SETI in vivo: testing the we-are-them hypothesis
After it was proposed that life on Earth might descend from seeding by an earlier civilization, some authors noted that this alternative offers a testable aspect: the seeds could be supplied with a signature that might be found in extant organisms. In particular, it was suggested that the optimal location for such an artifact is the genetic code, as the least evolving part of cells. However, as the mainstream view goes, this scenario is too speculative and cannot be meaningfully tested because encoding/decoding a signature within the genetic code is ill-defined, so any retrieval attempt is doomed to guesswork. Here we refresh the seeded-Earth hypothesis and discuss the motivation for inserting a signature. We then show that "biological SETI" involves even weaker assumptions than traditional SETI and admits a well-defined methodological framework. After assessing the possibility in terms of molecular and evolutionary biology, we formalize the approach and, adopting the guideline of SETI that encoding/decoding should follow from first principles and be convention-free, develop a retrieval strategy. Applied to the canonical code, it reveals a nontrivial precision structure of interlocked systematic attributes. To assess this result in view of the initial assumption, we perform statistical, comparison, interdependence, and semiotic analyses. Statistical analysis reveals no causal connection to evolutionary models of the code, interdependence analysis precludes overinterpretation, and comparison analysis shows that known code variations lack any precision-logic structures, in agreement with these variations being post-seeding deviations from the canonical code. Finally, semiotic analysis shows that not only the found attributes are consistent with the initial assumption, but that they make perfect sense from SETI perspective, as they maintain some of the most universal codes of culture.