Although different species might look dissimilar, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment. Fossils indicate that many organisms that lived long ago are extinct. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships.
Species is the most fundamental unit of classification.
Though the national standards and other guidelines present biodiversity in the traditional way as an important topic in the life sciences, they do not directly address the importance of biodivesity from either an ecological point of view or quality of life perspective. The concept of biodiversity takes on increased importance and meaning when we think of the many reasons to be concerned about the current threats to biodiversity. It is also important to protect the diversity of life because it helps maintain important ecological functions, such as oxygen production, pollination, and flood control, which in turn help support all life on Earth. Biodiversity, then, is more than a biology or science topic. It is a concept that cuts across disciplinary boundaries, and it is an environmental issue with board ramifications for the quality of human life.