The mutation theory from the standpoint of cytology
The mutation theory from the standpoint of cytology
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DOI：
10.1126/science.21.536.525
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发表时间：
1905-01-01
期刊：
影响因子：
56.9
通讯作者：
Conklin, EG
中科院分区：
文献类型：
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作者：
Conklin, EG
I.突变理论是建立在这样一种观点之上的，即突变主要是生殖细胞，它们出现在一个或两个性细胞中，然后才出现在成年生物体中。与某些进化论不同的是，这些进化论主要与进化论有关。在成体结构的改变方面，突变理论主要与（胚芽的）改变有关，在这里它与细胞学科学有直接的关系。德弗里斯告诉我们，突变理论的基础奠定在他的学说细胞内泛生。像达尔文、高尔顿、魏斯曼和其他许多人一样，他认识到进化的方法本质上是一个遗传的问题，用奥斯本的话来说，“当我们找到一种能解释遗传现象的遗传理论时，进化的方法本身将成为过去。”“动物和植物的进化必须伴随着它们的生殖细胞的进化，进化的主要问题不是如何在成年人中产生变化，而是它们如何在胚芽中出现。然而，除了少数例外，以前的进化理论只关心成年形式的转变，而没有注意到卵子或精子或胚胎的变化。突变理论是一种关于生物体通过生殖细胞进化而进化的理论，因此它主要是建立在细胞学现象的基础上的。对任何这样的理论的一个先前的反对意见是非常普遍的观点，即生殖细胞是由“简单的、未分化的原生质”组成的，它们不包含进化力量可能作用于其上的特定形态要素。然而，这种观点既没有得到观察的支持，也没有得到最新和最仔细的实验的支持。我们知道鳗鱼比几年前想象的要复杂得多，并且没有充分的理由假设它所有的可见结构现在都是已知的。在某些情况下，卵的碎片可能产生内胚，这一事实并不象通常所认为的那样，必然地意味着卵是未分化的。在卵中，就像在成体形式中一样，分化的程度可能在很大程度上与再生或调节的能力无关，当然，这些实验并不能否定从许多来源得出的关于胚芽复杂性的最积极和最直接的证据。人们对细胞核的结构进行了广泛的研究，揭示了细胞这一部分的组织程度，这是完全出乎意料的。人们早就知道，在任何一个物种中，细胞核中的染色丝或染色体的数目，在各种细胞中总是相同的，只有在性细胞形成的最后阶段，其数目是正常的一半;在受精卵中的卵核和精核的结合中，
I. The mutation theory is founded upon the idea that mutations are primarily germinal, that they arise in one or both of the sex cells and only later appear in the adult organism. In contradistinction to certain theories of evolution which are con-cerhed chiefly with t. he modifications of adult structures, the mutation theory is primarily conieerned with modifications (of the germ, and here it comes intodirect re-lation with the science of cytology. De Vries tells us that the foundations of the mutation theory were laid in his doctrine of intracellular pangenesis. Like Darwin, Galton, Weismannand many others, he recognized the faet that the method of evolution is at bottom a problem of inheritance and that, in the words of Osborn,'When we have reached a heredity theory that will explain the phenomena of inheritance, the method of evolution will itself be a thingof the past.'It seeims like a mere truism to affirm that the evolution of animals and plants must be accompanied by an evolution of their germn cells, and that the principal problem of evolution is not how modifications are preduced in adults, but how they arise in the germ. And yet with few exceptions previous theories of evolution have concerned themselves only with the transmutations of adult forms and have paid no at-tention to the modifications of the egg or sperm or embryo. The mutaticn theory is a theory of the evolution of organisms through the evolution of their germ cells and it is, therefore, founded primarily uponr cytological phenomena. An antecedent objection to any such theory is the very general opinion that the germ cells are composed of'simple, undifferentiated protoplasm'and that they do not contain specific morphological elements upon which evolutionary forces might act. However, such a view is supported neither by observation nor by the latest and most careful experiments. We know that the eell is vastly more complex than was as-sumed a few years ago, and there is no good reason for supposing that all of its visible structures are now known. The fact that fragments of eggs may in some instances give rise to entjxe embryos does not neces-sarily imply, as is usually assumed, that the egg is undifferentiated. In eggs, as in adult forms, the degree of differentiation may be largely independent of the power of regeneration or regulation, and certainly such experiments do not nullify the most positive and direct evidence, drawn from many sources, as to the com-plexity of the germ. Extensive studies which have been made upon the structure of the nucleus have brought to light a degree of organization in this part of the cell which was wholly unexpected. It has long been known that in any given species the number of chro-matic threads or chromosomes in the nucleus is constantly the same in all kinds of cells, except in the last stages of the formation of thesex cells, where the num-ber is one half the normal; in the union of the egg and sperm nuclei in the fertiliza-