“Devolution” of bipedality

Abstract

Ozcelik et al. (1) report mutations in very-low-density lipoprotein receptor (VLDLR) that are associated with quadrupedal gait. They propose a pivotal role for VLDLR in the transition from quadrupedal to bipedal locomotion in man. VLDLR is a key regulator of cerebellar development in vertebrates (2). All VLDLR mutations reported to date result in disequilibirium syndrome (DES) with cerebellar hypoplasia and are neuroanatomically indistinguishable (1, 3, 4). In contrast to the Turkish population reported by Ozcelik et al., Hutterites carrying a complete deletion of VLDLR are bipedal (3). Ozcelik et al. hypothesize that the Hutterites are more severely afflicted because of a chromosomal deletion and that this causes loss of motor skills required for quadrupedal locomotion, thereby forcing them to habitually walk upright. Quadrupedal locomotion in individuals with cerebellar hypoplasia has been proposed to define a distinct genetic syndrome of “human devolution” or “reverse evolution” (“Unertan syndrome”) (5).