關於天擇本性的爭論

Abstract

近期關於天擇本性的爭論關注在兩個問題上：天擇是否是因果過程，以及天擇應如何刻畫。本論文檢視在此爭論中最具代表性的三個理論：Matthen和Ariew的形式樣式觀，Bouchard和Rosenberg依附於適存性概念的刻畫，以及Millstein不倚靠適存性概念的刻畫。Matthen和Ariew主張一般所認為的作為因果過程的天擇並不存在，天擇其實是由特定一個數學定理所代表的形式樣式。Bouchard和Rosenberg認為天擇是一類因果過程，其原因為適存度關係而結果是生殖成功度差異。Millstein則認為天擇是一類因果過程，其原因是族群的性狀差異性而結果是生殖成功度差異。他並認為性狀差異性是一個族群層次的性質。這三個說法都有重大缺陷。其中，前兩個主張因為錯誤太過根本所以必須完全放棄。Millstein的說法雖然概念上有混淆之處且形上學上也有瑕疵，但經過進一步釐清並重新詮釋之後可以引導出一個更令人滿意的對天擇的刻畫。此一刻畫是，之於不同可定性狀的天擇是不同類的涉及整個族群一整個世代的因果過程，每一個這樣的因果過程類是由複數個不同但相似的涉及生物一生的因果過程類所刻畫，而後面這些不同的因果過程類則是刻畫成同一可定性狀之下的不同類的確定性狀之對不同範圍的確定生殖成功度有因果貢獻。 本論文結構如下。第一章介紹這個爭論的背景，區分相關的問題與無關的議題，並指出一些基本假設以及本文的目標。第二章檢視天擇的形式樣式觀。本文認為作為形式樣式的天擇並非如Matthen和Ariew所稱是可多重實現的，而且此一意義下的天擇根本沒有解釋上的效用。進一步，本文反駁他們對於作為因果過程的天擇並不存在的論證，同時釐清並重建這個意義的天擇概念。第三章處理Bouchard和Rosenberg的看法。此處將指出，在適存性確實是生物的一個性質的假設下，適存性是一個二階功能性質，因此，說適存性對生殖成功度或其差異有因果貢獻會招致形上學上必然相依性問題以及原因互斥問題。對於幾個試圖解決前一個問題的方式以及對於原因互斥論證的反對此處亦將一一反駁。第四章處理Millstein的看法。本文澄清在他的說法裡，天擇其實並不是一類因果過程，而是一群不同類的因果過程。此處將詳細對比依附於適存性概念的刻畫以及獨立於適存性概念的刻畫，最終，適存性作為一個生物性質以及依附其上的對天擇的刻畫都將被揚棄。然而，Millstein所謂的族群層次性質本身也有原因互斥問題，本文亦將批評Haug對解決這個問題的嘗試。族群層次性質不具因果效力且其在存有論上是冗贅的將促使我們重新詮釋Millstein的看法。最終，我們可以得出一個更令人滿意的對天擇的刻畫，它不仰賴任何形上學上可疑或存有論上冗贅的設定，同時不會有任何語意上的扭曲或造成其他不必要的麻煩。第五章為本文結論。

Recent debate over the nature of selection centres upon the questions of whether selection is a type of causal process and how selection should be characterised. Three representative accounts of selection in this debate are critically examined in this thesis: Matthen and Ariew’s formal-pattern account, Bouchard and Rosenberg’s fitness-dependent characterisation of selection and Millstein’s fitness-independent characterisation of selection. Matthen and Ariew contend that there is no selection as a causal process as normally conceived; instead, selection is a formal pattern characterised by a mathematical theorem. Bouchard and Rosenberg assert that selection is a type of causal process identified by the fitter-than relation being the cause of difference in reproductive success. Millstein characterises selection to be such a causal process that trait-variations as population-level properties are causally relevant to differences in reproductive success. All these accounts will be shown to be seriously defective. However, the former two are so fundamentally mistaken that they will be rejected outright. On the other hand, Millstein’s account, while conceptually confused and metaphysically flawed as it stands, can be clarified and re-interpreted so that it can pave the way for a more satisfactory characterisation of selection. In this latter account, selections with respect to different trait-determinables are different types of population-wide, generation-long process each jointly identified by a plurality of distinct yet similar types of organismal-level generation-long process that are identified by different types of trait-determinates under a common trait-determinable being causally contributory to different ranges of determinate degrees of reproductive success. The present thesis proceeds as follows. Chapter one introduces the background of the current debate, distinguishes what is at issue from what is not, and states some basic assumptions and the objective of the thesis. Chapter two examines the formal-pattern account. It is argued that selection as a formal pattern is, contrary to what Matthen and Ariew claim, not multiply realisable and has no explanatory utility at all. Meanwhile, their arguments against the ordinary talk of selection as a causal process will be refuted and the ordinary idea be clarified and re-established. Chapter three is devoted to Bouchard and Rosenberg’s account. I’ll show that, on the assumption that fitness is an organismal property, it is a second-order functional property, and therefore the assertion that fitness is causally responsible for reproductive success or the difference thereof suffers from the problem of metaphysically necessary dependency and the causal exclusion problem. Some specific attempts to solve the former problem and some general objections to the exclusion argument will be rejected. Chapter four explores Millstein’s fitness-independent characterisation. It will be revealed that selection in her account is actually a family of different types of process rather than a single type of process. This leads to a comparison between the fitness-dependent characterisation and the fitness-independent one and ultimately to the rejection of the posit of the property of fitness as well as the fitness-dependent characterisation. Yet, the posit of the so-called population-level properties also has the exclusion problem; Haug’s attempt to save their causal efficacy will be criticised and rejected. Their causal inefficacy and ontological redundancy prompts a re-interpretation of Millstein’s characterisation and eventually a more satisfactory alternative that does not rest upon any ontologically redundant or metaphysically suspicious posit and does not create any semantic twist or other unnecessary complications. Chapter five is the conclusion.