Apparently the human condition has a built-in fascination with classification. There are, however, many other compelling reasons to have a 'universally' accepted classification system for all life as we know it. One of the most compelling is the need to communicate exactly what organism is meant to people with other languages or common names for that organism. Leaving a clear record for posterity may also be simplified by a clear and planet-wide classification system. Another need is the ability to draw previously unseen similarities across organisms that might be grouped together for a different similarity.

How Do we Classify?

Humans classify things in their minds every moment they are alive. The mind is a great pattern recognition device, and groups things of similar patterns together - things to eat, things to fear, things to drool over. These would all be informal classifications. Taxonomy is the formal classification of things, almost always referring to living organisms.

Classification in the Past

Several people are responsible for how living things are currently classified. It may be impossible to recognise every scientist who left their mark on the system of classification, but some of the biggies are:

Aristotle

He formed a system of classification around 300 BC. It was first based on whether the organism had red blood or didn't have red blood. He then subdivided organisms by physically observable characteristics. This is called a hierarchal classification system. The idea of a hierarchal system is to start by making broad groups and then subdividing those groups into smaller groups, repeating until you have small enough groups to easily handle.

Carolus Linnaeus (1707 - 1778)

A botanist who is considered the 'father of taxonomy' for publishing Systema Naturae, a book that contained a classification system for living things. His method of hierarchical classification forms the basis of today's taxonomy of living organisms. Although the structure of his system may be sound, he often focused on a single common feature for relating species, eg the reproductive organs of flowering plants.

John Ray (1628-1705)

John Ray - the 'father of natural history' - was the man who started the practice of using total morphology to classify species rather than focus on one feature.

Current Classification System

This is called Linnaean Taxonomy (named after Carolus Linnaeus). The hierarchy of classification is as follows:

1. Kingdom
2. Phylum (or Division in Botanics)
3. Class
4. Order
5. Family
6. Genus
7. Species

There are five Kingdoms in our current system:

• Animalia - over 1 million known species:
  
  • Multicellular
  • Specialised eukaryotic cells¹
  • Self-locomotion
  • Do not produce their own food, they rely on ingestion
• Plantea - over 300,000 known species
  
  • Multicellular
  • Specialised eukaryotic cells
  • No self-locomotion
  • Produce their own food through photosynthesis
• Fungi - about 100,000 known species
  
  • Multicellular
  • Specialised eukaryotic cells
  • Do not produce their own food, rely only on absorbtion of nutrients
• Protista - about 100,000 known species
  
  • Single cellular
  • Eukaryotic cells
• Monera - about 10,000 known species (often separated into Eubacteria and Archaebacteria)
  
  • Single cellular
  • Prokaryotic cells²

When referencing a particular organism, it is with the last two parts of the hierarchy (genus and species) that a unique name is made. This is called binomial (literally 'two names') nomenclature. It is general practice to italicise the genus and species, and often the genus is abbreviated to the first letter and capitalised. So that a wolf might be referred to as C Lupus.

As more organisms were classified, certain taxa became uncomfortably large. For instance, 75% of all living organisms are insects. This has led to the practice of having other groups between the levels of the hierarchy, such as subclass and superfamily. These in-between levels allow scientists to group organisms in a way that may more easily show evolutionary significance.

The classification of humans:

• Kingdom: Animalia
  
  • Multicellular
  • Specialised eukaryotic cells
  • Self-locomotion
  • Doesn't produce own food
• Phylum: Chordata
  
  • Bilateral symmetry
  • Notochord³
• Subphylum: Vertebrata
  
  • Segmented spinal column
  • Central nervous system
• Class: Mammalia
  
  • Young nourished by milk
  • Specialised teeth
  • Endothermic (warm-blooded)
• Subclass: Theria
  
  • Give birth to live young
• Infraclass: Eutheria
  
  • 'True' Theria, meaning that live birth happens at an advanced stage
• Order: Primates
  
  • Opposable thumbs
  • Separate and well-developed radius and ulna in the forearm and tibia and fibula in the hind leg
  • Presence of a clavicle
  • Several other skeletal traits
• Suborder: Anthropoidea
  
  • All higher primates: apes, monkeys, and humans
• Superfamily: Hominoidea
  
  • Apes and humans
• Family: Hominidae
  
  • Early man and modern humans
• Genus: Homo
  
  • Brain size
  • Complex tool making
• Species: Sapiens
  
  • Humans and sometimes direct ancestors who would be listed as a subspecies

Where did they get Whereus whatus?

When Linnaean Taxonomy was first started, the common language of science was Latin. A person naming a new species, generally the person who discovered it, would pick a Latin name having some relation to the species. Favourites include the name of the discoverer, the place it was discovered, obvious physical feature, and mythological references. Taxa other than species were generally a description of the morphological differences that defined that group.

The Future of Classification

Many people feel that our current classification system is woefully out of date, especially in light of our DNA sequencing technology. Other options do exist such as Cladistics and Gradistic Taxonomy (also called Evolutionary Systematics). However, moving the scientific community out of traditional practices has often gotten people burned at the stake. Perhaps in this information age the ease of interconnectivity will allow both systems to be used to the fullest extent.