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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Gavin de Beer

de Beer: bibliographical excerpts


"To put the matter as succinctly as possible, no case has yet been satisfactorily proved in which, as a result of external factors, the development of an animal has undergone a modification and in which these external factors have become internal and transmitted, so that the same modification has come to be invariably produced in all the subsequent ontogenies of descendant animals without the necessity for the external factors which orginally evoked the modification. Until such a case has been proved, it cannot be believed that the effects of external factors and of use and disuse on body or mind are transmitted or play any part in ontogeny in subsequent generations. Somatic induction, or the transmission of the effects of use and disuse, constitute the kernel of the Lamarckian point of view; and it is curious that while we still lack evidence, viz. direct induction, though of course he was prophetic and correct in rejecting the view that direct induction can produce an adaptive inherited response to the environmental stimulus. It would be very convenient if it were possible to accept an explanation of the origin of internal factors and of their adaptive nature on the lines of Lamarck's hypothesis of the effects of use and disuse, but in the present state of knowledge it is not possible. It is necessary to adopt a humbler position and admit that the causes of origin and change in the genetical factors of organisms are unknown. Once they have arisen or changed (mutated), selection plays an all-important part in moulding their effects." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 15-6)

"That the general idea is true that the genes produce their different effects by working at definite speeds, can further be shown by raising or lowering the temperature of the environment, which accelerates or retards the rate of action. This is why a primrose which at a temperature of 20 degrees C. has red flowers, will have white flowers if it is grown at 30 degrees C. It also supplies the reason why the fur of the extremities (ear, paws, and the tip of the tail) of Siamese cats is dark, for the temperature of these places is lower than in the body generally." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 19-20)

"The result of the last few chapters has been to show that each of the theoretically possible effects of heterochrony in producing phylogeny has actually accurred in the evolution of different animals." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 88)

"Thus, before getting into his analysis of the role of ontogeny in phylogeny, de Beer establishes the interactional or coactional nature of what he calls internal and external factors in embryonic development. He notes that ever since the Silurian period, about 300 million years ago, vertebrate animals have had two eyes, as is borne out by the fossil record. Thus, there must be a hereditary or genetic capacity to develop two eyes in vertebrates, and this capacity has been transmitted to every generation for a considerable period. "But these hereditary factors are not self-sufficient, for if a few pinches of simple salt (magnisium chloride) are added to the water in which a fish (Fundulus) is developing, that fish will undergo a modified process of development and have not two eyes, but one....Countless similar examples might be given, but this one suffices to show that by themselves the internal and therefore transmitted factors are not able to "produce" a normal animal" (de Beer, 1958, p. 14). De Beer then goes on to cite others who have shown that internal and external factors cooperate in the production of all characters of an organism. He further exphasizes 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 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. " By way of establishing his frame of reference for the understanding of ontogeny itself, as well as the relationship between ontogeny and phylogeny, de Beer makes the point that ontogeny is not merely an extrapolation into the future of a chain of events that occured in past and previous generations: "Each ontogeny is a fresh creation to which the ancestors contribute only the internal factors by means of heredity. And this historic past is not the phylogenetic line of ancestral adults, but the line of the germ-plasm supplying the fertilized eggs for each and every generation. The action of the internal factors is to ensure that if the external factors are normal and do evoke any response in development and produce an animal at all, that animal will develop along the same lines as its parent. The internal factors are only a partial cause of ontogeny." " (de Beer, 1958, p. 17) (Gottlieb, G (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 96-97)

"Child has solved this problem by showing experimentally that the first thing which has to be settled in a developing egg is the polarity, i.e. which part of the egg will give rise to the front and which to the hind end of the future animal. As soon as the polarity is established, local diversities arise and result in the qualitative differentiation of the different parts. Now in many cases the determination of this polarity seems to be the result of the action of factors which are external to the fertilized egg. In other cases it is possible that the polarity of the egg is derived from that of the oogonium which gave rise to it, but this merely pushes the question of the origin of polarity back in time. However this may be, it is clear that all the way through development the internal factors produce nothing of themselves, but they enable the animal to react in definite ways to the external factors and by this means give rise to structure after structure in the process of development. Heredity does not account for the individual, but merely for the potentialities some of which are realized in the individual. In other words, the internal and transmitted factors are by themselves unable to 'produce' an animal at all. The first rigorous analysis of the relation of internal and external factors in development is due to Lankester, who showed that they can only be regarded as co-operating in the production of all the characteris of the organism. The same point of view has been developed by Goodrich, who stresses the distinction which has to be drawn 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. 'An organism is moulded as the result of the interaction between the conditions or 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.' Similar views have been expressed by Conklin. These conclusions, which are based on definite experimental evidence, have a far-reaching importance. In the first place they show that the question -- Are acquired characters inherited? -- has no meaning, for all he 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 of the external factors will result in a departure from normal development. What the questioners really mean is -- Can an effect originally produced as a response to an environmental stimulus come subsequently to be produced regularly without that stimulus? In other words, can external factors become internal? When, therefore, Hyatt defined an acquired character as 'a modification which makes its appearance in the adult or later stages of development and is obviously dependent for its origin upon other than hereditary causes', he is really describing the effect of an external factor, but that does not justify him in excluding the articipation of internal factors in producing that effect." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 12-13

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