THE NEUTRAL THEORY OF MOLECULAR EVOLUTION AND THE WORLD VIEW OF THE NEUTRALISTS
THE NEUTRAL THEORY OF MOLECULAR EVOLUTION AND THE WORLD VIEW OF THE NEUTRALISTS
复制标题
作者：
KIMURA, M
中性理论作为一种进化范式(“新达尔文主义”)。这一理论在20世纪50年代末的S到60年代初的S期间达到了鼎盛时期，其主要观点是，进化的速度和方向几乎完全由自然选择决定，突变只起到很小的辅助作用(例如，见Stebbins 1966，第29页)。当时大多数进化论者认为，选择性中性突变体即使存在，也是非常罕见的，既不会带来好处，也不会带来坏处。一个推论是，随机遗传漂移在物种的进化或形成遗传结构中没有显著作用。一个值得注意的例外是赖特的进化“转移平衡理论”，在该理论中，适应度和群体间选择中的上位性交互作用与每个Deme中的样本漂移相互作用。然而，赖特一再强调，他的平衡转移理论与进化论中选择性中性等位基因的“纯采样漂移”截然不同。(详情见莱特1978和普罗文1986；另见莱特1988年的最新观点。)与达尔文的自然选择进化论相反，中性理论(Kimura 1968；详情见Kimura 1983)声称，分子水平上的绝大多数进化变化不是由作用于有利突变体的自然选择引起的，而是由于在持续的突变压力下选择性中性或非常接近中性的突变体的随机固定(由于采样漂移)。换句话说，中性理论强调了突变压力和随机遗传漂移在分子水平上的进化变化中所起的主导作用。该理论并不否认自然选择在决定适应性进化过程中的作用，但它假设只有很小一部分DNA(或RNA)变化是适应性的。中性理论还认为，在分子水平上的大多数种内变异(包括蛋白质和DNA多态)基本上是中性的，因此大多数多态等位基因在物种中通过突变输入和随机灭绝之间的平衡来维持。换句话说，它将蛋白质和DNA的多态视为分子进化的一个短暂阶段，并拒绝接受这样的观点，即大多数这样的多态是达尔文(1859年)在他的关于物种起源的书中提出的，是适应性的，并通过某种形式的平衡选择来维持。他回避说“物种已经改变了，并且仍然在缓慢地改变--有一个简单的假设，即通过保存和积累连续的轻微变化，可以使用有利的方法计算出它的种群遗传学(见第一版第480页)。他的一种合适的数学方法，特别是自然选择进化的扩散理论规定，在方程式方法之间，或作为它们的“遗传偏差”(或突变，使用现代TER-(木村1964))。矿物学)在物种中持续出现的物种，那些通过自然选择传播到物种中的有利于个体生存和繁殖的物种。因此，每个物种都很好地适应了自己的环境。达尔文的自然选择进化论一直是生物学中的一个伟大的统一原则。在现代遗传学的强化下，它在20世纪30年代的S和1940年的S中形成了被称为“综合理论”(或称“综合理论”)的正统进化观
The neutral theory as an evolutionary paradigm" neo-Darwinism"). This theory, which reached its heyday during the period from the late 1950's until the early 1960's, was dominated by the view that the speed and direction of evolution are almost completely determined by natural selection, with mutation playing only a small and subsidiary role (see, for example, Stebbins 1966, p. 29). Most evolutionists at that time believed that selectively neutral mutants, which confer neither advantages nor disadvantages, are very rare, if they exist at all. A corollary was that random genetic drift plays no significant role in evolution or in forming the genetic structure of species. A notable exception to this was Wright's" shifting balance theory" of evolution, in which epistatic interaction in fitness and intergroup selection interact with sampling drift within each deme. Wright, however, repeatedly emphasized that his shifting balance theory differs sharply from" pure sampling drift" of selectively neutral alleles in evolution.(For details, see Wright 1978 and Provine 1986; see also Wright 1988 for his latest view.) In contrast to the Darwinian theory of evolution by natural selection, the neutral theory (Kimura 1968; for details, see Kimura 1983) claims that the great majority of evolutionary changes at the molecular level are caused not by natural selection acting on advantageous mutants, but by random fixation (due to sampling drift) of selectively neutral or very nearly neutral mutants under continued mutation pressure. In other words, the neutral theory emphasizes the predominant role that mutation pressure and random genetic drift play in evolutionary changes at the molecular level. The theory does not deny the role of natural selection in determining the course of adaptive evolution, but it assumes that only a minute fraction of DNA (or RNA) changes are adaptive. The neutral theory also asserts that most of the intraspecific variability at the molecular level (including protein and DNA polymorphism) is essentially neutral, so that the majority of polymorphic alleles are maintained in the species by the balance between mutational input and random extinction. In other words, it regards protein and DNA polymorphism~ as a transient phase of molecular evolution and rejects the notion that the majority of such polymorphisms areDarwin (1859), in his book on origin of species, con-adaptive and maintained by some form of balancing selection. eludes that" species have changed, and are still slowly chang- The has simple assumptions that ing by the preservation and accumulation of successive slight its population genetical can be worked out using favourable(see p. 480 of the first edition). His a suitable mathematical method, particularly the diffusion theory of evolution by natural selection states that among equation method, Or the as I them" inheritable deviations"(or mutations to use modern ter-(Kimura 1964). minology) which continuou~ ly appear in the species, those that are beneficial for the survival and reproduction of individuals spread through the species by natural selection. Thus each species is well adapted to its environment. The Darwinian theory of evolution by natural selection has served as a great unifying principle in biology. Augmented by modern genetics, it led in the 1930's and 1940's to the orthodox view of evolution known as the" synthetic theory"(or