Most behavioural genetic studies focus on genetic and environmental influences on inter-individual phenotypic differences at the population level. The growing collection of intensive longitudinal data in social and behavioural science offers a unique opportunity to examine genetic and environmental influences on intra-individual phenotypic variability at the individual level. The current study introduces a novel idiographic approach and one novel method to investigate genetic and environmental influences on intra-individual variability by a simple empirical demonstration. Person-specific non-shared environmental influences on intra-individual variability (...) of daily school feelings were estimated using time series data from twenty-one pairs of monozygotic twins over two consecutive weeks. Results showed substantial inter-individual heterogeneity in person- specific non-shared environmental influences. The current study represents a first step in investigating environmental influences on intra-individual variability with an idiographic approach, and provides implications for future behavioural genetic studies to examine developmental processes from a microscopic angle. (shrink)

Identical twins have attracted special attention for the study of behavior genetics. Some of the assumptions and results of these studies are reviewed with special attention given to the natural experiment of identical twins adopted by different families. However, the correlation for any behavior between the adopted twins of a monozygotic pair is affected by their common prenatal environment as well as by the pervasive similarity of the two adoptive environments. The genetic contribution to complex social phenomena, but also (...) to physical characteristics such as height, is usually overestimated. Both for adopted and unadopted twins differential effects of cultural, family, and prenatal environments, and the correlated experiences of twins and their physical appearance affect their development. Taxonomies and samples of environments need to be examined in order to be able to estimate the genetic contributions to behavioral traits. (shrink)

Children's understanding of the human mind has been found to be related to many social and experiential factors such as interactions with peers (Astington & Jenkins, 1995), parental socioeconomic a...

From fertilization to approximately the sixteenth day of development, human embryonic cells are said to have the capacities of totipotency and monozygotic twinning, both of which are problematic to a theory of ensoulment at fertilization. In this article I will address the problems which these capacities pose to such a theory and present an interpretation of the biological data which renders ensoulment at fertilization more plausible. I will then argue that not only is an ensoulment theory consistent with (...) current biological data on the human embryo, but it may offer an explanation for the phenomencon of monozygotic twinning. (shrink)

During the first 16 days after fertilization, the developing embryo has the capacity to separate into two genetically identical embryos, or monozygotic twins (triplets, etc.). Because of this capacity, philosophers typically argue that the pre-16 day embryo is not a human being. On a Biological Account of Personal Identity (BAPI), which considers us human beings as essentially organisms, the development of the embryo into an organism at 16 (or 21) days marks our origins. The development of an embryo into (...) an organism is also said to mark the point at which the embryo loses its potential to give rise to monozygotic twins. This is considered a strength of the Biological account of our origins. I will argue here that it is the BAPI's own criteria that will have to allow cases of monozygotic twinning occurring even after 16 days, and that in virtue of this a Biological Account faces twinning puzzles usually reserved for earlier accounts of our origins. (shrink)

According to kin selection theory, indirect reproductive advantages may induce individuals to care for others with whom they share genes by common descent, and the amount of care, including self-sacrifice, will increase with the proportion of genes shared. Twins represent a natural situation in which this hypothesis can be tested. Twin pairs experience the same early environment because they were born and raised at the same time and in the same family but their genetic relatedness differs depending on zygosity. We (...) compared the degree of willingness to fight and sacrifice for the co-twin among monozygotic and dizygotic pairs in a sample of 1443 same-sex and opposite-sex twins. We also analyzed the effect of the subject’s gender and that of the co-twin on those altruistic behaviors. Results partly supported the postulated explanation. MZ twins were significantly more likely than DZ twins to self-sacrifice for their co-twins, but zygosity did not affect willingness to fight for him/her. The genders of the subject and of the co-twin, not genetic relatedness, were the best predictors of aggressive altruistic intentions. (shrink)

According to kin selection theory, indirect reproductive advantages may induce individuals to care for others with whom they share genes by common descent, and the amount of care, including self-sacrifice, will increase with the proportion of genes shared. Twins represent a natural situation in which this hypothesis can be tested. Twin pairs experience the same early environment because they were born and raised at the same time and in the same family but their genetic relatedness differs depending on zygosity. We (...) compared the degree of willingness to fight and sacrifice for the co-twin among monozygotic and dizygotic pairs in a sample of 1443 same-sex and opposite-sex twins. We also analyzed the effect of the subject’s gender and that of the co-twin on those altruistic behaviors. Results partly supported the postulated explanation. MZ twins were significantly more likely than DZ twins to self-sacrifice for their co-twins, but zygosity did not affect willingness to fight for him/her. The genders of the subject and of the co-twin, not genetic relatedness, were the best predictors of aggressive altruistic intentions. (shrink)

SummaryThe menarcheal age and frequency of menstrual disorders in mothers of dizygotic and monozygotic twins born in Denmark in 1984 or 1985 were compared with a control sample of mothers of singleton infants born in the same period. Compared to control mothers, mothers of DZ twins had a lower menarcheal age and a lower frequency of menstrual irregularities—menstrual cycles exceeding 5 weeks duration, varying length of menstrual cycles and episodes of menostasia. Mothers of MZ twins had a higher frequency (...) of intermenstrual bleeding compared to mothers of singletons. All results were adjusted for maternal age and parity. The findings are relevant to the interpretation of aetiological factors leading to twin births and support the hypothesis of differences in sex hormone activity of the mothers of DZ twins in comparison with other women. (shrink)

This paper performs a critical review of twin and adoption studies looking at possible genetic factors in criminal and antisocial behavior. While most modern researchers acknowledge that family studies are unable to separate possible genetic and environmental influences, it is argued here that twin studies are similarly unable to disentangle these influences. The twin method of monozygotic–dizygotic comparison is predicated on the assumption that both types of twins share equal environments, and it is argued here that this assumption is (...) false. Adoption studies have been promoted as a better way of separating genetic and environmental influences. However, there is good reason to believe that adoption studies of criminal and antisocial behavior were confounded by selective placement factors. In addition, these studies suffered from bias and serious methodological errors. In spite of these problems, no adoption researcher claimed to have found evidence of a genetic predisposition for violent crime. It is concluded that the weight of the evidence from family, twin, and adoption studies does not support a genetic basis for any type of criminal or antisocial behavior. The historical background of genetic theories of criminality is also discussed. (shrink)

Alterations to cognitive function are often reported with depression and anxiety symptoms, yet few studies have examined the same associations with mental well-being. This study examined the association between mental well-being, depression and anxiety symptoms and cognitive function in 1502 healthy adult monozygotic and dizygotic twins, and the shared/unique contribution of genetic and environmental variance. Using linear mixed models, mental well-being was positively associated with sustained attention, inhibition, cognitive flexibility, motor coordination and working memory, whereas depression and anxiety symptoms (...) were associated with poorer sustained attention, inhibition, cognitive flexibility and executive function. Bivariate twin modelling showed well-being shared a small environmental correlation with motor coordination and a small genetic correlation with working memory. Trivariate twin modelling showed well-being shared a small genetic correlation with inhibition, whereas depression and anxiety symptoms shared a small environmental correlation with inhibition. The remaining variance was mostly driven by unique G and/or E variance. Overall, well-being and depression and anxiety symptoms show both independent and shared relationships with cognitive functions but this is largely attributable to unique G or E variance and small shared G/E variance between pairs of variables. (shrink)

When a human being comes into existence is crucial in bioethics. Conceptionism is the view that a human being comes into existence at conception. The twinning argument is an influential objection to this view. All versions of the twinning argument rely on a metaphysics of material objects, namely, endurantism. Given this, a strategy for defending conceptionism against the twinning argument is to deny endurantism and adopt an alternative metaphysics of material objects. A version of this strategy which (...) has been debated in this journal is to adopt perdurantism, or the ‘multiple occupancy view’, on which monozygotic twins share the zygote region as a temporal part. We present a novel version of this strategy: conceptionists can evade the twinning argument by adopting an exdurantist metaphysics of material objects. We suggest reasons for thinking that this is a plausible and, indeed, preferable way for conceptionists to avoid the twinning argument. (shrink)

Galton greeted Darwin's theory of pangenesis with enthusiasm, and tried to test the assumption that the hereditary particles circulate in the blood by transfusion experiments on rabbits. The failure of these experiments led him to reject this assumption, and in the 1870s he developed an alternative theory of heredity, which incorporated those parts of Darwin's theory that did not involve the transportation of hereditary particles throughout the system. He supposed that the fertilized ovum contains a large number of hereditary elements, (...) which he collectively called the "stirp," a few of which are patent, developing into particular cell types, while the rest remain latent; the latent elements can be transmitted to the next generation, while the patent elements, with rare exceptions, cannot since they have developed into cells. The problem with this theory is that it does not explain the similarity between parent and child unless there is a high correlation between latent and patent elements. Galton probably came to realize this problem during his subsequent statistical work on heredity, and he quietly dropped the idea that patent elements are not transmitted in Natural Inheritance (1889). Galton thought that brothers and sisters had identical stirps, and he attributed differences between them to variability in the choice of patent elements from the stirp, that is to say to developmental variability. He attributed the likeness of monozygotic twins to the similarity of their developmental environment. Galton's twin method was to track the life history changes of twins to see whether twins who were similar at birth diverged in dissimilar environments or whether twins who were dissimilar at birth converged in similar environments. It is quite different from the modern twin method of comparing the similarities between monozygotic and dizygotic twins, on the assumption that monozygotic twins are genetically identical whereas dizygotic twins are not. It has been argued that Galton foreshadowed Weismann's theory of the continuity of the germ-plasm, but this is only true in a weak sense. They both believed that the inheritance of acquired characters was either rare or impossible, but Galton did not forestall the essential part of Weismann's theory, that the germ-plasm of the zygote is doubled, with one part being reserved for the formation of the germ-cells. (shrink)

The main objection to human embryonic stem cell research is that it involves killing human embryos, which are essentially beings of the same sort that you and I are. This objection presupposes that we once existed as early embryos and that we had the same moral status then that we have now. This essay challenges both those presuppositions, but focuses primarily on the first. I argue first that these presuppositions are incompatible with widely accepted beliefs about both assisted conception and (...) monozygotic twinning. I then argue that we never existed as embryos. If this last claim is right, killing an embryo does not kill someone like you or me but merely prevents one of us from existing. (shrink)

In various places we have defended the position that a new human organism, that is, an individual member of the human species, comes to be at fertilization, the union of the spermatozoon and the oocyte. This individual organism, during the ordinary course of embryological development, remains the same individual and does not undergo any further substantial change, unless monozygotic twinning, or some form of chimerism occurs. Recently, in this Journal Jason Morris has challenged our position, claiming that recent (...) findings in reproductive and stem cell biology have falsified our view. He objects to our claim that a discernible substantial change occurs at conception, giving rise to the existence of a new individual of the human species. In addition, he objects to our claim that the embryo is an individual, a unified whole that persists through various changes, and thus something other than a mere aggregate of cells. Morris raises a number of objections to these claims. However, we will show that his arguments overlook key data and confuse biological, metaphysical, and ethical questions. As a result, his attempts to rebut our arguments fail. (shrink)

The process of embryogenesis poses numerous philosophical puzzles. Conceptual difficulties encountered while attempting to clarify the ontological and moral status of the fertilized ovum, for example, are compounded in the minds of some philosophers by the possible occurrence of monozygotic twinning during the earliest stages of embryological development. In light of certain conceptual complexities engendered by this possibility, G.E.M. Anscombe, for example, has come to believe that the pivotal metaphysical query in need of an adequate response is the (...) following: Is the human zygote a single human? The answer to this question is of interest to Anscombe primarily for the role it would play in solving the following puzzle: Suppose that zygote A divides into twins B and B1, such that neither B nor B1 is identical with its twin or with A. It then seems clear that either A, prior to its division, was somehow already B and B1; or A was a single human out of which another human grew ; or A, which was a single human, became two humans, much like an amoeba becomes two amoebae; or A is a "whole human substantial entity". (shrink)

abstract This paper re‐examines some well‐known and commonly accepted arguments for the non‐individuality of the embryo, due mainly to the work of John Harris. The first concerns the alleged non‐differentiation of the embryoblast from the trophoblast. The second concerns monozygotic twinning and the relevance of the primitive streak. The third concerns the totipotency of the cells of the early embryo. I argue that on a proper analysis of both the empirical facts of embryological development, and the metaphysical importance (...) or otherwise of those facts, all three arguments are found wanting. None of them establishes that the embryo is not an individual human being from the moment of conception. (shrink)

Quantitative genetics (QG) analyses variation in traits of humans, other animals, or plants in ways that take account of the genealogical relatedness of the individuals whose traits are observed. “Classical” QG, where the analysis of variation does not involve data on measurable genetic or environmental entities or factors, is reformulated in this article using models that are free of hypothetical, idealized versions of such factors, while still allowing for defined degrees of relatedness among kinds of individuals or “varieties.” The gene (...) - free formulation encompasses situations encountered in human QG as well as in agricultural QG. This formulation is used to describe three standard assumptions involved in classical QG and provide plausible alternatives. Several concerns about the partitioning of trait variation into components and its interpretation, most of which have a long history of debate, are discussed in light of the gene-free formulation and alternative assumptions. That discussion is at a theoretical level, not dependent on empirical data in any particular situation. Additional lines of work to put the gene-free formulation and alternative assumptions into practice and to assess their empirical consequences are noted, but lie beyond the scope of this article. The three standard QG assumptions examined are: (1) partitioning of trait variation into components requires models of hypothetical, idealized genes with simple Mendelian inheritance and direct contributions to the trait; (2) all other things being equal, similarity in traits for relatives is proportional to the fraction shared by the relatives of all the genes that vary in the population (e.g., fraternal or dizygotic twins share half of the variable genes that identical or monozygotic twins share); (3) in analyses of human data, genotype-environment interaction variance (in the classical QG sense) can be discounted. The concerns about the partitioning of trait variation discussed include: the distinction between traits and underlying measurable factors; the possible heterogeneity in factors underlying the development of a trait; the kinds of data needed to estimate key empirical parameters; and interpretations based on contributions of hypothetical genes; as well as, in human studies, the labeling of residual variance as a non-shared environmental effect; and the importance of estimating interaction variance. (shrink)

I consider the argument, thought to clinch the moral case for use of a human embryo solely as a means, that only a human individual can be a person, because it can happen at any time before formation of the primitive streak that an embryo splits into monozygotic twins, no embryo in which the primitive streak has not formed is a human individual, and therefore no embryo in which the primitive streak has not formed is a person. I explore (...) the following proffered arguments for : indivisibility is a necessary condition of individuality, nonidentity of an embryo with successor twins impugns the embryo’s individuality, and totipotency of an embryo’s constituents is inconsistent with the embryo’s being a human individual. These arguments are tested and found wanting; so too is an alternative to , the argument that indivisibility is intrinsic to personhood. Whereupon is unsustained. In search of ways to rehabilitate the nonindividuation argument, I canvass alternative metaphysical views and inquire further into biological individuality, but find that the argument cannot be saved. I conclude by analyzing where this leaves matters concerning the morality of embryo use. (shrink)

I consider the argument, thought to clinch the moral case for use of a human embryo solely as a means, that only a human individual can be a person, because it can happen at any time before formation of the primitive streak that an embryo splits into monozygotic twins, no embryo in which the primitive streak has not formed is a human individual, and therefore no embryo in which the primitive streak has not formed is a person. I explore (...) the following proffered arguments for : indivisibility is a necessary condition of individuality, nonidentity of an embryo with successor twins impugns the embryo’s individuality, and totipotency of an embryo’s constituents is inconsistent with the embryo’s being a human individual. These arguments are tested and found wanting; so too is an alternative to, the argument that indivisibility is intrinsic to personhood. Whereupon is unsustained. In search of ways to rehabilitate the nonindividuation argument, I canvass alternative metaphysical views and inquire further into biological individuality, but find that the argument cannot be saved. I conclude by analyzing where this leaves matters concerning the morality of embryo use. (shrink)

I begin by examining how genetics drivesschizophrenia research, and raise both familiar andrelatively novel criticisms of the evidence putativelysupporting the genetic basis of schizophrenia. Inparticular, I call attention to a set of concernsabout the effects of placentation on concordance ratesof schizophrenia in monozygotic twins, which furtherweakens the case for schizophrenia''s so-called stronggenetic component. I then underscore two criticalpoints. First, I emphasize the importance of takingseriously considerations about the complexity of bothontogenesis and the development of hereditarydiseases. The recognition of developmentalconstraints (...) and supports is crucial, for attention todevelopment exposes the naivete of too many models ofgene action in the aetiology of disease. Secondly, Iattend to those schizophreniologists who ignoremethodological criticisms and thus presume a geneticbasis for schizophrenia, and then seek the schizophrenic genotype lacking an adequatephenotype. In response I attempt to demonstrate thenecessity of a sustained effort at characterizing thephenotype of schizophrenia as an enabling conditionfor the whole enterprise of psychiatric genetics – andfor psychiatry itself. Without the organism-levelphenotype, research at the level of genes will remainunproductive – assuming of course that research at thegenetic level is appropriate at all. (shrink)

Um argumento recorrente contra a liberalização do aborto parte do pressuposto de que, desde o momento da fertilização, seres humanos são indivíduos (no sentido de serem algo que necessariamente ocorre em uma entidade apenas). Nesse artigo, argumento que esse não é um caso a partir da possibilidade de geminação monozigótica e do fato de identidades serem necessárias. Defendo as premissas do argumento e discuto as possíveis interpretações de sua conclusão. Argumento que a interpretação completa da conclusão desse argumento está em (...) concordância com a conclusão de um argumento semelhante, que parte de noção de organismo. -/- ENGLISH: A common pro-life argument assumes that humans are individuals (in the sense that they necessarily occur in one entity only) from the moment of fertilization. In this paper, argue that this is not the case because of the possibility of monozygotic twinning and the necessity of identities. I will defend the premises of the argument and discuss the possible interpretations of its conclusion. I argue that the correct interpretation of the conclusion of this argument is in agreement with the conclusion of a similar arguments from the notion of organism. (shrink)

Many aspects of biology, such as population genetics and senescence, are predicated on identifying individuals and generations. Conventional demarcations of individuals and generations, such as physiological autonomy, unicellular bottlenecks, and alternation of generation, are rife with problems. Do physically separated cuttings or plant ramets constitute separate individuals or generations? Are chimaeras one or more individuals? To resolve these problems, Clarke : 321–361, 2012) proposed that individuals are circumscribed by mechanisms that constrain heritable variance in fitness. Simultaneously, Gorelick and Heng : (...) 1088–1098 2011) showed that sex constrains heritable variance Therefore, for eukaryotes, meiosis and karyogamy provide a consistent way to demarcate individuals and generations. Epigenetic reset associated with meiosis and karyogamy rejuvenates the next generation, but not the parent that engaged in the sex act. Wholesale epigenetic resets that probably only occur with meiosis and karyogamy imply that monozygotic twins are two different individuals, but apomictic progeny are diffuse parts of one disaggregated individual. Mitotic heritability circumscribes an individual, whereas meiotic heritability demarcates new individuals and generations. (shrink)

Australian legislation at both state and federal levels has been passed in the last two years enabling the creation and use of cloned embryos up until their fourteenth day of development. Yet for this fourteen-day threshold to carry moral weight it must be shown that an embryo may be plausibly attributed some kind of moral standing after this point that it cannot be accorded before it Moral standing may be conferred using Steven Buckle’s account of potential to become (after one (...) problem with his account is dealt with) but such standing has often been withheld from the embryo prior to the fourteenth day due to the possibility of monozygotic twinning and the violation of numerical continuity this represents. This article discusses the influential argument regarding monozygotic twinning articulated by Peter Singer and Helga Kuhse, and finds it insufficient to negate either the ‘identity thesis’ they describe or Buckle’s account of potential to become. (shrink)

Recently David S. Oderberg has tried to refute three arguments that have been advanced in favour of the view that a human being does not begin to exist at fertilization. These arguments turn on the absence of differentiation between the embryoblast and trophoblast, the possibility of monozygotic twinning, and the totipotency of the cells during the first days after fertilization. It is here contended that Oderberg fails to rebut these arguments, though it is conceded that the first two (...) arguments are not conclusive. They do, however, make it at least as reasonable to deny this early origination as to affirm it. It should be noticed that this is all that is needed by those who have used these arguments to dispute that something with a special moral status exists right from fertilization. Nonetheless, it will be seen that the third argument could be developed to the point of giving a conclusive reason to believe that a human being does not begin to exist at fertilization. (shrink)

This paper re-examines some well-known and commonly accepted arguments for the non-individuality of the embryo, due mainly to the work of John Harris. The first concerns the alleged non-differentiation of the embryoblast from the trophoblast. The second concerns monozygotic twinning and the relevance of the primitive streak. The third concerns the totipotency of the cells of the early embryo. I argue that on a proper analysis of both the empirical facts of embryological development, and the metaphysical importance or (...) otherwise of those facts, all three arguments are found wanting. None of them establishes that the embryo is not an individual human being from the moment of conception. (shrink)

Pharmacogenetics and pharmacogenomics are related facets of cutting edge therapeutic research in a field that relates pharmacological properties to the genetic characteristics of human beings. An optimistic interpretation suggests that “One-Size-Fits-All” therapeutics, whose effects can only be predicted in probabilistic terms, will give way eventually to individual tailor-made therapies with entirely predictable properties in each patient. Yet the concept of anticipating individual pharmacotherapeutic response appears to disregard some of the fundamental limitations of causal understanding in the biological world of structure–action (...) relationships. It is not simply a problem of confronting complexity – which might be overcome in time with advances in biotechnology and computing power – but the inescapable paradox of the genetic characteristics of individuals within the human species. The aleatory process of evolution ensures that with the exception of monozygotic twins, every human being is genetically unique. At the same time there appears to be more in common than divides. Pharmacogenomics provides a climate in which to explore and better understand the variable causal relationships between genetic element, protein and therapeutic or toxic actions, but can only do so in abstraction. Thus␣predictive power may be enhanced but is ultimately constrained by insuperable probabilistic considerations. (shrink)

Starting from the conceptual premises of Garrod, who as long ago as 1902 spoke of chemical individuality, and of Burnet (1949), who recognized as self one's own molecular antigenic structures (as opposed to the antigenic alien: the non- self), the discovery and understanding of HLA antigens and of their extraordinarily individual and differentiated polymorphisms have gained universal recognition. Transplant medicine has now dramatically stressed, within man's knowledge of himself, the characteristic of his biological uniqueness. Today man, having become aware of (...) being a biological antigenic-molecular individuality which is unique and different from that of all of his fellow men (except for monozygotic twins), can therefore easily consider himself a true biological Ego. (shrink)

Pharmacogenetics and pharmacogenomics are related facets of cutting edge therapeutic research in a field that relates pharmacological properties to the genetic characteristics of human beings. An optimistic interpretation suggests that “One-Size-Fits-All” therapeutics, whose effects can only be predicted in probabilistic terms, will give way eventually to individual tailor-made therapies with entirely predictable properties in each patient. Yet the concept of anticipating individual pharmacotherapeutic response appears to disregard some of the fundamental limitations of causal understanding in the biological world of structure–action (...) relationships. It is not simply a problem of confronting complexity – which might be overcome in time with advances in biotechnology and computing power – but the inescapable paradox of the genetic characteristics of individuals within the human species. The aleatory process of evolution ensures that with the exception of monozygotic twins, every human being is genetically unique. At the same time there appears to be more in common than divides. Pharmacogenomics provides a climate in which to explore and better understand the variable causal relationships between genetic element, protein and therapeutic or toxic actions, but can only do so in abstraction. Thus␣predictive power may be enhanced but is ultimately constrained by insuperable probabilistic considerations. (shrink)

The Continuous Parameter Estimation Model is applied to develop individual genomic-level heritabilities for the latent hierarchical structure and developmental dynamics of Life History (LH) strategy LH strategies relate to the allocations of bioenergetic resources into different domains of fitness. LH has moderate to high population-level heritability in humans, both at the level of the high-order Super-K Factor and the lower-order factors, the K-Factor, Covitality Factor, and General Factor of Personality (GFP). Several important questions remain unexplored. We developed measures of genome-level (...) heritabilities employing an American sample of 316 monozygotic (MZ) and 274 dizygotic (DZ) twin dyads and a Swedish sample of 863 MZ and 475 DZ twin dyads. This novel heritability index measures individual genetic transmissibility, therefore opening new avenues for analyzing complex interactions among heritable traits inaccessible to standard structural equations methods. For these samples: (1) moderate to high heritability of factor loadings of Super-K on its lower-order factors is demonstrated, evidencing biological preparedness, genetic accommodation, and the gene-culture coevolution of biased epigenetic rules of development; (2) moderate to high heritability of the magnitudes of the effect of the higher-order factors upon their loadings on their constituent factors, evidencing genetic constraints upon phenotypic plasticity; and (3) that heritability of the LH factors, of factor loadings, and of the magnitudes of the correlations among factors are weaker among those with slower LH speeds, demonstrating that inter-individual variation in transmissibility is a function of individual socioecological selection pressures. (shrink)

Relationships of physical resemblance to personality similarity and social affiliation have generated considerable discussion among behavioral science researchers. A “twin-like” experimental design explores associations among resemblance in appearance, the Big Five personality traits, self-esteem, and social attraction within an evolutionary framework. The Personality for Professionals Inventory, NEO/NEO-FFI-3, Rosenberg Self-Esteem Scale, and a Social Relationship Survey were variously completed by 45 U-LA pairs, identified from the “I’m Not a Look-Alike” project, Mentorn Media, and personal referrals. The mean U-LA intraclass correlations were (...) negligible for all Big Five personality traits on the PfPI and NEO/NEO-FFI-3. In contrast, mean ri values of.53 and.15 for monozygotic and dizygotic reared-apart twins, respectively, have been reported for these personality measures. The U-LA self-esteem correlation was also below the correlations reported for MZ and DZ reared-together twins. Finally, far fewer U-LAs expressed close social relationships than MZA and DZA twins. The present study extends earlier findings indicating that appearance is not meaningfully related to personality similarity and social relatedness. The criticism that MZ twins are alike in personality because their matched looks invite similar treatment by others is refuted. A more judicious interpretation is reactive genotype-environment correlation, namely that MZ twins’ similar personalities evoke similar reactions from others. MZ twins’ close social relations most likely derive from their perceptions of genetically based within-pair similarities that are lacking in U-LAs. (shrink)

Dissociation is commonly regarded as a disruption in the normally integrated functions of memory, knowledge, affect, sensation or behavior. The present study utilized behavioral genetics’ methodology to investigate genetic and environmental basis of the relationship between dissociation and Cloninger’s temperament and character traits. A sample of 83 monozygotic and 65 dizygotic twins were administered self-report measures which assessed dissociative experiences along with personality dimensions. Significant correlations and high loads of common genetic variance between dissociative experiences and personality traits of (...) novelty seeking, self-directedness, cooperativeness and self-transcendence were identified. Heritability of dissociative experiences was estimated at 62%. The study shows that there exists a considerable amount of genetic variance overlap between dissociation and personality dimensions. It also supports the hypothesis that propensity to dissociate is highly heritable. (shrink)

Edward Lee Thorndike (August 31, 1874 Williamsburg, Massachusetts 1] - August 9, 1949) was an American psychologist who spent nearly his entire career at Teachers College, Columbia University. His work on animal behavior and the learning process led to the theory of connectionism and helped lay the scientific foundation for modern educational psychology. He also worked on solving industrial problems, such as employee exams and testing. He was a member of the board of the Psychological Corporation, and served as president (...) of the American Psychological Association in 1912 This book, Measurements Of Twins (1905), by Edward L. Thorndike, is a replication of a book originally published before 1905. It has been restored by human beings, page by page, so that you may enjoy it in a form as close to the original as possible. This book was created using print-on-demand technology. Thank you for supporting classic literature. (shrink)

Fetal reduction is the practice of reducing the number of fetuses in a multiple pregnancy, such as quadruplets, to a twin or singleton pregnancy. Use of assisted reproductive technologies increases the likelihood of multiple pregnancies, and many fetal reductions are done after in vitro fertilisation and embryo transfer, either because of social or health-related reasons. In this paper, I apply Joe Horton’s all or nothing problem to the ethics of fetal reduction in the case of a twin pregnancy. I argue (...) that in the case of a twin pregnancy, there are two intuitively plausible claims: abortion is morally permissible, and it is morally wrong to abort just one of the fetuses. But since we should choose morally permissible acts rather than impermissible ones, the two claims lead to another highly implausible claim: the woman ought to abort both fetuses rather than only one. Yet, this does not seem right. A plausible moral theory cannot advocate such a pro-death view. Or can it? I suggest ways to solve this problem and draw implications for each solution. There are no data in this work. (shrink)

We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization Specrel of special relativity from the literature. Specrel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove the usual relativistic properties of (...) accelerated motion (e.g., clocks in acceleration) in Specrel. As it turns out, this is practically equivalent to asking whether Specrel is strong enough to “handle” (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to Specrel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of Specrel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that~the Twin Paradox becomes provable in AccRel, but it is not provable without IND. (shrink)

In dicephalus conjoined twinning, it appears that two heads share a body; in cephalopagus, it appears that two bodies share a head. How many human animals are present in these cases? One answer is that there are two in both cases—conjoined twins are precisely that, conjoined twins. Another is that the number of humans corresponds to the number of bodies—so there is one in dicephalus and two in cephalopagus. I show that both of these answers are incorrect. Prominent accounts (...) of biological individuation, which treat the organism as an integrated whole, reveal that in these and other cases of conjoined twinning the ‘twins’ share a single human animal. This has a number of consequences for the debate about what we are. First, if animalism is true, individuals of our kind can be—and are—profoundly psychologically divided. Second, cephalopagus twinning does not divide animalism from its rivals, as has been claimed. Finally, animalists can reply to a vicious species of the ‘too many thinkers’ problem to which they are allegedly uniquely vulnerable. (shrink)

This article explores the elective affinities between Actor-Network Theory (ANT) and the sociology of critical capacities. It argues that these two research programmes can be understood as symmetrical twins. We show the extent to which the exchange between Bruno Latour and Luc Boltanski has influenced their respective theoretical developments. Three strong encounters between the twin research programmes may be distinguished. The first encounter concerns explanations for social change. The second encounter focuses on the status of objects and their relationship to (...) places. The third encounter is about the concept of critique. Drawing on their long-term mutual readings, we gain insight into how pleas for symmetrical analysis raised in response to Bourdieu’s theory of fields have evolved within both ANT and the sociology of critical capacity. We conclude by relating the development of the respective research programmes to the issue of disciplinary boundaries. (shrink)

We examine the philosophical and ethical issues associated with conjoined twins and their surgical separation. In cases in which there is an extensive sharing of organs, but nevertheless two distinguishable functioning brains, there are a number of philosophical and ethical challenges. This is because such conjoined twins: 1. give rise to puzzles concerning our identity, about whether we are identical to something psychological or biological;2. force us to decide whether what matters from an ethical point of view is the biological (...) life of our organisms or the existence of our consciousness or mind; 3. raise questions concerning when, if ever, it is morally acceptable to sacrifice one of us to save another;4. force us to reflect on the conditions for ownership of organs and the justification of removal of organs for transplantation which causes the death of the donor; 5. raise questions about who should take decisions about life-risking treatments when this cannot be decided by patients themselves.We examine and suggest answers to these questions. (shrink)

Horgan and Timmons have argued that our intuitions about the semantics of non-moral language and moral language differ, and that while twin-earth semantic intuitions generate one result in Putnam´s twater case, moral twin-earth fails to generate comparable results for moral terms. Horgan and Timmon´s conclude from this that the semantic norms governing the use of natural kind terms differ from the semantic norms governing the use of moral terms. I will argue that Horgan and Timmons’ intuitive moral twin-earth argument fails (...) to derail the new moral realism. Further, I will discuss Boyd’s semantic theory and raise problems for it that do not rely on the use of moral twin-earth. (shrink)

Robert Stalnaker; XVI*—Twin Earth Revisited, Proceedings of the Aristotelian Society, Volume 93, Issue 1, 1 June 1993, Pages 297–312, https://doi.org/10.1093/ar.

Twelve years ago the British media got wind of a London gynecologist who performed an elective reduction on a twin pregnancy reducing it to a singleton. Perhaps not surprisingly, opinion on the moral status of twin reductions was divided. But in the last few years new evidence regarding the medical risks of twin pregnancies has emerged, suggesting that twin reductions are relevantly similar to the reductions performed on high‐end multi‐fetal pregnancies. This evidence has appeared to resolve the moral debate.In this (...) paper I look at the role of clinical evidence in medical ethics. In particular I examine the role of clinical evidence in determining what counts as a significant harm or risk. First, I challenge the extent to which these empirical claims are descriptive, suggesting instead that the evidence is to some degree normative in character. Second, I question whether such empirical claims should count as evidence for what are essentially difficult ethical decisions – a role they appear to play in the case of elective reductions. I will argue that they should not, primarily because the value‐laden nature of this evidence conceals much of what is ethically at stake. It is important to recognize that empirical evidence cannot be a substitute for ethical deliberation. (shrink)

A brief account of Putnam's Twin Earth thought experiment and its significance, written for a general audience. Sadly, I can't include Helen De Cruz's drawing of it - check out the beautiful book!

In a recent paper in this journal, McCall and Lowe (2003) argue that an understanding of Special Relativity reveals that the A theorist’s notion of temporal passage is consistent with the B theory of time. They arrive at this conclusion by considering the twins’ paradox, where one of two twins (T) travels to Alpha Centauri and back and upon her return has aged 30 years, while her earth-bound twin (S) has aged 40 years. This paper argues that their account of (...) temporal passage fails to reconcile the A theoretic notion of temporal passage with the B theory of time since the B theorist is at liberty to adopt this as an account of temporal passage as understood by the B theorist. (shrink)

In his paper, ‘Twin pregnancy, fetal reduction and the ‘all or nothing problem’, Räsänen sets out to apply Horton’s ‘all or nothing’ problem to the ethics of multifetal pregnancy reduction from a twin to a singleton pregnancy. Horton’s problem involves the following scenario: imagine that two children are about to be crushed by a collapsing building. An observer would have three options: do nothing, save one child by allowing their arms to be crushed, or save both by allowing their arms (...) to be crushed. Horton offers two intuitively plausible claims: it is morally permissible not to save either child and it is morally impermissible to save only one of the children, which taken together lead to the problematic conclusion that if an observer does not save both children, then it is better to save neither than save only one. Räsänen applies this problem to the case of 2-to-1 MFPR, arguing ultimately that, in cases where there is no medical reason to reduce, the woman ought to bring both fetuses to term. We will argue that Räsänen does not provide adequate support for the claim, crucial to his argument, that aborting only one of the fetuses in a twin pregnancy is wrong, so the ‘all or nothing’ problem does not arise in this context. Furthermore, we argue that the scenario Räsänen presents is highly unrealistic because of the clinical realities of 2-to-1 MFPR, making his argument of limited use for real-life decision making in this area. (shrink)