There are three main theories for the history of life.

1. Evolution. The idea that all living organisms are descended from a common ancestor.

2. Transformism. The theory that changes occur within a lineage of populations but that lineages do not split - there is no speciation - and lineages do not become extinct. This idea is associated with Lamarckism.

3. Separate creation, in which species have separate origins and never change after their origin.

It has been falsely claimed that the theory of evolution is unfalsifiable and it is impossible to find evidence which either proves or disproves different theories of life. In fact, there are a number of lines of biological evidence that can be used to test between the three theories.

Figure: (a) evolution supposes that species have a common origin and do change. (b) Transformism that they have separate origins and do change. (c) Creationism that they have separate origins and do not change. Each line represents a species in time: deviations to the left or right indicate the species is changing in form.