An adaptationist programme has dominated evolutionary thought in England and the United States during the past 40 years. It is based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an organism into unitary ‘traits’ and proposing an adaptive story for each considered separately. Trade-offs among competing selective demands exert the only brake upon perfection; non-optimality is thereby rendered as a result of adaptation as well. We criticize this approach and attempt to reassert a competing notion (long popular in continental Europe) that organisms must be analysed as integrated wholes, with Baupläne so constrained by phyletic heritage, pathways of development and general architecture that the constraints themselves become more interesting and more important in delimiting pathways of change than the selective force that may mediate change when it occurs. We fault the adaptationist programme for its failure to distinguish current utility from reasons for origin (male tyrannosaurs may have used their diminutive front legs to titillate female partners, but this will not explain why they got so small); for its unwillingness to consider alternatives to adaptive stories; for its reliance upon plausibility alone as a criterion for accepting speculative tales; and for its failure to consider adequately such competing themes as random fixation of alleles, production of non-adaptive structures by developmental correlation with selected features (allometry, pleiotropy, material compensation, mechanically forced correlation), the separability of adaptation and selection, multiple adaptive peaks, and current utility as an epiphenomenon of non-adaptive structures. We support Darwin’s own pluralistic approach to identifying the agents of evolutionary change.

The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme

An adaptationist programme has dominated evolutionary thought in England and the United States during the past 40 years. It is based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an organism into unitary 'traits' and proposing an adaptive story for each considered separately. Trade-offs among competing selective demands exert the onlv brake upon perfection; non-optimality is thereby rendered as a result of adaptation as well. We criticize this approach and attempt to reassert a competing notion (long popular in continental Europe) that organisms must be analysed as integrated wholes, with Bauplane so constrained by phyletic heritage, pathways of development and general architecture that the constraints themselves become more interesting and more important in delimiting pathways of change than the selective force that may mediate change when it occurs. We fault the adaptationist programme for its failure to distinguish current utility from reasons for origin (male tyrannosaurs may have used their diminutive front legs to titillate female partners, but this will not explain why they got so small); for its unwillingness to consider alternatives to adaptive stories; for its reliance upon plausibility alone as a criterion for accepting speculative tales; and for its failure to consider adequately such competing themes as random fixation of alleles, production of nonadaptive structures by developmental correlation with selected features (allometry, pleiotropy, material compensation, mechanically forced correlation), the separability of adaptation and selection, multiple adaptive peaks, and current utility as an epiphenomenon of non-adaptive structures. We support Darwin's own pluralistic approach to identifying the agents of evolutionary change.

/pdf/the-spandrels-of-san-marco-and-the-panglossian-paradigm-a-19fdlsieru.pdf

Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions.

/pdf/ocean-acidification-the-other-co-2-problem-4h18mw2cpj.pdf

Ocean Acidification: The Other CO 2 Problem

We review the biogeography of microorganisms in light of the biogeography of macroorganisms A large body of research supports the idea that free-living microbial taxa exhibit biogeographic patterns Current evidence confirms that, as proposed by the Baas-Becking hypothesis, 'the environment selects' and is, in part, responsible for spatial variation in microbial diversity However, recent studies also dispute the idea that 'everything is everywhere' We also consider how the processes that generate and maintain biogeographic patterns in macroorganisms could operate in the microbial world

/pdf/microbial-biogeography-putting-microorganisms-on-the-map-1k7e5do5pn.pdf

Microbial biogeography : putting microorganisms on the map

Darwin (1859, pp. 11-14, 143-150) stressed the evolutionary importance of covariation between characters in populations and its "most imperfectly understood" connection with correlated responses to artificial and natural selection. After the turn of the century the discoveries of pervasive pleiotropy and linkage of Mendelian factors revealed the underlying genetic mechanisms. Existing theory on the dynamics of correlated characters has been developed in the limited framework of practical plant and animal breeding. Methods of multivariate analysis, functional analysis and optimality criteria popular among evolutionists, do not account for dynamical constraints imposed by the pattern of genetic variation within populations. Consideration of phenotypic variation often does not suggest any clear mechanism connecting growth patterns or adult variation to interspecific evolution. When there is individual variation in development, no necessary correspondence exists between ontogenetic and adult variation in a population (Cock, 1966, pp. 148-15 1). It is also common for the pattern of adult variation within a species to differ from that at higher taxonomic levels (Simpson, 1953, pp. 25-29). An example which will be investigated here is the brain weight:body weight relationship. At various taxonomic levels, brain and body weights tend to follow the allometric equation

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1979.tb04694.x

Quantitative genetic analysis of multivariate evolution, applied to brain:body size allometry.

There is considerable evidence that changes in seawater chemistry over the course of geologic time have profoundly influenced biomineralization by marine organisms. This evidence, some of it based on experiments with living organisms, has revealed that many algae and invertebrates have less control over the chemical composition of their skeletons (are more at the mercy of seawater chemistry) than has traditionally been recognized. Nearly all of these organisms produce skeletons that consist largely of CaCO3. There is also much evidence that future changes in atmospheric pCO2 will affect calcifying organisms and that feedbacks entailing these organisms will exert a strong influence on the level of atmospheric pCO2. Lime sediments, which consist of CaCO3 with a varying percentage of Mg substituting for Ca, are the precursors of limestone. Abiotic lime sediments form by precipitation in shallow tropical seas, where relatively high temperatures reduce the solubility of CO2 in seawater. These inorganic precipitates consist largely of three materials: (1) cement that forms in cavities within organic reefs, (2) ooids, which are roughly spherical, sand-sized grains that form by accretion * Phone: (443) 600-2435. Fax: (808) 956-5512. E-mail: stevenst@hawaii.edu. Steven Stanley grew up in a village several miles east of Cleveland, Ohio. He received his bachelor’s degree from Princeton University (1963) and his Ph.D. from Yale University (1968). After two years as an assistant professor at the University of Rochester, he moved to Johns Hopkins University, where he was promoted to full professor in 1974 and remained until 2005, when he became a research professor at the University of Hawaii at Manoa. Much of his work has concerned rates, trends, and patterns of macroevolution, and for more than twenty years, it has focused on the history of life in the context of past environmental change. He has served as president of the Paleontological Society and American Geological Institute and was elected to the National Academy of Sciences in 1994. His most recent awards have been the National Academy’s Mary Clark Thomson Medal, the Paleontological Society Medal, and the Twenhofel Medal of the Society for Sedimentary Geology (SEPM). Chem. Rev. 2008, 108, 4483–4498 4483

Effects of global seawater chemistry on biomineralization: past, present, and future.

Two kinds of adaptation aid infaunal bivalve mollusks in sustaining their life positions against potentially disruptive water movements: (1) ability to retard scour of surrounding sediment and (2) ability to reburrow rapidly if exhumed. The shell of the venerid Anomalocardia brasiliana is ornamented with concentric ridges that are asymmetrical in cross-section; experiments show that these ridges aid the animal in burrowing by grip- ping the sediment during backward rotation of the shell. The shell of the less deeply burrowing venerid Chione cancellata also bears concentric ridges, but these are symmetrical and experiments show that they hinder burrowing; other experiments demonstrate that these ridges reduce scour of sand from around a partly exposed animal. The single cardiid species Trachycardium egmontianum possesses ad- aptations comparable to those of the two venerid species, in the form of spines of two varieties; experi- ments show that the flared anterior spines facilitate burrowing and the cupped posterior spines reduce scour. Conspicuous ornamentation of the kinds considered here was rare throughout the Paleozoic. Its evo- lutionary deployment occurred primarily during the post-Paleozoic adaptive diversification of infaunal bivalves, which was triggered by the evolution of efficient burrowing mechanisms. The general premium on maintaining infaunal life positions was accentuated for bivalves after the Paleozoic by the origins of important modern predatory taxa.

Infaunal survival: alternative functions of shell ornamentation in the Bivalvia (Mollusca)

The past few years have been marked by enlivened controversy about the tempo of evolution, the legitimacy of the concept of macroevolution, and the history of these and related questions. At the core of the debate is what has become known as punctuational evolution. I have suggested that the punctuational model be defined as the assertion that most evolution is associated with speciation by way of localized populations (Stanley, 1979 p. 16). The traditional, gradualistic model represents the alternative position, that most evolution occurs within established species. The known fossil record, in failing to document important gradual evolutionary transitions, has long been recognized to have a punctuational appearance. Darwin (1859) claimed that the record itself is at fault here, rather than the gradualistic scheme of evolution that he proposed, and Darwin's view prevailed for more than a century. A decade ago, the punctuational model attracted attention through the advocacy of Eldredge (1971) and Eldredge and Gould (1972), who favored it as being most compatible with biological concepts of speciation. Certainly it is not compatible with many (and I would argue most) traditional concepts of speciation. Dobzhansky (1972) referred to the slow divergence of new species from their ancestors as the "usual and by now orthodox view," and earlier Huxley (1942 p. 389) wrote: "Species formation constitutes one aspect of evolution; but a large fraction of it is in a sense an accident, a biological luxury, without bearing on the major and continuing trends of the evolutionary process. " In fact, it has been Mayr (1954, 1963, 1970) who since mid-century has argued most forcefully for the importance of rapidly divergent speciation events. Mayr (1954) suggested that sudden appearances of evolutionary novelties in the fossil record have resulted from rapid transitions in local areas. Rapid transformation of entire species after long periods of stasis is an alternative to rapidly divergent speciation, and in this paper I will also examine this alternative, which some might include within the punctuational model. My interest in the punctuational question was stimulated by statements of earlier workers that the fossil record's testimony is equivocal. Believing that the analysis of fossil data could indeed resolve the issue, I proposed formal tests, whose outcomes favored the punctuational model (Stanley, 1975). The most general of these tests, more fully developed in a later contribution (Stanley, 1979), relates to the great longevity of species in the fossil record. This test is labeled the test of adaptive radiation because its conclusion is that during a typical adaptive radiation, major evolutionary transitions have occurred during geological intervals that have been brief relative to intervals over which species produced during the radiation have survived almost without change. Established species are evolving so slowly that major transitions between genera and higher taxa must be occurring within small, rapidly evolving populations that leave no legible fossil record. In the present contribution I will describe new evidence that strengthens the verdict of the test of adaptive radiation in favor of the punctuational model.

Macroevolution and the fossil record.

Approximate periodicity for peak rates of global extinction during the past 250 m.y. may have resulted from delayed recovery following major extinction events. Two components can be envisioned for such delays: persistence of inimical environmental conditions for some time after the onset of the crisis, and slow restoration of vulnerable taxa. This general hypothesis is consistent with statistical evidence of linkage between measured rates of extinction of marine invertebrate genera for contiguous stages and substages of the geologic column. The nine broad valleys between the “periodic” peak rates for the past 250 m.y. exhibit only three trivial secondary peaks, indicating that, if the pattern is not artifactual, trends in global rates of extinction have not readily been abruptly reversed. Moreover, the smooth observed trends reflect the fact that regional crises tend to remove many species but few genera. To some degree, high rates of extinction that precede peak rates must represent bias of the incomplete fossil record (the Signor-Lipps effect). High rates that immediately follow peak rates also may, to a degree, reflect biological legacy: (1) final extinction of weakened genera or (2) extinction of new genera that contain few species or represent failed evolutionary “experiments.” Nonetheless, there is evidence that protracted intervals of stressful environmental conditions contributed to high rates of extinction preceding or following certain peak intervals, including the Scythian, Cenomanian, Early Paleocene, and Early Oligocene. The reef-building rudists, for example, suffered heavy extinction during both Cenomanian and Turonian time and then failed to recover quickly.The late Neogene record of bivalve molluscs in the Western Atlantic offers a more detailed picture of delayed recovery. Here early intervals of glacial expansion caused heavy extinction, leaving an impoverished, eurythermal fauna that was virtually unaffected by late Pleistocene glacial episodes. The episode of heavy extinction in Late Eocene time exhibits a similar phenomenon on a worldwide scale. Among the planktonic foraminifera, warm-adapted stenothermal species died out, and eurythermal forms predominated throughout Oligocene time; restoration of vulnerable, stenothermal species proceeded gradually during the Miocene Epoch. This example of delayed recovery and others like it following earlier global crises may have prevented such crises from following one another in rapid succession, yielding an appearance of periodicity.

Delayed recovery and the spacing of major extinctions

Taxonomists working with late Cenozoic faunas tend to view living species as starting points for the evaluation of chronospecies (i.e., segments of evolutionary lineages subjectively designated as species) that extend backward in time from the Recent. This practice makes it possible to construct a survivorship curve for late Cenozoic chronospecies by evaluating all fossil lineages believed to have survived to the present day. A survivorship curve is produced by plotting the fraction of these lineages existing at any time that have not undergone enough phyletic evolution that their extant representatives are assigned to new species. This kind of surviviorship curve has been plotted for chronospecies of mammals using the beginning of the Wurm, rather than the Recent, as an endpoint in order to avoid the effects of the Wurm and post-Wurm mass extinction. The survivorship curve reveals that all but a small fraction of established chronospecies have long durations relative to intervals of time during which distinctive higher taxa have arisen. Phyletic turnover of species has been remarkably slow. Most net evolutionary change must have been associated with saltational speciation. Even the large majority of genera must have arisen rapidly by one or more divergent speciation events. Estimates of rates of extinction suggest that the bottleneck effect, in which constriction of a lineage is followed by re-expansion as a distinct species, cannot be a major source of evolutionary change. These conclusions, based on the evaluation of mammalian phylogeny, seem also to apply to other taxa of animals, supporting the punctuational model of evolution. The long durations of hominid species imply that the evolution of humans, like that of other mammals, conforms to this model.

Steven M. Stanley

Papers

Effects of global seawater chemistry on biomineralization: past, present, and future.

Infaunal survival: alternative functions of shell ornamentation in the Bivalvia (Mollusca)

Macroevolution and the fossil record.

Delayed recovery and the spacing of major extinctions

Chronospecies' longevities, the origin of genera, and the punctuational model of evolution