From Jane Harris-Zsovan’s recent story at Design of Life blog:
Darwin’s theory of natural selection requires offspring to diverge from a common ancestor to create new species. It requires genetic differences to increase as descendants adapt to their environmental niches.
It is this ‘natural selection’ and ‘adaptation’ that creates species. And, as the newly created species continue to adapt, they should become more different over time. Following this line of thought, hybrids should be less viable than their parents.
Not only is there evidence that natural selection oscillates over time, but some hybrids, in both plant and animal kingdoms, are better suited to their environments than their parents.
In the case of the Darwin’s finches, even the ‘purebred’ finch populations show little tendency to sustain changes in size or shape of their beaks over the long term. This scenario is exactly what Darwinian theory doesn’t predict.
For more go here.