An infant with caudal appendage.

There are several human atavisms that reflect our common genetic heritage with other mammals. One of the most striking is the existence of the rare 'true human tail'. It is a rare event with fewer than 40 cases reported in the literature. The authors report a case of an infant born with the true tail. A 3-month-old baby girl, presented with an 11 cm long tail, which was successfully surgically removed. Human embryos normally have a prenatal tail, which disappears in the course of embryogenesis by programmed cell death. Recent advances in genetic research reveal that 'of those organs lost, in evolution, most species carry 'genetic blue prints'. Thus, rarely the appearance of ancient organs like tail may be the result of re-expression of these switched off gene.