Advances in multiagent simulation techniques make it possible to study more realistic dynamics of complex systems and allow evolutionary theories to be tested. Here I use simulations to assess the relative importance of reproductive systems (haplodiploidy vs. diploidy), mate selection (assortative mating vs. random mating) and social economics (pay-off matrices of evolutionary games) in the evolutionary dynamics leading to the emergence of social cooperation in the provision of parental care. The simulations confirm that haplo-diploid organisms and organisms mating assortatively have (...) a higher probability for fixing alleles and require less favorable conditions for their fixation, than diploids or organisms mating randomly. The simulations showed that social behavior was most likely to emerge a) when the cost for parental investment was much lower than the benefits to the offspring, b) when cooperation improved synergistically the fitness of offspring compared to the corresponding egoistic behavior and c) when alleles coding for altruistic or social behavior could be rapidly fixed in the population, thanks to mechanisms such as haplo-diploidy and/or assortative mating. Cooperative social behavior always appeared if sociality conferred much higher fitness gains compared to non cooperative alternatives suggesting that the most important factors for the emergence and maintenance of social behavior are those based on energetic or efficiency considerations. The simulations, in congruence with the scant experimental evidence available, suggest that economic considerations rather than genetic ones are critical in explaining the emergence and maintenance of sociality. (shrink)

Sex allocation research has primarily focused on offspring sex‐ratio adjustment by mothers. Yet, fathers also benefit from producing more of the sex with greater fitness returns. Here, we review the state‐of‐the art in the study of male‐driven sex allocation and, counter to the current paradigm, we propose that males can adaptively influence offspring sex ratio through a wide variety of mechanisms. This includes differential production and motility of X‐ versus Y‐bearing sperms in mammals, variation in seminal fluid composition in haplo‐diploid (...) invertebrates, and epigenetic mechanisms in some fish and lizards exhibiting environmental sex determination. Conflicts of interest between mothers and fathers over offspring sex ratios can emerge, although many more studies are needed in this area. While many studies of sex allocation have focused on adaptive explanations with little attention to mechanisms, and vice versa, the integration of these two topics is essential for understanding male‐driven sex allocation. (shrink)

The term ‘breeding system’ is used to describe the morphological and behavioural aspects of the sexual life cycle of a species. The yeast breeding system provides three alternatives that enable hapoids to return to the diploid state that is necessary for meiosis: mating of unrelated haploids (amphimixis), mating between spores from the same tetrad (intratetrad mating, automixis) and mother daughter mating upon mating type switching (haplo‐selfing). The frequency of specific mating events affects the level of heterozygosity present in individuals and (...) the genetic diversity of populations. This review discuses the reproductive strategies of yeasts, in particular S. cerevisiae (Bakers' or budding yeast). Emphasis is put on intratetrad mating, its implication for diversity, and how the particular genome structure could have evolved to ensure the preservation of a high degree of heterozygosity in conjunction with frequent intratetrad matings. I also discuss how the ability of yeast to control the number of spores that are formed accounts for high intratetrad mating rates and for enhanced transmission of genomic variation. I extend the discussion to natural genetic variation and propose that a high level of plasticity is inherent in the yeast breeding system, which may allow variation of the breeding behaviour in accordance with the needs imposed by the environment. BioEssays 28: 696–708, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

The present study aims at understanding how Ethica Nicomachea V.6 relates to its preceding chapters, V.1-5. On the one hand, the interpreter wonders for what purpose Aristotle introduces a topic named ‘the civic just’ (to politikon dikaion) in V.6, since V.1-5 treats extensively of matters of justice in the city. On the other hand, the same text posits that there is a certain ‘just without qualification’ (to haplōs dikaion), which may or may not be the civic just itself; compared to (...) the just without qualification, other forms of just are so by similitude (kath’homoiteta). In attempting to clear the confusion around those two points, the present study proposes the following: (1) the civic just is the just without qualification insofar as it is the primordial form of the just, in which only humans who are cumulatively free, equals and self-sufficient have a share; (2) the description of the civic just recapitulates several aspects of the discussions of justice in V.1-5 – the laws, the kinds of equality, rule, the legal suit - because the civic just encompasses all the forms of just (dikaion) related to the virtues of universal justice (V.1) and partial justice (V.2-5); (3) the expression to politikon dikaion is introduced in V.6 in order to contrast everything treated in V.1-5 with the domestic just, to oikonomikon dikaion, mentioned for the first time in V.6; (4) the forms of the domestic just are just only by similitude with the civic just because justice loses density outside the civic sphere, a situation which can be explained by the shortcomings Aristotle ascribes to women, children and slaves in EN V.6 (lack either of freedom or equality or yet self-sufficiency) as well as in Politica I (varying degrees of defective deliberation and virtue). (shrink)

In lieu of an abstract, here is a brief excerpt of the content:Reviewed by:Aristotelian Explorations by G. E. R. LloydRosamond Kent SpragueG. E. R. Lloyd. Aristotelian Explorations. Cambridge: Cambridge University Press, 1996. Pp. ix + 242. Cloth, $49.95.Although the essays in this richly rewarding book were given as lectures and seminars in a variety of places over a period of eight years, they possess a unity of theme that welds them into a satisfying whole. Furthermore, by the judicious use of (...) postscripts and additional notes, the author keeps us abreast of current discussion. [End Page 126]Lloyd’s chief concern is to compare Aristotle’s theory (notably as expressed in the Posterior Analytics) with his practice (especially in the zoology). The topic may be, as he admits in his 1990 Boston Colloquium lecture, “The Theories and Practices of Demonstration,” a “hoary old chestnut,” but his response to it is not; as is evident from the very title of his paper, he adopts a pluralistic approach to Aristotle’s methodology. Lloyd’s minute and extensive knowledge of the texts, as when he studies passages in the Topics in which what is there called apodeixis does not meet the conditions laid down in Posterior Analytics, makes his view compelling. Again, a careful study of Parts of Animals I, 1 issues in the caveat that “we had better be careful when talking about demonstration in the physical treatises, to examine what mode or manner of demonstration is in question” (33); it could be the method of deduction of antecedents, for instance, where we start with what will be rather than what is. In general, it needs to be considered not just whether a particular theory of demonstration is applied, but whether it is applicable.In a chapter entitled “The Relationship of Psychology to Zoology,” Lloyd discusses Aristotle’s theory of matter, particularly “the problem of reconciling what is true of earth, water, air, and fire haplōs... and what is true of them as the constituent elements of living uniform parts” (64). This difficulty has its repercussions for his form/matter distinction: the difference between the two is best illustrated by artefacts (as, I might add, is evident to those who attempt to teach it), but the unity of the sonolon by the cases in which the soul is form and the matter a living body of which the soul is the actuality.In this connection Lloyd makes reference to Aristotle’s “top-down theory of life” as being one quite definitely held by him (64, 99). I think that this is only partially the case. A passage such as De Anima 415a25ff. in which not only animals but plants are said, through reproduction, to aim at the eternal and divine, suggests that a “bottom-up” theory of life is equally important in his psychology, especially in view of his pervasive desire to stress the final cause. I think that Lloyd’s own principle of plurality in relation to context could well be applied here. The overall structure of the De Anima illustrates Aristotle’s use of both methods: bottom-up from nutrition through sensation to thought, but top-down from sight to touch. It is, of course, true that the De Anima is not concerned to address the question of how life emerges from not-life, but its discussion of living things quite definitely begins at the bottom of the scala naturae, with plants. Again, at History of Animals 588b4ff. (a passage crucial to Lloyd’s consideration of borderline cases in his chapter entitled “Fuzzy Natures?”), we find that Nature proceeds from the inanimate to the animate, and that first after the inanimate come plants. It also strikes me as being of interest that, when Aristotle discusses the difficult topic of growth in Generation and Corruption 321b16ff., he does so at the level of flesh and not of hands, from the bottom up, that is.Of other topics on which Lloyd has things to say, that of spontaneous generation is of particular interest. Here he points out that spontaneously generated creatures are of regular kinds; they have determinate material causes. As to whether Aristotle’s recognition of such cases has driven him “into admitting a principle that offers a glaring... (shrink)

In Aristotle's views on cognition a series of terms – hupolêpsis, doxa, and epistêmê – play key roles. But it has not been noticed that each of these comes in two kinds – one unqualified and the other qualified. When these and their interrelations are properly explored, a deeply systematic picture of cognition emerges, in which doxa is best understood as ‘belief’, hupolêpsis as ‘supposition’, and epistêmê as a sort of belief, so that – contrary to orthodoxy – we can (...) have belief and knowledge of the same things at the same time. Many of these conclusions are shown to mark a continuity with Plato, in that neither thinker, it is argued, holds a so-called ‘two-worlds’ picture of cognition. (shrink)