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the claim
All mammals sleep.
the verdict
INSUFFICIENT LEANING
Recorded sources
5 sources for · 0 against
Is it true that all mammals sleep?
Unclear. The retrieved sources indicate that sleep, including REM-like states, is widespread among mammals, with some noting it occurs in all land mammals or almost all terrestrial mammals. None directly establishes that every mammal species sleeps; the closest statements are partial and hedged.
Verdict: PARTIAL LEAN · 5 sources for, 0 against · Last checked
Evidence for · 5
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Sleep in animals - Wikipedia. (n.d.). en.wikipedia.org. https://en.wikipedia.org/wiki/Sleep_in_animals
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More for · 4
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Rapid eye movement sleep. (n.d.). en.wikipedia.org. https://en.wikipedia.org/wiki/Rapid_eye_movement_sleep
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1947-, N. D. (2014). Sleep problems. archive.org. https://archive.org/details/sleepproblems0000nard
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Sleep alterations in mammals: Did aquatic conditions inhibit rapid eye movement sleep?. (2012). doi.org. https://doi.org/10.1007/s12264-012-1285-8
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Yin, D., Zhong, Z., Zeng, F., Xu, Z., Li, J., & Ren, W. (2025). Evolution of canonical circadian clock genes underlies unique sleep strategies of marine mammals for secondary aquatic adaptation. doi.org. https://doi.org/10.1371/journal.pgen.1011598
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held for human review17 Oct 2026
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