What (if any) is the shortest evolutionary process observed by humans?
Definition of evolution

The whole problem boils down to the definition of the term "evolution". Typically, evolution is defined as a change in allele frequency over time. See wikipedia > allele if needed.

Answer with definition "evolution = change in allele frequency over time"

Using this definition, any event of death or birth is an evolutionary event. As such, in the human species, there are about 6 evolutionary events per second! This number will vary a lot among species / lineage of course.

Do you want to consider another definition?

If you are willing to use another definition, I am happy to investigate how common are events matching this definition. Please make sure to clearly define the term so as to leave out possibility for subjective appreciation. If you need inspiration for definitions, you might want to have a look at this post.

Sidenote: Evolutionary experiments

You might be interest in evolutionary experiments. An evolutionary experiment consists at putting individuals in a lab, let them breed under some circumstances and let them evolve. Of course, doing such experiment with elephants would be pointless as the generation time is so long. Common species that we use for such experiments include E.coli, S. cervisae (yeast) and D. melanogaster (fruit fly). Some of these experiments can be as short as a few days while others have been running for decades.

Somewhat related posts


How come most animals never seem to evolve over millenia?
Evolutionary chronology - if any, which species have evolved in the last 100 years
Why don't we keep evolving until we are super-human?


For a very introductive source of information in evolutionary biology, you can have a look at the website that @BryanKrause recommended: evo101