Jongeling T B
Department of Philosophy, Free University, Amsterdam, Netherlands.
J Theor Biol. 1996 Feb 21;178(4):369-73. doi: 10.1006/jtbi.1996.0032.
Recently it has been claimed that certain macroevolutionary patterns, such as the contrast between the Cambrian explosion and the Permian quiescence, can be explained as generic properties of selection processes, i.e. as features that are not caused by specific selection pressures, but that are to be expected in any selection process. The explanations are based on models of motions on randomly generated fitness landscapes, which are assumed to be representative of fitness landscapes in general. In this paper I show that such explanations of macroevolutionary patterns are conceptually flawed. If the concept of fitness used in the model is not the customary biological notion of fitness, there is no reason why organisms with higher fitness should displace organisms with lower fitness, and as a result the motion of a point representing a population is no longer determined by the shape of the fitness landscape. Nothing can be derived about the motions on the landscape, and the explanation collapses. If the model is based on the customary fitness concept, non-competing species have to be assigned the same fitnesses. As most species belonging to a radiation such as the Cambrian explosion are assumed to coexist, the majority of species will have the same fitness. A radiation of species can therefore not be modeled meaningfully on a fitness landscape.
最近有人声称，某些宏观进化模式，比如寒武纪大爆发与二叠纪静止期之间的对比，可以解释为选择过程的一般属性，也就是说，这些特征不是由特定的选择压力导致的，而是在任何选择过程中都可以预期出现的。这些解释基于随机生成的适应度景观上的运动模型，而这些模型被假定为总体上代表了适应度景观。在本文中，我指出这种对宏观进化模式的解释在概念上存在缺陷。如果模型中使用的适应度概念不是生物学中惯常的适应度概念，那么就没有理由说明具有较高适应度的生物体应该取代具有较低适应度的生物体，结果代表种群的点的运动就不再由适应度景观的形状决定。关于景观上的运动就无法得出任何结论，解释也就不成立了。如果模型基于惯常的适应度概念，那么非竞争物种必须被赋予相同的适应度。由于像寒武纪大爆发这样的辐射事件中的大多数物种被假定为共存，那么大多数物种将具有相同的适应度。因此，在适应度景观上无法有意义地模拟物种的辐射。
