Blog 1 Why is evolution a theory and not a law?

The statement "evolution is both a theory and a fact" is often seen in biological literature. Evolution is a "theory" in the scientific sense of the term "theory"; it is an established scientific model of a portion of the universe that generates propositions with observational consequences. Such a model both helps generate new research and helps us understand observed phenomena. When scientists say "evolution is a fact", they are using one of two meanings of the word "fact". One meaning is empirical: evolution can be observed through changes in allele frequencies or traits of a population over successive generations. Another way "fact" is used is to refer to a certain kind of theory, one that has been so powerful and productive for such a long time that it is universally accepted by scientists. When scientists say evolution is a fact in this sense, they mean it is a fact that all living organisms have descended from a common ancestor (or ancestral gene pool) even though this cannot be directly observed. This implies more tangibly that it is a fact that humans share a common ancestor with all living organisms. Evolution is usually defined simply as changes in trait or gene frequency in a population of organisms from one generation to the next. However, "evolution" is often used to include the following additional claims:

1. Differences in trait composition between isolated populations over many generations may result in the origin of new species.
2. All living organisms alive today have descended from a common ancestor (or ancestral gene pool).