The theory of Evolution is a well known and accepted theory by people all around the world, but still has a great amount of controversy around it, simply because of the connotation that comes along with the word ‘theory’. Biologists and the rest of the scientific community considers the existence of biological evolution to be a fact. However, biologists admit that they are less certain of the exact mechanisms of evolution. Everything that is observable, can be considered fact if tested, and given the same results no matter what. But because evolution is something that happens over time, and cannot be viewed with our own eyes, unlike say gravity for example (also a theory), it is much harder for people to accept as a fact, or an observation in progress.
Biological evolution is defined as any genetic change in a population that is inherited over several generations; Darwin also called this descent with modification. It can be demonstrated today and the historical evidence for its occurrence in the past is overwhelming. It explains both the unity of life and the diversity of life. The unity of life comes from descent; offspring resemble their parents, even over many generations. But organisms are not identical to their parents, they are also modified in the process; and this - over long periods of time - explains the diversity of life. “Variations are the cornerstones of natural selection, the beginning of the beginning of evolution” (Weiner 37) So for example, the homology between the forelimbs of a human, a bat, a porpoise, and a horse are explained by descent with modification. They have the same pattern of bones because all of those animals descended from a common ancestor, but the bones are not identical because they were modified for different functions -- grasping, flight, swimming, and running. Evolution is the process by which all living things have developed from primitive organisms