In order for the human infant to safely pass through its mother's small pelvic outlet, which is an architectural requirement to walk upright, the infant has to be born with only 25 percent of its adult brain volume. (huffingtonpost.com)
The combination of increased brain size and a mother's narrower pelvic outlet (due to standing), caused a major change in human's gestation length. (boba.com)
Oxytocin triggers the primal birth instincts and and allows your partner to play a supportive role and reduces the risk of interventions by correcting mal - positions, opening the pelvic outlet wider, reducing shaking and pain, and increasing the mother's comfort. (montereybirthcenter.com)