Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.

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20th Century Theoreticians

bibliographical excerpts


"The comparative developmental psychologist James Mark Baldwin (1861-1934) was among the few scientists preceding Schmalhausen to appreciate the evolutionary significance of individual differences in adaptability. In fact, Baldwin published a book on the topic--Development and Evolution--in 1902, to which Schmalhausen himself (pp. 197-198) makes a glowing, if fleeting, reference. As was well understood at the time, individual differences (variation) are at the root of the Darwinian theory of evolution. Those individuals that are most adapted leave the most offspring and thus their genotypes shape, circumscibe, and give "direction" to the capabilities of the next generation, and so on, indefinitely. What Baldwin perceived, along witht he comparative psychologist Conway Lloyd Morgan (1852-1936) and the biologist Henry Fairfield Osborn (1857-1935), was that individuals differ in their modifiability or adaptability to changed circumstances, and it is those who can adapt that differentially affect the course of the next generation's adaptability and thus shape the direction of future lineages. Here is the way Baldwin (1902) expressed it: 'The variations which have been utilized for ontogenetic accomadation in the earlier generations, being thus kept in existence, are utilized more widely in the subseqent generations. Congenital variations, on the one hand, are kept alive and made effective by their use for adjustments in the life of the individual; and, on the other hand, (this is the new notion) adaptations become congenital by further progress and refinement of variation in the same lines of function as those which their acquisition by the individual called into play. But there is no need in either case to assume the Lamarckian factor. (p. 98)' " (Gottlieb, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 129)

"How are parallels between ontogeny and phylogeny produced? We have seen that the relations between embryology and evolution can be classified on the basis of two contentions well summarized by Garstang: 'I shall simply assume...(1) that, instead of new characters tending to arise only towards the end of the ontogeny, they may arise at any stage in the ontogenetic sequence; and (2) that, instead of new characters always tending to push their way backwards in the ontogeny, they may extend into adjoining stages in either direction, either backwards from the adult towards the larva and the embryo (tachygenesis) or forwards tothe adult from the embryo and the larva (paedomorphosis).' (1928, p, 62; see also de Beer, 1958, p. 170) Which of these phenomena produces a parallel between ontogeny and phylogeny? Not the first one, for the introduction of an evolutionary novelty at an early or intermediate stage of ontogeny only makes a descendant different from its ancestor. such an introduction produces the deviation of von Baer's law if its effects persist (and increase) throughout ontogeny, or a juvenile adaptation if they do not persist. Since the effects of such novelties vary according to their time of introduction in ontogeny (and since we must know the ontogenies of ancestor and descendant in order to assess them properly), we may say that they "relate" the study of growth and evolution. But, to repeat, they produce no parallel between the stages of ontogeny and phylogeny." (Gould, S.J. (1977) Ontegeny and Phylogeny. Cambridge: Belknap Press. p. 213)

"Recently, Garstang has elaborated this view very skilfully, and has shown that there has been an evolution along the line of fertilized eggs (or zygotes), in consequence of which animals have modified their ontogenies and so changed the shape of the final stage of development, viz. the adult. But a series of adult forms modified in this way is phylogeny, and as phylogeny is the result of ontogeny instead of being its cause. Garstang has thus arrived at the same point of view as Hurst, who wrote: 'I do deny that the phylogeny can so control the ontogeny as to make the latter a record of the former.' An identical point of view has since been expressed by Ekman, Franz, Fuchs, Nauck, Schindewolf, and Shumway. Similarly, Berg allows that ontogeny anticipates phylogeny." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 8)

"In Garstang's scheme, later evolving ontogenies are seen as modifications of earlier occuring ontogenies, as a consequence of changes in the zygote or fertilized germ. Thus, changes in ontogeny are the expression of an altered zygote and that expression is not merely one of terminal addition but represents changes in earlier stages of ontogeny. ... Garstang's mechanism of early ontogenetic modification was embryonic mutation. These mutations, he held, would be subjected continuously to selective tests of their physiological efficiency, and those that passed such tests would survive. In his usual succinct way Garstang stated that "age bears the buffets of the world, but youth regenerates it." This is most reminiscent of Mivart's contention that what survived selection was born fit. Other than "embryonic mutation." arising either from a presumtively changed zygote or a developmental accident of some sort, Garstang cannot give us any further hints of how the ontogenetic changes so critical to evolution originate. But Garstang unflinchingly faces the logical conclusion from his analysis, to the effect that the first metazoan was not produced by a metazoan but by a "genius among Protozoan zygotes." " (Gottlieb, Gilbert (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 93)

[Gottlieb quoting Garstang] " 'Every elaboration of adult form, even of its degree of pliability under environmental influence...was preceded by a corresponding elaboration of zygotic structure, nuclear or cytoplasmic or both, determining, under suitable conditions, the form and character of the ontogenetic changes and their result. Through the whole course of evolution, every adult Metazoan has been the climax of a separate ontogeny or life-cycle, which has always intervened between adult and adult in that succession of forms which Haeckel terms "Phylogenesis." The real Phylogeny of Metazoa has never been direct succession of adult forms, but a succession of ontogenies or life-cycles. (Garstang, 1922, p. 82).' Phylogeny is thus not the cause but the product of a succession of different ontogenies. Consequently, Garstang held that ontogeny does not recapitulate phylogeny: it creates it. In essence, what Garstang did was to put von Baer's nonevolutionary generalizations concerning ontogeny into an evolutionary framework..." (Gottlieb, Gilbert (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 90)

"In light of this historical development, the significance of which cannot be overestimated, it is fascinating that Sewall Wright, in one of his first papers on the subject, found that he needed not only heredity (h2) and what he called the tangible environment (e2) but a developmental factor (d2) to understand the course of coat-color differences in the stocks of guinea pigs he studied for over twenty generations (Wright, 1920). Since despite intensive inbreeding no particular patterns of coat color ever became well fixed -- that is, variations covering almost the entire range from solid color to solid white were continuously found within each inbred line -- Wright was forced to conclude that a dominant-gene factor was lacking with respect to the determination of coat color. It occured to him that there must be irregularities of individual coat-color development not under strict genetic control so he factored in "irregularity of development" to attempt to account for the results of his selective breeding experiment. When he did the calculations, Wright found that in the control (randomly bred) stock coat-color variations were determined 42 percent by heredity and 58 percent by irregularity of development, leaving no variation ascribable to tangible environmental factors (feed, weather, health of dam, etc.) The developmental factor was even stronger in the inbred line, where only 3 percent of the variation was ascribable to differences in heredity (they were almost completely homozygous), 5 percent to tangible environmental differences, and 92 percent to irregularities in individual development. It is most unfortunate that Wright's tripartite scheme did not take hold, as it could have encouraged a way of thinking that would have possibly overcome the inadequacies of the more simple view that the phenotype or phenotypic differences are a consequence of only genetic and tangible environmental causes. The genuine conceptual significance of Wright's need to incorporate developmental considerations into his genetic framework for thinking about heredity became even clearer after the discovery of DNA and the identification of the genic material as DNA. Now, at least is Wright's system, DNA (i.e., the genes) explicitly became part of the total developmental-physiological system for producing an organism, entailing all the internal and external interactions alluded to in the chapter that dicussed the developmental considerations of de Beer.....[what follows is a quote from Wright] 'If, instead of tracing forward from primary gene action ... we consider everything that may affect a particular process at a particular time in development, these fall naturally into four categories: (1) local gene action, (2) the chain of past events in the line of cells in question, (3) correlative influences from adjacent cells and from other parts of the body, and (4) external environmental differences. Since the second and third may be analyzed, step by step, on this fourfold basis, and local gene action must be evoked by products of previous events, the ultimate factors are the array of hereditary entities in the egg and sperm and the succession of external influences." (Wright. 1968, pp. 58-59). (Gottlieb, Gilbert (1992) Individual Development & Evolution. Oxford Univ. Press: New York pp. 115-117)

"The only contributor to the modern synthesis who saw a significant role for the individual ontogenetic development in evolution was the Russian biologist Ivan Ivanovich Schmalhausen. In 1949, an English translation ofhis book appeared in the United States, Factors of Evolution: The Theory of Stabilizing Selection, under the supervision of Theodosius Dobzhansky, himself a Russian expatriate. Dobzhansky, in the forward to Schmalhausen's book, credits the latter with going beyond the synthesis achieved by Dobshansky and the other principle architects of the triumph of neo-Darwinism (Ernst Mayr, Julian Huxley, George Gaylor Simpson, Bernhard Rensch, G. Ledyard Stebbins, Jr.). Dobxhansy writes , "Schmalhausen advances the sythetic treatment of evolution starting from a broad base of comparative embryology, comparative anatomy, and the mechanics of development. It supplies, as it were, an important missing link in the modern view of evolution." Building on the experimental and theoretical work of this foremost teacher, A. N. Severtov, Schmalhausen's essential insight is to see evolution as a process wherein favorable adaptabilities instigated by the environment eventually become genetically assimulated adaptations, in the sense of moving from external dependency to complete internal control. Schmalhausen's idea is that organisms have a tremendous gentic reserve that is only tapped and revealed when the organism encounters a new environment (a change of climate, food, new competitors for resources, etc.). In stark contrast to other contributors to the modern synthesis, Schmauhausen sees that adaptability itself has genetic correlates, whether through mutation or otherwise, so a favored adaptability can immediately become, in a single generation, the subject of natural selection. The long-term operation of natural selection eventually leads to changes in the development control factors that give rise to the feature in question, shifting the locus of control from the external environment to the internal workings of the organism, an outcome now known as the "genetic assimilation of an acquired charcter." Here is the way Schmalhausen (1949, p. 175) introduced his discussion of what he called "elementary dependent reactions and their transformation": "The individual adaptability of the organism creates for it a condition of what may be called flexible stability or lability. This condition enables the organism to survive sudden and considerable variations of the external environment. Also, it can thereby actively migrate from one environment to another and even reorganize its structure. Hence, a knowledge of the development of the organism's system of adaptive reactions is very important in understanding the laws of evolution. Finally, the origin of adaptability is an insufficiently studied aspect of evolutionary theory. (Why? Because) The Lamarckians based their theory upon the premise of an already existing individual adaptability and did not examine its origin while the neo-Darwinians regarded it as unimportant since they assumed that the results of individual adaptability, being nonheritable, have no evolutionary value. (italics added)" (Gottlieb, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 126-7)

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