One is in nomadic, hunter-gather societies that often shift camp and that are physically incapable of transporting old people who can't walk when the able-bodied younger people already have to carry their young children and all their physical possessions.
一个情况是游牧部落，打猎和采摘为食的社会 这些部落常常需要迁移， 他们没有能力 带着无法自己迁移的老人， 四肢健全的年轻人 要携带年幼的子女 和其所有的物质财产。