language that would be universal, unambiguous and infintely expandable to accomodate new names when needed. Once upon a time there was such a 'universal' science language - Latin. Latin was used not only to name creatures but also to write science papers and even letters! Today, English has largely replaced Latin as the 'universal' language of science, but within strongly nationalistic countries such as France, there is resistance to this and Anglesized words are frequently purged from the lexion by the French 'word police'. (Yes, such police actually exist and fine people, shopkeepers, etc. for using English words!).

Image Instead, nomenclature, the scientific names given to new and old creatures, draws its inspiration from almost all languages and then 'latinizes' the word(s) to make them sound as if they could be latin. For example, when a new type of mosquito found the London underground, a new name was needed. The discoverers thought the word 'molest' (from the English word to attack) would be a good one so they chose the word, and then latinized it by adding "-us" to the end. The new mosquito is now known as Culex molestus.

Most scientific names for creatures are binomial, meaning that they have "two words" in them. Every distinct species has a bionomial name, both of which are italicized when printed (or underlined if written out by hand). The first word is the genus name (Culex, in the example given above), and is always written with a capital letter. The second name is the specific epithet, or the word that assignes it to the particular species within that genus.

Occasionally, when it is necessary to designate a subspecies, a third italicized, but uncapitalized name is added.

Larger groups or groups of groups are also often written in latin (Animalia for the Animal Kingdom), and consist of one capitalized word.

CLAS Taxonomy A largely theoretical branch of biological science in which appropriate groups and grouping schemes are developed.

The word 'taxonomy' comes from two Greek words taxis (meaning "arrangement") and nomos (meaning "law"). Taxonomy, therefore, is the "law of arranging things" or the methods and principles of arranging the many diverse kinds of plants and animals into appropriate sets or groups.

Although taxonomy and classification appear to be very old practices that must have had common usage long before the written word, the first recognized classification scheme that had a rational basis was that invented by Aristotle. He also invented the science of logic, and brought the two together. Aristotle seems to have been a keen naturalist and studied hundreds of species during his stay on the island of Lesbos. Like all taxonomists, however, he was imediately faced with a problem; on what basic principle should the arrangements of groups be founded.

This is the fundamental problem faced by all taxonomic schemes. Try it for your self, how would you divide up the shapes in the figure given below. Think about it, what principle would you use. Then move the cursor over the buttons at the bottom of the diagram and see some of the possible solutions.

Taxonomy


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The 'species' in the "World of 2D Shapes" could be organized by several different principles; the could be grouped by color, size or type of shape (circle, square, triangle). Each principle appears equally valid, so how and what do you choose?

Aristotle chose as his 'oranizing principle' the concept of complexity. He ranked all the organisms he found in a "ladder of life" that started with the simplest creatures (such as small invertebrates), and rose as the complexity rose into groups such as plants, molluscs, reptiles and mammals, eventually ending up with humans at the top of his ladder.

This sounds suspiciously evolutionary, but Aristotle was not really an early evolutionist, he was just using complexity (often an evolutionary trend) as a taxanomic organizing principle. His results were far enough ahead of his time, that the principle lasted for about 2,000 years.


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Science at a Distance
© 1998 Professor John Blamire