社會階級作為一個普遍的社會結構，支持著族群的穩定性以及有效減少成員間的衝突所造成的不必要消耗。目前科學家對於成年時期的社會階級已有一定的了解，但是對於社會階級在幼年時期的研究卻仍未被完整地探討，因此本研究致力於探討幼年期小鼠的社會階級發展及相關的影響因子。利用鑽管測試 (Tube test)，我們發現幼年小鼠表現出穩定的社會階級且能保持相同的階級狀況直至成年期；同時我們也意外地發現在鑽管測試中服從者傾向於選擇主動退離衝突環境，而這個選擇並不是受到對於對手的認知或是感官訊息的影響，而是服從者的自我認知影響了它在衝突中所選擇的決策。另一方面，探討社會階級相關影響因子的實驗並沒有顯示壓力及憂鬱、焦慮行為在支配者與服從者間有差異，但是在記憶能力方面，支配者在物體認知及空間記憶能力皆優於服從者，遺憾的是，我們未能成功了解記憶及社會階級之間的因果關係。未來我們將繼續探討服從者自我認知的形成機制及記憶與社會階級間的交互作用，並期望本研究能提供新的觀點去了解社會階級在幼年時期形成的意義及相關形成機制。

Social hierarchy, as a universal social structure, maintains the stability of the group and reduces unnecessary conflicts between members. While current research has mostly focused on the studies of adult social hierarchy, social status in young animals was rarely explored. In this study, we aim to evaluate a social hierarchy in young mice and explore the related characteristics. In tube test, weanling mice showed a stable social hierarchy, which could consistently continue into adulthood. In addition, we unexpectedly observed that the conflict was not resolved by dominant but by subordinate mice, who were tended to voluntarily withdraw in tube test. This decision was mainly affected by internal status rather than recognition or social sensory signals from opponents. In addition, we also investigated different factors potentially involved in social hierarchy, and found dominants showed a significantly better ability of recognition and spatial working memory than subordinates. The relationship among stress, anxiety, depressive behavior and social hierarchy were not detected. Unfortunately, our experimental designs fail to clarify the cause and effect between memory and social hierarchy. In the future, we will continue to explore the mechanism of internal status in subordinate mice and the connection between memory and social hierarchy, and hope this research can provide new perspectives of the formation of social hierarchy in young animals

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