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Earliest evidence of hominin bipedalism in <i>Sahelanthropus tchadensis</i>
No full textBipedalism is a key adaptation that differentiates hominins (humans and our extinct relatives) from living and fossil apes. The earliest putative hominin, Sahelanthropus tchadensis (~7 million years old), was originally represented by a cranium, the reconstruction of which suggested to its discoverers that Sahelanthropus carried its head in a manner similar to known bipedal hominins. Recently, two partial ulnae and a femur shaft were announced as evidence in support of the contention that Sahelanthropus was an early biped, but those interpretations have been challenged. Here, while we find that both limb bones are most similar in size and geometric morphometric shape to chimpanzees (genus Pan), we demonstrate that their relative proportion is more hominin-like. Furthermore, we confirm two features linked to hominin-like hip and knee function and identify a femoral tubercle, a feature only found in bipedal hominins. Our results suggest that Sahelanthropus was an early biped that evolved from a Pan-like Miocene ape ancestor
The structure of an actin nucleus stabilized by villin
No full textVillin is an actin filament nucleating, severing, capping and bundling protein; however, the structural basis for villin’s functions and the characteristics of the actin polymerization nucleus remain poorly understood. Here, we present the structure of vent-worm villin bound to a trimeric actin nucleus. Villin wraps around and caps the barbed end of the actin trimer. Its headpiece domain interacts at the junction of two laterally associated actin protomers, leaving the pointed-end subunits open for elongation. Within the actin trimer, the two longitudinally associated subunits adopt barbed and pointed-end subunit conformations, while the lateral protomer exhibits a monomeric conformation. This provides the first view of an actin-filament nucleus, revealing that the transition into the filamentous form is stimulated and stabilized by the interactions with the pointed-end subunits. Our results also illuminate mechanisms of actin-filament dynamics and villin capping and severing, suggesting that F-to-G actin conformational transitions facilitate the later process.</p
Ancestry gaps in cardiovascular GWAS: a multi-database review of African representation in genomic studies
No full textCardiovascular diseases (CVDs) are the leading cause of death worldwide, claiming millions of lives each year. Genome-wide association studies (GWASs) have identified thousands of CVD-associated variants and have created the foundation for risk assessment and prevention through genetic testing. However, despite all the progress in understanding cardiovascular genomics, our genetic research and findings are overwhelmingly skewed towards individuals of European ancestry. This fact has limited our understanding and effectiveness for the diagnosis and treatment of CVDs in underrepresented populations, such as individuals of African ancestry. This gap is especially consequential because African ancestry populations harbor the greatest global genetic diversity, with variant frequencies and haplotypes that are often poorly captured by current reference datasets. In this review, we highlight recent efforts to understand the effectiveness of current tools in accurately diagnosing and treating CVDs in individuals of African ancestry compared to other populations. Additionally, we also performed a multi-database analysis to explore the persistent diversity gap in cardiovascular genetics. In doing so, we aim to raise awareness about the ancestry gaps faced in disease genomic research, supported by recent findings and the current landscape of our genetic databases.</p
The Life of the Animal: A Hegelian Account of Life and Ideas of Reason
No full textIn this dissertation, I offer a new interpretation of Hegel’s philosophy of organic life and show its relevance in light of contemporary approaches to the same topic. I argue that the notion of animal reproduction — i.e., reproduction from two parents — is essential to the idea of life, although not all living things reproduce in this way. Only in the case of living things that reproduce in this way do we have a determinate view of the organic unity of a living substance. Other forms of life — for example, plants that reproduce incidentally, and viruses that do not reproduce within their own kind — are intelligible only derivatively, from the primary occurrence of the idea of life in the animal. In other words, I argue that the idea of life differentiates into primary, paradigmatic, and complete occurrences, and secondary, privative, and incomplete occurrences. My dissertation comprises both a systematic and a historical-exegetical aspect. On the systematic side, I put Hegel’s view into conversation with more contemporary analytic approaches to the topic of life. I discuss two important examples of such contemporary approaches, namely the Natural Kind Sortalist approach developed by David Wiggins and the Formal-Inferentialist approach developed by Michael Thompson. These two views represent two possible ways of explicating the concept of life that exhaust the logical space within a certain framework. In that framework, a concept can be either a material concept or a formal concept in judgment. The meaning of a concept would be explicable through reflection on its use in judgments. Each approach faces internal problems that point toward the advantages of the Hegelian framework. I explain the Hegelian framework by proposing a new understanding of the influence of Kant’s critical philosophy on Hegel. On my reading, Hegel explicates life dialectically as an idea of reason. This means that Hegel’s Science of Logic must be understood as a contribution to the same part of philosophy as Kant’s transcendental dialectic. However, Hegel proposes a different mode of dialectics, according to which ideas genuinely capture the being of things as they are in themselves. This mode of dialectical explication involves relating forms of judgment to ideas of reason, which are themselves divided into privative and paradigmatic exemplifications
Accounting for Protest Voting in the U.S. Congress
No full textMembers of the majority party in Congress sometimes vote against bills that they prefer over the status quo. We estimate a model of congressional roll-call voting that allows for this kind of non-ideological protest voting. We find that protest voting has significant implications for roll-call-based estimates of ideology and other analyses that rely upon them. For example, a traditional item response theory model curiously identifies members of the Squad as relatively moderate Democrats, but our protest-voting-adjusted scores identify them as the most liberal members of Congress. We also find that previous studies may have underestimated responsiveness, the effects of ideology in elections, the utility of non-roll-call-based measures of ideology, and the increase in congressional polarization. Although the implications for most substantive applications are likely modest, our analyses suggest that future researchers can better measure legislative ideology by accounting for a small number of non-ideological votes
Principles for Coarse-Graining in Biological Systems
Full text linkLife presents us with bewildering phenomenology, from robust self-replication and morphogenesis, to learning, adaptation, and evolution. These phenomena are collective and typically carry no precedent in the inanimate world, which presents an exciting opportunity in the search for new emergent physics. Modern experimental methods offer increasingly high-resolution and large-scale data on the inner workings of biology, making conceivable the establishment of precise theories about the organization of living systems. As first steps towards this lofty and long-term goal, we need principles to define the most biologically relevant features in high-dimensional datasets, as well as tools to identify them and constrain theory. Motivated by the successes of many-body theory in physics, we examine how the renormalization group (RG) and information bottleneck (IB), two paradigmatic coarse-graining approaches, may contribute to the search for simplifying structure in large-scale biology. First, to explore how top-down and bottom-up coarse-graining might be reconciled, we demonstrate a formal theoretical connection between IB and RG. We find that the choice of relevance variable in IB determines the collective variables and their order of elimination in the RG scheme, suggesting IB can be used to select a notion of ‘large scale’ structure, such as a particular biological function. One especially exciting application of this idea may be to use it as a bridge, revealing how effective models in the language of RG can be read out of IB analyses on biological data. Next, prompted by multi-functionality in biology, we examine the idea that a given system might have multiple notions of large scale structure. We construct a simple model which exhibits this property, in that its correlations are best described in terms of two coexisting but independent RG flows, each coarse-graining with respect to a different collective basis. The failure of RG to predict large-scale correlations in a certain phase of this model points to a potential pitfall in interpreting maximum-entropy models of biological data as many-body systems. Finally, we turn our attention to real biological systems, and use IB to coarse-grain data taken from a large population of neurons in the salamander retina. By optimizing collective variables to predict future responses, we identify features in the retinal code that may enable downstream visual prediction. We also reveal that the encoding of predictive information in the retina becomes increasingly collective at long times, accompanied by a shift in the most relevant collective variables. This highlights the importance of adapting coarse-graining to function in biology
Gesture counteracts gender stereotypes conveyed through subtle linguistic cues
Full text linkDespite increased attempts to express equality in speech, biases often leak out through subtle linguistic cues. For example, the subject–complement statement (SCS, “Girls are as good as boys at math”) is used to advocate for equality but often reinforces gender stereotypes (boys are the standard against which girls are judged). We ask whether stereotypes conveyed by SCS can be counteracted by gesture. Two preregistered studies with 8- to 11-y-old children (N = 320 total) investigate whether an equal gesture—two palms placed at the same height—mitigates the gender stereotype induced by SCS. Children who saw the equal gesture along with SCS were more likely to express egalitarian beliefs than children who saw no gesture or an unequal gesture. Children can extract meaning from gesture when making stereotypical inferences, suggesting that the equal gesture may prove to be an innovative, and simple, intervention to counteract stereotypes introduced by subtle language
Valuing the benefits of reducing firearm violence in the United States
Full text linkJustifying a proposed government regulation intended to reduce firearm violence requires a conceptually sound estimate of the monetized value of that impact and how that value is distributed across the population. Some previous estimates do not serve as a valid basis for policy evaluation or are out of date. A nationally representative survey was conducted by the AP-NORC Center for Public Affairs Research in August 2022 (n = 660). The authors designed and added a series of contingent-valuation items to the questionnaire. Double-bounded estimates of willingness-to-pay (WTP) were derived from a regression analysis of responses regarding voting on a hypothetical referendum on a state-wide package of measures designed to reduce gun violence at specified cost to taxpayers. Average WTP for a reduction of 20% in the state rate of gun violence was 744 USD per household (IQR:668 USD–928 USD), implying a national total of 97.6 billion USD. Household WTP was positively associated with household income, the respondent’s assessment of the seriousness of gun violence in their community and the subjective likelihood that they would become a victim of gun violence. A variety of tests support the claim that this application of the contingent-valuation method provided valid results. WTP is the recognized basis for assessing the value of proposed federal regulations. The estimated WTP for reducing gun violence is about twice as high as a recent cost-of-injury estimate and provides a much different picture of the incidence of costs by income and demographic characteristics
Stratospheric transport and tropospheric sink of solar geoengineering aerosol: a Lagrangian analysis
Full text linkStratospheric aerosol injection (SAI) aims to reflect solar radiation by increasing the stratospheric aerosol burden. To understand how the background circulation influences stratospheric transport of injected particles, we use a Lagrangian trajectory model (lacking numerical diffusion) to quantify particles’ number, flux, lifetime, and tropospheric sinks from a SAI injection strategy under present-day conditions. While particles are being injected, stratospheric particle number increases until reaching a steady-state. During the steady-state, the time series of particle number shows a dominant period of ~2 years (rather than a 1-year cycle), suggesting modulation by the quasi-biannual oscillation. More than half of particles, injected in the tropical lower stratosphere (15° S to 15° N, 65 hPa), undergo quasi-horizontal transport to the midlatitude. We find a zonal asymmetry of particles’ tropospheric sinks that are co-located with tropopause folding beneath the midlatitude jet stream, which can help predict tropospheric impacts of SAI (e.g., cirrus cloud thinning)
Enduring Legacies of Agriculture: Long-term Vegetation Impacts of Ancestral Menominee Agriculture, Wisconsin, USA
Full text linkAgriculture significantly reshapes soils and ecology, often with lasting ecological impacts. For over a millennium, the Menominee Indian Tribe of Wisconsin have practiced maize agriculture in the upper Great Lakes. Though the vast majority of ancestral Indigenous agricultural sites have been destroyed in the American Midwest, the Menominee have documented numerous archaeological, raised garden bed sites at their Reservation, enabling an investigation into the lasting vegetation impacts of ancestral Menominee agricultural practices. Here, we report findings from our pilot vegetation surveys of three ancestral raised garden bed sites. Results show that all sites surveyed are high quality ecosystems. We observed differences in species richness between agricultural and non-agricultural places, although findings varied based on location. Overall, our surveys illustrate the complexity of these anthropogenic, biologically diverse landscapes shaped by past and contemporary Menominee land use and illustrate how today’s ecology is in part an enduring legacy of past practices