一个相关的概念是，双火焰或者双灵魂。一个人只有一半的灵魂，而所有的灵魂就是要找到另外一个灵魂并且二合为一。

A related concept is that of the twin flame or twin soul - which is thought to be the ultimate soulmate, the one and only other half of ones soul, for which all souls are driven to find and join.

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北美部落习俗中将有男女特性的人称为“双灵魂”（人类学家称之为“berdache”从法语借来的词，意指双体人）。

North American tribal customs feature “two-spirit” people who combined male and female attributes (anthropologists call these “berdache”, from a French word for catamite).

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