Historical contingency

Historical contingency is an important idea in biology and evolution. It is the theory that the paths that life can evolve on are constrained by historical events that are often random. This was perhaps most succinctly described by Stephen Jay Gould, when he proposed the thought experiment of rewinding the tape of evolution backwards and replaying it. The question is: "would life evolve in the same way or in some very different manner?" This idea cuts to the heart of many issues surrounding the inevitability of humanity and determinism.

Historical events that can constrain evolutionary pathways are varied. They can include things that work at the genetic level such as genetic drift, population bottlenecks, neutral selection, exaptation, and potentiating mutations, but also external phenomena in the environment, such as climate cycles and meteorites.

Recent work by biologist Richard Lenski has looked at the role of potentiating mutations in historical contingency. The ability for multiple neutral mutations to add up and eventually allow for a beneficial mutation provides a vivid counter-example to the intelligent design propaganda of Michael Behe's book The Edge of Evolution.