Considerable research has been performed on the association between sibling composition and various characteristics, including personality, intelligence, and social attitudes. These studies suggest that birth order among siblings could weakly but significantly affect the development of personality traits and intelligence. However, few studies on the association between sibling composition and moral foundations have been conducted. Therefore, the present study investigated whether sibling composition (only child, firstborn, laterborn) is related to moral values with a between-family design. A sample of 500 Japanese adults (250 women) completed the self-administered online questionnaire. The mean age was 45.42 years (SD = 8.53, range = 20–60, median = 46). The general linear model was used to test the association between sibling composition and moral values. The results showed no differences in five moral foundation and two higher-order moral dimension scores between firstborns and laterborns. However, only children scored lower on care/harm, fairness/cheating, and individualizing foundation than laterborns. This finding might indicate that growing up with their siblings positively affects the development of care/harm and fairness/cheating (individualizing foundation) regardless of one's position among those siblings.

已经对同胞组成与各种特征（包括个性，智力和社会态度）之间的关联进行了大量研究。这些研究表明，兄弟姐妹之间的出生顺序可能较弱，但会显着影响人格特质和智力的发展。但是，关于同胞组成与道德基础之间的关联的研究很少。因此，本研究调查了同胞组成（独生，长子，后代）是否与家庭设计有关的道德价值观有关。500名日本成年人（250名妇女）的样本完成了自我管理的在线调查问卷。平均年龄为45.42岁（SD = 8.53，范围= 20-60，中位数= 46）。通用线性模型用于测试兄弟姐妹组成与道德价值观之间的关联。结果显示，长子与后代的五个道德基础和两个更高阶的道德维度得分没有差异。但是，只有儿童在照顾/伤害，公平/作弊和比后代个性化的基础。这一发现可能表明，与兄弟姐妹一起长大会对照顾/伤害和公平/作弊（个性化基金会）的发展产生积极影响，无论他们在兄弟姐妹中的地位如何。