Theoretical Biology Forum最新文献

The 'provisional hypothesis' of pangenesis seems to be associated with a reduction of the role of geographical isolation as a factor of speciation or novelty in Darwinian thinking. On the one hand, this fact draws the attention on the interacting processes concerning the internal dynamics of organisms' development together with their effects on evolution and, on the other, the defense of the gradual action of natural selection in changing living forms. Nevertheless, these ways reveal an intimate contrast which brings to a missed synthesis. Our purpose is to show how the pangenesis could be the compromise between environment's action and the constitution of specific adaptive traits, without resorting to the idea of environment as something which gives instructions or to the idea of the organism as a vehicle. To this purpose it seems interesting to start from the speciation's problem and the origin of adaptive traits at the heart of Wagner-Darwin debate.

Fractal analysis has proven to be a useful tool in analysis of various phenomena in numerous naturel sciences including biology and medicine. It has been widely used in quantitative morphologic studies mainly in calculating the fractal dimension of objects. The fractal dimension describes an object's complexity: it is higher if the object is more complex, that is, its border more rugged, its linear structure more winding, or its space more filled. We use a manual version of Richardson's (ruler-based) method and a most popular computer-based box-counting method applying to the problem of measuring the fractal dimension of dendritic arborization in neurons. We also compare how these methods work with skeletonized vs. unskeletonized binary images. We show that for dendrite arborization, the mean box dimension of unskeletonized images is significantly larger than that of skeletonized images. We also show that the box-counting method is sensitive to an object's orientation, whereas the ruler-based dimension is unaffected by skeletonizing and orientation. We show that the mean fractal dimension measured using the ruler-based method is significantly smaller than that measured using the box-counting method. Whereas the box-counting method requires defined usage that limits its utility for analyzing dendritic arborization, the ruler-based method based on Richardson's model presented here can be used more liberally. Although this method is rather tedious to use manually, an accessible computer-based implementation for the neuroscientist has not yet been made available.

In this paper we now focus on critically examining the theoretical and methodological conceptual foundations in the particular field of science of the living, namely the philosophy of biology. The latter seems to draw attention to two disparate disciplines in methods and scope of interest. On the one hand there seems to be a point of view that considers the cognitive phenomenon in question in a way so as to say "abstract", i.e. as something that seeks to determine the nature or essence, to use a term dear to many philosophers. On the other hand, there is a point of view that considers these phenomena in the actual place, the result of a process caused by the cognitive system of the subject, if the latter, of course, does not mean that they are human beings. We will argue that the two approaches do not represent two distinct planes of research: in fact philosophy takes on a main task, namely helping to lay the foundations for a philosophy of nature capable of meeting first a completeness, that is, to describe and explain what is special in all the different layers of the different natural systems.

Modularity in biological systems is a central theme in current research. However, there are some problems related to the vague definitions of the concept of a module that impede both its empirical application and the comparison of data from different studies. In this article, we propose to characterize this concept which is consistent with the diverse ways in which it is conceptualized in the specialist literature. We test our characterization by analyzing the case study of the craniofacial complex. We conclude that the proposed delimitation allows a better understanding of modules since it differentiates between the concept of the module as a state (morphofunctional modules) and as a process (a product of ontogenetic or phylogenetic history).

In this paper we discuss a proposal on the essential structural aspects of Darwinian Evolution Theory. Using this point of view we apply a mathematical ago-antagonist theory inspired by Y. Cherruault's (1998) ideas, which we have extended. In the ago-antagonist model, the phenotype characters measure the individual propensity to perform an innovative x(t) (agonist) or conservative y(t) (antagonist) action with respect to mutation and to speciation process. We have mathematically introduced the conflict concept and we present a model that takes into account the environmental effects by means of a stochastic multiplicative process. We shortly discuss the properties of the related stochastic differential equations.

Using classical or traditional plant growth regulators, calli or plant tumors have been produced in vitro and subsequently have been induced to produce buds and plantlets, a process referred to as regeneration. For many years, this has been a successful procedure for in vitro, plant propagation. However, for a number of plant species investigators could not induce calli in vitro to produce buds. Organogenesis was still recalcitrant for various plants in 1980. New types or nonconventional growth regulators, such as methylglyoxal and ascorbic acid, were then found to overcome recalcitrant organogenesis in vitro. Their successful or effective use gave support to a theory that stressful, non-uniform cohesive force-fields, electromagnetic in nature, occurring through the application of certain chemicals, are necessary for in vitro morphogenesis from plant neoplasm or callus. Morphogenesis is seen as an adaptive accommodation to the inner stresses from such non-uniform, cohesive forces. Diverse chemicals, not considered traditional plant growth regulators would, it has been conjectured, enable the generation of such cohesive forces, in non-uniform arrays, and it has been predicted that more chemicals of this type will be discovered. A new constructive approach to agriculture and medicine, using a new plant tissue-culture model, based on new theory, has also been predicted.

We have investigated the microvascular pattern in acquired or genetic diseases in humans. The lower gingival and vestibular oral mucosa, as well as the optic nerve head, was chosen to characterize the vascular pattern complexity due to the simple accessibility and visibility Local fractal dimensions, fractal dimension of the minimum path and Lempel-Ziv complexity have been used as operational numerical tools to characterize the microvascular networks. In the normal healthy subjects microvascular networks show nonlinear values corresponding to the complexity of a diffusion limited aggregation (DLA) model, while in several acquired or genetic diseases they are approaching the ones of an invasion percolation model.