The causes of genetic change are manifold. We must pin this question down a bit. By one definition, evolution is changes in the genetic composition of populations. Thus this question asks for nothing less than an explanation of the mechanisms of evolution. The short answer is simply a list of all those processes which can result in changes in the genetic composition of a population. • drift • bottlenecks • founder effects • selection • migration • mutation For all of these except mutation, change can result only when there is pre-existing variation. Mutation is the process which introduces variation in the first place. The process of mutation has many causes, involving chemical details of DNA replication, proofreading, and repair. The topic of mutation lies beyond the scope of this course. Return to question list.