  We consider a stochastic model for species evolution. A new species is born
at rate lambda and a species dies at rate mu. A random number, sampled from a
given distribution F, is associated with each new species at the time of birth.
Every time there is a death event, the species that is killed is the one with
the smallest fitness. We consider the (random) survival time of a species with
a given fitness f. We show that the survival time distribution depends
crucially on whether f<f_c, f=f_c or f>f_c where f_c is a critical fitness that
is computed explicitly.
