Bayes’ Theorem proves Evolution beyond reasonable doubt. Before we can start talking about how likely the evidence is if evolution is true, we need to make sure we understand what the theory of evolution is. The theory of evolution says that:
- All living species descend from one or a few original species. This is known as universal common ancestry.
- Over time, populations of living things have split apart and since then they have changed (evolved) and gradually accumulated genetic differences. Species have been modified through natural processes over the course of many generations. This is known as Descent with Modification or just “Descent” for short.
- The processes that we can observe in evolution now are the same types of processes that caused evolution in the past. Probably the most important process that results in a species being well-suited to its environment and way of life is natural selection (which we’ll discuss later in more detail).
Some years ago there was a study done in which a population of Thermus Aquaticus bacteria were split into two. Those two populations were split up once again, and the splitting went on until 16 different populations had been created. Unsurprisingly, a genetic analysis revealed that populations that had split apart recently were genetically more similar (more closely related) to one another than to populations that had been apart split longer ago.* The scientists who studied them had even been able to predict the time when these groups had been split apart “with very small error” based solely on the genetic data. This experiment represents a miniature version of the evolution of all life; Just as the experiment begins with one population and spits populations as they change over time, Darwin had postulated the same explanation for all existing species. According to him, in the past there had been a single species of a single, common population which split apart, that later populations had split apart from the first split-offs, and so on, and throughout the split-offs life had changed genetically (just as it changed in the experiment).
* See discussion and references in Douglas Theobald, Phylogenetics Primer.