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.

Three tests based on fossil data indicate that high rates of extinction recorded in the penultimate (Guadalupian) stage of the Paleozoic era are not artifacts of a poor fossil record. Instead, they represent an abrupt mass extinction that was one of the largest to occur in the past half billion years. The final mass extinction of the era, which took place about 5 million years after the Guadalupian event, remains the most severe biotic crisis of all time. Taxonomic losses in the Late Permian were partitioned among the two crises and the intervening interval, however, and the terminal Permian crisis eliminated only about 80 percent of marine species, not 95 or 96 percent as earlier estimates have suggested.

https://science.sciencemag.org/content/sci/266/5189/1340.full.pdf

A Double Mass Extinction at the End of the Paleozoic Era

Functional morphology and evolution of byssally attached bivalve mollusks

The Nature of the Fossil Record Growth and Form Populations and Species Systematics Evolutionary Morphology Biostratigraphy Evolutionary Rates and Trends Global Diversity and Extinctions Paleoecology and Paleobiogeography Multidisciplinary Studies in Paleontology

Principles of paleontology

According to modern ecological theory, high diversity at any trophic level of a community is possible only under the influence of cropping. Until herbivores evolved, single-celled algae of the Precambrain were resource-limited, and a small number of species saturated aquatic environments. In the near-absence of vacant niches, life diversified slowly. Because the changes required to produce the first algae-eating heterotrophs were therefore delayed, the entire system was self-limiting. When the “heterotroph barrier” was finally crossed in the late Precambrian, herbivorous and carnivorous protists arose almost simultaneously, for no major biological differences separate the two groups. These events automatically triggered the formation of a series of self-propagating feedback systems of diversification between adjacent trophic levels. Comparable systems arose among multi-cellular groups, which radiated rapidly from the newly diversifying protist taxa. The sudden proliferation of complex food webs formed by taxa invading previously vacant adaptive zones produced an explosive diversification of life over a period of a few tens of millions of years. The rapid appearance of skeletons in various groups, though of special geological importance, was no more dramatic than other aspects of the radiation. The overall rate of diversification was comparable to rates for less-extensive adaptive radiations of the Phanerozoic.

https://www.pnas.org/content/pnas/70/5/1486.full.pdf

An ecological theory for the sudden origin of multicellular life in the late precambrian.

The Bivalvia have undergone two principal adaptive radiations since their ap- pearance in the Ordovician. The initial, Early Paleozoic radiation gave rise to epifaunal and primitive infaunal groups and was followed by a period of relative evolutionary stability in the Late Paleozoic. A second, more spectacular radiation took place during the Mesozoic and Cenozoic Eras and brought the bivalves into their present position of prominence. The well-established idea that the many new epifaunal bivalve taxa of the Mesozoic evolved to replace extinct Paleo- zoic brachiopod groups has merit, but fails to explain the rise of the 15 new infaunal bivalve superfamilies of the post-Paleozoic radiation. All new infaunal superfamilies were siphon- feeding groups, whereas siphon feeding had been virtually absent in the Paleozoic Era. Most new siphonate taxa were eulamellibranch heterodonts or their derivatives and possessed crossed-lamellar shell structure. They probably descended from a non-siphonate Paleozoic group with similar features, such as the Astartacea. Their post-Paleozoic radiation was a consequence of mantle fusion and siphon formation, which opened the way for the occupa- tion of many new infaunal ways of life that had been inaccessible to Paleozoic bivalve and brachiopod groups. radiation of infaunal bivalves in terms of life habits has revealed that the preponderance of new Mesozoic and Cenozoic groups were bur- rowers and borers that fed by means of siphons, whereas siphon feeders had been virtually ab- sent in the Paleozoic Era. Similarity of hinge dentition, gill type, and shell structure among siphon-feeding groups suggest that most shared a common ancestry, and life habit data suggest that their adaptive radiation was a consequence of mantle fusion and the evolutionary develop- ment of siphons, which enabled them to invade many new ecologic niches. Before considering the evidence for the role of mantle fusion in bivalve diversification, three in- troductory subjects will be given brief considera- tion: the criteria to be used in measuring bivalve diversity, the general evolutionary history of the Bivalvia, and the classification of bivalves according to feeding type. MEASUREMENT OF TAXONOMIC DIVERSITY

Steven M. Stanley

Papers

A Double Mass Extinction at the End of the Paleozoic Era

Functional morphology and evolution of byssally attached bivalve mollusks

Principles of paleontology

An ecological theory for the sudden origin of multicellular life in the late precambrian.

Post-Paleozoic adaptive radiation of infaunal bivalve molluscs; a consequence of mantle fusion and siphon formation