Actually, evolution and the beginnings of speciation have been observed. And we have, in the veterinary field, seen a new "species" emerge. Species is in quotes there for two reasons: one, viruses are technically not 'alive'. and two, we don't know exactly which strain it mutated from.
And that is the parvovirus that infects dogs. It likely either came from a type that infects cats (98% identical), or one that infects raccoons and foxes. The cat one is more likely.
This virus developed a mutation that made it different enough to jump hosts, and because dogs had no exposure to this before the 1970s, they are decimated by it. Untreated, 9 out of 10 dogs die of it.
Other examples: bacteria that can eat nylon and rubber and paint. They evolved that trait.
http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment
A particularly important bit from the above article: