I think that other people have accurately described how pulling out desirable traits from a variable population is actually a kind of evolution. There are however examples more like you seem to be looking for, new mutations leading to new traits for natural selection to act on:
Take, for example, the parasite that causes malaria
There is very little variation in the genepool of the parasite that causes malaria, probably because it is only about 10 000 years old as a species. Chloroquine has been used as an antimalrial drug since about the 1930s and worked for a very long time without any resistance, presumably because resistant parasites did not exist in the population.
So, in order to generate resistant parasites a new mutation will have to arise somewhere in the world. If this was to occur we would expect to see resistance to arise in one location and spread slowly across the world with the migration of people. This is exactly what happened, in the late 1950’s the first cases of chloroquine resistant malaria started showing up in Asia, but it took another 20 years to make it to Africa. Now it is hard to find a non-resistant malaria parasite in Africa, Asia or South America.
So there you have it, a novel and random mutation being favoured in a population by a selection within a human lifetime.
Pubmed citation to a recent review on this and other malaria information
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