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.

twitter / andrewL9

Environmental Influences

bibliographical excerpts


"In arguing that a single ancestral form might diverge into a number of "species," Buffon came close to the modern concept of evolution. His recognition that migration to different parts of the world might cause the divergence also marks a pioneering effort in the study of geographical distribution as a clue to the history of life. But his idea that the environment acts directly on the organism through organic particles is a long way from the theory of natural selection. There is also the question of the origin of ancestral forms from which members of each family have diverged. In the modern theory, these too must have evolved from some even more basic form, whereas Buffon insisted that the character of each family is permanently fixed by its internal mold. Yet families must have had a starting point in time, because Buffon believed that the earth at first would have been too hot to support life. His alternative to evolution on a large scale was, in fact, spontaneous generation (Wilkie, 1956; Roger, 1963; Bowler, 1973).(Bowler PJ (1984) Evolution, The HIstory of an Idea. Univ of California Press: Berkeley p. 71)

[Corsi quoting Lamarck's Discours d'ouverture prononce' le 21 floreal an 8, 1801 p. 13]"As for the circumstances that [nature] required and still uses every day to vary its productions, one can say that they are in certain sense inexhaustible. The main [circumstances] derive from the effects of climates, from temperature variations in the atmosphere and in all surrounding environments [milieux], from the diversity of places, from that of habits and actions, reproduction, etc. etc. Now, as a result of these various influences, properties develop and strengthen the use, and diversify under the effect of new, long-preserved habits. And, imperceptibly, the configuration and consistency -- in a word, the nature and state -- of parts as well as organs, share in the succession of all these influences, and are preserved and propagated by generation." (Corsi, Pietro (1988) The Age of Lamarck. Univ. of California Press: Berkeley p. 93)

"In the present context, Mivart is of particular interest because he appears to be the first systematic thinker to make individual ontogentic development central to his view of the basis for evolutionary change. Like most writers who followed him in this vein, Mivart stressed the definite or constrained nature of individual variation, so that such variations were neither random nor indefinite, as they were in Darwin's version. ... Mivart is not interested in the complete overthrow of natural selection but merely wishes to demote it to the subordinate context of operating along with many other known and unknown causes or influences, which he explicitly labels as "obscure and mysterious." He views for an internal natural law that causes organisms to change rapidly and harmoniously: "the efficient presence of an unknown internal natural law or laws conditioning the evolution of new species forms from preceding ones, modified by the action of surrounding conditions, by 'Natural Selection' and by other controlling influencs" (p. 45). So Mivart, like Thomas Huxley before him, believes in evolution as a fact without believing in natural selection as its main or most formidable agency. ... As stated previously, Mivart differs from Darwin in his (Mivart's) stress on the internally constrained variation of each species. He also differs with Darwin in the way he sees changes in the environment operating. With his eye always on the individual, especially the environing conditions of individual development, Mivart sees severe changes in the environment as bringing out new phenotypes or variations as a consequence of an alteration in the conditions of development: this is the developing organism's direct response to altered conditions of the developmental medium. Thus, Mivart takesDarwin's enormous catalogue of changes in plants and animals under domestication as an occasion to point out that the enormous change in environing conditions brings out new variations on which selection can now operate-- Mivert's point throughout his book being that natural selection works on "what was born fit." Mivarts also takes pains to point out that such changes are not infinite and are stricktly limited by unknown internal factors." Gottlieb, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 40-42)

"He [de Beer] further emphasizes the distinction between the process of transmission of the internal factors from parent to offspring, and the process of production in the offspring of characters similar to those which were possessed by the parent. He cites E. S. Goodrich (1924), who said, "An organism is moulded as the result of the interaction between the conditions of stimuli which make up its environment and the factors of inheritance. No single part is completely acquired, or due to inheritance alone. Characters are due to responses, and have to be made anew at every generation." De Beer's point is that the question, Are acquired characters inherited? has no meaning, for all characters of an organism are both inherited and acquired; "they would not be developed at all unless the organism possessed the requisite internal and inherited factors, and unless the external factors were sufficiently 'normal' to evoke the 'normal' developmental responses. A change in either the internal or the external factors will result in a departure from normal development." (Gottlieb, Gilbert (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 96)

"Even if it is true that a male-related factor modulates intrauterine growth of certain cortical regions, it is obvious that cortical development will be susceptible to many other influences, some closely related to the hormonal effects, some more remote. Ward and Weisz (1980) showed that if a female rat is stressed during the course of pregnancy, the male offspring show demasculinization. After the stress there is a rapid rise of testosterone in male fetuses, followed by a fall to subnormal levels. It is not clear exactly how stress on the mother leads to this sequence of changes. It is interesting to note that the female offspring of such a stressed mother will also tend to have demasculinized male offspring, even though these famales are not themselves stressed in pregnancy. Phenobarbital administered during pregnancy has similar effects, and the male offspring have permanently low testosterone levels.This is an example of a phenomenon already mentioned, whereby chemical effects on the fetus may produce permanent alterations in metabolism. When present in the female they can lead to a mechanism of nongenetic transmission to the following generation. Sherman et al. (1980) have also demonstrated an environmental effect on lateralization. In studies carried out some years earlier it had been shown that brief periods of handling of newborn rats exerted permanent effects on emotionality and on other traits such as resistance to infection. In the more recent experiments it was shown that male rats who had been handled showed a greater right hemisphere lateralization in tests of emotionality and spatial performance than animals who had not been." (Geschwind & Galaburda (1987) Cerebral Lateralizaton. p. 115)

"In the light of modern genetics, it is presently considered that IAC is practically an impossibility. In metazoans, the germline and the genetic material are supposed to be isolated form perturbations coming from the environment. Thus, ontogentic changes may not effect heredity. This assumption seems correct for metazoans, in whom the majority of phenotypic traits is indirectly inherited. However, as already mentioned, inheritance of acquired characteristics becomes more plausible in cases in which direct inheritance makes a significant portion of the phenotype, as in cell division. If, for example, a cytoskeletal feature is modified during a cell's ontogeny, this is likely to be inherited by descendants. This point was referred to as the transgenerational dimension of modifications to directly inherited characters." (Aboitiz, F. (1992) Mechanisms of adaptive evolution. Darwinism and Lamarkism restated. Medical Hypothesis 38(3): pp. 196)

"Environmental factors can be an important source of nongenetic influences on laterality. Since the effect of a gene is to play a role in some form of chemical reaction, it is not surprising that genetic determination is not absolute. Every chemical reaction can be modified by alterations in pressure, temperature, pH, light, the presence of other substances, the availability of chemical precursors, and the rate at which products are removed. With growing sophistication of molecular genetics, it has become increasingly clear that nongenetic effects can play a powerful role; methylation, for example, has been shown to suppress expression of many genes. We will now consider some of the random effects that might modify lateralization. One implication of our hypothesis is that even if the genetic endowment of any particular fetus were known precisely, it would not be possible to make predictions concerning the distribution in a population basis. One of the reasons for this relative freedom from genetic determination is that if hormones do play a role in determining laterality, then the effects of testosterone or related substances on the developing brain will be modified by factors not under the control of the fetal genes. Androgens are produced not only by fetal testes and the placenta but also by the maternal ovaries, adrenals, and nonglandular tissues. The fetus can be influenced by the actions of many of the unshared maternal genes. It is reasonable to expect that if a fertilized ovum were transplanted into the uterus of an unrelated female, the final pattern of the brain would be quite different, because the brain would develop in an environment of hormones and other substances that would certainly differ in many respects. It might therefore be reasonable to take a different approach than usual to the genetics of many condiditons. One should perhaps consider, not the genes carried by the offspring alone, but rather the genes of that organism existing or active only for the nine months of pregnancy; in other words, one should consider the mother and the fetus as a unit. This unit contains three groups of different genes: one paternal set present in the fetus, one maternal set present in the mother, and another maternal set present both in the mother and in the fetus. The situation is even more complex when dizygotic twins are involved, since the maternal-fetal unit will contain another group of paternal genes. (Geschwind & Galaburda 1987: 133-134, Cerebral Lateralization)

"The flounder had both eyes on one side of its head. In some individuals the eyes are on the right; in others they are on the left. The distribution on the two sides varies in the different species that occupy particular geographic niches. Cross-breeding experiments between species have been carried out, with findings that do not fit readily into any standard nuclear genetic model (Policansky 1982). It is possible that variations in the distribution to asymmetry may be determined to a great extent by differing environmental conditions, such as water temperature or food supply. This possibility gains credence form the fact that sex ratio of the offspring of certain species shifts sharply from female predominant to male predominant depending on temperature or food supply. (Clutton-Brock 1982); Harvey and Slatkin 1982). In several species the sex ratio can vary considerably depending on the hormonal conditions of pregnancy. James (1980a,b) has suggested that this may be true even in humans. It is thus also conceivable that there is a genetic bias toward one form of laterality, which is modified by environmental conditions that alter hormonal milieu or the time of fertilization." (Geschwind & Galaburda 1987: 128-9, Cerebral Lateralization)

"A disproportionate number of parents, both fathers and mothers, of austistic children are reported to have had contact with chemicals." (Geschwind, N. & Galaburda, A.M. (1985) Cerebral Lateralization. Biological mechanisms, associations, and pathology: II. A hypothesis and a progam for research. Archives of Neurology 42(6): pp. 532)

"Another example is much more common, but less acknowledged. It is the case of cell differentiation in embryonic development. Once a cell differentiates by responding to an environmental factor (i.e. an inductor substance), it usually passes its characteristics to descendants. (Alberts et. al. 1989, Blau, 1989). Again, after the acquisition of the differentiated character, there is hereditary transmission of it." (Aboitiz, F. (1992) Mechanisms of adaptive evolution. Darwinism and Lamarkism restated. Medical Hypothesis 38(3): pp. 196) evidence of the uterine effect

"A corollary of our hypothesis is that hormonal effects on the brains of offspring may vary with the time of conception. The activity of the pineal gland changes seasonally with alterations in day length. As a general rule, during the dark winter months the pineal becomes active and suppresses both ovaries and testes, whereas in the summer it is inactive and sex hormone levels are higher. For this reason many animals bear young in the spring, an advantageous situation since temperature and food supplies are more suitable for survival. An example of such seasonal modulation of hormonal effects on the brain is observed in the HVc nucleus of the singing bird (Nottebohm 1981). This description of pineal physiology is, however, somewhat oversimplified. An animal's sensitivity to light may vary through the year. Gonadal hormones may thus become activated in the spring, but as a result of loss of sensitivity to light over the summer hormone levels may diminish as fall approaches. Despite these facts, day length is a powerful influence. Thus, steers increase their weight more rapidly in the winter when artificial light is supplied to lengthen the day. This light-enhanced growth of muscle mass does not take place if the bull is castrated, suggesting that the effect of light is mediated through a rise in testosterone effect (Tucker and Ringer 1982).....If pineal effects on sex hormone levels are important, then the birth months of lefthanders, and of those with learning disorders, might not be uniform throughout the year, since fetuses conceived at different seasons might be subjected to very different hormonal environments. These effects should differ in the Northern and Southern Hemispheres and at the equator, although other factors, such as variations in the ethnic composition of populations, would also have to be considered. Data are still very sparse. Badian (1983) found that in males born in each of the six months beginning in September, the rate of nonrighthandedness was higher than that found in any of the other six months, but no clear trend was observed for female births." (Geschwind & Galaburda 1987: 116-7, Cerebral Lateralization)

"One of the greatest recent incentives to the re-examination of the question of the inheritance of acquired characteristics was the somatic selection hypothesis of Steele (1979). Basicly the theory is 'somatic-Darwinism' and is founded on the combination of two hypotheses: Burnet's (1959) clonal selection theory of immunity, and Temin's (1971; 1976) proto- and pro- virus hypothesis. It is known that mutant somatic information can confer on a stem cell an altered phenotype such that under the appropriate conditions this cell will be preferentially selected until it may dominate the whole somatic compartment. Under conventional Darwinian hypotheses this mutant somatic information is of no consequence, except in as much as it confers fitness on the individual. However, Steele (1979) invoked Temin's proto-virus hypothesis -- which suggests that RNA tumour viruses are pathological offspring of naturally-occurring endogenous retroviruses involved in inter-cellular communications -- and proposed that endogenous retroviruses targeted to the germline may act as vectors for the mutant somatic information by capturing RNA's from the somatic cells and transducing them to the germline. Once inthe germline, the passenger RNA may be copied by the virally encoded reverse transcriptase (RNA - dependent DNA-polymerase) into DNA which is able to align with the parent gene and to replace it (or segments of its) by recombination. Biologically, this hypothesis is best illustrated in the immune system. The lymphoid compartment contains progenitor lymphocytes displaying a vast array of antigenic specificities in part encoded by the germline genes and in part arising by somatic mutation (Cohn et al., 1981). When an antigen interacts with a precursor cel that particular clone is stimulated to proliferate, such that in cases of chronic antigen exposure it can dominate the whole lymphoid system (Burnett, 1959). Thus, once the clone is selected by virtue of its unique antigenic specificity, it may constitute a substantial percentage of the somatic compartment. Under there circumstances, Steele (1979) suggested that this information would be captured from the lymphocyte cytoplasm as mRNA, by retroviruses during their muturation and packaging and transduced to the germline. Once in the germline the retroviruses would infect either the germ cells or be carried in the seminal fluid and infect the fertilized embryo, with the resultant introduction of the somatic information into the germline by reverse transcription of the mRNA molecules into DNA. The progeny, therefore, would develop with a biased immune repertoire encoded in their germline genes." Pollard JW (1984) Is Weismann’s Barrier Absolute? in Beyond Neo-Darwinism. Hoo M, Sauders PT (eds.) Academic Press: London pp. 292-293)

"The hypothesis states that new adaptive processes begin within the somatic cell populations of individual organisms. Environmental stimuli select and order genetic mutations occurring by chance in somatic cells of a given tissue or organ; if the selection stimulus is intense and chronic, there is an increased probability that these new "adaptive" genes are captured by the appropriate endogenous viral vector and integrated back into their homologous Medelian loci in the germline DNA of that individual. In this way, the organism both adapts to its own environment and anticipates, to some extent, the future environment of its offspring: allowing them to adapt instictively, if this selection process continues. The synthesis of this hypothesis is achieved by fusing two widely acknowledged theories, both of which enjoy considerable experimental support: (1) the clonal selection and somatic mutation theory of antibody production and (2) the proto-virus and provirus hypothesis of the endogenous RNA tumor viruses." (Steele, E. J. (1979) Somatic Selection and Adative Evolution. Chicago: Chicago University Press. pp. 60)

"Further work showed that for most genes, corrections would be made---splicing out the nonsense---after an RNA copy is made of a DNA gene. Even with "interrupted" DNA, an edited and corrected message in RNA could be used by the cell's machinery to make the correct protein. Even more surprisingly, for antibody genes the DNA itself can also be spliced. In other words, DNA that is inherited can be altered. Amazing!" (Behe 1996: 127, Darwin's Black Box.)

"... development and evolution are formally and materially connected. Organisms develop in accordance partly with the assimilated experiences of their forebears and partly with their own experiences. Development evolves through the internalization of new enviroments. The material link between organism and environment, and development and evolution alike is the hereditary apparatus which realistically includes both cytoplasm and nuclear genes. The cytoplasm registers the somatic imprint of experienced environments which can be transmitted to the next generation independently of the nuclear genes. At the same time, it acts as a true communication channel between the nuclear genome inthe coordination of development and evolutionary processes." Mae-Wan Ho (1984) Environment and Heredity in Development and Evolution in Beyond Neo-Darwinism. Hoo M, Sauders PT (eds.) Academic Press: London pp. 284-5)

" 'As I have already pointed out, there is an interesting problem concerning the possible interaction between the chromatin of the cells and the protoplasm during development. The visible differentiation of the embryonic cells takes place in the protoplasm. The most common genetic assumption is that the genes remain the same throughout this time. It is, however, conceivable that the genes also are building up more and more, or are changing in some way, as development procedes in response to that part of the protoplasm in which they come to lie, and that these changes have a reciprocal influence on the protoplasm. It may be objected that this view is incompatible with the evidence that by changing the location of cells, as in grafting experiments and in regeneration, the cells may come to differentiate in another direction. But the objection is not so serious as it may appear if the basic constitution of the gene remains always the same, the postulated additions or changes in the genes being of the same order as those that take place in the protoplasm. If the latter can change its differentiation in a new environment without losing its fundamental properties, why may not the genes also? This question is clearly beyond the range of present evidence, but as a possibility it need not be rejected. The answer, for or against such an assumption, will have to wait until evidence can be obtained from experimental investigation. (Morgan, 1934, p. 234)' What Morgan is proposing here, in the final paragraph of his 1934 book, is that the integration of genetics with development could be achieved only when the gene is activly incorporated into the developmental process and that its activity is seen as reciprocally altered thereby (i.e., not only feedforward effects {gene [arrow right] protein} but feedback effects as well {gene [arrow left] protein}). To those who viewed (and view) the integrity of the gene as absolutely constant, operating essentially outside the reciprocally interactive developmental system, the notion that "genes are changing in some way" was, and is, indeed a radical suggestion. But if there is to be a truly developmental genetics, genes will have to be viewed in some sense as Morgan suggested (and as the geneticist Sewall Wright suggested) and thus become part of the entire system of mutual interactions that is the hallmark of embryological analysis and that characterizes the epigenetic development of the individual." (Gottlieb, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 138-9)

"Although we do not know what actually causes cells to differentiate appropriately according to their surround, we do now that is is the cell's interaction with its surround, including other cells in that same area, that causes the cell to differentiate appropriately. The actual role of genes (DNA) is not to produce an arm of a leg or fingers, but to produce protein (through the coactions inherent in the formula DNA [both ways] RNA [both ways] protein). The protein produced by the DNA - RNA - cytoplasm coaction then differentiates according to coactions with other cells in its surround. Thus, differentiation occurs according to coactions above the level of DNA - RNA coaction (i.e., at the supragenetic level). The DNA - RNA coaction produces protein and that protein subsequently differentiates according to where it finds itself in the three-dimensional space of the embryo (the anterior-posterior, lateral, and dorsal-ventral spatial dimensions), plus the temporal dimension alluded to earlier. Thus it is the coactions during each phase of embryonic development that somehow, by means not yet understood, eventually produce a mature organism." (Gottlieb G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 165)

"The term mnemogenesis is employed by Professor Hyatt [Proceeds. Boston Soc. Nat. History, 1893, p. 73] to characterize the manner in which kinetogenesis is supposed to produce results in inheritance. I have suggested that the phenomena of recapitulation, characteristic of ontogeny (American Naturalist, Dec., 1889), are due to the presence of a record in the germ cells, having a molecular basis similar to that of memory. This view is adopted by Professor Hyatt. I have already referred to it in the proceding pages. A general statement of this doctrine was made by Mr. Sedgwick in The British and Foreign Medico-Chirurgical Review for July 1863 in the following language: 'For atavism in disease appears to be but an instance of memory in reproduction, as imitation is expressed in direct descent; and in the same way that memory never, as it were, dies out, but in some state always exists, so the previous existence of some peculiarity in organizaton may likewise be regarded as never absolutely lost in suceeding generations, except by extinction of race.' " (Cope, CD (1896) Organic Evolution. Open Court Publishing: London p 492)

"A simple counter-example comes from the work of Sonneborn (1970) and others on the ciliate protozoa, in which specific patterns of cortical morphology such as reversed orientation of cilia in a kinety (row) or presence of a second mouth is inherited by a mechanism that is independent of the genotype. Thus the specific causes of morphology in these organisms certainly do not come solely form the genes, and other biochemical mechanisms, involving nucleation centres in the cortex, have been proposed as proximal causes of cortical morphology. The point that emerges here is that perfectly respectable and comprehensible forces affecting the assembly of proteins can be embodies in cytoplasmic organization; and, in the case of ciliate protozoa, these can be inherited by virtue of the self-organizing nature of the cell cortex. Of course gene products are involved in this process, for without the snythesis of cortical proteins there could be no reproduction at all. But the causal relationship between cortical proteins and morphology is not direct. Furthermore, species with very different cortical structure can have practically identical proteins, while species withalmost identical morphology can differ greatly in their cortical proteins. There and related questions are addressed in an extremely illuminating paper by Frankel (1983). From these considerations, we see that neither genes nor cytoplasm define sufficient conditions for the specific morphology which is generated in protozoa; both must be considered as souces of information constraint on biological form, so that reproduction in this large category of organisms does not conform to Weismann's scheme of Fig. 9-1, nor to any of its subsequent modifications. Hence on these ground alone, this theory cannot be used as a general description of generation (reproduction) in organisms." (Goodwin BC (1984) A Relational or Field Theory of Reproduction and its Evolutionary Implications in Beyond Neo-Darwinism. Hoo M, Sauders PT (eds.) Academic Press: London pp. 225-6)

"My own expectation is that when the almost totally unknown realm of processes whereby DNA determines embryology is studied, it will be found that DNA mentions nothing but relations." (Bateson 1979: 174, Mind and Nature)

"The term mnemogenesis is employed by Professor Hyatt [Proceeds. Boston Soc. Nat. History, 1893, p. 73] to characterize the manner in which kinetogenesis is supposed to produce results in inheritance. I have suggested that the phenomena of recapitulation, characteristic of ontogeny (American Naturalist, Dec., 1889), are due to the presence of a record in the germ cells, having a molecular basis similar to that of memory. This view is adopted by Professor Hyatt. I have already referred to it in the proceding pages. A general statement of this doctrine was made by Mr. Sedgwick in The British and Foreign Medico-Chirurgical Review for July 1863 in the following language: 'For atavism in disease appears to be but an instance of memory in reproduction, as imitation is expressed in direct descent; and in the same way that memory never, as it were, dies out, but in some state always exists, so the previous existence of some peculiarity in organizaton may likewise be regarded as never absolutely lost in suceeding generations, except by extinction of race.' " (Cope, CD (1896) Organic Evolution. Open Court Publishing: London p 492)

Essays

Databases

Related Links

Contact