Reciprocal altruism and kin selection are the two main theories.
互利主义和亲族选择是两个主要理论。
2
One we lost in Moria. Two were my kin.
我们在摩瑞亚失去一个…两个是我的亲戚。
3
Like humans, wolves display a variety of temperaments. Their family structure more closely resembles ours. Loyalty and affection toward kin are two of a Wolf's more observable characteristics.