The science behind evolution suggests that the transition from cells without a nucleus to cells with a nucleus is perhaps the single greatest leap between there and here, and that it came about by the inclusion of some cells in some other cells. The term of art here, endosymbiosis, credits the ability to respire, move, and photosynthesize as results of the inclusion of more primitive forms within other forms, and that this inclusion, being beneficial to both the outside and the inside, was durable because it was symbiotic and vice versa. As Margulis and Sagan famously said, "Life did not take over the globe by combat, but by networking." Columnist Dan Geer takes a look at how this concept translates over into networked systems.Jumping to the digital world, you could say that invasive, kernel- resident computer security tools are candidates for being called symbionts. The operating system's original designers didn't code for these programs, others did, and these others didn't code for standalone independence of their products, but rather for extracting all the necessities of persistence from the host operating system and giving something in return that the host operating system needed. Both are better off as both have runtimes (lifespans) that depend on the presence of the other. Unfortunately, the host's operational cost is often profoundly visible, whereas the security tool's benefit degrades over time.