The yearly population explosion of crabs on Christmas Island was possibly due to the extinction of a native predator; the recent introduction of the yellow crazy ant has started bringing this population back down |
By this point in our walkthrough of Dobzhansky’s biological classic, Genetics and the Origin of Species, we have seen how much raw phenotypic variation exists in the wild, and how this variation is generated by several different mechanisms, including mutations. And we have discovered that some of this phenotypic variation, namely, genetic variation, is passed from parents to offspring. Without heritable genetic variation, there can be no evolution. But what drives evolution? As we saw last week, evolution can be driven by mutation pressures and genetic drift. But usually when we think of evolution, we are thinking of evolution by natural selection. Dobzhansky devotes chapter six to this important topic.