Carolyn-- See Mike Rogin's piece in Gillman and Robinson, eds. _Mark Twain's PW: Race, Conflict and Culture (Duke UP, 1990) on the connection between _PW_ and Francis Galton's _Fingerprints_ published in 1892. I think it's worth noting, though, that _LOM_'s Karl Ritter story turns on the identification of a murderer on the basis of a thumbprint. And Poe's detective Dupin used pantograph tracings of the finger marks left on the victim's throat in "Rue Morgue" to identify the murderer as an orangutan. This takes nothing away from Rogin's thesis regarding Dalton, but it does suggest that Twain's interest in fingerprints and the idea of their significance long before that was scientifically confirmed no doubt whetted Twain's interest in Galton all the more. Larry Howe