In Matter of Acosta, 19 I. & N. Dec. 211 (BIA 1985), overruled on other grounds by Matter of Mogharrabi, 19 I. & N. Dec. 439 (BIA 1987), the alien argued that he was a member of a particular social group comprising members of a taxi driver cooperative in El Salvador. 19 I. & N. Dec. at 232. The BIA defined a particular social group as follows: We interpret the phrase persecution on account of membership in a particular social group to mean persecution that is directed toward an individual who is a member of a group of persons all of whom share a common, immutable characteristic. The shared characteristic might be an innate one such as sex, color, or kinship ties, or in some circumstances it might be a shared past experience such as former military leadership or land ownership. The particular kind of group characteristic that will qualify under this construction remains to be determined on a case-by-case basis. However, whatever the common characteristic that defines the group, it must be one that the members of the group either cannot change, or should not be required to change because it is fundamental to their individual identities or consciences. Id. at 233. Applying that definition in Acosta, the BIA rejected the aliens arguments because the identifying characteristic of the group (working as a taxi driver) was not immutable. Taxi drivers could change jobs at any time. Id. at 234.