If you're a rabbit you live in a world that's made of food. Being able to eat almost anything is a great strategy for survival. I imagine our own success as a species has a lot to do with our far-off ancestors going omnivore. A few weeks back the TV programme Countryfile featured a shiny little beetle that has backed itself into an evolutionary cul-de-sac by specializing in eating tansy leaves and nothing else. Silly beetle! It's survival now depends on mad humans planting meadows of tansy for its benefit.
Ailz was saying that squirrels have stopped retiring for the winter. Once they stayed in their drays and lived off stockpiled nuts, now they bounce around and eat the things we put out for the birds. This is evolution in our time. Is a squirrel that no longer squirrels things away still a squirrel or should we be looking to call it something else? And if we stopped feeding the birds would the squirrels die out or revert to their great-great-grandparents' behaviour? How many generations does it take for a species that has changed its modus vivendi to pass the point of no return?