ABSTRACT
The elimination of practices with a low survival value is as essential to the directionality of human evolution as is the occurrence of the conditions for innovation of new elements with high survival value. The sense of inevitability which pervades White's work results from his concentration on sets of events that did occur. Steward's work is less deterministic insofar as he includes situations in which specific development might have occurred but did not, and to the extent that he sets these nonoccurrences over against a large set of sequences. Directionality in evolution is assured only at those levels at which the primary specifications needed are: the size of the group of human beings, the level of culture, and the available types of protection against events that could annihilate the group and/or destroy the culture altogether.
