How are living organisms grouped? In this eight-minute video clip, the system of grouping them according to similarities and relationships is broken down straightforwardly. Sal explains the definition of species and how they must be able to produce fertile offspring. He mentions that offspring of two different species result in hybrids. Finally, he explains how humans have bred different breeds of dogs to interbreed, resulting in fertile offspring, which means they are all of the same species. This lesson makes a nice support for your taxonomy lesson.