I didn’t make it to many talks yesterday, spending a good part of the day in meetings, including a meeting of the NASA Postdoctoral Program fellows and alumni. The plenary by Nicholas Hud and Rachel Whitaker was fascinating. I’m not sure it lived up to the very ambitious title, “The origin and subsequent evolution of life,” but it did give some ideas about the transition from prebiotic chemistry to cellular life.
Betul Kacar and Rika Anderson’s session “Chance and necessity: from molecules and viruses to cells and populations I” was the most interesting to me. James Cleaves asked and (partly) answered the question ‘is the set of biological molecules on Earth the best or even the only possible set?’ For RNA at least, there are a huge number of closely related, stable molecules that, by all appearances, should operate just as well as the canonical ribosides that all life on Earth actually uses. If so, it would suggest that the particular molecules that polymerize into RNA are more of a ‘frozen accident’ than anything inevitable.
Arshan Nasir examined the protein fold superfamilies in all seven major types of viruses, concluding that viruses originated from ancient cells with segmented RNA genomes. Viruses, in other words, predate the divergences among bacteria, Archaea, and eukaryotes, and Nasir argues that they should be recognized as a ‘fourth supergroup.’
Paul Sniegowski filled in for Phil Gerrish to present work that attempts to extend Fisher’s fundamental theorem of natural selection to multiple generations. Fisher’s theorem predicts adaptive change over a single generation, but the process of adaptive change itself causes the two key terms, mean fitness and additive variance in fitness, to change, requiring these terms to be re-estimated. I’m afraid I didn’t follow the whole argument, but for those of you who are more mathematically minded, it required estimating the ith cumulant of the distribution of fitness effects (where i is the generation). The distribution of fitness effects and its cumulants are, in principle, measurable, so (again in principle) evolutionary dynamics over an arbitrary number of generations should be predictable.
Part II of the chance and necessity session is this afternoon, and I’ll be looking forward to it.
After the last talk, a bunch of us went out to Wrigley Field and watched the Cubs get crushed by the Indians, 6-0.