Postal address is another, familiar classification hierarchy. Today, the classification hierarchy makes biological sense because it reflects the relatedness among the living descendants of past evolutionary branchings in the tree of life . Perhaps surprisingly, because the kingdom is the highest level of organization, the number of kingdoms of life is uncertain. This might make more sense when we think that to define a kingdom one must reach back to the very origins of life, and attempt to locate the most fundamental branchings. Whether fungi evolved from photosynthetic green algae, losing their capacity to photosynthesize, or evolved from a non-photosynthetic precursor, also is uncertain.
Further changes affecting bacteria and protozoans are almost certain to occur.
Figure 2 portrays the eight kingdom classification as a tree, in which the positions of the branches suggest the timing and branching points of the evolutionary process. A comparison of the five and eight kingdom classifications. This process, continued indefinitely, results in a sequence of speciation events extending through time. There are two main ways to construct such a diagram, called a phylogenetic tree . One is the fossil record, wherever it is reasonably complete and accurate dates can be obtained from stratigraphic layers and radioactive decay methods.