. Lamarck and Darwin agreed on the inconstancy of species and on the exclusive gradualism of evolution. Darwinism, revived as neo-Darwinism, was almost generally accepted from about 1930 till 1960. In the sixties the evolutionary importance of selection has been called in question by the neutralists. The traditional conception of the gene is disarranged by recent molecular-biological findings. Owing to the increasing confusion about the concept of genotype, this concept is reconsidered. The idea of the genotype as a cluster of (...) genes is replaced by a cybernetical interpretation of the genotype. As nature does jump, exclusive gradualism is dismissed. Saltatory evolution is a natural phenomenon, provoked by a sudden collapse of the thresholds which resist against evolution. The fossil record and the taxonomic system call for a macromutational interpretation. As Lamarck and Darwin overlooked the resistance of evolutionary thresholds, an alternative evolution model is needed, the first to be constructed on a palaeontological and taxonomic basis. (shrink)

La parution récente en français du livre de M. Denton : “Evolution. Une théorie en crise” , qui traite des theories explicatives actuelles de l'évolution, nous amine à rappeler les caracteres généraux des grandes theories biologiques et à présenter une critique sommaire du livre en question.La science West pas une simple accumulation de connaissances. Le scientifique ne doit pas se contenter de decrire et de mesurer des faits. Son but eat d'essayer de les relier et de construire des théories qui (...) tentent de nous faire comprendre le “reel”, objet de ses recherches.Cependant, la nature du matériel biologique — c'est-à-dire les espèces vivantes et les catégories qu'on y a reconnues, classe ou ordre par exemple — est si complexe qua la biologie actuelle est fort loin encore Wavoir réalisé une synthèse qui ressemble, méme très approximativement, à la classification de Mendéleiev pour les éléments chimiques.Malgré cette complexité, les biologques ont réussi à construire la th6orie du fait de l'evolution et ils proposent aujourd'hui une théorie explicative de cette évolution qui, bien qua critiquée, est incontestablement bien étayee. Nous allons essayer de définir la structure des grandes théories biologiques; ensuite nous analyserons sommairement quelques-unes des critiques qui sont adressees aux theories de l'évolution.Considering the publication in French version of Michael Denton's book, Evolution : A Theory in crisis , in which he critizes the synthetical theory of the biological evolution, we thought it useful to point out the main errors of argumentation contained in that book by first referring to the characteristics of general biological theories.In biology, there exist elementary theories - such as that dealing with the extinction of giant Reptiles - and general theories - such as the chromosomic theory of heredity and the explanatory theory of evolution. The latter generally consist of a group of elementary theories imbricated so that they form a whole like a jig-saw puzzle. An example is provided by the synthetic theory of evolution that can be defined in 20 propositions divided into two categories : the propositions relating to the naturalists' observations - which correspond to descriptive concepts - and those relating to the data of the population genetics - which correspond to explanatory concepts . The general scheme of the theory is formed by a network of relations between the descriptive concepts and the explanatory concepts. There also exist other theories in general biology supported by thousands of minor facts which only together can be of proof of validity. These theories are quite reliable and cannot be questioned by facts still to be explained. Questioning can only happen if they are confronted to well-established data in nearly equal numbers.In his work, Denton does not deny the phenomenon of biological evolution, but he criticizes the syntheticians' ideas by emphasizing that no great evolutive changes can be accounted for by the complex mechanism of random mutations and selection. He goes back to a typological concept of the zoological classification in some way similar to that of Vialleton's. However, Denton agrees with the phenomenon of the biological evolution and accepts the existence of "saltations" among the great zoological groups. The arguments used by Denton merely show that he is not conversant with the complexity of sciences particularly in comparative anatomy and zoology, the teaching of which is being somehow neglected today.By giving as an example the structure of the aortic arches in Amphibians and by a summary of the variations of those structures and the evolution of the blood-circulation in Vertebrates, we proved that the typological argument is of no value. As a matter of fact, a study of the now living beings clearly shows the gradual transition - e.g. a transition by a very large number of feasible stages - from the Lower Vertebrates to the Higher Vertebrates. In particular, there have been several attempts at double circulation and there still exist many species in which the blood of the double circulation is mixed. It seems therefore obvious that the double circulation has been achieved, stage by stage, with many intermediate schemes; we are inclined, therefore, to conclude that this succession of small transformations was produced by a huge mechanism of selected small mutations.Our present-day biological knowledge includes a number of examples large enough to consider the “argument of the impossible” used by Denton is due to inadequate fossil data and not to any mysterious mechanism such as macromutations. Let us say again that the typological structures seem to occur only when the data of comparative anatomy and zoology are over-simplified. (shrink)

It is useful to envision two fundamentally different ways by which the timing of plant development is regulated: developmental stage‐transition mechanisms and time‐to‐flowering mechanisms. The existence of both mechanisms is indicated by the behavior of various mutants. Shoot stage transitions are defined by dominant mutants representing at least four different genes; each mutant retards transitions from juvenile shoot stages to more adult shoot stages. In addition, dominant leaf stage‐transition mutants in at least seven different genes have similar phenotypes, but the (...) leaf rather than the shoot is the. focus (and at least two of these genes encode domain proteins.) One mutant, Hairy sheath frayed 1‐0 (Hsf1‐O) simultaneously affects shoot and leaf; this mutant's behavior initiated our interest in plant heterochronism(1). The second type of timekeeping involves time‐to‐flowering. As with most plant but not animals species, cultivars of the maize species vary greatly for the time‐to‐flowering quantitative trait: between 6 and 14 weeks is common. It is via the 'slipping time frames' interaction that takes place between stage‐transition mutants and time‐to‐flowering genetic back‐grounds that unexpected and radical phenotypes occur. We see a reservoir of previously unsuspected morphological possibilities among the few heterochronic genotypes we have constructed, possibilities that may mimic the sort of variation needed to fuel macroevolution without having to posit (as done by Goldschmidt(2)) any special macromutational mechanisms. (shrink)

In this commentary on Berwick and Chomsky's “Why Only Us,” I discuss three key points. I first offer a brief critique of their scholarship, notably their often unjustified dismissal of previous thinking about language evolution. But my main focus concerns two arguments central to the book's thesis: the irrelevance of externalization to language evolution and the discontinuity between human conceptual representations and those of other animals. I argue against both stances, using cognitive data from nonhuman species to show that externalization (...) is not irrelevant to understanding the biology of language, and that many human conceptual structures have clear animal homologs. (shrink)