The ability to make fertile offspring is an important quality. For example, donkeys and horses can interbreed to make a baby mule. However, mules are infertile, which means donkeys and horses are separate species.

There’s also another way to define species, called the phylogenetic species concept. This concept separates species that could interbreed, but don’t because they live so far apart. If they live far apart for long enough, then they could eventually change too much to interbreed and become different biological species as well. One thing I always used to remember the different categories the animal kingdom is divided was to remember:

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Or in other words…..

Keep Plucking Chickens or Fear Getting Sacked

The definition of species is a difficult concept to define; these are two commonly agreed upon definitions, but the exact separations are still debated. Species classification isn’t a natural phenomenon, but rather one used by biologists to help them talk about the plants and animals that they study.

Centuries ago, scientists used the physical appearance or anatomy of the organism to figure out its species. Does it have hair, fur, feathers or scales? How many legs does it have? Does it live in oceans, lakes or on land? If it’s a plant, how many leaves or flowers does it have?

Appearances can be deceiving, though. For example, one species can also have multiple breeds, like dogs. All domesticated dogs are considered the same species (even though they came from not only wolves, but foxes and even coyotes) because they can make crossbreeds, but their widely varied appearance makes it easier to talk about separate breeds.

Today, scientists have more advanced technology. Researchers use the DNA of the organism to determine its species; the more similar DNA is to another animal, the more likely it is that they belong to the same species.