It's a blog! Mainly of book reviews.
I would hazard a guess that Feynman's favourite science outside physics was molecular biology and it appears here in the guise of a naturally occurring "computer"; the copying of base sequences to mRNA is the computation at hand and is completely reversible. The computation is made to go in the desired direction by the relative abundance of necessary chemicals in the cell. Illustrates what reversible computing really means better than anything preceding.