I am currently reading Methusaleh’s Children by Heinlein. A quote:
Out, out and still farther out…out to the lonely depths where world lines are almost straight, undistorted by gravitation. Each day, each month…each year…their headlong flight took them farther from all humanity. (p. 114)
It reminded me of phylogenic trees. The forks that represent the divergence of species are good at approximating time and distance. But not rate. How fast can one species diverge from another? If one species goes extinct, the new species is “created” in that instant. In addition, do nearby species create a sort of “gravity” which pulls against the divergence and slows its spread?