Author’s Note: This is the first SiMF post picked up for reprinting by io9 — I know it will be the first of many!
Extraterrestrial life is a staple of SF and the focus of astrobiology and SETI. Yet whereas SF has populated countless worlds with varying success, from Tiptree’s haunting Flenni (Your Haploid Heart) to Lucas’ annoying Ewoks, real ETs remain stubbornly elusive: nobody has received a transmission demanding more Chuck Berry, and the data from the planetary probes are maddeningly inconclusive. Equally controversial are the shadowy forms on Martian asteroid ALH84001, although the pendulum has swung toward cautious favoring of the biological possibility after scientists discovered nanobacteria on earth and water on Mars.
In part, we’re hobbled by the limits of our technology, including the problems of sample contamination and method-specific artifacts. But we’re also severely limited by having a single life sample. Despite its dizzying variations in form and function, extant terrestrial life arose from one source. We know this because our genetic blueprint and its associated molecular machinery are identical across the three domains (archaea, eubacteria, eukarya). So to be able to determine if something is alive, we need to decide what is universal and what is parochial. We stumble through redefinitions each time our paradigms shift or our techniques achieve higher resolution. Worse yet, our practices lag considerably behind our theories.