There were originally as many as five dialects of Yaghan, but the Yamana people who historically spoke the language have diminished in numbers and shifted to Spanish following the arrival of Europeans in Tierra del Fuego (Aguilera 214).
One reason for the decline is the drastic reduction in size of the indigenous populations who historically spoke these languages.
The Yaghan population, for example, was between 2,500 and 3,000 in the late nineteenth century and plummeted to as low as 40 by 1933, partly by diseases like smallpox, whooping cough and typhoid, introduced by incoming Europeans (Aguilera 214).
As the indigenous languages of South America have declined, the inhabitants of Tierra del Fuego have come to use Spanish instead.
The Fuegian languages are unified in having infrequent "retroflex articulations" and rare instances of suppletion (Adelaar and Mysken 578).
A significant obstacle preventing a consensus on any kind of direct relation among the Fuegian languages is the lack of sufficient data.