One consequence of speciation being a population event is that populations have genetic diversity – not all members of the population are genetically identical. For any particular gene, then, a population may have several slightly different forms present within it. These different forms are called alleles.

Last week I came across a blog post by Intelligent Design leader Bill Dembski, provocatively titled "Craig Venter denies common descent — Dawkins incredulous." Surprised by the headline, I clicked over to read the story.

Many evolutionary critics have identified the Cambrian Explosion as a stumbling block to the theory of evolution, arguing that the “expected transitions between major invertebrate phyla are absent, and that the suddenness of their appearance in the fossil record demonstrates that evolutionary explanations are not viable.” Keith Miller argues that the Cambrian Explosion is not so problematic as these opponents claim after all.