From Halopedia, the Halo wiki
Unmutuals are male Yanme'e who suffer from one (or possibly more) rare personality disorder(s), where the affected creatures are unable to function as a single coherent low grade hive-mind, leading to significant problems in such a rigid socialized species. This inability to function turns them into psychopaths. They brutally attack other Yanme'e—sometimes with little provocation—and smash eggs. These individuals are outcasts and banished from their hives, and usually dwell in small cavernous spaces in between hive territories. After the Yanme'e joined the Covenant, the amount of unmutuals began to significantly increase. As a result, the Covenant sentenced unmutuals to work as slaves in penal work colonies operated by Kig-Yar, where they are worked to death and often tortured. However, despite their violent, random natures, some Unmutuals can be clever and intelligent.
One such penal colony was transferred to Verge, where they worked to maintain the local beacon with a constant supply of helium-3. They were accidentally freed by Team Black, tricked by a lone individual who offered an alliance between the Yanme'e and the UNSC. While many of these Yanme'e were killed by the destruction of the beacon by Black-Two, there may have been survivors.
The term "unmutuals" is an inexact translation from the original Yanme'e word. Another descriptive term is "incapable of socialization."
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