 The similarities noted between many of the languages of Mesoamerica have led linguistic scholars to propose the constitution of a sprachbund, from as early as 1959.The proposal was not consolidated until 1986, however, when Lyle Campbell, Terrence Kaufman and Thomas Smith-Stark employed a rigid linguistic analysis to demonstrate that the similarities between a number of languages were indeed considerable, with the conclusion that their origins were very likely caused by diffusion rather than inheritance, the standard criteria for defining a sprachbund.In their 1986 paper "Meso-America as a Linguistic Area" the above authors explored several proposed areal features of which they discarded most as being weakly attested, possibly by chance or inheritance or not confined to the Mesoamerican region.