Even as new species are evolving, however, others may become extinct. The rate at which species become extinct may be low in one lineage and high in another. It’s also possible for the rate of extinction to rise, only to drop again later. All of these processes can also unfold at the same time, and so the range of possible long-term patterns in evolution can be enormous. A lineage with a low rate of speciation may end up enormously diverse because its rate of extinction is even lower. On the other hand, a lineage that produces new species at a rapid rate may still have relatively few.
