The modern biological definition of evolutionEvolution:
Inheritable change within a lineage, or the change that occurs between generations within one population of a species. This refers of course to change expressed from one individual to another, but we are usually most interested in the changes so great that the later generation is considered a different species. is inheritedInherited:
Derived from a preformed genetic code present in an ancestor. change within a lineageLineage:
Line of descent from an ancestor.. There is extensive evidence, provided by all fields of biological study that evolution has and is still occurring. The evidence is all around us, if we choose to look for it. Diversity, complexity, and adaptation are three observable phenomena that, when viewed together and within context of Earth’s history, provide powerful evidence of evolution.

In the following sections, each biological field is introduced along with the main tools that researchers in that field use in studying evolution. Then some of the associated evidence for bivalve evolution is discussed in terms of diversity, complexity, and adaptation. Each biological field is discussed independently, however in reality, these fields are not isolated. For example, paleontology is a field of its own, but paleontologists use information from many other fields of biology to fully understand the fossil record. The evidence provided by fossils of the Cambrian Period is all the more powerful when understood within the additional context of the morphological evidence and ecology of the time period, etc.