Modeling the Pre-Industrial Roots of Modern Super-Exponential Population Growth

To Malthus, rapid human population growth—so evident in 18th Century Europe—was obviously unsustainable. In his Essay on the Principle of Population, Malthus cogently argued that environmental and socioeconomic constraints on population rise were inevitable. Yet, he penned his essay on the eve of the global census size reaching one billion, as nearly two centuries of super-exponential increase were taking off. Introducing a novel extension of J. E. Cohen''s hallmark coupled difference equation model of human population dynamics and carrying capacity, this article examines just how elastic population growth limits may be in response to demographic change. The revised model involves a simple formalization of how consumption costs influence carrying capacity elasticity over time. Recognizing that complex social resource-extraction networks support ongoing consumption-based investment in family formation and intergenerational resource transfers, it is important to consider how consumption has impacted the human environment and demography—especially as global population has become very large. Sensitivity analysis of the consumption-cost model''s fit to historical population estimates, modern census data, and 21^st Century demographic projections supports a critical conclusion. The recent population explosion was systemically determined by long-term, distinctly pre-industrial cultural evolution. It is suggested that modern globalizing transitions in technology, susceptibility to infectious disease, information flows and accumulation, and economic complexity were endogenous products of much earlier biocultural evolution of family formation''s embeddedness in larger, hierarchically self-organizing cultural systems, which could potentially support high population elasticity of carrying capacity. Modern super-exponential population growth cannot be considered separately from long-term change in the multi-scalar political economy that connects family formation and intergenerational resource transfers to wider institutions and social networks.     

Social network- and community-level influences on contraceptive use: evidence from rural Poland

The diffusion of ‘modern’ contraceptives—as a proxy for the spread of low-fertility norms—has long interested researchers wishing to understand global fertility decline. A fundamental question is how local cultural norms and other people''s behaviour influence the probability of contraceptive use, independent of women''s socioeconomic and life-history characteristics. However, few studies have combined data at individual, social network and community levels to simultaneously capture multiple levels of influence. Fewer still have tested if the same predictors matter for different contraceptive types. Here, we use new data from 22 high-fertility communities in Poland to compare predictors of the use of (i) any contraceptives—a proxy for the decision to control fertility—with those of (ii) ‘artificial’ contraceptives—a subset of more culturally taboo methods. We find that the contraceptive behaviour of friends and family is more influential than are women''s own characteristics and that community level characteristics additionally influence contraceptive use. Highly educated neighbours accelerate women''s contraceptive use overall, but not their artificial method use. Highly religious neighbours slow women''s artificial method use, but not their contraceptive use overall. Our results highlight different dimensions of sociocultural influence on contraceptive diffusion and suggest that these may be more influential than are individual characteristics. A comparative multilevel framework is needed to understand these dynamics.     

Constraints and variation in food web link-species space

Predicting food web structure in future climates is a pressing goal of ecology. These predictions may be impossible without a solid understanding of the factors that structure current food webs. The most fundamental aspect of food web structure—the relationship between the number of links and species—is still poorly understood. Some species interactions may be physically or physiologically ‘forbidden''—like consumption by non-consumer species—with possible consequences for food web structure. We show that accounting for these ‘forbidden interactions'' constrains the feasible link-species space, in tight agreement with empirical data. Rather than following one particular scaling relationship, food webs are distributed throughout this space according to shared biotic and abiotic features. Our study provides new insights into the long-standing question of which factors determine this fundamental aspect of food web structure.     

Dog Movie Stars and Dog Breed Popularity: A Case Study in Media Influence on Choice

Fashions and fads are important phenomena that influence many individual choices. They are ubiquitous in human societies, and have recently been used as a source of data to test models of cultural dynamics. Although a few statistical regularities have been observed in fashion cycles, their empirical characterization is still incomplete. Here we consider the impact of mass media on popular culture, showing that the release of movies featuring dogs is often associated with an increase in the popularity of featured breeds, for up to 10 years after movie release. We also find that a movie''s impact on breed popularity correlates with the estimated number of viewers during the movie''s opening weekend—a proxy of the movie''s reach among the general public. Movies'' influence on breed popularity was strongest in the early 20^th century, and has declined since. We reach these conclusions through a new, widely applicable method to measure the cultural impact of events, capable of disentangling the event''s effect from ongoing cultural trends.     

Long-Branch Attraction Bias and Inconsistency in Bayesian Phylogenetics

Bayesian inference (BI) of phylogenetic relationships uses the same probabilistic models of evolution as its precursor maximum likelihood (ML), so BI has generally been assumed to share ML''s desirable statistical properties, such as largely unbiased inference of topology given an accurate model and increasingly reliable inferences as the amount of data increases. Here we show that BI, unlike ML, is biased in favor of topologies that group long branches together, even when the true model and prior distributions of evolutionary parameters over a group of phylogenies are known. Using experimental simulation studies and numerical and mathematical analyses, we show that this bias becomes more severe as more data are analyzed, causing BI to infer an incorrect tree as the maximum a posteriori phylogeny with asymptotically high support as sequence length approaches infinity. BI''s long branch attraction bias is relatively weak when the true model is simple but becomes pronounced when sequence sites evolve heterogeneously, even when this complexity is incorporated in the model. This bias—which is apparent under both controlled simulation conditions and in analyses of empirical sequence data—also makes BI less efficient and less robust to the use of an incorrect evolutionary model than ML. Surprisingly, BI''s bias is caused by one of the method''s stated advantages—that it incorporates uncertainty about branch lengths by integrating over a distribution of possible values instead of estimating them from the data, as ML does. Our findings suggest that trees inferred using BI should be interpreted with caution and that ML may be a more reliable framework for modern phylogenetic analysis.     

Biopedagogy

The world is changing fast and teachers are struggling to familiarize children and young people with the norms and values of society. Biopedagogy—the biology behind pedagogy approaches—might provide some insights and guidance.Humans are the only animals that are subject to cumulative cultural evolution. Biological evolution would be too slow to allow for the invention and continuous improvement of complex artefacts, both material and abstract. One of the mechanisms that makes it possible for humans to pass on social, cultural and technological advances over generations is teaching. Some scholars believe that teaching itself might be an exclusive human trait; others argue that teaching is more prevalent in nature, if it is defined as cooperative behaviour that promotes learning, independent of the mental states and cognitive intentions [1].The science, art and profession of teaching is known as ‘pedagogy'' and its biological basis might well be dubbed ‘biopedagogy''. Pedagogy embeds the learner into a particular culture by exposing the developing mind to cultural values and practices. Human teaching represents two disparate but closely linked activities—education and instruction. To ‘educate'' means to unfold the latent potential of the learner and to cultivate human nature by promoting impulses that conform to a culture and inhibiting those that contradict it. ‘Instruction'' is the provision of knowledge and skills.According to the ethologist Konrad Lorenz, human nature, which is a result of biological evolution, functions as the “inborn schoolmaster” [2] by both allowing and constraining the learning of all the products of cultural evolution. Lorenz received the Nobel Prize for his discovery of ‘imprinting'': the irreversible, life-long fixation of a response to a situation encountered by an organism during development. Imprinting is not specific to humans, but humans have evolved, along with the formation of the central nervous system, more sophisticated mental organs that we call the social brain, the group mind and the darwinian soul. As the physical development of an organism proceeds in stages, so does the mental development. Some of these stages represent critical periods that are particularly sensitive to imprinting. The rapid acquisition of the mother tongue for instance apparently represents such a specific period in human development.According to Lorenz, during and shortly after puberty, humans are prone to a specific kind of imprinting from a culture and its abstract norms and values, driven by a need to become members of a reference group striving for a common ideal [2]. We might call this developmental stage of humans the ‘second (or ideational) imprinting''. This imprinting presupposes a stable society with firmly established norms and values and, in turn, it serves to ensure that stability. The British neuroscientist Sarah-Jayne Blakemore [3] corroborated that the human brain undergoes protracted development and demonstrated that adolescence, in particular, represents a period during which the neuronal basis of the social brain reorganizes. This provides opportunities, but also imposes great responsibility to high-school and university teachers.Jan Amos Comenius, a seventeenth century Moravian educator, already suggested that the mastery of teaching consists in recognizing stages of mental development in which a student is prepared and eager to learn stage-specific knowledge spontaneously. In his view, a teacher is more similar to a gardener, who gives plants care and nutrients to allow them to develop, grow and flourish. Comenius also anticipated the crucial role of positive emotions in pedagogy. His commandment Scola ludus—The School of Play—expresses the fact that teaching and learning can, and should be, associated with pleasure and joy by both teachers and students.Human nature evolved during the Pleistocene about 1.8 million to 10,000 years ago to cope with a hunter–gatherer lifestyle. Yet, modern humans live in and adapt to vastly different environments created by cultural evolution. Apparently, the human genetic outfit is highly versatile and encompasses abstract ‘cultural loci''. Such a cultural locus is an ‘empty slot'' that functions only when it is filled with a meme from the cultural environment; memes would be akin to ‘alleles'' that are specific to a particular cultural locus. This cross-talk of biology and culture makes humans symbolic animals—our social brain allows us to behave altruistically towards ‘symbolic kin'' with whom we share no genetic relationship; and our group mind embraces not only our relatives and friends, but also our tribe or nation and possibly humanity as a whole. Education, and in particular imprinting, essentially determines the extent, quality and scope of this deployment.A developing child has to pass all crucial periods of learning successfully to become a mature human—and humane—being. As Lorenz noted, once a sensitive period has elapsed and the opportunity to learn has been missed, the ability to catch up is considerably reduced or irreversibly lost. We live in a time when cultural values and norms are rapidly changing, often within less than a generation. The ideational imprinting of developing adolescents becomes a problem when the traditional role of family and school is displaced by new social forces such as the internet, Facebook, Twitter and the blogosphere. How to preclude that young people do not develop as persons with stunted social brains, with narrow group minds attuned to fleeting reference groups and with fragmented darwinian souls, and how to promote the development of strong personalities is a challenge for the education of the twenty-first century.     

Why Do Some People Do “More” to Mitigate Climate Change than Others? Exploring Heterogeneity in Psycho-Social Associations

The urgency of climate change mitigation calls for a profound shift in personal behavior. This paper investigates psycho-social correlates of extra mitigation behavior in response to climate change, while also testing for potential (unobserved) heterogeneity in European citizens'' decision-making. A person''s extra mitigation behavior in response to climate change is conceptualized—and differentiated from common mitigation behavior—as some people''s broader and greater levels of behavioral engagement (compared to others) across specific self-reported mitigation actions and behavioral domains. Regression analyses highlight the importance of environmental psychographics (i.e., attitudes, motivations, and knowledge about climate change) and socio-demographics (especially country-level variables) in understanding extra mitigation behavior. By looking at the data through the lens of segmentation, significant heterogeneity is uncovered in the associations of attitudes and knowledge about climate change—but not in motivational or socio-demographic links—with extra mitigation behavior in response to climate change, across two groups of environmentally active respondents. The study has implications for promoting more ambitious behavioral responses to climate change, both at the individual level and across countries.     

Coevolution Drives the Emergence of Complex Traits and Promotes Evolvability

The evolution of complex organismal traits is obvious as a historical fact, but the underlying causes—including the role of natural selection—are contested. Gould argued that a random walk from a necessarily simple beginning would produce the appearance of increasing complexity over time. Others contend that selection, including coevolutionary arms races, can systematically push organisms toward more complex traits. Methodological challenges have largely precluded experimental tests of these hypotheses. Using the Avida platform for digital evolution, we show that coevolution of hosts and parasites greatly increases organismal complexity relative to that otherwise achieved. As parasites evolve to counter the rise of resistant hosts, parasite populations retain a genetic record of past coevolutionary states. As a consequence, hosts differentially escape by performing progressively more complex functions. We show that coevolution''s unique feedback between host and parasite frequencies is a key process in the evolution of complexity. Strikingly, the hosts evolve genomes that are also more phenotypically evolvable, similar to the phenomenon of contingency loci observed in bacterial pathogens. Because coevolution is ubiquitous in nature, our results support a general model whereby antagonistic interactions and natural selection together favor both increased complexity and evolvability.     

A demographic approach to study effects of climate change in desert plants

Desert species respond strongly to infrequent, intense pulses of precipitation. Consequently, indigenous flora has developed a rich repertoire of life-history strategies to deal with fluctuations in resource availability. Examinations of how future climate change will affect the biota often forecast negative impacts, but these—usually correlative—approaches overlook precipitation variation because they are based on averages. Here, we provide an overview of how variable precipitation affects perennial and annual desert plants, and then implement an innovative, mechanistic approach to examine the effects of precipitation on populations of two desert plant species. This approach couples robust climatic projections, including variable precipitation, with stochastic, stage-structured models constructed from long-term demographic datasets of the short-lived Cryptantha flava in the Colorado Plateau Desert (USA) and the annual Carrichtera annua in the Negev Desert (Israel). Our results highlight these populations'' potential to buffer future stochastic precipitation. Population growth rates in both species increased under future conditions: wetter, longer growing seasons for Cryptantha and drier years for Carrichtera. We determined that such changes are primarily due to survival and size changes for Cryptantha and the role of seed bank for Carrichtera. Our work suggests that desert plants, and thus the resources they provide, might be more resilient to climate change than previously thought.     

Nutritional Systems Biology Modeling: From Molecular Mechanisms to Physiology

The use of computational modeling and simulation has increased in many biological fields, but despite their potential these techniques are only marginally applied in nutritional sciences. Nevertheless, recent applications of modeling have been instrumental in answering important nutritional questions from the cellular up to the physiological levels. Capturing the complexity of today''s important nutritional research questions poses a challenge for modeling to become truly integrative in the consideration and interpretation of experimental data at widely differing scales of space and time. In this review, we discuss a selection of available modeling approaches and applications relevant for nutrition. We then put these models into perspective by categorizing them according to their space and time domain. Through this categorization process, we identified a dearth of models that consider processes occurring between the microscopic and macroscopic scale. We propose a “middle-out” strategy to develop the required full-scale, multilevel computational models. Exhaustive and accurate phenotyping, the use of the virtual patient concept, and the development of biomarkers from “-omics” signatures are identified as key elements of a successful systems biology modeling approach in nutrition research—one that integrates physiological mechanisms and data at multiple space and time scales.     

Almost 20 years of Neanderthal palaeogenetics: adaptation,admixture, diversity,demography and extinction

Nearly two decades since the first retrieval of Neanderthal DNA, recent advances in next-generation sequencing technologies have allowed the generation of high-coverage genomes from two archaic hominins, a Neanderthal and a Denisovan, as well as a complete mitochondrial genome from remains which probably represent early members of the Neanderthal lineage. This genomic information, coupled with diversity exome data from several Neanderthal specimens is shedding new light on evolutionary processes such as the genetic basis of Neanderthal and modern human-specific adaptations—including morphological and behavioural traits—as well as the extent and nature of the admixture events between them. An emerging picture is that Neanderthals had a long-term small population size, lived in small and isolated groups and probably practised inbreeding at times. Deleterious genetic effects associated with these demographic factors could have played a role in their extinction. The analysis of DNA from further remains making use of new large-scale hybridization-capture-based methods as well as of new approaches to discriminate contaminant DNA sequences will provide genetic information in spatial and temporal scales that could help clarify the Neanderthal''s—and our very own—evolutionary history.     

Documenting Differences between Early Stone Age Flake Production Systems: An Experimental Model and Archaeological Verification

This study investigates morphological differences between flakes produced via “core and flake” technologies and those resulting from bifacial shaping strategies. We investigate systematic variation between two technological groups of flakes using experimentally produced assemblages, and then apply the experimental model to the Cutting 10 Mid -Pleistocene archaeological collection from Elandsfontein, South Africa. We argue that a specific set of independent variables—and their interactions—including external platform angle, platform depth, measures of thickness variance and flake curvature should distinguish between these two technological groups. The role of these variables in technological group separation was further investigated using the Generalized Linear Model as well as Linear Discriminant Analysis. The Discriminant model was used to classify archaeological flakes from the Cutting 10 locality in terms of their probability of association, within either experimentally developed technological group. The results indicate that the selected independent variables play a central role in separating core and flake from bifacial technologies. Thickness evenness and curvature had the greatest effect sizes in both the Generalized Linear and Discriminant models. Interestingly the interaction between thickness evenness and platform depth was significant and played an important role in influencing technological group membership. The identified interaction emphasizes the complexity in attempting to distinguish flake production strategies based on flake morphological attributes. The results of the discriminant function analysis demonstrate that the majority of flakes at the Cutting 10 locality were not associated with the production of the numerous Large Cutting Tools found at the site, which corresponds with previous suggestions regarding technological behaviors reflected in this assemblage.     

The cultural evolution of fertility decline

Cultural evolutionists have long been interested in the problem of why fertility declines as populations develop. By outlining plausible mechanistic links between individual decision-making, information flow in populations and competition between groups, models of cultural evolution offer a novel and powerful approach for integrating multiple levels of explanation of fertility transitions. However, only a modest number of models have been published. Their assumptions often differ from those in other evolutionary approaches to social behaviour, but their empirical predictions are often similar. Here I offer the first overview of cultural evolutionary research on demographic transition, critically compare it with approaches taken by other evolutionary researchers, identify gaps and overlaps, and highlight parallel debates in demography. I suggest that researchers divide their labour between three distinct phases of fertility decline—the origin, spread and maintenance of low fertility—each of which may be driven by different causal processes, at different scales, requiring different theoretical and empirical tools. A comparative, multi-level and mechanistic framework is essential for elucidating both the evolved aspects of our psychology that govern reproductive decision-making, and the social, ecological and cultural contingencies that precipitate and sustain fertility decline.     

Broad supernatural punishment but not moralizing high gods precede the evolution of political complexity in Austronesia

Supernatural belief presents an explanatory challenge to evolutionary theorists—it is both costly and prevalent. One influential functional explanation claims that the imagined threat of supernatural punishment can suppress selfishness and enhance cooperation. Specifically, morally concerned supreme deities or ‘moralizing high gods'' have been argued to reduce free-riding in large social groups, enabling believers to build the kind of complex societies that define modern humanity. Previous cross-cultural studies claiming to support the MHG hypothesis rely on correlational analyses only and do not correct for the statistical non-independence of sampled cultures. Here we use a Bayesian phylogenetic approach with a sample of 96 Austronesian cultures to test the MHG hypothesis as well as an alternative supernatural punishment hypothesis that allows punishment by a broad range of moralizing agents. We find evidence that broad supernatural punishment drives political complexity, whereas MHGs follow political complexity. We suggest that the concept of MHGs diffused as part of a suite of traits arising from cultural exchange between complex societies. Our results show the power of phylogenetic methods to address long-standing debates about the origins and functions of religion in human society.     

The ontogeny of visual–motor memory and its importance in handwriting and reading: a developing construct

Humans have evolved a remarkable ability to remember visual shapes and use these representations to generate motor activity (from Palaeolithic cave drawings through Jiahu symbols to cursive handwriting). The term visual–motor memory (VMM) describes this psychological ability, which must have conveyed an evolutionary advantage and remains critically important to humans (e.g. when learning to write). Surprisingly, little empirical investigation of this unique human ability exists—almost certainly because of the technological difficulties involved in measuring VMM. We deployed a novel technique for measuring this construct in 87 children (6–11 years old, 44 females). Children drew novel shapes presented briefly on a tablet laptop screen, drawing their responses from memory on the screen using a digitizer stylus. Sophisticated algorithms (using point-registration techniques) objectively quantified the accuracy of the children''s reproductions. VMM improved with age and performance decreased with shape complexity, indicating that the measure captured meaningful developmental changes. The relationship between VMM and scores on nationally standardized writing assessments were explored with the results showing a clear relationship between these measures, even after controlling for age. Moreover, a relationship between VMM and the nationally standardized reading test was mediated via writing ability, suggesting VMM''s wider importance within language development.     

The Academic Advantage: Gender Disparities in Patenting

We analyzed gender disparities in patenting by country, technological area, and type of assignee using the 4.6 million utility patents issued between 1976 and 2013 by the United States Patent and Trade Office (USPTO). Our analyses of fractionalized inventorships demonstrate that women’s rate of patenting has increased from 2.7% of total patenting activity to 10.8% over the nearly 40-year period. Our results show that, in every technological area, female patenting is proportionally more likely to occur in academic institutions than in corporate or government environments. However, women’s patents have a lower technological impact than that of men, and that gap is wider in the case of academic patents. We also provide evidence that patents to which women—and in particular academic women—contributed are associated with a higher number of International Patent Classification (IPC) codes and co-inventors than men. The policy implications of these disparities and academic setting advantages are discussed.     

Integrating multiple lines of evidence into historical biogeography hypothesis testing: a Bison bison case study

One of the grand goals of historical biogeography is to understand how and why species'' population sizes and distributions change over time. Multiple types of data drawn from disparate fields, combined into a single modelling framework, are necessary to document changes in a species''s demography and distribution, and to determine the drivers responsible for change. Yet truly integrated approaches are challenging and rarely performed. Here, we discuss a modelling framework that integrates spatio-temporal fossil data, ancient DNA, palaeoclimatological reconstructions, bioclimatic envelope modelling and coalescence models in order to statistically test alternative hypotheses of demographic and potential distributional changes for the iconic American bison (Bison bison). Using different assumptions about the evolution of the bioclimatic niche, we generate hypothetical distributional and demographic histories of the species. We then test these demographic models by comparing the genetic signature predicted by serial coalescence against sequence data derived from subfossils and modern populations. Our results supported demographic models that include both climate and human-associated drivers of population declines. This synthetic approach, integrating palaeoclimatology, bioclimatic envelopes, serial coalescence, spatio-temporal fossil data and heterochronous DNA sequences, improves understanding of species'' historical biogeography by allowing consideration of both abiotic and biotic interactions at the population level.     

An Analysis of Sponsors/Collaborators of 69,160 Drug Trials Registered with ClinicalTrials.gov

Background

Clinical trials have been criticized on various counts. Any attempt to improve how trials are conducted or reported requires—amongst other things—an understanding of the number, the nature and the location of those that sponsor them or collaborate on them. Here we sought to identify the nature and location of each sponsor/collaborator.

Methods and Findings

We examined the ''sponsor/collaborator'' field for the 69,160 drug trials that were registered with ClinicalTrials.gov over a 9-year period (2005–2014). Of the 12,823 unique sponsors, 56% had sponsored only one and 27% had sponsored 2–5 trials each. Just 18% were involved with six or more trials each, and we have (arbitrarily) labeled these organizations as ''more experienced'' in sponsoring/collaborating on trials. These 18% (2,266 sponsors/collaborators) were analyzed further: (a) 951 were corporate organizations and (b) 1,145 were non-corporates (including 31 individuals) with (c) 170 unclassified. Further, we identified the location of each organization in (a) and (b).

Conclusions

Clinical trials are an important part of a nation''s research endeavors, and ultimately contribute to the health of its people. Thus, understanding the clinical trial landscape—including the number and nature of sponsors, and how active they are—is important for every country. We believe that policy makers in particular should be interested in this study to understand the current situation, and to use the numbers as a baseline for the evolving landscape, to assess the impact of their strategies in future.     

A Mechanistic Niche Model for Measuring Species' Distributional Responses to Seasonal Temperature Gradients

Niche theory is central to understanding how species respond geographically to climate change. It defines a species'' realized niche in a biological community, its fundamental niche as determined by physiology, and its potential niche—the fundamental niche in a given environment or geographic space. However, most predictions of the effects of climate change on species'' distributions are limited to correlative models of the realized niche, which assume that species are in distributional equilibrium with respect to the variables or gradients included in the model. Here, I present a mechanistic niche model that measures species'' responses to major seasonal temperature gradients that interact with the physiology of the organism. I then use lethal physiological temperatures to parameterize the model for bird species in North and South America and show that most focal bird species are not in direct physiological equilibrium with the gradients. Results also show that most focal bird species possess broad thermal tolerances encompassing novel climates that could become available with climate change. I conclude with discussion of how mechanistic niche models may be used to (i) gain insights into the processes that cause species to respond to climate change and (ii) build more accurate correlative distribution models in birds and other species.     

The beak of the other finch: coevolution of genetic covariance structure and developmental modularity during adaptive evolution

The link between adaptation and evolutionary change remains the most central and least understood evolutionary problem. Rapid evolution and diversification of avian beaks is a textbook example of such a link, yet the mechanisms that enable beak''s precise adaptation and extensive adaptability are poorly understood. Often observed rapid evolutionary change in beaks is particularly puzzling in light of the neo-Darwinian model that necessitates coordinated changes in developmentally distinct precursors and correspondence between functional and genetic modularity, which should preclude evolutionary diversification. I show that during first 19 generations after colonization of a novel environment, house finches (Carpodacus mexicanus) express an array of distinct, but adaptively equivalent beak morphologies—a result of compensatory developmental interactions between beak length and width in accommodating microevolutionary change in beak depth. Directional selection was largely confined to the elimination of extremes formed by these developmental interactions, while long-term stabilizing selection along a single axis—beak depth—was mirrored in the structure of beak''s additive genetic covariance. These results emphasize three principal points. First, additive genetic covariance structure may represent a historical record of the most recurrent developmental and functional interactions. Second, adaptive equivalence of beak configurations shields genetic and developmental variation in individual components from depletion by natural selection. Third, compensatory developmental interactions among beak components can generate rapid reorganization of beak morphology under novel conditions and thus greatly facilitate both the evolution of precise adaptation and extensive diversification, thereby linking adaptation and adaptability in this classic example of Darwinian evolution.