Theories of evolution provide a provisional explanation for these facts. Each of the words “evolution”, “fact” and “theory” has several meanings in different contexts. Evidence for evolution continues to be why is evolution true pdf and tested.
The disagreements among these statements, however, have more to do with the meaning of words than the substantial issues and this controversy is discussed below. You can edit this timeline. Please use the preview button before saving. Life on earth evolved gradually beginning with one primitive species—perhaps a self-replicating molecule—that lived more than 3.
But the central core of evolution is generally defined as changes in trait or gene frequency in a population of organisms from one generation to the next. This has been dubbed the standard genetic definition of evolution. Natural selection is only one of several mechanisms in the theory of evolutionary change that explains how organisms historically adapt to changing environments. In biology, the meaning is more specific: heritable changes which accumulate over generations of a population.