Characterization of a branch of the phylogenetic tree (Q2177081)

Computer simulations show that the branch of the evolutionary tree corresponding to a genus consists of three stages: at stage (1) there is a significant probability that the genus will die out. Stage (2) is characterized by exponential growth in time with a certain time constant. At stage (3), the number of pedigree species is close to the maximum value, but this stage is quasi-stable in the sense that extinction will eventually occur, but on a long timescale. The authors identified two new types of contingencies: (a) extinction associated with ``bad luck'' during stage (1), and (b) extinction associated with quasi-stability of stage (3). Analysis and modeling techniques create a new picture of diversity: first, diversity must grow exponentially and then slowly increase with little setbacks due to mass extinctions. This picture combines the features of gradualness and intermittent balance. Using reasonable values for the temporal scales of speciation and catastrophes, speciation is shown to be more important during ``quiet'' periods than immediately after a catastrophe. The catastrophic rebound is due to intermittent equilibrium, and speciation at other times occurs gradually. The formation of new species from intermittent periods occurs approximately two orders of magnitude less than in other periods. Complex behavior, such as chaos, cannot arise for averaged quantities: since all of the above systems are linear and exactly solvable, they cannot be chaotic, although evolution of a certain kind is stochastic and involves significant random effects.