Neutral Theory Research Articles

Stable isotopes disentangle niche partitioning and co‐occurrence in a multi‐species marine mutualism

Ecologists have long sought general explanations for the co‐occurrence of ecologically similar taxa. Niche theory explains co‐occurrence via functional differences among taxa that reduce competition and promote resource partitioning. Alternatively, the unified neutral theory of biodiversity and biogeography suggests that co‐occurrence can be attributed to stochastic processes, and thus, presupposes that ecologically similar species that occur in sympatry are functionally analogous. We test these hypotheses using the most diverse crustacean‐sea anemone symbiosis from coral reefs in the Tropical Western Atlantic. δ13C and δ15N stable isotope analyses of six crustacean symbionts that co‐occur around the host anemone Bartholomea annulata exhibit highly differentiated isotopic niche space spanning several trophic levels. As multiple crustacean species within the symbiosis have been documented as cleaners that remove parasites from reef fishes, we extended our investigation into the broader cleaner community. Our stable isotope analyses of cleaners shows that Pederson's cleaner shrimp Ancylomenes pedersoni exhibits the highest δ15N isotopic values‐ significantly higher than all other putative cleaner species and consistent with expectations of a dedicated cleaning lifestyle. However, for other species previously described or observed to clean reef fishes, including Periclimenes yucatanicus, Stenopus hispidus and Stenorhynchus seticornis, δ15N isotopic values were substantially lower, raising questions about the degree to which these species rely on cleaning interactions to meet their nutritional requirements. Taken together, our data are consistent with the expectations of niche theory: co‐occurring symbiotic crustaceans have highly partitioned niche space with low levels of functional redundancy.

A primer of community ecology using the R language

AbstractCommunity ecology beginners often struggle to understand theories expressed in complex mathematical formulas and to master computer programming. To remedy this situation, this article provides a practical, R‐based introduction to community ecology by illustrating core concepts (vital rates, carrying capacity, density dependence) and models that can be used to explore the patterns of species abundance and diversity. The structure of this article consists of three modeling exercises, each asking a general question that can be answered by a combination of theory and R programming: (1) what determines the abundance of species, and what makes a population persist and go extinct?; (2) what determines the distribution of species and species diversity?; (3) what determines the relative abundance of species and what allows species to coexist? Through the exercises, I discuss the following five concepts and ideas that provide valuable insights into the questions: (i) the tragedy of the commons, (ii) the theory of island biogeography, (iii) competitive exclusion, (iv) the neutral theory of biodiversity, and (v) frequency dependence. These materials are thus designed to guide the reader in developing an intuition for ecological thinking that will help capture the essence of the global environmental and biodiversity crisis. Although this article does not delineate the scope and depth of the vast field of community ecology, I hope that it will motivate the reader to step up to a more formal introduction to community ecology.

Trait-based ecology, trait-free ecology, and in between.

Trait-based ecology has become a popular phrase. But all species have traits, and their contributions to ecological processes are governed by those traits. So then, is not all ecology trait-based? Actually, there do exist areas of ecology that are consciously trait-free, such as neutral theory and species abundance distributions. But much of ecology could be considered actually or potentially trait-based. A spectrum is described, from trait-free through trait-implicit and trait-explicit to trait-centric. Trait-centric ecology includes positioning ecological strategies along trait dimensions, with a view to inferring commonalities and to generalizing from species studied in more detail. Trait-explicit includes physiological and functional ecology, and areas of community ecology and ecosystem function that invoke traits. Trait-implicit topics are those where it is important that species are different, but formulations did not initially characterize the differences via traits. Subsequently, strands within these trait-implicit topics have often moved towards making use of species traits, so the boundary with trait-explicit is permeable. Trait-based ecology is productive because of the dialogue between understanding processes in detail, via traits that relate most closely, and generalizing across many species, via traits that can be compared widely. An enduring key question for trait-based ecology is which traits for which processes.

Hydrodynamic cloaks with isotropic and homogeneous viscosity for multi-object in collaborative operations

Although significant efforts have been devoted to advancing hydrodynamic cloaks for a single object, limited exploration has focused on cloaking multiple objects. By cloak, we mean a state of hydrodynamic invisibility achieved by eliminating flow disturbances caused by intrusive objects in the surrounding fluids. These gaps in understanding present challenges in developing effective strategies for achieving hydrodynamic stealth for multiple objects in collaborative operations. To address these issues, we propose a multi-object hydrodynamic cloak with isotropic and homogeneous fluid viscosity in viscous potential flows through a combination of neutral inclusion theory and convection-diffusion-balance method. By effectively transforming the intrusive objects into one single object while maintaining the overall invasive volume unchanged—a critical factor in flow disturbances—we successfully derive the analytical solution of fluid viscosity for multi-object hydrodynamic cloaks. Numerical simulations demonstrate the proposed cloaks considerably minimize the hydrodynamic perturbations generated by objects in groups with symmetric or asymmetric distributions, various sizes, and even arbitrary shapes. In addition, we reveal that the antagonism between the defined boundary effect of flow disturbances and vorticity magnitudes primarily determines the effectiveness of the proposed cloaks, laying the foundation for the future development of multi-object hydrodynamic cloaks involving interactions among objects. Hopefully, this research will advance the fields of hydrodynamic metamaterials for multiple objects in collaborative settings and contribute to the broader understanding of complexity science.

Ethical Dilemma and Technology Misuse in Medical Fiction of Rebecca Skloot’s The Immortal Life of Henrietta Lacks

The rapid advancement of medical technology has introduced new ethical quandaries that are increasingly explored within medical fiction. To explore these ethical misconducts and implications of technology misuse, the study selects the medical novel Rebecca Skloot's The Immortal Life of Henrietta Lacks. This study uses the Neutralization Theory of Sykes and Matza to examine the moral arguments and ethical conundrums raised in Rebecca Skloot's The Immortal Life of Henrietta Lacks. In that, the novel investigates how authors use the medium of fiction to not only highlight the profound ethical questions surrounding the development and application of new technologies but also to expose the fragility of the systems and individuals tasked with wielding such power. This selected medical narrative serves as cautionary tales that force readers to confront the moral and philosophical implications of technological progress in the medical field, calling doctors to consider the delicate balance between scientific advancement and preserving human dignity, autonomy, and the sanctity of life.

Różne teorie części

Mereology is as a theory of collective sets (or mereological sums). It was formulated by the Polish logician Stanisław Leśniewski. Collective sets are wholes composed of parts, and the concept of being a collective set itself can be defined with the help of the concept of being a part. Mereology may therefore be considered as a theory of „the relation of a part to the whole” (from the Greek: μέρος – „part”). Leśniewski’s mereology was an untypical conception, for it differed from the standard formulations. However, it can be reformulated in the language of structure theory. In the paper, firstly, I examine existentially neutral theories, in which one may prove the existence of only those mereological sums that it is possible to obtain exclusively via the definition of and fundamental properties of the concept of being a part. Moreover, I examine some existentially involved theories of parts (Grzegorczykian mereology and Leśniewskian mereology). One of the main principles of mereology is the transitivity of the concept being a part. This property is often called into question in the literature. Finally, I present an analysis without the assumed transitivity.

Non-darwinian theories of biological evolution

The article presents material related to evolutionary theories such as Berg’s nomogenesis, Kimura’s theory of neutral evolution, and neo-Lamarckism, the content of which is opposed to Darwin’s doctrine of natural selection as a leading factor in biological evolution. Nomogenesis, a hypothesis according to which the evolution of organisms is based on internal laws. The general thesis of Berg’s worldview was that evolution occurs naturally, in accordance with a pre-existing – pre-established – law of development. The neutral theory of molecular evolution was put forward by Motoo Kimura. It argues that the vast majority of mutations at the molecular level are neutral in nature with respect to the action of natural selection. Thus, the theory of neutral evolution contradicted Darwinism, pointing to the fixation of neutral mutations in the population without the participation of natural selection. Neo-Lamarckism is a combination of three heterogeneous trends in evolutionary doctrine. Despite the fact that neo-Lamarckists have deviated from the basic postulates of Lamarck, most of their concepts contain two provisions that correspond to Lamarck's laws. The first is the recognition of adequate variability that occurs under the direct or indirect influence of the environment and creates well-acquired adaptive traits. The second is the inheritance of similar traits in individual life.

Stochastic processes driving cyanobacterial temporal succession in response to typhoons in a coastal reservoir

Typhoons associated with heavy rainfall events, potentially triggering harmful algal blooms (cyanoHABs) dominated by cyanobacteria in coastal reservoirs. These blooms deteriorate water quality and produce toxins, posing a threat to aquatic ecosystems. However, the ecological mechanisms driving cyanobacteria communities in response to typhoons remain unclear. To address this gap, we investigated a coastal reservoir with high-frequency sampling during two typhoon seasons. We employed comprehensive statistical methods under neutral and evolutionary theories to analyze environmental dynamics and cyanobacterial genus succession. Our findings revealed a significant increase in nutrient loads following typhoons, with concentrations of total nitrogen (TN), total phosphorus (TP), and ammonia-nitrogen (NH4+-N) rising from 0.4 mg/L to 1.0 mg/L, 0.02 mg/L to 0.63 mg/L, and 0.03 mg/L to 0.26 mg/L, respectively. These changes coincided with fluctuations in other physicochemical parameters under changing hydrometeorological conditions. Despite significant environmental disturbances, the cyanobacterial community exhibited a remarkable recovery within 15–25 days following the typhoons. This recovery progressed through four distinct successional phases, with a notable shift in community composition from Raphidiopsis and Pseudoanabaena to Aphanocapsa, subsequently replaced by Raphidiopsis and Microcystis, before reverting to the pre-typhoon community structure. During the entire successional phase, the availability of TN and the TN/TP ratio played a dominant role, as indicated by PLS-PM analysis (total effects = -0.6; p < 0.05). Pre-typhoon, environmental factors primarily influenced community structure (54 %) based on modified stochasticity ratio. However, following the typhoons, stochastic fluctuations took precedence (71 %-91 %). The rapid recovery of cyanobacterial communities and the shift in driving mechanisms from deterministic to stochastic processes underscore the complex ecological responses to typhoon events. This study provides essential insights for biodiversity preservation and ecosystem restoration, emphasizing the need to consider both stochastic and deterministic processes in ecological management strategies.

Previously unmeasured genetic diversity explains part of Lewontin's paradox in a -mer-based meta-analysis of 112 plant species.

At the molecular level, most evolution is expected to be neutral. A key prediction of this expectation is that the level of genetic diversity in a population should scale with population size. However, as was noted by Richard Lewontin in 1974 and reaffirmed by later studies, the slope of the population size-diversity relationship in nature is much weaker than expected under neutral theory. We hypothesize that one contributor to this paradox is that current methods relying on single nucleotide polymorphisms (SNPs) called from aligning short reads to a reference genome underestimate levels of genetic diversity in many species. To test this idea, we calculated nucleotide diversity ( ) and -mer-based metrics of genetic diversity across 112 plant species, amounting to over 205 terabases of DNA sequencing data from 27,488 individual plants. We then compared how these different metrics correlated with proxies of population size that account for both range size and population density variation across species. We found that our population size proxies scaled anywhere from about 3 to over 20 times faster with -mer diversity than nucleotide diversity after adjusting for evolutionary history, mating system, life cycle habit, cultivation status, and invasiveness. The relationship between -mer diversity and population size proxies also remains significant after correcting for genome size, whereas the analogous relationship for nucleotide diversity does not. These results suggest that variation not captured by common SNP-based analyses explains part of Lewontin's paradox in plants.

The protein domains of vertebrate species in which selection is more effective have greater intrinsic structural disorder.

The nearly neutral theory of molecular evolution posits variation among species in the effectiveness of selection. In an idealized model, the census population size determines both this minimum magnitude of the selection coefficient required for deleterious variants to be reliably purged, and the amount of neutral diversity. Empirically, an 'effective population size' is often estimated from the amount of putatively neutral genetic diversity and is assumed to also capture a species' effectiveness of selection. A potentially more direct measure of the effectiveness of selection is the degree to which selection maintains preferred codons. However, past metrics that compare codon bias across species are confounded by among-species variation in %GC content and/or amino acid composition. Here, we propose a new Codon Adaptation Index of Species (CAIS), based on Kullback-Leibler divergence, that corrects for both confounders. We demonstrate the use of CAIS correlations, as well as the Effective Number of Codons, to show that the protein domains of more highly adapted vertebrate species evolve higher intrinsic structural disorder.

Can Legal Sanctions Reduce Cyberviolence? How Changes in Cost-Benefit Calculations and Norm Neutralizations Affect Self-Censorship

This study examines whether and how legal sanctions help reduce cyberviolence. Interviews were conducted with offenders who were legally sanctioned for posting criminal online comments in Switzerland. The results of the thematic analysis indicate that offenders self-censor after facing legal sanctions. This is explained with reference to rational choice theory and neutralization theory. The study contributes to the hitherto lacking knowledge about the effectiveness of legal countermeasures against cyberviolence.

Econometric Analysis of South Africa’s Fiscal and Monetary Policy Effects on Economic Growth from 1980 to 2022

This study examined South Africa’s economic growth rate from 1980 to 2022 through an econometric analysis of fiscal and monetary policies. The study sought to investigate the relationships between the economy’s growth rate and various fiscal and monetary policy variables, taking into account different economic approaches such as Keynesian, monetarist, and Wagner’s perspectives. The methodology used consisted of data preparation, multiple unit root tests, Autoregressive Distributed Lag (ARDL) cointegration analysis, diagnostic tests, and pairwise Granger causality analysis. The empirical analysis found a long-term cointegration among the economic growth rate, government debt, expenditure, and revenue in fiscal policy, though government debt and expenditure were not statistically significant. Contrary to economic theory, increased government revenue had a negative correlation with economic growth. There was no long-term relationship found between the economic growth rate and monetary policy variables such as the official exchange rate, inflation rate, real interest rates, and M3 money supply. Pairwise Granger causality tests revealed a one-way relationship between government spending and economic growth, providing support to the Keynesian approach to fiscal policy. This study also discovered evidence that economic growth Granger-causes inflation, implying that economic growth may have predictive power for inflation, consistent with the demand-pull inflation hypothesis. However, no direct predictive relationships were found between the selected monetary policy variables and economic growth, supporting the long-run theory of monetary neutrality. This study suggests evaluating spending, managing inflation, implementing reforms, closing infrastructure gaps, encouraging investment, and ensuring fiscal sustainability.

Within-host adaptive speciation of commensal yoyo clams leads to ecological exclusion, not co-existence.

Symbionts dominate planetary diversity and three primary symbiont diversification processes have been proposed: co-speciation with hosts, speciation by host-switching, and within-host speciation. The last mechanism is prevalent among members of an extraordinary marine symbiosis in the Indian River Lagoon, Florida, composed of a host mantis shrimp, Lysiosquilla scabricauda, and seven host-specific commensal vasconielline "yoyo" clams (Galeommatoidea) that collectively occupy two distinct niches: burrow-wall-attached, and host-attached/ectocommensal. This within-host symbiont radiation provides a natural experiment to test how symbiont coexistence patterns are regulated in a common ancestral habitat. The competitive exclusion principle predicts that sister taxa produced by adaptive speciation (with distinct morphologies and within-burrow niches) are most likely to coexist whereas the neutral theory predicts no difference among adaptive and non-adaptive sister taxa co-occurrence. To test these predictions, we engaged in (1) field-censusing commensal species assemblages; (2) trophic niche analyses; (3) laboratory behavioral observations. Although predicted by both models, the field census found no mixed-niche commensal assemblages: multi-species burrows were exclusively composed of burrow-wall commensals. Their co-occurrence matched random assembly process expectations, but presence of the single ectocommensal species had a highly significant negative effect on recruitment of all burrow-wall commensal species (P<0.001), including on its burrow-wall commensal sister species (P < 0.001). Our stable isotope data indicated that commensals are suspension feeders and that co-occurring burrow-wall commensals may exhibit trophic niche differentiation. The artificial burrow behavioral experiment yielded no evidence of spatial segregation among burrow-wall commensals, and it was terminated by a sudden breakdown of the host-commensal relationship resulting in a mass mortality of all commensals unattached to the host. This study system appears to contain two distinct, superimposed patterns of commensal distribution: (1) all burrow-wall commensal species; (2) the ectocommensal species. Burrow-wall commensals (the plesiomorphic condition) broadly adhere to neutral theory expectations of species assembly but the adaptive evolution of ectocommensalism has apparently led to ecological exclusion rather than coexistence, an inverse outcome of theoretical expectations. The ecological factors regulating the observed burrow-wall/ectocommensal exclusion are currently obscure but potentially include differential recruitment to host burrows and/or differential survival in "mixed" burrow assemblages, the latter potentially due to changes in host predatory behavior. Resampling host burrows during commensal recruitment peak periods and tracking burrow-wall commensal survival in host burrows with and without added ectocommensals could resolve this outstanding issue.

FTSE 100 Index Linked Structured Financial Product Pricing Analysis

Since facing widespread skepticism after the 2008 economic crisis, nowadays structured products have gradually become the preferred investment choice for individual consumers, driven by the development of technology and economy. This study analyzes the price of the two most recent structured products offered by Lowes, which closely resemble the FTSE 100 index. It focuses on analyzing the differences in predicted returns resulting from modest structural changes and explores the best solutions for different time periods. The variability is determined by combining historical variability with the GARCH model, based on the principle of Risk Neutral Pricing Theory. The final result is acquired by the application of the Monte Carlo simulation method. Based on the trial results, product B has a greater yield rate compared to product A, although being more conditional. This compensates for the shortage and resulting in a much higher yield rate for product B. Furthermore, based on the findings on the projected output of various investment goods over different time periods, it can be observed that as the length increases, the anticipated return also increases. Ultimately, the sensitivity analysis reveals that the primary source of product risk stems from the impact of risk-free yields on this particular product.

College Students are Helping Each Other Cheat in the Group Chat and Here’s Why

ABSTRACT When students have a space of their own, unobserved by professors and administrators, where they can freely talk about their classes and share their coursework, many engage in academic dishonesty. But, as observed in the present study, cheating is not a foregone conclusion for students who decide to join an online group chat. The present study examined N = 30 GroupMe chatrooms associated with undergraduate classes at a mid-sized “Southern State University” – observing academic dishonesty how it happens, when it happens. Significant associations rooted in techniques of neutralization and general strain theory were observed for both the solicitation of academic dishonesty and responses to those solicitations. As hypothesized, greater academic dishonesty was observed for appeals to higher loyalties and denial of responsibility. While the denial of injury and condemnation of the condemners each corresponded with greater solicitation of academic dishonesty, no effects were observed for responses to solicitation. The removal of positively valued stimuli also corresponded with more academic dishonesty. However, the presentation of negatively valued stimuli and failure to achieve positively valued goals were, unexpectedly, associated with less of this kind of behavior. Implications for designing out academic dishonesty are proposed within the context of these findings.

Nonlinear change of ion-induced secondary electron emission in the κ-Al2O3 surface charging from first-principle modelling

Secondary electron emission (SEE) induced by the positive ion is an essential physical process to influence the dynamics of gas discharge which relies on the specific surface material. Surface charging has a significant impact on the material properties, thereby affecting the SEE in the plasma-surface interactions. However, it does not attract enough attention in the previous studies. In this paper, SEE dependent on the charged surface of specific materials is described with the computational method combining a density functional theory (DFT) model from the first-principle theory and the theory of Auger neutralization. The effect of κ-Al2O3 surface charge, as an example, on the ion-induced secondary electron emission coefficient (SEEC) is investigated by analyzing the defect energy level and band structure on the charged surface. Simulation results indicate that, with the surface charge from negative to positive, the SEEC of a part of low ionization energy ions (such as E i = 12.6 eV) increases first and then decreases, exhibiting a nonlinear changing trend. This is quite different from the monotonic decreasing tendency observed in the previous model which simplifies the electronic structure. This irregular increase of the SEEC can be attributed to the lower escaped probability of orbital energy. The results further illustrate that the excessive charge could cause the bottom of the conduction band close to the valence band, thus leading to the decrease of the orbital energy occupied by the excited electrons. The nonlinear change of SEEC demonstrates a more realistic situation of how the electronic structure of material surface influences the SEE process. This work provides an accurate method of calculating SEEC from specific materials, which is urgent in widespread physical scenarios sensitive to surface materials, such as increasingly growing practical applications concerning plasma-surface interactions.

Vibration Study of Functionally Graded Microcantilever Beams in Fluids Based on Modified Couple Stress Theory by Considering the Physical Neutral Plane

Theoretical studies on the vibration of microcantilever beams in fluids, which are commonly used in micro- and nanoelectromechanical systems (MEMS/NEMS). When microcantilever beams are subjected to photo-thermal excitation, they show that the material properties such as the dynamic response and the one-dimensional temperature field will show significant differences from the macroscopic properties when the size appearance of the microbeam decreases to the scale below a dozen micrometers. In this paper, by correcting the scale constants of the beams, the photothermal vibration model of the microbeam is established using the physical neutral plane theory. The one-dimensional heat transfer equations and scale-corrected temperature field of the microcantilever beam under laser excitation are derived, which are solved by Galerkin’s method, based on the theory of thermoelasticity, the hydrodynamic model of the beams vibrating in incompressible liquids proposed by Sader et al. and the theory of Euler–Bernoulli beams. The equations governing the vibration of micro-cantilever beams corrected for scale effects in different fluids when subjected to photothermal excitation are obtained. The results show that the temperature field, resonant frequency, and quality factor of the microbeam will have a significant upward drift when the size of the microbeam is close to the scale parameter, and the scale effect has a non-negligible influence on the macroscopic performance parameters; the upward drift is gradually weakening when the thickness to scale ratio gradually increases. Finally, the property of the beam is almost the same as that of the theory when the thickness of the beam is 10 times the scale constant. The correction of the theory by the scale effect is insignificant.

Vibration Analysis of Porous Cu-Si Microcantilever Beams in Fluids Based on Modified Couple Stress Theory.

The vibrations in functionally graded porous Cu-Si microcantilever beams are investigated based on physical neutral plane theory, modified coupled stress theory, and scale distribution theory (MCST&SDT). Porous microcantilever beams define four pore distributions. Considering the physical neutral plane theory, the material properties of the beams are computed through four different power-law distributions. The material properties of microcantilever beams are corrected by scale effects based on modified coupled stress theory. Considering the fluid driving force, the amplitude-frequency response spectra and resonant frequencies of the porous microcantilever beam in three different fluids are obtained based on the Euler-Bernoulli beam theory. The quality factors of porous microcantilever beams in three different fluids are derived by estimating the equation. The computational analysis shows that the presence of pores in microcantilever beams leads to a decrease in Young's modulus. Different pore distributions affect the material properties to different degrees. The gain effect of the scale effect is weakened, but the one-dimensional temperature field and amplitude-frequency response spectra show an increasing trend. The quality factor is decreased by porosity, and the degree of influence of porosity increases as the beam thickness increases. The gradient factor n has a greater effect on the resonant frequency. The effect of porosity on the resonant frequency is negatively correlated when the gradient factor is small (n<1) but positively correlated when the gradient factor is large (n>1).

Understanding consumers’ digital piracy behaviour: Explanation and prediction

This research aims to examine the explanatory and predictive power of seven theoretical models based on neutralisation theory, perceived risk theory, the theory of interpersonal behaviour, the theory of reasoned action, the theory of planned behaviour, the theory of self-regulation, and the norm activation theory. A total of 247 usable data were collected through a survey and analysed using partial least squares structural equation modelling. The in-sample and out-of-sample predictive power of each model was assessed. The results indicate that there are different factors influencing consumers’ intentions to pirate digital products. Among the seven theories, the theory of interpersonal behaviour ranks first, and perceived risk theory last in terms of explanatory and predictive power. This study is the very first to examine the explanatory and predictive power of seven different theoretical models using advanced PLS-SEM techniques.

The effectiveness of selection in a species affects the direction of amino acid frequency evolution.

Nearly neutral theory predicts that species with higher effective population size (N e ) are better able to purge slightly deleterious mutations. We compare evolution in high-N e vs. low-N e vertebrates to reveal which amino acid frequencies are subject to subtle selective preferences. We take three complementary approaches, two measuring flux and one measuring outcomes. First, we fit non-stationary substitution models of amino acid flux using maximum likelihood, comparing the high-N e clade of rodents and lagomorphs to its low-N e sister clade of primates and colugos. Second, we compare evolutionary outcomes across a wider range of vertebrates, via correlations between amino acid frequencies and N e . Third, we dissect the details of flux in human, chimpanzee, mouse, and rat, as scored by parsimony - this also enables comparison to a historical paper. All three methods agree on which amino acids are preferred under more effective selection. Preferred amino acids tend to be smaller, less costly to synthesize, and to promote intrinsic structural disorder. Parsimony-induced bias in the historical study produces an apparent reduction in structural disorder, perhaps driven by slightly deleterious substitutions. Within highly exchangeable pairs of amino acids, arginine is strongly preferred over lysine, and valine over isoleucine, consistent with more effective selection preferring a marginally larger free energy of folding. These two preferences match differences between thermophiles and mesophilic relatives. These results reveal the biophysical consequences of mutation-selection-drift balance, and demonstrate the utility of nearly neutral theory for understanding protein evolution.