Contingency-theorists have put forth differing accounts of evolutionary contingency. The bulk of these accounts abstractly refer to certain causal structures in which an evolutionarily contingent outcome is supposedly embedded. For example, an outcome is evolutionarily contingent if it is at the end of a 'path-dependent' or 'causally dependent' causal chain. However, this paper argues that many of these proposals fail to include a desideratum - the notion of biological evitability or that evolutionary outcomes could have been otherwise - that for good theoretical reasons ought to be part of an account of evolutionary contingency. Although an inclusion of this desideratum might seem obvious enough, under some existing accounts, an outcome can be contingent yet inevitable all the same. In my diagnosis of this issue, I develop the idea of trajectory propensity to highlight the fact that there are plausible biological scenarios in which causal structures, alone, fail to exhaustively determine the biological evitability of evolutionary forms. In the second half of the paper, I present two additional desiderata of an account of evolutionary contingency and, subsequently, proffer a novel account of evolutionary contingency as non-trivial objective probability, which overcomes the shortcomings of some previous proposals. According to this outcome-based account, contingency claims are probabilistic statements about an evolutionary outcome's objective probability of evolution within a specifically defined modal range: an outcome, O, is evolutionarily contingent in modal range, R, to the degree of objective probability, P (where P is in between 1 and 0).

中文翻译：

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进化偶然性作为非平凡的客观概率：生物可避免性和进化轨迹。

权变理论家对进化权变提出了不同的解释。这些说明中的大部分抽象地指某些因果结构，据推测这些因果结构嵌入了进化的或有结果。例如，如果结果位于“路径相关”或“因果相关”因果链的末尾，则该结果在进化上是偶然的。但是，本文认为，这些建议中有许多都没有包含希望的内容-生物可生性的概念，或者进化结果本来可以是-出于良好的理论原因，应该将其作为进化偶然性的一部分。尽管似乎已经很明显地包含了这一愿望，但根据一些现有的说法，结果可能是偶然的，但不可避免的是一样的。在我对这个问题的诊断中，我提出了轨迹倾向性的概念，以强调以下事实：在某些合理的生物学场景中，仅因果结构无法详尽地确定进化形式的生物学可避免性。在本文的后半部分，我提出了另外两个关于进化偶然性的描述，并随后提出了一个关于进化偶然性的新描述作为非平凡的客观概率，从而克服了先前一些提议的缺点。根据这种基于结果的描述，或有索赔是关于在特定定义的模态范围内进化结果的客观进化概率的概率陈述：结果O在模态范围R内在进化上具有偶然性，达到客观概率P的程度（其中P在1到0之间）。