Imagine a large branching tree representing all life on earth, the tip of each bud at the end of a twig represents a species. To try and make sense of this complex tree of life, scientists have devised a system of hierarchical groupings that get more specific the deeper you go (think of those Russian nested dolls) known as taxonomy, to try and keep things organized. But, like living things, branches on the tree don’t neatly divide into predetermined groups, so, the taxonomic groupings are somewhat arbitrary and are constantly in revision. Groupings are generally made based on either morphology (the physical appearance of an organism), or genetics (the organisms DNA). The generally accepted taxonomic divisions used today goes from very broad (Domain) to very specific (species) with six groupings in between. Every organism we’ve named thus far, more than one and a half million of them, from the bacteria, to blue whales, shrimp to sequoias has been categorized according to this system. To get a better idea of how the system works, let’s trace through the phylogeny of a few organisms you may be familiar with, starting with one extremely distant relative that you are intricately involved with.
E. coli is a bacterium that is commonly found in the intestinal tracts of larger organisms, yourself included. As a bacterium, E. coli belongs to the Domain Bacteria, the broadest classification level. Domain is the broadest classification level with three groupings, Bacteria (single celled with no cell nucleus), Archaea (single celled organisms superficially similar to the Bacteria), and Eukarya (single or multicellular organisms with a true nucleus). Now, classification of the Bacteria and Archaea is a bit unusual because they are so different from the Eukarya that scientists have a lot of trouble identifying species and groups, so let’s run through the rest of E. coli somewhat quickly (check out the chart to the right). The important thing to notice here is the last two categories, Genus and Species, the two most important names for any organism it is by these two names that we are able to identify every individual organism and how biologists in Baltimore and Bangkok know they are dealing with the same thing.
Dogs belong to the Class Mammalia, meaning they are animals with backbones that have fur and provide their young with milk from mammary glands. This distinguishes them from other vertebrate animals such as cartilaginous fish (Chondrichthyes) bony fish (Osteichthyes), or amphibians (Amphibia). Of the many types of mammals, from bats (Chiroptera), Anteaters and sloths (Xenarthera), or horses (Perrisodactyla), Dogs, along with cats, weasels, seals, and more are grouped in the Order Carnivora based on the unique arrangement and morphology of their teeth.
We have now, at long last, arrived at the final levels of classification for my pup Marcy, Family, Genus, and Species. The Family level represents a group of highly related, yet diverse organisms, in fact, it is very much like your last name. I share a lot of characteristics with other Padillas, but some are very different. Marcy belongs to the family of Carnivora known as the Canids, or generally speaking, the dogs. Other members of family Canidae include well known species like the Red Fox (Vulpes vulpes), the beautiful African Wild Dog (Lycaon pictus), and lesser known species like the Short-eared Dog (Atelocynus microtis), this is Mary's extended family.
Within your family (aunts, uncles, cousins, grandparents, etc), you have your immediate family that you are most closely related to. In taxonomy this is the Genus level. Marcy's immediate family includes nine living species of the genus Canis which includes the Ethiopian wolf (Canis simensis), coyote (Canis latrans), and Grey Wolf (Canis lupus). Members of this genus are all very closely related, and all have relatively large skulls, long legs, and are generally fairly large for Canids. Within a genus, every different species gets its own Species name to distinguish it. This is similar to your first name, which distinguishes you from your brothers, sisters, mom and dad; Marcy's given species name is lupus. Unfortunately, Marcy shares her name with another member of the genus, the Gray Wolf. Like a son with the same name as his father who adds Junior to their name, we must tag another name to the end of Marcy's Genus and Species so we don't get confused, this is known as the subspecies.
We did it! We made it all the way from Marcy's Domain (Eukaria), all the way down to her genus, species and subspecies (Canis lupus familiaris). Domestic dogs are the same species as their wild ancestor the wolf. This means that they can successfully interbreed, and share the vast majority of their physical and genetic characteristics.
This was a whirlwind tour of the taxonomic system, and it is very likely that you now are even more confused than you were when you began reading. Biological classification is an incredibly complex subject, one rife with controversy and differing ideas within the scientific community, so it is extremely difficult to distilled to a single blog post. But, rest assured, there will be future posts on taxonomy here in the future! I plan on providing a brief introduction to the amazing organisms in different phyla, classes, or families of plants and animals, so if you have any suggestions leave a comment, please!
Any questions, or thoughts, after reading? Did I screw up in here anywhere (I probably did), please, comment!! And as always, thanks for reading!
Buffington, Matthew L., et al. "The Description of Zapatella davisae, New Species,(Hymenoptera: Cynipidae) a Pest Gallwasp of Black Oak (Quercus velutina) in New England, USA." Proceedings of the Entomological Society of Washington 118.1 (2016): 14-26.
Locey, Kenneth J., and Jay T. Lennon. "Scaling laws predict global microbial diversity." Proceedings of the National Academy of Sciences (2016): 201521291.