'self-selected' originates from English, specifically the compound of 'self' and 'select': 'self' from Old English 'self' meaning 'oneself', and 'select' from Latin 'seligere' (via past participle 'selectus'), where 'se-' meant 'apart' and 'legere' meant 'to pick/choose'.

'select' came into English from Latin 'selectus' (past participle of 'seligere') via Old French/Medieval Latin and Middle English as 'select'; the verb 'self-select' is a modern compound of 'self' + 'select', and 'self-selected' is the past participle/adjectival form derived from that verb.

Initially the components meant 'oneself' + 'to choose apart'; over time the compound has come to mean 'chosen by oneself' or (in technical contexts) 'chosen voluntarily by participants', without significant shift from the literal sense.