Biological Classification

It's no secret that humans (with the notable exception of college students) like to keep things organized. Garages, libraries, laboratories and workshops are easier to work in if there is a system in place to keep track of things. Wrenches go in this drawer, screwdrivers go in that drawer, drills go in that cabinet. Biology is no exception. Its a lot easier to study living things if we have a system that keeps some things apart from other things. Biologists call this system taxonomy . Taxonomy took a great leap forward thanks to the efforts of an 18th century biologist named Linnaeus. What Linnaeus did was devise a system of binomial nomenclature . A hundred years later, the International Congress of Zoologists set formal rules for systematically naming things. The rules are:

  1. Names must be Latin or latinized and are printed in italics. Like everything else printed in italics, they are underlined when handwritten.
  2. The genus name (the Homo in Homo sapiens) is capitalized and must be a single word.
  3. The species name ( sapiens in Homo sapiens) can be either a single word or a compound word (a new word made up of two words).
  4. Credit for authorship of names will be given to the person who first publishes it with an accurate and recognizable description of the organism.

I won't go crazy about describing binomial nomenclature. The most important thing for this lab is yet to come. What you should know are these 4 rules. Typically, you'll see questions on quizzes or exams like, "Which one of these is the accepted name for a horse?"

  1. equus cabballus
  2. Equus Cabballus
  3. Equus cabbalus
  4. equus Caballus

Even if you didn't know the scientific name of a horse, you would know 3 is correct because the others break one of the rules

What Linnaeus also did was systematically categorize all known organisms. Linnaeus came up with a hierachy of ways to classify plants and animals. The different levels are called taxa (plural of taxon). The different taxa are:

Kingdom is the broadest of the taxa, all animals are in Kingdom Animalia. All plants are in Kingdom Plantae. Phyla are slightly less broad. There are usually a few phyla in each kingdom. Species is the most restricted.

The easiest way to remember the different levels (I can guarantee you'll see this on one or more tests):

King Philip Came Over For Good Soup

King = Kingdom, Philip = Phylum, Came = Class, Over = Order, For = Family, Good = Genus, Soup = Species.

Dichotomous keys, phenograms, phylogenies and other words you'll learn all too well


Dichotomous Keys

[Shown here is a picture of a branching dichotomous

Dichotomous keys will typically be either a diagram or a table. The diagrammatic format will typically look like the picture shown at the right

It is important to note that dichotmous keys have NOTHING to do with biology alone. They are simply a tool. You can make a dichotmous key to describe ANYTHING.

Dichotomous keys are fairly simple to make up IF you understand what they're all about. They go step by step - each splitting of a branch tells you which things have what characteristics.

Key To Things In My Room

1 - Things on My Desk

2 - Electronic Equipment - my computer
2' - Non-electronic Equipment - a book

1' - Things on My Bed

2 - Things That Belong on a Bed
3 - Things For Your Head - pillow
3' - Things For Your Body - blanket
2' - Things That Don't Belong on a Bed
3 - My Ashtray


Phenograms are very easy - group the things that look alike. Tigers look more like lions than ants so you arrange them closer to the lion than to the ant. You won't see too many phenograms because there are flaws to them. As you will learn later, even though they look nothing like chordates, echinoderms are the chordate's closest relative. A typical phenogram is shown below. When phenograms are accurate, they are usually the best way of showing evolutionary relationships. They can typically lead you in the right direction, but ideally they should be corroborated by other methods.


Phylogenies are what you will undoubtedly see the most of. A phylogeny (phylo- = "arranged" or "ordered"/ -geny = "birth" or "start") arranges organisms by where they developed from. Phylogenies are the family tree of a group of animals. Typically, you will see questions that give you 4 or 5 organisms to arrange. More often than not, two of them will be similar and the others will be distantly related. A past exam question:

"Draw a likely phylogeny of [a whale, a bat, a starfish, a pine tree, a crab]" - It should look like this:

It is set up this way because whales and bats are both mammals. Starfish is next because it is an echinoderm and most closely related to the invertebrates. The crab comes next because arthropods are closer to the echinoderms than conifers (a group that includes pine trees) are. Generally, the easiest way to actually make a phylogeny is to take the organisms that belong in the same category (ie mammals with mammals) and then branch off to the more distantly related organisms. Practice making phylogenies. If you can consistently make phylogenies, you're just adding up the points because you will see them again and again. They're free points.