Structural reduction through the probable mutation effect. A critique with questions regarding human evolution

Brace's adaptation of Sewall Wright's concept of “mutation pressure” is critically examined. It is concluded that while Brace's adaptation of this principle is probably valid and useful in explaining certain aspects of structural reduction in human evolution, three criticisms can be made: (1) in its present form, the hypothesis does not provide any explanation of foci for positive selection pressures; (2) the hypothesis is overextened to include all cases of reduction, offering no guidelines to select among alternative hypotheses: (3) the hypothesis has more credibility if Wright's original observations regarding pleiotrophy are included.