[The Green Lantern]

I like biology, but as a mathematician I am drawn to the elegance of the very simplest forms of life: the subcellular life forms. They are so simple, in fact, that even calling them "alive" can be controversial. They lack many of the usual features of life. They don't have cell walls, most of them don't metabolize, and they are all parasitic, depending on other organisms for their ability to reproduce! Some of them even have no genetic code! Many of them cause diseases, but others are crucial to the well-being of their host, and many are so well integrated with their host that it becomes difficult to decide whether they are part of the host or a separate entity.

Indeed, besides my love of elegance and my morbid fascination with parasites, the main reason subcellular life forms appeal to me is that they challenge our naive notion of organisms as entities with clear, well-defined boundaries. It's clear by now that life doesn't respect this simple picture. Whenever a pattern of any sort, however abstract, is able to replicate itself, it does! Typically these patterns overlap and interact in subtle ways, so one can't easily say where one ends and the other begins.