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Saturday, January 12, 2008



Lenneberg (1967)



The multiple unfolding that takes place is entirely dependent upon temporo-spatial overlapping, a continuous meeting in time and space, a sequence of events that must be precisely synchronized so that one phenomenon may act on another at the right time at the right place. The entire ontogenetic process must be seen as a precision schedule that determines the evolvement of a temporo-spatial pattern of interactions between cells and tissues.

Some geneticists believe that induction comes about through the biochemical alteration of regional, cellular environments (Bonner, 1952). These alterations have the effect of activating specific genes that had been present earlier but had been in some state of dormancy. Gene activation induces a new type of protein-synthesis within the cell, a molecular reconstitution, resulting in cell and tissue differentiation (Markert, 1963). Different internal environments activate different genes. Thus cells are acted upon by their environment which, however, is itself made up of cells and their metabolic products; a very complex chain of events ensues, until a relatively steady state, called maturity, is reached.

As cells become differentiated, various kinds of enzymes are produced by them that serve as catalysts for the biochemical reactions involved in development as well as in general metabolic function of the whole organism. The synthesis and biochemical structure of the enzymes are directly controlled by the molecular structure of genes, and small alterations in the latter (due to mutation) may easily affect the catalyzing efficiency of the enzymes and thereby change the temporal proportions of many far reaching reactions. The untoward temporal irregularities may affect growth rates by failing to initiate or inhibit growth activities, and this may result in irregularities of spatial contiguities and relations, thereby altering the entire spatial-temporal pattern. We see now how genes may be responsible for the inheritance of certain structural characteristics such as the famous Hapsburg lip, or a shortening of the chin, or excessively long legs. In these instances, growth is allowed to continue unhampered for a slightly longer time than is common, or it may be inhibited at a slightly earlier period.

But, as is well known, genes do not merely control the size and shape of structure but skills and capacities as well (Bernstein, 1925; Haecker and Ziehen, 1922, McClearn, 1964). These too may very well be due to spatio-temporal alterations in the ontogenetic schedules. For instance, the differential growth of internal or peripheral organs may clearly be accompanied by differences in capacities; enlarged heart and lung may improve the ability to run; an enlarged liver the endurance for prolonged intake of alcoholic beverages; a thinning of the fingers, the capacity for assembling electronic equipment. Some skills may beimproved through structural alterations that have the effect of lowering sensory thresholds, whereas the ability to dive may be enhanced by a heightening of tolerance for CO concentration in the blood.

More directly related to temporal events during ontogeny may be the prolongation of certain primitive undifferentiated stages. By postponing differentiation, either specific tissues or perhaps the entire developing individual, may become more susceptible to environmental influences (either the internal or external environment) and this may result in the creation of various types of critical periods such as have been briefly discussed in Chapter Four. These considerations make it clear that it is not strictly correct to speak of genes for long ears, for auditory acuity, or for the capacity for language. Genes can only affect ontogenesis through varying the cells’ repertoire of differentiation, but this, in turn, may have secondary effects upon structure, function, and capacities.

(2) Relative Growth

Certain aspects of growth can be quantified and treated mathematically. Let us merely refer to one instance, namely the phenomenon of allometric growth. Different portions of the body and limbs grow at different rates, and, therefore, an animal’s proportions are altered throughout development (Fig. 6.5). This is partly due to the existence of growth gradients (J. Huxley, 1932) along various axes of trunk and limbs. It has been found empirically (Reeve and Huxley, 1945) that the relation between the size and weight of two parts of the body (y and x) is that of an exponential function of the form

y = ax,

where a and b are constants. It is convenient to write this formula in its logarithmic form

log y = log a + b log x

and to plot measurements on double logarithmic paper so that all exponential functions appear as straight lines. If, for instance, we plot the weight of cats’ brains against the weight of the same animals’ body weights and take measurements at various stages of development, we find that the simple relationship, expressed by the allometric formula holds fairly well throughout ontogenetic development. The curves indicate differences in growth rate in various parts of the body and show that the proportion between such rates remains constant. The curves do not reflect the actual time it takes the animal to attain any of the values.

supplement information:


『生物技術』可說是無所不包,人類日常生活上的食衣住行,幾乎全部離不開生物技術的影響;通常可把『生物技術』的意義定義如下:利用生物 (動物、植物或微生物) 或其產物,來生產對人類醫學或農業有用的物質或生物。
主要有 基因操作、細胞培養、單株抗體、酵素工技 等四大領域 以及其他生命科學相關的科技。


brief summary:

基因的活化會引起細胞內產生新的形式的蛋白質複合體,而細胞和組織之間的差異會導致分子的重新構成,不同的內部環境會活化出不同的基因。當細胞變得有差異時,不同種的酵素也因此產生,它們用來當作整個生物體新陳代謝和生化反應的催化劑。酵素的综合體和生化結構是經由基因的分子結構直接控制,一點後來的改變可能很簡單就會影響它的催化效率。基因不僅控制生物體的大小和外型,同時也決定了技巧和能力。例如,內部或者外圍器官的不同發展,顯然地伴隨著能力的差別; 擴大的心臟和肺可以增進跑步的能力; 一個擴大的肝較有忍耐力對於喝較長期酒類的飲料等。

(2)相對的發展 發展的某些方面可能被確定數量並且以數學的方式測量。 讓我們僅僅提及一個實例,即異速生長的現象。身體和四肢的不同部份以不同的速度生長,動物比例在整個發展期間中會改變。

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