I have always been a firm believer of gradualism. A packet of light sensitive cells is better than no such cells at all, half an eye is better than none. Life changes in small gradual steps. Whatever 'miraculous' structures we see today are the result of millions of years of change and adjustments.
How could I have forgotten about hybridisation? Afterall, being a botanist, I know that plants do it all the time. Animals do hybridise too and this has been suggested to be a powerful driving force for evolution.
Bruce McPheron and his colleagues (1997) at Pennsylvania State University in University Park, US, noticed a fruit maggot infestation on introduced Asian honeysuckle bushes in north-eastern Pennsylvania. Genetically, McPheron found that the fruit maggot infesting the introduced plant is the result of hybridisation between two native species - the blueberry maggot and the snowberry maggot. This phenomena is confirmed by The Penn State University team, this time led by Dietmar Schwarz, in five different geographic locations. Their findings suggest that hybridisation could lead to shift in host preference by parasites and this could be a powerful factor in generating biodiversity and speed up the rate of evolution.
Read the complete article at New Scientist
The same story was reported at National Geographic Magazine
For more information - Nature (vol 436, p 546)