genes are better or worse timekeepers

An example of a metaphor used to explain a scientific idea:

"Following the theory that mitochondrial DNA was passed down only from the mother (recently shown to be only approximately correct, as many such dogmas are) and that it mutated at a constant rate (recently shown to be probably incorrect; and certainly requiring ranking of different parts of the mitochondrion as better or worse timekeepers), one could argue for a 'mitochondrial Eve' for various species – producing a clock that throws key evolutionary events much further back in time than would be indicated by paleontological evidence in the form of fossil remains…"

Geoffrey C. Bowker

Bowker, G. C. (2005). Memory Practices in the Sciences. The MIT Press.