ABSTRACT
The many differences in human pregnancy and new-born infants compared with other primates are discussed. The ‘obstetric dilemma’ is explained, and how strategies were evolved in hominins to accommodate an increasing size of foetal brain/skull and the changing shape of the hominin pelvis.
The early bipedal australopithecines needed a wider and stronger pelvis to support their internal organs, which previously had been supported by a horizontal spine. Increased musculature of the lower limbs was also required to support a vertical body on two legs rather than four. Developing stability on two legs to walk and run was much easier in water, aided by support and buoyancy.
At the same time, their pelvis needed to be narrower to enable bipedal mobility. The result was a shorter gestation period to allow the bigger skull to be delivered safely and delayed ossification of the skull bones to allow rapid expansion of brain size during the first two years of life. This resulted in a prolonged period of maternal care until the baby was more mature and independent.
The unique human features of lanugo, fat buoyant babies and vernix caseosa are discussed which are characteristic of aquatic rather than terrestrial mammals.(198 words)
