“If that part of the story is true, it tells us that humans have actually been the selective agents, which [have] caused this evolutionary change in great tits.”
via Humans May Be Influencing Bird Evolution in Their Backyards – Scientific American
It is interesting to be able to observe changes like this happening even during human lifetimes, and to be able to understand the reasoning and the science behind these changes.
I found the the following article in the Washington Post fascinating. These scientists working in the Galapagos have been able to observe the progress of evolution even during their own lifetimes. Not only that, they have been able to associate the evolutionary change to the DNA that is responsible for it. Darwin had to do his work without the benefit of the tools of genetic engineering.