Typicaly human investigators don't live long enough to observe speciation in animals. However, the rapid evolution response of bacteria to the stressor of antibiotics is a well-documented phenomenon that has been known for many years.
True. But propose an experiment. Take a bacteria with flagella, then create environmental conditions in which those flagella are not conducive to functioning well in that environment ( or, conversely, take a simple cell organism without flagella, and produce an environment in which they are necessary to function ), and slowly change the environment to produce the necessary changes ( intermediate forms ) for the characteristics to evolve.
Successful, this establishes a certain baseline case to formulate prediction, and have it verified by discovery. I haven't seen this yet.