Paper No. 8
Presentation Time: 3:30 PM
CLASSIC METRARABDOTOS TEST FOR PUNCTUATED EQUILIBRIUM: AN EVOLUTIONARY-PROCESS PERSPECTIVE
GINGERICH, Philip D., Department of Geological Sciences and Museum of Paleontology, The Univ of Michigan, Ann Arbor, MI 48109-1079, gingeric@umich.edu
The classic
Metrarabdotos test for punctuated equilibria claims that rates of change observed long-term over the history of a species are too low (too slow) to explain rates of change observed on shorter time scales during speciation. However the real question is whether rates observed
within species lineages can explain change
between lineages when compared on the generation-to-generation time scale of the process of natural selection. This is illustrated by quantifying change in species of the bryozoan genus
Metrarabdotos. The rates observed in species lineages of
Metrarabdotos are comparable to those quantified for change in fossil horses and many other paleontological and neontological case studies. At these rates, as few as 15 generations are required to explain the differences observed between species of
Metrarabdotos. The fossil record is sometimes punctuated by rapid change on short time scales. However, the process of evolution, while fast, is also gradual, proceeding step-by-step, generation-by-generation through time.
Natural selection is a process that takes place on a time scale of generations– sometimes for millions of generations and millions of years. Morphology is limited by functional constraints. The interaction of morphological constraint and essentially-endless time has a non-intuitive effect on resulting rates of change. What we see on longer time scales is not representative of rates of evolution on the time scale of the generating process. Rates are ratios, and rates are dependent on their denominators as well as their numerators. Knowing this, we see that evolutionary rates are fractal, and rates scale with their denominators in interpretable ways (best appreciated by modeling).
The fossil record is representative of slow change on long time scales, but change in the fossil record shows too that evolution is fast on the timescale of the natural selection process. In Metrarabdotos change was much faster than that typically quantified in the fossil record.
