Louis Ard A
Rudolph Peierls Centre for Theoretical Physics, Univeristy of Oxford, 1 Keble Road, Ox1 3NP, United Kingdom.
Stud Hist Philos Biol Biomed Sci. 2016 Aug;58:107-16. doi: 10.1016/j.shpsc.2015.12.014. Epub 2016 Feb 8.
Counterfactual questions such as "what would happen if you re-run the tape of life?" turn on the nature of the landscape of biological possibilities. Since the number of potential sequences that store genetic information grows exponentially with length, genetic possibility spaces can be so unimaginably vast that commentators frequently reach of hyper-astronomical metaphors that compare their size to that of the universe. Re-run the tape of life and the likelihood of encountering the same sequences in such hyper-astronomically large spaces is infinitesimally small, suggesting that evolutionary outcomes are highly contingent. On the other hand, the wide-spread occurrence of evolutionary convergence implies that similar phenotypes can be found again with relative ease. How can this be? Part of the solution to this conundrum must lie in the manner that genotypes map to phenotypes. By studying simple genotype-phenotype maps, where the counterfactual space of all possible phenotypes can be enumerated, it is shown that strong bias in the arrival of variation may explain why certain phenotypes are (repeatedly) observed in nature, while others never appear. This biased variation provides a non-selective cause for certain types of convergence. It illustrates how the role of randomness and contingency may differ significantly between genetic and phenotype spaces.
诸如“如果重新播放生命的磁带会发生什么？”这类反事实问题取决于生物可能性景观的本质。由于存储遗传信息的潜在序列数量随长度呈指数增长，遗传可能性空间可能大到难以想象，以至于评论者常常使用超天文的隐喻来将其大小与宇宙相比较。重新播放生命的磁带，在如此超天文规模的空间中遇到相同序列的可能性微乎其微，这表明进化结果具有高度的偶然性。另一方面，进化趋同的广泛存在意味着相似的表型能够相对容易地再次出现。这是怎么回事呢？这个难题的部分解决方案必定在于基因型映射到表型的方式。通过研究简单的基因型 - 表型图谱，在其中所有可能表型的反事实空间可以被列举出来，结果表明变异出现过程中的强烈偏向性或许可以解释为什么某些表型在自然界中（反复）被观察到，而其他表型却从未出现。这种有偏向性的变异为某些类型的趋同提供了一个非选择性的原因。它说明了随机性和偶然性在遗传空间和表型空间中的作用可能存在显著差异。
