Today is Stephen Jay Gould's birthday. Were he still alive, he would be eighty-two years old. As it happened, he died in 2002 when he was only sixty.
As if to commemorate this occasion, a paper appeared yesterday in Nature Communications (“Bayesian Analyses Indicate Bivalves did not Drive the Downfall of Brachiopods Following the Permian-Triassic Mass Extinction”). In a nutshell, it is a Bayesian analysis of diversification dynamics in brachiopods and bivalves, using data from the Paleobiology Database. Here is how the authors describe the study:
First, we estimate the origination and extinction rates, and diversity of the post-Cambrian brachiopods and bivalves using fossil occurrence data from the Paleobiology Database (PBDB). This analysis shows the long-term pattern of their diversification history and highlights the importance of the Permian–Jurassic interval in assessing the brachiopod-bivalve switch. We then exhaustively revise the taxonomy and stratigraphy of the global fossil record of Permian–Jurassic brachiopods and bivalves and use these bespoke datasets to examine the dynamics of the brachiopod-bivalve switch at high temporal resolution, with emphasis on differences between ecological guilds and geographical regions. Finally, we use a multivariate birth-death model (PyRateMBD38) to evaluate the potential factors driving the extinction and recovery of brachiopods and bivalves across the [Permian-Triassic mass extinction]. (Guo et al. 2023, 1)
What does this have to do with Gould? In 1980, Gould and C. Bradford Calloway published an article called, “Clams and Brachiopods—Ships that Pass in the Night.” The allusion is to Longfellow, who wrote of “Ships that pass in the night, and speak each other in passing; Only a signal shown and a distant voice in the darkness.” What Gould and Calloway tried to show was that clams and brachiopods spoke to each other only in passing; that in spite of the fact that brachiopod decline roughly tracked bivalve diversification, the case for competitive displacement was thin. Instead, the “supposed replacement of clams and brachiopods” was produced by a single event, the Permian-Triassic mass extinction, “which affected brachiopods profoundly and clams relatively little” (Gould and Calloway 1980, 383). From this they concluded that “passive extrapolation of microevolutionary theory into the vastness of geological time [often leads] paleontologist astray.” Although competitive interaction “may rule in local populations,” differential response to mass extinction “[sets] the relative histories of large groups through geological time. Similarly, adaptive superiority and design cannot have much to do with the macroevolutionary success of clams.”
Gould and Calloway’s argument was influential but hardly decisive. As Guo et al. report, “the decline of brachiopods after the PTME has [subsequently] been attributed to intense predation, decreased ability to expand habitat distribution, or increased energy flux”(Guo et al. 2023, 2). All these scenarios imply the competitive replacement of brachiopods by bivalves. But the new analysis favors the Gould/Calloway scenario. As the authors write: “Insight from a multivariate birth-death model shows that the extinction of major brachiopod clades during the PTME set the stage for the brachiopod-bivalve switch, with differential responses to high ocean temperatures post-extinction further facilitating their displacement by bivalves. Our study strengthens evidence that brachiopods and bivalves were not competitors over macroevolutionary time scales, with extinction events and environmental stresses shaping their divergent fates” (Guo et al. 2023, 1).
“So on the ocean of life we pass and speak one another; Only a look and a voice, then darkness again and a silence.” Happy birthday, Gould.