Simple models for the evolution of qualitative multistate traits are considered, in which the traits are permitted to evolve in time-dependent versus speciation-dependent fashion. Of particular interest are the means and variances of distances for these traits in evolutionary phylads characterized by different rates of speciation, when alternative characters are neutral with respect to fitness, and when the total number of observable characters is limited to small values. As attainable character states are increasingly restricted, mean distance (D) in a phylad (...) decreases, regardless of whether evolution is a function of time or of rate of speciation. The ratio of mean distances in species-rich and species-poor phylads of comparable evolutionary age (DR/DP) remains near one when differentiation is proportional to time, even when attainable character states are severely restricted. DR/DP also nears one as a result of restricting character states when differentiation is proportional to rate of speciation, but the effect is not severe unless the number of character states is very small and the probability of change per speciation very large. These and other results are discussed with reference to available data sets on qualitative multistate traits. (shrink)

Traces scholarly thought from the nineteenth-century birth of evolutionary biology to the mapping of the human genome through forty-eight essays, arranged in chronological order, each preceded by a one-page essay that explains the significance of the chosen work.

Traces scholarly thought from the nineteenth-century birth of evolutionary biology to the mapping of the human genome through forty-eight essays, arranged in chronological order, each preceded by a one-page essay that explains the significance of the chosen work.