Taxonomy is a big word for a simple concept: fitting things into groups according to their shared characteristics. Humans are generally very good at grouping things into categories according to their similarities. We have named and described the world around us for as long as we have been on Earth. If you know anything about common names, you know how confusing they can be and that there are often several names for the same thing. Take dragonflies for example. They are known by many common names, including dragonflies, devil’s darning needles, snake doctors, horse stingers, mosquito hawks, and sewing needles. (Dragonflies get a lot of their common names from the fact that people used to think that dragonflies could sting or would sew up your ears while you slept!) A person who knows a dragonfly as a snake doctor might not know what you’re talking about if you use the name mosquito hawk. Scientists are a notoriously anal bunch (or they go the other way too, but that’s a story for another time!), so it was natural that early scientists wanted to create a formal system to eliminate the confusion of having several names for the same thing. All scientists now use the same words to describe an organism so everyone knows when they are talking about the same thing. You can thank Carolus Linnaeus for modern taxonomy.
In the current taxonomic system, biological organisms are fitted into groups according to their characteristics. Historically, this was done based on the morphology, or structure, of the organisms, but DNA had recently been added to the mix as well. Things that fall into the same group all share a set of characteristics that distinguish them from all other groups. So, for example, all organisms in the kingdom Animalia share characteristics that make them different from organisms in another kingdom, Plantae. We humans, as animals, are very different from plants in our structure and our DNA, so we belong to different a different kingdom than the plants. Let’s take a closer look at where humans fall in the classification scheme to get a good idea of how the system works.
We’ve already established that humans belong to the kingdom Animalia. Animalia is divided into things that have spinal cords and other groups that do not. Humans do have spinal cords, so we belong to the phylum (the level under kingdom) Chordata. Chordata is divided into groups called classes. Among these, humans belong to the group that has hair and mammary glands. We therefore fit into the class Mammalia. Mammalia contains a whole bunch of families, but humans belong to the family Primate. We are apes. Finally, we belong to the genus Homo and the species sapiens. When we refer to our species, we use both the genus and the species: Homo sapiens. This name tells us that we are humans. There have been other species within the genus Homo such as Homo erectus and Homo habilis, but we are the only Homo sapiens.
There are several great mnemonics for remembering the order of classification in biological organisms, but this is the one I prefer (okay, okay, so I actually prefers a slightly more PG-13 version of mnemonic, but this is supposed to be a family friendly blog!):
The first letter of each word reminds you which level of classification comes next:
So there you have it. All biological organisms that are known to exist (with the exception of several bacteria and other things that have not yet been described) are fitted into this classification scheme according to their characteristics. Classifying organisms in this way is useful. It helps us keep track of which particular organism has which particular name, which means we can be sure that everyone is talking about the exact same thing when they use a name. Taxonomy also helps us see the interrelationships between organisms. For example, the phyla (plural of phylum) within the Kingdom Animalia are more closely related to each other than they are to the phyla within the Kingdom Plantae. Humans are more closely related to cows and mice (all Mammalia) than we are to animals in other classes, such as snakes (Reptilia) or fish (Osteichthyes). For more information on how biological organisms are related to one another, I recommend the Tree of Life website. It’s full of great information and has hundreds of experts from around the world contributing the information.
To learn more about how scientific names work, see my page about it! In it, you’ll learn more about what scientific names mean, why some things are italicized, and how scientists shorten scientific names when they write or talk about specific groups.
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