Classification of Living Things
Scientists study lots and lots of living things. There are up to 10 million kinds of living things on Earth. This number doesn’t even include bacteria! Scientists have a system for the classification of living things that helps them keep track of all the kinds of living things.
The classification system divides living things into categories. There are eight different categories in the classification system. They are domain, kingdom, phylum, class, order, family, genus, and species. Each category gets more and more specific. By the time you get to the species category, you are only looking at one specific type of living thing!
There are a lot of different ways we could classify living things. For example, we could classify them based on where they live. You might then imagine we would have a forest group, and a desert group, and an ocean group. We could also classify living things based on what color they are or what type of food they eat. What are some other ways you can think of to classify living things?
The Scientific Classification of Living Things
The scientific classification system, or taxonomy, is a little different than those suggestions. Scientists classify organisms based on their physical characteristics. This can include whether the living thing has teeth, a backbone, or a brain. They also consider how closely related species are, based on evolution. To see how this might be helpful, let’s use an orca, or killer whale, as an example.
An orca and a bottlenose dolphin are alike. They both live underwater but have to come to the surface to breathe. They also both have a backbone, a brain, fins, and teeth. Both animals evolved from land mammals who moved back into the water. They are classified in the same family, called Delphinidae.
You would then think that an orca and a blue whale are even more alike. They are both called whales! But the most specific level of classification that the orca and blue whale have in common is their order. An orca and a bottlenose dolphin are more alike and are closer relatives than an orca and a blue whale! All three are classified in the order Cetacea.
While this may seem confusing, there’s a good reason for these classifications. The classification whale is not actually a scientific classification! It’s an informal group that people use to describe certain types of sea animals. Orcas and blue whales are both whales, but orcas have more characteristics in common with dolphins. For example, while orcas and dolphins both have teeth, blue whales do not have teeth! Dolphins and orcas are also more closely related.
Let’s think of one more comparison. Are an orca and a jellyfish more similar than an orca and a lion are? If you said the orca and the lion are more similar, you’re right! The orca and the jellyfish both live in the ocean. But that’s really the only thing they have in common! Orcas and lions both have backbones and brains, but a jellyfish doesn’t have either of those.
Click on the links above for more information about each of the different categories in the classification of living things!
Other Great Resources
Written by: Alexa Wnorowski