Social Preference behind the Veil of Ignorance, Experiments Conducted on Formosan Rock Macaques

想像問一個人他所認為公平的社會財富應該如何分配，一個資本家可能認為現有的財富分配是公平的，因為個人憑藉自己的能力累積財富；一個乞丐則可能認會平均的財富分配才是公平的社會。這個例子告訴我們一個人對於公平的財富分配的看法，會受到他原有的社會經濟地位所影響。John Rawls在1971年提出「無知之幕」的概念，他認為當人們處在一個無法得知自己社會經濟地位的無知之幕後面，選擇心中理想的社會財富分配，公平的社會便能由此建構。在上述的例子中，亦即人們在選擇心中公平的財富分配時，並不知道自己會落在分配完後的哪個位置，藉由處在無知之幕後方，反映出心中對於公平分配的真正看法。 本文的目的有二：首先，過去的文獻中發現，人們處於無知之幕後的選擇相較於一般(處於幕前)的選擇，更偏好選較平均的財富分配。然而，關於無知之幕幕後及幕前的社會偏好之間的連結，文獻上仍然缺乏實驗結果探討該問題，我們的實驗可以檢視受試者幕後及幕前社會偏好之間的關係。另外，關於社會偏好是否為人類特有，在其他演化地位相近的靈長類動物上是否存在社會偏好的問題，過去的研究中尚未有定論，因此，若無知之幕後的選擇反映一人對於公平分配的真正看法，則我們的實驗提供了演化議題上的新證據。 本文中，我們設計一系列類似獨裁者賽局(dictator games)的選擇實驗，測量台灣獼猴的在無知之幕幕後及幕前的社會偏好及風險偏好，結果顯示台灣獼猴無論在幕前或幕後皆具有社會偏好，並且無知之幕後的社會偏好可以被一部份幕前的社會偏好解釋。我們從實驗結果推論，人類的社會偏好可能演化自我們及其他靈長類的共同祖先，而非人類特有。Rawls (1971) argued that a just society could be constructed by the way that people choose their ideal wealth distribution behind the veil of ignorance which keeps agents uninformed of their social status. Past study had presented that human subjects had stronger social preference of inequity aversion when behind the veil of ignorance compared with the situation in front of the veil. However, there still lacks empirical evidence associating preference behind the veil with preference in front of it. Moreover, evidence for the evolutionary issue whether social preference is specific to humans or shared with our genetic relatives, primates, were still divergent; thus, preference behind the veil provides new evidence to probe into their true social preference. In this study, we implemented a series of modified dictator games on Formosan Rock Macaques (Macaca cyclopis) to measure their social preference in front of and behind the veil as well as their risk preference. The result showed that our subjects had social preference both in front of and behind the veil; further, preference behind the veil can be partly explained by the preference in front of the veil. Our finding supports that humans’ social preference may evolve from the common ancestor shared with other primates