One of the most common methods of differentiating between early hominid stages of human evolution is through examining what?

The early hominid stages can be differentiated from one another based on the complexity of the tools used by these species. The tool evolved along with the evolution of the humans. The more the hominids evolved by more complex their tools became. The tools made by the earliest hominids were used to fish out the termites. These tool developed and became more widely used as the humans evolved.

Hence, the answer is 'by observing the complexity of the tools'.