Research into the origins and nature of EVK did not begin until the late 1980s, so many details remain unknown.
[2] Ulrike Zeshan (2005) concluded that, based on the historical influence of the German and Russian communist oral methods of deaf education, the fact that the first deaf school in Estonia was established in 1866 in Vändra in the Governorate of Livonia of the Russian Empire and the evident influence of Russian Sign Language (RSL) present in EVK, it most likely either derived from or was strongly influenced by RSL, thus making Estonian Sign Language a member of the French Sign Language family.
[2] Taniroo (2007) found that 61% of Estonian and Russian signs of the 200-word Swadesh list were identical, confirming the hypothesis that EVK is either related to or has been significantly influenced by RSL through language contact.
Mahoney (2017) conducted the first-known 100-word Swadesh–Woodward list comparison of EVK and Latvian Sign Language, concluding that a possible relationship between them – as descending from VLFS, perhaps via ÖGS and/or RSL, as Wittmann (1991) and Bickford (2005) proposed – was 'still uncertain as it is unclear how sign languages disseminated in Eastern European countries during the Soviet Union, but aside from superficial impressions that the core lexicons are similar, signs with shared parameters displaying small variation in handshape while retaining 4 selected fingers suggests that these languages share a parent'.
She added that '[a]t present there is no reason to assume that Estonian and Latvian sign language have a mother-daughter relationship'.