Suppose a glucose-powered nanobiobot has been created to hunt cancer cells via a component antibody moiety. In effect, this nanobiobot has a protein grappling hook designed to dock it with a specific type of tumor cell. Standard dosing therapy will require that billions of these nanobiobots be released into their human "host." If the antibody arm on even one of these nanobiobots is modified (either by some type of catalytic recombination with circulating antibodies or by simple chemical damage) so that it binds to a different type of cell, it could stay in that body for life, like cryptic viruses such as Epstein-Barr. If this nanobiobot is modified so that it can attach to a human sperm or egg cell, it could theoretically stay in the population for generations.

If this type of nanobiotechnology-based cancer therapy becomes common (and according to the NCI's nanomedicine site, that is a real possibility), we could have tens of thousands of people carrying cryptic nanobiobots. Even though these nanobiobots were designed for different functions, it is reasonable to assume that they will have a number of components in common. For example, many of them may have antibody components that, in turn, have regions of identical protein structure. These interchangeable parts could act just like the repetitive DNA of introns in eukaryotic genomes. What happens when one nanobiobot (say) on a sperm cell meets a second one on an egg cell? The probability of this is, of course, extremely low. But if the population of nanobiobots introduced into the body is high (say, billions), then a one-in-a-million event becomes common. In fact, microbial and viral systems like E. coli and bacteriophages enabled the molecular genetics revolution precisely because with billions (or even trillions) of test organisms in hand, one-in-a-million events become commonplace.

Suppose in the near future, a routine nanomedical procedure involved the introduction of billions of nanobiobots designed to scour the arteries dissolving plaque. Cleaning out the circulatory system would be considered a "one shot" treatment so that these therapeutic nanomedical devices (nanobiobots) would not have the engine necessary to use human metabolic energy as a power source. But what if, during another "routine" nanomedical procedure, a second therapeutic nanomedical device (nanobiobot) designed to vaccinate against cancer is introduced into the same person? This latter nanobiobot would, by definition, be designed for longevity so that metabolic energy would likely be the power source. Now, what if these two meet up and combine, or exhange vital components? This could happen through physico-chemical damage or perhaps via some type of catalysis mediated by the host's own complex biochemistry. Now we have a novel, hybrid nanobiobot capable of crawling through our circulatory system for life. Or until it exchanges even more information — either with another nanobiobot or with the body itself. In the world of biology, this type of event would be called a mutation.