Fission of cellular membranes is ubiquitous and essential for life. Complex protein machineries, such as the dynamin and ESCRT spirals, have evolved to mediate membrane fission during diverse cellular processes, for example, vesicle budding. A new study suggests that non-specialized membrane-bound proteins can induce membrane fission through mass action due to protein crowding. Because up to 2/3 of the mass of cellular membranes is contributed by proteins, membrane protein crowding is an important physiological (...) parameter. Considering the complexity of membrane shape transitions during a fission reaction, spatial and temporal variability in protein distribution, and the abundance of intrinsically disordered regions in proteins on an invaginating membrane, protein crowding can have diverse consequences for fission in the cell. The question is, how and to what extent this mechanism combines with the action of dedicated fission machineries. Membrane fission, which is required for formation of vesicles or cytokinesis, can be carried out by specialized proteins like dynamin and the ESCRT complex. Recent work suggests that fission of cellular membranes, which are densely packed with proteins, can also be induced by protein crowding due to high entropic tension. (shrink)

Both RalA and RalB interact with the ubiquitous calcium sensor, calmodulin (CaM). New structural and biophysical characterisation of these interactions strongly suggests that, in the native membrane‐associated state, only RalA can be extracted from the membrane by CaM and this non‐canonical interaction could underpin the divergent signalling roles of these closely related GTPases. The isoform specificity for RalA exhibited by CaM is hypothesised to contribute to the disparate signalling roles of RalA and RalB in mitochondrial dynamics. This would (...) lead to CaM shuttling RalA to the mitochondrial membrane but leaving RalB localisation unperturbed, and in doing so triggering mitochondrial fission pathways rather than mitophagy. (shrink)

Joining an antagonistic phosphoinositide (PtdInsP) kinase and phosphatase into a single protein complex may regulate rapid and local PtdInsP changes. This may be important for processes such as membrane fission that require a specific PtdInsP and that are innately local and rapid. Such a complex could couple vesicle formation, with erasing of the identity of the donor organelle from the vesicle prior to its fusion with target organelles, thus preventing organelle identity intermixing. Coordinating signals are postulated to switch (...) the relative activities of the kinase and phosphatase in a spatio‐temporal manner that matches membrane fission events. The discovery of two such complexes supports this hypothesis. One regulates the interconversion of phosphatidylinositol and PtdIns(3)P by joining the Vps34 PtdIns 3‐kinase and the myotubularin 3‐phosphatases. The other regulates the interconversion between PtdIns(3)P and PtdIns(3,5)P2 through the Fab1/PIKfyve kinase and the Fig4/mFig4 phosphatase. These lipids are essential components of the endosomal identity code. (shrink)

Intercellular communication is an essential process in all multicellular organisms. During this process, molecules secreted by one cell will bind to a receptor on the cognate cell leading to the subsequent uptake of the receptor‐ligand complex. Once inside, the cell then determines the fate of the receptor‐ligand complex and any other proteins that were endocytosed together. Approximately 80% of endocytosed material is recycled back to the plasma membrane either directly or indirectly via the Golgi apparatus and the remaining 20% (...) is delivered to the lysosome for degradation. Although most pathways have been identified, we still lack understanding on how specificity in sorting of recycling cargos into different pathways is achieved, and how the cell reaches high accuracy of these processes in the absence of clear sorting signals in the bulk of the client proteins. In this review, we will summarize our current understanding of the mechanism behind recycling cargo sorting and propose a model of differential affinities between cargo and cargo receptors/adaptors with regards to iterative sorting in endosomes. (shrink)

Tissue P systems with evolutional communication rules are computational models inspired by biochemical systems consisting of multiple individuals living and cooperating in a certain environment, where objects can be modified when moving from one region to another region. In this work, cell separation, inspired from membrane fission process, is introduced in the framework of tissue P systems with evolutional communication rules. The computational complexity of this kind of P systems is investigated. It is proved that only problems in (...) class P can be efficiently solved by tissue P systems with cell separation with evolutional communication rules of length at most, for each natural number n≥1. In the case where that length is upper bounded by, a polynomial time solution to the SAT problem is provided, hence, assuming that P≠NP a new boundary between tractability and NP-hardness on the basis of the length of evolutional communication rules is provided. Finally, a new simulator for tissue P systems with evolutional communication rules is designed and is used to check the correctness of the solution to the SAT problem. (shrink)

Recently, a review regarding the mechanics and evolution of mitochondrial fission appeared in Nature. Surprisingly, it stated authoritatively that the mitochondrial outer membrane, in contrast with the inner membrane of bacterial descent, was acquired from the host, presumably during uptake. However, it has been known for quite some time that this membrane was also derived from the Gram‐negative, alpha‐proteobacterium related precursor of present‐day mitochondria. The zombie idea of the host membrane still surrounding the endosymbiont is (...) not only wrong, but more importantly, might hamper the proper conception of possible scenarios of eukaryogenesis. Why? Because it steers the imagination not only with regard to possible uptake mechanisms, but also regarding what went on before. Here I critically discuss both the evidence for the continuity of the bacterial outer membrane, the reasons for the persistence of the erroneous host membrane hypothesis and the wider implications of these misconceptions for the ideas regarding events occurring during the first steps towards the evolution of the eukaryotes and later major eukaryotic differentiations. I will also highlight some of the latest insights regarding different instances of endosymbiont evolution. (shrink)

The direction and specificity of endolysosomal membrane trafficking is tightly regulated by various cytosolic and membrane‐bound factors, including soluble NSF attachment protein receptors (SNAREs), Rab GTPases, and phosphoinositides. Another trafficking regulatory factor is juxta‐organellar Ca2+, which is hypothesized to be released from the lumen of endolysosomes and to be present at higher concentrations near fusion/fission sites. The recent identification and characterization of several Ca2+ channel proteins from endolysosomal membranes has provided a unique opportunity to examine the roles (...) of Ca2+ and Ca2+ channels in the membrane trafficking of endolysosomes. SNAREs, Rab GTPases, and phosphoinositides have been reported to regulate plasma membrane ion channels, thereby suggesting that these trafficking regulators may also modulate endolysosomal dynamics by controlling Ca2+ flux across endolysosomal membranes. In this paper, we discuss the roles of phosphoinositides, Ca2+, and potential interactions between endolysosomal Ca2+ channels and phosphoinositides in endolysosomal dynamics. (shrink)

Recently, Gao et al. and Chappie et al. elucidated the crystal structures of the polytetrameric stalk domain of the dynamin‐like virus resistance protein, MxA, and of the G‐domain dimer of the large, membrane‐deforming GTPase, dynamin, respectively. Combined, they provide a hypothetical oligomeric structure for the complete dynamin protein. Here, it is discussed how the oligomers are expected to form and how they participate in dynamin mediated vesicle fission during the process of endocytosis. The proposed oligomeric structure is compared (...) with the novel mechanochemical model of dynamin function recently proposed by Bashkirov et al. and Pucadyil and Schmid. In conclusion, the new model of the dynamin oligomer has the potential to explain how short self‐limiting fissogenic dynamin assemblies are formed and how concerted GTP hydrolysis is achieved. The oligomerisation of two other dynamin superfamily proteins, the guanylate binding proteins (GBPs) and the immunity‐related GTPases (IRGs), is addressed briefly. (shrink)

The aim of this paper is to provide a proof-theoretic characterization of relevant logics including fusion and fission connectives, as well as Ackermann’s truth constant. We achieve this by employing the well-established methodology of labelled sequent calculi. After having introduced several systems, we will conduct a detailed proof-theoretic analysis, show a cut-admissibility theorem, and establish soundness and completeness. The paper ends with a discussion that contextualizes our current work within the broader landscape of the proof theory of relevant logics.

Consider a specific type of fission where psychological continuity takes a branching form, and one of the offshoots comes into being later than the other offshoot. Let us say that the earlier offshoot comes into being in the left branch at t, and the later offshoot comes into being in the right branch at t+1. With regard to the question how many persons are involved in this case, three answers are worth considering: (i) The original subject persists up to (...) t; a distinct person comes into being immediately after t and continues to exist in the left branch; and the third person comes into being in the right branch at t+1. (ii) The original subject persists up to the moment immediately before t+1; a distinct person comes into being at t+1 and continues to exist in the left branch; and the third person comes into being in the right branch at t+1. (iii) The original subject continues to exist in the left branch; a distinct person comes into being in the right branch at t+1. For those who hold that personal identity consists in psychological continuity of some sort, the aforementioned three options exhaust the sensible ways of understanding how one persists in delayed fission. However, I argue that complications arise for each answer. Hence, delayed fission poses a challenge for the psychological approach to personal identity. (shrink)

According to a traditional conception, romantic love is both constant - if someone loves another, they continue to love them - and exclusive - if someone loves another, they love only the other. In this paper, we argue that the essentiality of constancy and exclusivity is incompatible with the possibilities of fission - roughly speaking, of one person becoming two - and fusion - roughly speaking, of two people becoming one. Moreover, if fission or fusion are possible, then (...) constancy and exclusivity are obligatory features of love only if there are moral dilemmas. We conclude by suggesting this casts doubt on the constancy and especially the exclusivity of love. (shrink)

(No abstract is available for this citation).

If a person, A, branches into B and C, then it is widely held that B and C are not identical to one another. Many think that this is because B and C have contradictory properties at the same time. In this paper, I show why this explanation cannot be right. I argue that contradictory properties at times are not necessary for non-identity between descendants, and that contradictory properties at times are not sufficient for non-identity. I also argue that the (...) standard explanation cannot be salvaged by a shift to personal time. Appeals to a lack of continuity, or to the absence of unity of consciousness likewise fail. Rather, B and C are non-identical simply because A branched into B and C. Why branching should be problematic for personal identity remains a deep puzzle though I offer some tentative suggestions. (shrink)

Mitochondrial shape change, brought about by molecules that promote either fission or fusion between individual mitochondria, has been documented in several model systems. However, the deeper significance of mitochondrial shape change has only recently begun to emerge: among others, it appears to play a role in the regulation of cell proliferation. Here, I review the emerging interplay between mitochondrial fission‐fusion components with cell cycle regulatory machineries and how that may impact cell differentiation. Regulation of mitochondrial shape may modulate (...) mitochondrial metabolism and/or energetics to promote crosstalk between signaling components and the cell cycle machinery. Focused research in this area will reveal the exact role of mitochondria in development and disease, specifically in stem cell regulation and tumorigenesis. Such research may also reveal whether and how the endosymbiotic event that gave rise to the mitochondrion was crucial for the evolution of cell cycle regulatory mechanisms in eukaryotes that are absent in prokaryotes. (shrink)

In “The Argument for Subject Body Dualism from Transtemporal Identity Defended” (PPR 2013), Martine Nida-Rümelin (NR) responded to my (PPR 2013) criticism of her (2010) argument for subject-body dualism. The crucial premise of her (2010) argument was that there is a factual difference between the claims that in a fission case the original person is identical with one, or the other, of the successors. I argued that, on the three most plausible interpretations of ‘factual difference’, the argument fails. NR (...) responds that I missed the intended, fourth interpretation, and that, in any case, with an additional assumption, the argument on the third interpretation goes through. I argue that the fourth interpretation, while insufficient as stated, reveals an assumption that provides an independent argument, namely, that in first person thought about future properties we have a positive conception of the self that rules out having empirical criteria of transtemporal identity. I argue that the considerations offered for this thesis fail to establish it, and that we do not bring ourselves under any positive conception in first person thought. I argue also that on the third interpretation, the first premise of the argument is inconsistent with the necessity of identity. (shrink)

Most metazoan organisms have evolved a mildly acidified and calcium diminished sorting hub in the early secretory pathway commonly referred to as the Endoplasmic Reticulum‐Golgi intermediate compartment (ERGIC). These membranous vesicular‐tubular clusters are found tightly juxtaposed to ER subdomains that are competent for the production of COPII‐coated transport carriers. In contrast to many unicellular systems, metazoan COPII carriers largely transit just a few hundred nanometers to the ERGIC, prior to COPI‐dependent transport on to the cis‐Golgi. The mechanisms underlying formation and (...) maintenance of ERGIC membranes are poorly defined. However, recent evidence suggests an important role for Trk‐fused gene (TFG) in regulating the integrity of the ER/ERGIC interface. Moreover, in the absence of cytoskeletal elements to scaffold tracks on which COPII carriers might move, TFG appears to promote anterograde cargo transport by locally tethering COPII carriers adjacent to ERGIC membranes. This action, regulated in part by the intrinsically disordered domain of TFG, provides sufficient time for COPII coat disassembly prior to heterotypic membrane fusion and cargo delivery to the ERGIC. -/- . (shrink)

It has long been known that the red blood cell contains a membrane skeleton that stabilizes the plasma membrane, determines its shape, and regulates the lateral distribution of the membrane glyco‐proteins to which it is attached. The way in which these functions are regulated in other cells has not been understood. It has now been shown that platelets also contain a membrane skeleton. In contrast to the membrane skeleton of the red blood cell, the platelet (...) membrane skeleton has actin‐binding protein, not spectrin, as a major component. The platelet membrane skeleton regulates the same cellular functions as the red blood cell membrane skeleton. Other cells may contain a membrane skeleton that is critical to their viability and normal functioning. (shrink)

Catholic opponents of abortion and embryonic stem cell research usually base their position on a hylomorphic account of ensoulment at fertilization. They maintain that we each started out as one-cell ensouled organisms. Critics of this position argue that it is plagued by a number of intractable problems due to fission (twinning) and fusion. We're unconvinced that such objections to early ensoulment provide any reason to doubt the coherence of the hylomorphic account. However, we do maintain that a defense of (...) ensoulment at fertilization must deny that we're essentially organisms. (shrink)

Microfilament interactions with the plasma membranes of animal cells appear to vary with cell type and localization. In the erythrocyte, actin oligomers are associated with the membrane via spectrin and ankyrin. The ends of stress fibers in cultured cells, such as fibroblasts, are attached to the plasma membrane at focal adhesion sites and may involve the protein vinculin as a linking protein. In intestinal brush border microvilli a 110,000 dalton protein links the microfilament bundles to sites on the (...) microvillus. A transmembrane complex containing actin stably associated with a cell surface glycoprotein can be isolated from ascites tumor cell microvilli and can be obtained still associated with microfilaments by gentle extraction and gradient centrifugation of the microvilli. These varied interaction mechanisms are believed to be needed to satisfy the different structural and dynamic requirements of the particular systems. (shrink)

Undoubtedly the Penrose-Hameroff Orch OR model may be considered as a good theory for describing information processing mechanisms and holistic phenomena in the human brain, but it doesn’t give us satisfactory explanation of human perception. In this work a new approach explaining our perception is introduced, which is in good agreement with Orch OR model and other mainstream science theories such as string theory, loop quantum gravity and holographic principle. It is shown that human perception cannot be explained in the (...) terms of elementary particles and we should introduce new indivisible holistic objects with geometry based on smooth infinitesimal analysis - elastic membranes. The example of such a membrane is our Universe which is an indivisible whole. It is shown that our perception may be considered as the result of elastic oscillations of two dimensional (2D) elastic membranes with closed topology embedded in our bodies. Only one elastic membrane responsible for its perceptions will correspond to the selected organism, but there may be other membranes, even at the cell level. In other words, reality may be considered as the process of time evolution of holistic energetically very weak macro objects - elastic membranes with the geometry based on smooth infinitesimal analysis. An embedded membrane in this multidimensional world will look different for the external and internal observers: from the outside it will look like a material object with smooth infinitesimal geometry, while from the inside our Universe-like space-time fabric. When interacting with elementary particles and other membranes, a membrane will transform their energy into its elastic energy (a new form of energy) - the energy of stretching of the infinitesimal segments. The theory postulates that these elastic deformations will not be observable from the point of view of the internal observer. Heisenberg’s uncertainty principle will work in this physics only from the point of view of the internal observer. For the external observer each embedded elastic membrane may be stretched and even a very small region will become observable. For example, living organisms play the role of internal observers of the Universe, and at the same time they serve as external observers for 2D membranes embedded into our Universe. We can observe our 2D self-membranes through our perceptions, which are encoded in elastic oscillations of the elastic membrane. According to the theory, elastic membranes occupy energetically favorable positions around microtubules involved into Orch OR. The theory not only gives us a really multidimensional holistic picture of reality, but it also provides us with a new method for understanding such phenomena as perception, self-awareness and will. (shrink)

I introduce a new approach to fission puzzles called the Diversified Approach that proceeds by distinguishing different kinds of fission and assimilating each kind to a different ordinary phenomenon, such as breaking apart, replication, or part loss. To illustrate this approach, I apply it to the case of amoebic fission. The upshot is a novel account of amoebic fission according to which the dividing amoeba ceases to exist because it breaks apart. After developing this solution and (...) highlighting some of its advantages, I discuss briefly how the Diversified Approach can be extended to other varieties of fission. (shrink)

When an agent undergoes fission, how should the beliefs of the fission results relate to the pre-fission beliefs? This question is important for the Everett interpretation of quantum mechanics, but it is of independent philosophical interest. Among other things, fission scenarios demonstrate that ‘self-locating’ information can affect the probability of uncentred propositions even if an agent has no essentially self-locating uncertainty. I present a general update rule for centred beliefs that gives sensible verdicts in cases of (...) fission, without relying on controversial metaphysical or linguistic assumptions. The rule is supported by the same considerations that support standard conditioning in the traditional framework of uncentred propositions. (shrink)

The synthesis of biological membranes requires the insertion of proteins into a lipid bilayer. The rough endoplasmic reticulum of eukaryotic cells is a principal site of membrane biogenesis. The insertion of proteins into the membrane of the endoplasmic reticulum is mediated by a resident proteinaceous machinery. Over the last five years several different experimental approaches have provided information about the components of the machinery and how it may function.

Derek Parfit famously defends a number of surprising views about "fission." One is that, in such a scenario, it is indeterminate whether I have survived or not. Another is that the fission case shows that it does not matter, in itself, whether I survive or not. Most critics of the first view contend that fission makes me cease to exist. Most opponents of the second view contend that fission does not preserve everything that matters in ordinary (...) survival. In this paper I shall provide a critique that does not rely on either of these contentions. There are other, interrelated reasons to reject Parfit's defense of the two theses. In particular, the availability of the following view creates trouble for Parfit: I determinately survive fission, but it is indeterminate which fission product I am. (shrink)

Reflection on the state of contemporary epistemology leaves many of us bewildered and baffled. Without naming personal names, let's mention just a sample of the kinds of epistemological theory now in circulation; foundationalism, coherentism, contextualism, reliabilism, evidentialism, explanationism, pragmatism, internalism, externalism, deontologism, naturalism, skepticism. These general positions do not all compete to explain the same epistemological phenomena, and for this we should always be grateful. They do, however, all subsume remarkably diverse species of epistemological theory. For example, reliabilism now comes (...) in many manifestations, including process reliabilism, indicator reliabilism, and virtue reliabilism. Likewise, foundationalism admits of considerable subsidiary variety, including radical foundationalism and modest foundationalism; and coherentism yields subjectivist and objectivist species, among many others. Within internalism, furthermore, we find access internalism, awareness internalism, and a host of additional intriguing species. Not to be outdone, epistemological naturalism, too, offers taxonomic complexity, including for example eliminative, noneliminative, and pragmatic species. (shrink)

Closest‐continuer or best‐candidate accounts of persistence seem deeply unsatisfactory, but it is hard to say why. the standard criticism is that such accounts violate the ‘only a and b’ rule, but this criticism merely highlights a feature of the accounts without explaining why the feature is unacceptable. Another concern is that such accounts violate some principle about the supervenience of persistence facts upon local or intrinsic facts. But, again, we do not seem to have an independent justification for this supervenience (...) claim. Instead, I argue that closest continuer accounts are committed to unexplained correlations between distinct existences, and that this is their fundamental flaw. We can have independent justification for rejecting such correlations, but what the justification is depends upon much broader issues in ontology. There is no one‐size‐fits all objection to closest‐continuer accounts of persistence. (shrink)

Closest-continuer or best-candidate accounts of persistence seem deeply unsatisfactory, but it’s hard to say why. The standard criticism is that such accounts violate the ‘only a and b’ rule, but this criticism merely highlights a feature of the accounts without explaining why the feature is unacceptable. Another concern is that such accounts violate some principle about the supervenience of persistence facts upon local or intrinsic facts. But, again, we do not seem to have an independent justification for this supervenience claim. (...) Instead, I argue that closest continuer accounts are committed to unexplained correlations between distinct existences, and that this is their fundamental flaw. We can have independent justification for rejecting such correlations, but what the justification is depends upon much broader issues in ontology. There is no one-size-fits all objection to closest-continuer accounts of persistence. (shrink)

Tubulin is the ubiquitous protein that makes up the walls of the cytoskeletal elements known as microtubules. These 20 nm diameter cylindrical fibers are the spindle fibers for mitosis, provide the skeletal framework for cellular elongation, constitute the major structural and motile elements of cilia and flagella and probably play a number of other roles in eukaryote cells. In the electron microscope, they are never seen to attach or protrude directly into or on cellular membranes. It was therefore with much (...) skepticism that cell biologists responded to recent claims purporting to show that tubulin is (or can be) a membrane protein. This skepticism comes from a bias based on the generally understood function of cytoskeletal proteins as representing the intracellular ‘bones’ of cells. The traditional thinking was that microtubules may attach to cellular membranes but only via a cross‐linking connecting protein. In recent years, however, an increasing number of workers have come to believe that tubulin can exist as a normal membrane protein possibly independent of its role in microtubule function. (shrink)

This paper considers two among the several points of intersection in the work of Roberto Esposito and Jacques Derrida. First, and most obviously: in the context of conceptualizing community, and more broadly, Esposito and Derrida have elaborated concepts of immunity and auto-immunity to refer to auto-destructive modes of defense which profoundly threaten what – seemingly – ought to have been safeguarded through their mechanism. The second point of proximity is the use both make of figures of maternity and birth in (...) these conceptualizations. This comparison not only illuminates the differing philosophical commitments of Derrida and Esposito but also offers a means of challenging the fate of sexual difference in the work of Esposito. (shrink)

In his work on personal identity, Derek Parfit makes two revolutionary claims: firstly, that personal identity is not what matters in survival; and secondly, that what does matter is relation R. In this article I demonstrate his position here to be inconsistent, with the former claim being defensible only in case the latter is false. Parfit intends his famous fission argument to establish the unimportance of identity – a conclusion disputed by, among others, Mark Johnston. My approach is to (...) critically assess their debate, focusing on Johnston's reductio of Parfit's position. I contend that although Parfit's own response fails, there are other ways to save the fission argument. The unimportance of identity then comes at a cost, however, because the reductio can only be avoided by accepting either that nothing matters in survival, or else that facts about particles and forces do. Either way, relation R cannot be what matters. (shrink)

Abstract: Those who endorse the Psychological Continuity Approach (PCA) to analyzing personal identity need to impose a non-branching constraint to get the intuitively correct result that in the case of fission, one person becomes two. With the help of Brueckner's (2005) discussion, it is shown here that the sort of non-branching clause that allows proponents of PCA to provide sufficient conditions for being the same person actually runs contrary to the very spirit of their theory. The problem is first (...) presented in connection with perdurantist versions of PCA. The difficulty is then shown to apply to endurantist versions as well. -/- . (shrink)

Institutional religious structures are the most damaged in an industrialized society, and in postmodern times, instead of rectifying these harms in religious structures, the individual’s quest for meaning is becoming more and more unstable by various religious groups, new religious movements, or the blows of an aggressively and persistently secularist world. Even instability or the possibility of reduction in their field of power has given institutional religions sufficient reason to intensify their efforts to preserve their normative measurements and to protect (...) their existing allies with an attempt to return to their old glorious days, driven by utopian optimism. However, among these movements which are institutional religions with their normative structures, settled organizations, experiences dating back to ancient times and followers reaching up to billions, pure and non-political religious and energetic groups that claim to meet the expectations of millennium or the phenomenon of deism and atheism claiming secular and superficial answers to individual’s postmodern search of meaning. The question of which one will be victorious in this field of battle has not been able to be answered yet. Probably, it will be the correct analysis of target group, convenience of methods to reach the receiver and the opponents’ relative endurance in this global war in a market, which is liable to the capitalist market conditions to the end to determine the result. It is essential that Islamic societies prepare for a healthy future with their own and objective evaluations in order to survive in this struggle. The study, using literature review and meta-synthesis methods, aims to make inferences about the future of perceptions of religiosity in Islamic societies. (shrink)

One problem that has formed the focus of much recent discussion on personal identity is the Fission Problem. The aim of this paper is to offer a novel solution to this problem.

Jacob Ross argues that the fission cases discussed in the personal identity literature cannot be accommodated without rejecting basic intuitions of everyday ethical thinking. He notes that many philosophers have responded to the challenge of fission ‘by rejecting the metaphysical assumptions on which it rests’. In particular, that many have denied that in fission one ceases to exist. He contends that these denials do not meet the challenge to commonsense ethical thinking. I reject these claims. One of (...) the metaphysical views he considers is the multiple occupancy view of Lewis and Robinson, according to which in fission there are all along two numerically distinct, initially collocated, persons. I claim that Ross has not shown that this view has counterintuitive ethical implications. (shrink)

In this discussion paper, I evaluate some arguments of Mark Johnston's which appear in his articles «Fission and the Facts» and «Reasons and Reductionism» . My primary concern is with his description of fission cases, and his assessment of the implications of such cases for value theory. In particular, Johnston advances the following three claims:Rejecting the intrinsicness of identity is an arbitrary response to the paradox of fission;Fission cases involve indeterminate identity;Contra Parfit, fission cases have (...) no implications for value theory in the actual world.I argue that and are false, and that , if true, is not true for any reason that Johnston gives. (shrink)