Hair is a unique mammalian trait that is absent in all other animal forms. Hairlessness is rare in mammals and humans are exceptional among primates in lacking dense layer of hair covering. HR was the first gene identified to be implicated in hair-cycle regulation. Point mutations in HR lead to congenital human hair loss, which results in the complete loss of body and scalp hairs. HR functions are indispensable for initiation of postnatal hair follicular cycling. This study investigates the phylogenetic history and analyzes the protein evolutionary rate to provide useful insight into the molecular evolution of HR. The data demonstrates an acceleration of HR sequence evolution in human branch and suggests that the ability of HR protein to mediate postnatal hair-cycling has been altered in the course of human evolution. In particular those residues were pinpointed which should be regarded as target of positive Darwinian selection during human evolution.

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