《论衡·卷十七·指瑞篇》
人与人的禀性和种类是相同的，好恶也是相等的，尚且不能相互了解，鸟兽与人的禀性不同，怎么能够了解人呢？
人同性类，好恶均等，尚不相知；鸟兽与人异性，何能知之？
Human nature and disposition are the same, and likes and dislikes are also the same. They still cannot understand each other, how can birds and beasts with different nature understand humans?