Dykhuizen Daniel
Department of Ecology and Evolution, Stony Brook University, Stony Brook, New York 11794.
Cold Spring Harb Perspect Biol. 2016 Jan 8;8(3):a018044. doi: 10.1101/cshperspect.a018044.
Natural selection should no longer be thought of simply as a primitive (magical) concept that can be used to support all kinds of evolutionary theorizing. We need to develop causal theories of natural selection; how it arises. Because the factors contributing to the creation of natural selection are expected to be complex and intertwined, theories explaining the causes of natural selection can only be developed through the experimental method. Microbial experimental evolution provides many benefits that using other organisms does not. Microorganisms are small, so millions can be housed in a test tube; they have short generation times, so evolution over hundreds of generations can be easily studied; they can grow in chemically defined media, so the environment can be precisely defined; and they can be frozen, so the fitness of strains or populations can be directly compared across time. Microbial evolution experiments can be divided into two types. The first is to measure the selection coefficient of two known strains over the first 50 or so generations, before advantageous mutations rise to high frequency. This type of experiment can be used to directly test hypotheses. The second is to allow microbial cultures to evolve over many hundreds or thousands of generations and follow the genetic changes, to infer what phenotypes are selected. In the last section of this article, I propose that selection coefficients are not constant, but change as the population becomes fitter, introducing the idea of the selection space.
自然选择不应再被简单地视为一个可用于支持各种进化理论的原始（神奇）概念。我们需要发展自然选择的因果理论，即它是如何产生的。由于促成自然选择产生的因素预计是复杂且相互交织的，所以解释自然选择原因的理论只能通过实验方法来发展。微生物实验进化具有许多使用其他生物体所不具备的优势。微生物体积小，因此数百万个微生物可以容纳在一个试管中；它们的世代时间短，所以可以轻松研究数百代的进化；它们可以在化学成分明确的培养基中生长，因此环境可以被精确界定；而且它们可以被冷冻，所以可以直接比较不同时间菌株或种群的适应性。微生物进化实验可分为两种类型。第一种是在前50代左右测量两种已知菌株的选择系数，此时有利突变尚未上升到高频。这种类型的实验可用于直接检验假设。第二种是让微生物培养物进化数百代或数千代，并追踪遗传变化，以推断哪些表型被选择。在本文的最后一部分，我提出选择系数并非恒定不变，而是会随着种群变得更适应环境而变化，从而引入了选择空间的概念。
