polydactylism (n.)

"condition of having more than the normal number of fingers and toes," 1850, with -ism + Greek polydaktylos "having many digits;" from poly- "much, many" (see poly-) + daktylos "finger, toe" (see dactyl). Related: Polydactyl (1874 as an adjective, 1894 as a noun); polydactyly.