Abstract. Recently discovered representatives of the Class Bdelloidea from Tertiary amber from the DominicanRepublic represent the oldest known fossils of the Phylum Rotifera. Assuming that the fossil bdelloids had a similar mode of reproduction as present day members of the Class (apomictic thelytoky), then contrary to current thought, some lines of parthenogenetic organisms are not doomed to an early extinction and have evolved built-in mechanisms for genetic diversity.Key words. Fossil rotifers; Bdelloidea; Tertiary amber; Dominican Republic.Representatives of the Phylum Rotifera are poorly represented in the fossil record, being known only from the Holocene (8000 years and younger) 1. A piece of amber from the Dominican Republic was found to contain a population of 22 rotifers as well as another organism that could be a rotifer but cannot be assigned with certainty to this or any other Phylum. At least 18 of the 22 rotifers could be assigned to the Order Bdelloida. All of these animals were associated with the cap of the fossil gilled mushroom Coprinites dominicana Poinar and Singer 2.The total fossil assemblage represents a palaeobiocoenosis or 'fossil community'. The amber containing the fossils originated from the La Toca mine, located between Santiago and Puerto Plata in the Cordillera Septentrional of the Dominican Republic. This mine is in the Altimira facies of the E1 Mamey Formation (upper Eocene), which is shale-sandstone interspersed with a conglomerate of well-rounded pebbles 3. Differences in the magnitudes of absorption peaks in nuclear magnetic resonance spectra of the exomethylene group of amber 4 from different mines in the Dominican Republic were used to calibrate the ages of the various mines, with the age (20 million to 23 million years); (based on foraminifera counts) of the Palo Alto mine used as a standard 5. The ages of various pieces of Dominican amber ranged from 15 million to 40 million years with that from the La Toca mine being the oldest, some 35 million to 40 million years old (lower Oligocene to upper Eocene). This age is within the independent dating reported by Cepek 6 who gave a range of 30 to 45 million years for "La Toca" mine.The piece of amber containing the fossils (AF-9-11) had all the visual characteristics of natural Dominican amber. A series of chemical and physical tests 7 performed on a small portion of the amber piece verified that it was authentic. The piece of yellow transparent amber containing the rotifers weighed 0.5 g and was elliptical in shape, 9 mm long and 6 mm wide. It is deposited in the Poinar collection of Dominican amber maintained at the University of California, Berkeley. All of the bdelloid rotifers were contracted so that the corona and foot were unrecognizable. Because it was impossible to observe the number of toes, the stomach lumen and the shape of the trochi and the mastax, it was not possible to place them in any existing family with certainty. The size of the bdelloid rotifers ranged from 126 to 504 gm in length (av = 266 Ixm) and from 76...
The literature on neighborhood effects frequently is evaluated or interpreted in relation to the question, "Do neighborhoods matter?" We argue that this question has had a disproportionate influence on the field and does not align with the complexity of theoretical models of neighborhood effects or empirical findings that have arisen from the literature. In this article, we focus on empirical work that considers how different dimensions of individuals' residential contexts become salient in their lives, how contexts influence individuals' lives over different timeframes, how individuals are affected by social processes operating at different scales, and how residential contexts influence the lives of individuals in heterogeneous ways. In other words, we review research that examines where, when, why, and for whom do residential contexts matter. Using the large literature on neighborhoods and educational and cognitive outcomes as an example, the research we review suggests that any attempt to reduce the literature to a single answer about whether neighborhoods matter is misguided. We call for a more flexible study of context effects in which theory, measurement, and methods are more closely aligned with the specific mechanisms and social processes under study.The Annual Review of Statistics and Its Application aims to inform statisticians and quantitative methodologists, as well as all scientists and users of statistics about major methodological advances and the computational tools that allow for their implementation. It will include developments in the field of statistics, including theoretical statistical underpinnings of new methodology, as well as developments in specific application domains such as biostatistics and bioinformatics, economics, machine learning, psychology, sociology, and aspects of the physical sciences.Complimentary online access to the first volume will be available until January 2015. table of contents:
The contemporary practice of homeownership in the United States was born out of government programs adopted during the New Deal. The Home Owners Loan Corporation (HOLC)—and later the Federal Housing Administration and GI Bill—expanded home buying opportunity, although in segregationist fashion. Through mechanisms such as redlining, these policies fueled white suburbanization and black ghettoization, while laying the foundation for the racial wealth gap. This is the first article to investigate the long-term consequences of these policies on the segregation of cities. I combine a full century of census data with archival data to show that cities HOLC appraised became more segregated than those it ignored. The gap emerged between 1930 and 1950 and remains significant: in 2010, the black-white dissimilarity, black isolation, and white-black information theory indices are 12, 16, and 8 points higher in appraised cities, respectively. Results are consistent across a range of robustness checks, including exploitation of imperfect implementation of appraisal guidelines and geographic spillover. These results contribute to current theoretical discussions about the persistence of segregation. The long-term impact of these policies is a reminder of the intentionality that shaped racial geography in the United States, and the scale of intervention that will be required to disrupt the persistence of segregation.
The hypothesis of neighborhood stigma predicts that individuals who reside in areas known for high crime, poverty, disorder, and/or racial isolation embody the negative characteristics attributed to their communities and experience suspicion and mistrust in their interactions with strangers. This article provides an experimental test of whether neighborhood stigma affects individuals in one domain of social life: economic transactions. To evaluate the neighborhood stigma hypothesis, this study adopts an audit design in a locally organized, online classified market, using advertisements for used iPhones and randomly manipulating the neighborhood of the seller. The primary outcome under study is the number of responses generated by sellers from disadvantaged relative to advantaged neighborhoods. Advertisements from disadvantaged neighborhoods received significantly fewer responses than advertisements from advantaged neighborhoods. Results provide robust evidence that individuals from disadvantaged neighborhoods bear a stigma that influences their prospects in economic exchanges. The stigma is greater for advertisements originating from disadvantaged neighborhoods where the majority of residents are black. This evidence reveals that residence in a disadvantaged neighborhood not only affects individuals through mechanisms involving economic resources, institutional quality, and social networks but also affects residents through the perceptions of others.ities in the United States are characterized by high levels of racial segregation and by concentrated pockets of poverty and of affluence (1, 2). The stratification of American neighborhoods means that individuals living in disadvantaged communities are exposed to fewer economic opportunities, lower quality institutions, greater levels of crime and environmental pollution, and less advantaged social networks (3-6). However, extreme neighborhood inequality may also affect individuals through processes of association, perception, and stigma.The hypothesis of neighborhood stigma predicts that individuals who reside in areas known for high crime, poverty, disorder, and/or racial isolation embody the negative characteristics attributed to their communities, and experience suspicion and mistrust in their interactions with strangers when their neighborhood of residence is revealed (7-11). Similar to other forms of stereotype, the consequences of neighborhood stigma arise when negative perceptions of a place are attached to individuals, leading to systematic disapproval, discrimination, and/or exclusion (12, 13). Assumptions about residents from disadvantaged neighborhoods could have consequences in the form of lost job opportunities, suspicion by law enforcement, or mistrust in market transactions. Through all of these pathways, the stigma of place may be an important mechanism through which neighborhood segregation reinforces social inequality (5,(14)(15)(16)(17)(18)(19). Despite the strong theoretical support for this concept, no previous studies have estimated the effect...
Subprime mortgage lending in the early 2000s was a leading cause of the Great Recession. From 2003 to 2006, subprime loans jumped from 7.6% of the mortgage market to 20.1%, with black and Latino borrowers receiving a disproportionate share. This article leveraged the Home Mortgage Disclosure Act data and multinomial regression to model home-purchase mortgage lending in 2006, the peak of the housing boom. The findings expose a complicated story of race and income. Consistent with previous research, blacks and Latinos were more likely and Asians less likely to receive subprime loans than whites were. Income was positively associated with receipt of subprime loans for minorities, whereas the opposite was true for whites. When expensive (jumbo) loans were excluded from the sample, regressions found an even stronger, positive association between income and subprime likelihood for minorities, supporting the theory that wealthier minorities were targeted for subprime loans when they could have qualified for prime loans. This finding also provides another example of an aspect of American life in which minorities are unable to leverage higher class position in the same way as whites are. Contrary to previous research, model estimates did not find that borrowers paid a penalty (in increased likelihood of subprime outcome) for buying homes in minority communities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.