Scientific Realism

This article endeavors to identify the strongest versions of the two primary arguments against epistemic scientific realism: the historical argument—generally dubbed “the pessimistic meta-induction”—and the argument from underdetermination. It is shown that, contrary to the literature, both can be understood as historically informed but logically validmodus tollensarguments. After specifying the question relevant to underdetermination and showing why empirical equivalence is unnecessary, two types of competitors to contemporary scientific theories are identified, both of which are informed by science itself. With the content and structure of the two nonrealist arguments clarified, novel relations between them are uncovered, revealing the severity of their collective threat against epistemic realism and its “no-miracles” argument. The final section proposes, however, that the realist’s axiological tenet “science seeks truth” is not blocked. An attempt is made to indicate the promise for a nonepistemic, purely axiological scientific realism—here dubbed “Socratic scientific realism.

Structural realism versus deployment realism: A comparative evaluation

In this paper I challenge and adjudicate between the two positions that have come to prominence in the scientific realism debate: deployment realism and structural realism. I discuss a set of cases from the history of celestial mechanics, including some of the most important successes in the history of science. To the surprise of the deployment realist, these are novel predictive successes toward which theoretical constituents that are now seen to be patently false were genuinely deployed. Exploring the implications for structural realism, I show that the need to accommodate these cases forces our notion of “structure” toward a dramatic depletion of logical content, threatening to render it explanatorily vacuous: the better structuralism fares against these historical examples, in terms of retention, the worse it fares in content and explanatory strength. I conclude by considering recent restrictions that serve to make “structure” more specific. I show however that these refinements will not suffice: the better structuralism fares in specificity and explanatory strength, the worse it fares against history. In light of these case studies, both deployment realism and structural realism are significantly threatened by the very historical challenge they were introduced to answer

Diabetes, insulin treatment, and cancer risk: what is the evidence?

Diabetes, in particular type 2, is associated with an increased incidence of cancer. Although the mortality attributable to cancer in type 2 diabetes is overshadowed by that due to cardiovascular disease, emerging data from epidemiologic studies suggest that insulin therapy may confer added risk for cancer, perhaps mediated by signaling through the IGF-1 (insulin-like growth factor-1) receptor. Co-administered metformin seems to mitigate the risk associated with insulin. A recent series of publications in Diabetologia addresses the possibility that glargine, the most widely used long-acting insulin analogue, may confer a greater risk than other insulin preparations, particularly for breast cancer. This has led to a heated controversy. Despite this, there is a consensus that the currently available data are not conclusive and should not be the basis for any change in practice. Further studies and more thorough surveillance of cancer in diabetes are needed to address this important issue

A Limited Habitable Zone for Complex Life

The habitable zone (HZ) is commonly defined as the range of distances from a host star within which liquid water, a key requirement for life, may exist on a planet's surface. Substantially more CO2 than present in Earth's modern atmosphere is required to maintain clement temperatures for most of the HZ, with several bars required at the outer edge. However, most complex aerobic life on Earth is limited by CO2 concentrations of just fractions of a bar. At the same time, most exoplanets in the traditional HZ reside in proximity to M dwarfs, which are more numerous than Sun-like G dwarfs but are predicted to promote greater abundances of gases that can be toxic in the atmospheres of orbiting planets, such as carbon monoxide (CO). Here we show that the HZ for complex aerobic life is likely limited relative to that for microbial life. We use a 1D radiative-convective climate and photochemical models to circumscribe a Habitable Zone for Complex Life (HZCL) based on known toxicity limits for a range of organisms as a proof of concept. We find that for CO2 tolerances of 0.01, 0.1, and 1 bar, the HZCL is only 21%, 32%, and 50% as wide as the conventional HZ for a Sun-like star, and that CO concentrations may limit some complex life throughout the entire HZ of the coolest M dwarfs. These results cast new light on the likely distribution of complex life in the universe and have important ramifications for the search for exoplanet biosignatures and technosignatures.Comment: Revised including additional discussion. Published Gold OA in ApJ. 9 pages, 5 figures, 5 table

Nest predation and habitat selection in the grasshopper sparrow (Ammodramus savannarum)

Predation is the leading cause of nest failure for many birds and is an important source of natural selection that shapes avian behavior and life-history traits. However, our understanding of the relationship between habitat characteristics and nest loss and how predation affects nest-site selection is limited. Predators are not often identified, yet their behavior greatly influences nest loss patterns. Most studies of nest-site selection make unrealistic assumptions about the ability of birds to identify and access preferred habitat and few use unambiguous measures of selection. I studied how grassland management with fire and grazing influences predator-specific patterns of nest loss and whether predation influenced nest-site selection by grasshopper sparrows (Ammodramus savannarum). I used near-infrared video cameras to identify nest predators and followed breeding females on multiple nesting attempts within a breeding season. Burning reduced losses by snakes (Thamnophis and Coluber spp.), whereas predation by mammals and snakes increased with litter cover and fescue (Schedonorus phoenix) surrounding the nest. Mammals were less likely to prey upon nests with increased forb cover as well. Nest losses attributed to cowbirds (Molothrus ater) were unrelated to measured habitat or landscape variables and unaffected by management actions. Though nest sites did not differ from available habitat, female grasshopper sparrows did exhibit adaptive nest-site selection by selecting safer locations on subsequent breeding attempts. My results support that the use of fire can reduce nest loss, but success is contingent on predator identity. Reductions in litter and fescue and increasing forb cover can reduce predation as well. Further, grasshopper sparrows’ nest-site selection is adaptive in terms of reducing nest loss, but females make more adaptive choices when re-nesting. This information can help devise effective management strategies aimed at reducing nest loss and improve our understanding of avian behavior

Long-term sedimentary recycling of rare sulphur isotope anomalies

The accumulation of substantial quantities of O_2 in the atmosphere has come to control the chemistry and ecological structure of Earth’s surface. Non-mass-dependent (NMD) sulphur isotope anomalies in the rock record are the central tool used to reconstruct the redox history of the early atmosphere. The generation and initial delivery of these anomalies to marine sediments requires low partial pressures of atmospheric O_2 (PO_2; refs 2, 3), and the disappearance of NMD anomalies from the rock record 2.32 billion years ago is thought to have signalled a departure from persistently low atmospheric oxygen levels (less than about 10^(−5) times the present atmospheric level) during approximately the first two billion years of Earth’s history. Here we present a model study designed to describe the long-term surface recycling of crustal NMD anomalies, and show that the record of this geochemical signal is likely to display a ‘crustal memory effect’ following increases in atmospheric PO_2 above this threshold. Once NMD anomalies have been buried in the upper crust they are extremely resistant to removal, and can be erased only through successive cycles of weathering, dilution and burial on an oxygenated Earth surface. This recycling results in the residual incorporation of NMD anomalies into the sedimentary record long after synchronous atmospheric generation of the isotopic signal has ceased, with dynamic and measurable signals probably surviving for as long as 10–100 million years subsequent to an increase in atmospheric PO_2 to more than 10^(−5) times the present atmospheric level. Our results can reconcile geochemical evidence for oxygen production and transient accumulation with the maintenance of NMD anomalies on the early Earth, and suggest that future work should investigate the notion that temporally continuous generation of new NMD sulphur isotope anomalies in the atmosphere was likely to have ceased long before their ultimate disappearance from the rock record

Emerging biogeochemical views of Earth's ancient microbial worlds

This work was supported by the NASA Astrobiology Institute under Cooperative Agreement No. NNA15BB03A issued through the Science Mission Directorate (TWL), a Natural Environment Research Council Fellowship (NE/H016805/2) (AZ), and National Science Foundation grants (EAR-0951509, OCE-1061476, EAR-1124389, and OCE-1155346) and a Packard Fellowship (DAF).Microbial processes dominate geochemical cycles at and near the Earth’s surface today. Their role was even greater in the past, with microbes being the dominant life form for the first 90% of Earth’s history. Most of their metabolic pathways originated billions of years ago as both causes and effects of environmental changes of the highest order, such as the first accumulation of oxygen in the oceans and atmosphere. Microbial processes leave behind diverse geochemical fingerprints that can remain intact for billions of years. These rock-bound signatures are now steering our understanding of how life coevolved with the environments on early Earth and are guiding our search for life elsewhere in the universe.PostprintPeer reviewe