ASSISTED BIRTH DIFFERENCES BETWEEN HUMAN AND NONHUMAN PRIMATE

ASSISTED BIRTH

DIFFERENCES BETWEEN HUMAN AND NON-HUMAN PRIMATE BIRTHS Wenda Trevathan (1987) proposed three primary differences between human & non-human primate births. Trevathan’s conclusions are based upon observations of over 250 human births (out of the hospital) and a limited set of observations of non-human primate births (in and out of captivity).

DIFFERENCES BETWEEN PRIMATE BIRTHS Non-Human Primate 1. ) Birth tends to be nonrotational 2. ) Emerge from birth canal facing same direction as mother 3. ) Typically occur in isolation Human Primate 1. ) Almost universally rotate 2. ) Emerge from birth canal facing away from mother 3. ) Often occur with assistance

The Root of the Downward (Birth) Rotation • Quadrupedal • Bipedal • Upright walkers • “Knuckle-walkers” • About 5 million years ago, evolutionary selection for bipedalism began. • Skeletal changes in: • • Feet, spine, legs, knees, ribcage… PELVIS • Obstetrical dilemma

Evolution of Human Primate Brain Size

Bipedalism & Big Brain ■ The changes in the skeletal structure of the pelvis due to the evolution of bipedalism also changed the shape of the birth canal over time. (Weaver & Hublin 2009) • With the added increases in brain size, “the net effect is that human neonatal head size closely matches maternal pelvic dimensions, unlike in our closest living relatives, the great apes, whose pelvic dimensions are larger than neonatal head sizes. ” (Franciscus 2009)

FETAL ROTATION ■ Fetal rotation – Passive movement as a result of neonate coming into contact with bony portions of the pelvis and highly resistant muscles of the pelvic floor

EMERGING FROM THE BIRTH Non-Human Primates CANAL ■ Occiput posterior (OP) – Infants emerge from birth canal facing the same direction as the mother – The facial presentation of non-human primates allows the mother to easily access her infant once it emerges or during the birthing process. Human Primates ■ Occiput anterior (OA) – Infants emerge from birth canal facing away from the mother ■ If mother encounters some complication during birth, bending over could be detrimental to her and the infant.

Motor Skills ■ Infants often have the motor ability to use their hands to get out of the birth canal ■ Retained motor skills over course of evolution to grip fur – Possible relationship between brain growth of infant at birth ■ ■ Non-human primates: 50% Human primates: 29%

Complications During Human Birth ■ Shoulder dystocia - shoulders get stuck in the birth canal – Largest width of infant shoulders is perpendicular to the width of the head ■ Nuchal cord – umbilical cord wraps around infant’s neck – Occurs in 23 -33% of births ■ Mother unable to remove fluids preventing infant from breathing after emerging ■ Occipital posterior emergence – Occurs in about 1% of births

ASSISTED BIRTH: UNIQUELY HUMAN? ■ Assisted birth for human primates is largely universal – – ■ Obligate midwifery 296 cultures noted to have some mention of assistance during birth 24 of these report some form or custom of unattended birth ■ Assisted birth in non-human primates does occur: – – – Pair bonds in New World monkeys Orangutans Protecting mother from infanticide ■ Extends beyond the birthing process – Example: zuo yuezi (Raven et al. , 2007) Major difference in assisted birth in human primates versus non-human primates: Human primates more directly involved in assistance.

CONCLUSION “Selection for bipedalism set hominids on a trajectory toward the elaboration of cultural systems of authoritative knowledge about how childbirth could best be accomplished. ” (Trevathan 1996)