Without this one characteristic, the species would become extinct (one word)

Reproduction.

Without the ability to reproduce, the species would become extinct.
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Reproduction.re·pro·duc·tionˌrēprəˈdəkSH(ə)n/nounthe action or process of making a copy of something."the cost of color reproduction in publication is high"synonyms:copying, duplication, duplicating; Morethe production of offspring by a sexual or asexual process.synonyms:breeding, procreation, multiplying, propagation"the process of reproduction"a copy of a work of art, especially a print or photograph of a painting.plural noun: reproductionssynonyms:print, copy, reprint, duplicate, facsimile, carbon copy, photocopy; trademarkXerox"a reproduction of the original"