The obstetrical dilemma hypothesizes that when hominids began to develop bipedal locomotion, the conflict between these two opposing evolutionary pressures became greatly exacerbated. Because humans are currently the only recognized extant obligately bipedal primates, meaning our body shape requires to only use two legs, major evolutionary developments had to occur in order to alter to the shape of the female pelvis. Human males evolved narrower hips optimized for locomotion, whereas female hips evolved to be a wider optimization because of childbirthing needs. Human pelvises have no distinguishing skeletal markers for sex before puberty, meanwhile, with maturation, hormones and obstetrical demands alter the shape of the pelvis in females. Overall, through evolution of the species, a number of structures in the body have changed size, proportion, or location in order to accommodate bipedal locomotion and allow a person to stand upright and face forward. To help support the upper body, a number of structural changes were made to the pelvis. The ilial pelvic bone shifted forward and broadened, while the ischial pelvic bone shrank, narrowing the pelvic canal. These changes were occurring at the same time as humans were developing larger craniums.