There are as many ways to categorize animals as there are animals themselves. However, in biology some ways give us a better understanding of relatedness among animals. Homologous structures and DNA similarities are clear evidence of common origins among animals. Analogous structures and geographic speciation are ways we can establish differences among organisms. All of these tools help us understand the tree of life, with all living organisms sharing a singular origin, that has been branching into more and more complex organisms over the last 3.5 Billion years!
Mr. Powell is a High School Science Teacher in Western Colorado.