A classification key is a series of questions determining an organism’s physical characteristics. When you answer one question, it either branches off to another question or identifies the organism. Ultimately, they help to identify an unknown organism or work out how to categorize groups of similar organisms.
How do classification keys work?
There are a few different classification keys commonly used, and we’ll walk you through the three most common ones, but they all function similarly. At each stage, you have a question about the characteristics and features of the organism, and the answer narrows down the options, either leading to another question or identifying the organism. So, although it might take a while, the organism will eventually be recognized as each question gets more specific.
The most commonly used type of classification key is the Dichotomous Key. ‘Dichotomous’ means ‘split into two, which is the defining characteristic of this type of key. At each branch of the key, there are only two possible answers – almost always ‘yes’ or ‘no’ – and you decide whether the organism has a particular feature and characteristics to narrow it down, with a format that runs like a flowchart. Here’s an example, so you can see how this works in practice:
Another commonly used type of classification key is the Tabular Key. You read through the numbered items in the order in a tabular key. Each article presents two options. As you proceed, more and more information will be revealed until one of the organisms shown can be identified. When this happens, the organism’s name is stated. Now, if there isn’t enough information to identify the animal, you will be told to go to another numbered item and make another choice. Here’s an example:
The other main type of classification key is the Circular Key. Circular keys are most useful when you have a lot of organisms to sort rather than just a single one, but they can be used for individual organisms, too. To read a circular key, you first start in the middle of the circle and work your way outwards. As you go, you will choose one of the given options at each layer. When you get to the outer layer of the circle, you will have identified the organism. Here’s an example of how they work using a hypothetical set of alien organisms:
Why are Classification Keys so useful?
There’s an enormous range of life in the universe, even just among the existing organisms we know about on earth – so many that it’s impossible to grasp the sheer scale of life on Earth without a classification system to help sort the lifeforms into groups that we can then study in greater detail.
We mostly use the Linnaean classification system to help us make sense of the millions of different organisms known. Still, to classify something, we need tools to help us narrow down its characteristics and features, ruling out what it isn’t and narrowing down what it could be until we either identify an existing species or find a new group member! Classification keys are vital for this by providing a clear and straightforward framework that scientists can use during this process.
One of the most valuable benefits of classification is that it allows us to understand organisms better alive today and animals that used to exist. By carefully organizing and classifying different organisms, we can better understand how they first evolved and what they evolved from, helping us figure out how all life on Earth evolved from just a few organisms!
