Active evolution and current molecular learning.
It is sometimes said that one cannot have intermediary forms of organs or tissues in evolution that are useful, despite a great deal of data to show that this is simply not true (the eye, the subject of a previous Biologic, was formed in about 400 000 years1). Richard Dawkins has often written about the difficulties that creationists and others (he singles out lawyers as a group that believe in discontinuities rather than continuous variation) have with the absence of intermediate forms, perhaps because of a view of evolutionary action that is ‘progress driven’. But continuous variation is obvious, and runs from us through Homo erectus and Homo habilis , and so on. In evaluating this, we have looked at how the molecular clock runs in evolution in this series and discussed the point that while most mutations are neutral in genetic effect (and some are harmful), often phenotypic change over time does not depend on structural change in the genome—changes in gene expression may be more significant. So while it would be satisfying to be able to see continuous variation leading to phenotypic change, it is not often that one can study evolution as it happens. More observations of this kind are …