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found a file on the hard drive, called "Punctuated Equilibria":

Evolutionary Dynamics: Models of Extinction
Gunther Eble, Smithsonian Institution, SFI Postdoctoral Fellow
Mark Newman, SFI Research Professor
Kim Sneppen, Niels Bohr Institute
Per Bak, NORDITA, SFI External Faculty
David Raup, Palentology, University of Chicago (Retired), SFI Science Board
Simon Levin, Ecology, Princeton, SFI Science Board
Extinction has played an important role in the development of life on the Earth... It is important first to understand the nature of extinction in the fossil record, before one can undertake any modeling efforts to try to explain that extinction. In recent years a number of claims have been made about apparent trends in the fossil record of extinction which might point to interesting underlying dynamical processes in the biosphere. Stuart Kauffman (biology, Bios, SFI External Faculty), for example, has argued that the distribution of the sizes of extinction events approximately follows a power-law form, taken by some to be indicative of criticality in the processes giving rise to extinction. Sneppen et al. have suggested that the distribution of the lifetimes of genera may also be a power law, and Ricard Sole (ecology, Barcelona, SFI External Faculty) et al. have presented evidence that the power spectrum of extinction intensity during the Phanerozoic has a 1/f form.

Power Spectra of Extinction in the Fossil Record
M. E. J. Newman and Gunther J. Eble
1998-12
Abstract: Recent Fourier analyses of fossil extinction data have indicated that the power spectrum of extinction during the Phanerozoic may take the form of 1/f noise, a result which, it has been suggested, could be indicative of the presence of "critical dynamics" in the processes giving rise to extinction. In this paper we examine extinction power spectra in some detail, using family-level data from a variety of different sources. We find that although the average form of the power spectrum roughly obeys the 1/f law, the spectrum can be represented more accurately by dividing it into two regimes: a low-frequency one which is well fit by an exponential, and a high-frequency one in which it follows a power law with a 1/f2 form. We give explanations for the occurrence of each of thse behaviours and for the position of the cross-over between them.