Historical reconstruction as a tool to understand developmental signalling By acting on alleles that are generated by random mutation, organic evolution is intrinsically opportunistic. It does not create optimal design, but selects combinations of traits that provide the highest probability of reproduction in a specific ecological niche. Consequently, there are no unifying schemes to explain organismal development. The underlying molecular mechanisms only truely make sense in the context of their evolutionary history. What mechanisms were used by the ancestors and how were these mechanisms modified to improve functionality in the better adapted descendants?