Showing papers by "Steven M. Stanley published in 1976"

Ideas on the timing of metazoan diversification

Abstract: Fossil data suggest that the great majority of metazoan classes that existed in tlhe Early Cambrian arose after about 700 my ago. The rectangular model of evolution, which views most evolutionary change as being concentrated in speciation events, can easily ac- commodate the implied rate of divergence. If, as some authors believe, the eukaryotic cell arose long before the start of the Cambrian, an explanation is required for the delay of large-scale metazoan divergence. The advent of sexuality may have triggered diversification, not by accelerating phyletic evolution, as tra- ditionally believed, but by making possible speciation and, hence, adaptive radiation. An- other important delaying factor may have been the near-saturation of Precambrian algal systems in the absence of cropping by herbivores. Uncropped Precambrian systems should have been self-limiting in terms of diversification. When advanced heterotrophy finally arose, self-propagating feedback systems of diversification should have been set in motion. Even if the eukaryotic cell arose later than commonly envisioned and triggered the radia- tion of the Metazoa about 700 my ago, the earlier absence of sexuality and cropping may have delayed the transition from the prokaryotic condition to the eukaryotic condition.

Stability of species in geologic time.

Abstract: adaptive behavior\" as do associative procedures, they say; in both cases \"the propensity of the animal to adapt by rejecting a novel or distinctive fluid is revealed\" (18, pp. 18-19). As to mechanisms of associative predisposition, speculation seems to me to be premature. It might be wiser to wait until we have evidence that there is such a thing-evidence which the literature of flavor aversion, however voluminous, fails to provide. M. E. BITTERMAN Laboratorv of Sensor' Sciences, University of Hawaii, 1993 East-West Road, Honolulu 96822