[pjdorrell]

In the bacterial example, each individual tumble chooses a new direction at random, and the effectiveness of the algorithm depends on the smoothness of the chemical density function in the 3D space that the bacteria is swimming around in.

In his human examples, all the "tumbles" are conscious decisions made by the person in response to their circumstances.

If there was some human equivalent of the "tumble", it would have to be something that was change just for the sake of change. Like: "I'm bored and/or frustrated, so I am going to do something stupidly different".