Abstract
OBJECTIVE: Birth palsy, otherwise known as obstetric brachial plexus paralysis (OBPP), is a closed stretch injury to the brachial plexus of nerves during the birth process resulting in varying degree of paralysis and contractures of the upper limb. The study aimed to find out the susceptibility of humans and small-bodied primates to birth palsy. METHOD: A comparative study on parturition in modern humans, hominoids, hominids, small-bodied primates and great apes was done to determine if the changes in female pelvis and neonatal head and shoulder during human evolution is the real cause for OBPP. RESULTS: During evolution, the morphology of the female pelvis and birth canal changed into a narrow and twisted one and also the size of the fetal head increased. Thus, the narrow and twisted pelvis of the mother, and the relatively large head and broad shoulders of the newborn has made the birthing process of modern human and small bodied primates a precarious fine-tuned act with a very narrow margin for error. This has necessitated proper obstetric care to reduce or even at times obviate the incidence of birth injuries like OBPP. CONCLUSION: Human evolution has made human babies susceptible to birth palsy and thus is the real cause of birth palsy.