The above tree should illustrate that gram-positive bacteria represent only one of several major divisions of extant bacteria. Phylogeny organizes organisms based on their evolutionary relatedness and hence directly or indirectly by genetic markers. Evolutionary Analysis, Prentice Hall, Upper Saddle River. Species consist of groups of interbreeding populations. Species are fundamental unit of evolution.
Species share a distinguishing characteristic, which is evolutionary independence.
Evolution independence occurs when mutation, selection, migration, and drift operate on each species separately. This means that species form a boundary for the spread of alleles. Consequently, different speices follow independent evolutionary tragectories. However, there are documented cases where hybrid offspring successfully mate with members of one or the other species of their parents. In this case, the offspring will likely be viable.