1. Assisted Birth

2. 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).
Observations of non-human primate birth in either context is rare.
Typically, births occur at night in both contexts. In captivity, birth can also occur when there is no attendant present.
If the non-human primate, like a monkey, is not in captivity, birth often occurs in the trees.

3. DIFFERENCES BETWEEN PRIMATE BIRTHS
Non-Human Primate
1.) Birth tends to be non- rotational
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
So, how did our birthing process become so different from non-human primates and, ultimately, lead us to rely on assistance during birth?

4. The Root of the Downward (Birth) Rotation
Quadrupedal
“Knuckle-walkers”
Bipedal
Upright walkers
About 5 million years ago, evolutionary selection for bipedalism began.
Skeletal changes in:
Feet, spine, legs, knees, ribcage…
PELVIS
Obstetrical dilemma
To begin, all non-human primates are quadrapeds, or knuckle-walkers.
Advantages of quadrapeds: speed, agility, tree-climbing (which allows access to food resources not always accessible from the ground)
If I had another class, I would go into the multitude of theories as to what prompted the evolutionary selection to bipedalism. However, for this topic, it will suffice to say that evolutionary selection for bipedalism began about 5 million years ago. This caused morphological changes in the skeletal structure of humans as the center of gravity shifts and the muscle masses used for locomotion change, too.
Some changes in the skeletal structure that occurred were in the bones of the feet, spine, leg, knee, ribcage, aaaaand the PELVIS!

5. As humans evolved, our skull size also increased.
This illustrates the increase in skull (and brain size) during evolution and as we became to walk more upright.

6. Evolution of Human Primate Brain Size
For the first two-thirds of our history, our ancestor’s brains were within range of other living apes today
As you can see, around 4 million years ago, australopithecine brains began to change in shape and structure
Last third of evolution was primarily where brain sizes evolved to be exponentially larger
We’ve discussed the major theories behind this brain growth earlier in the semester – brains for brawn, expensive tissue, etc.

7. 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)
More recent in our evolution: female pelvis of Lucy, Homo erectus, and Modern Humans. Due the the fragility of pelvic bones, it is rare to find an intact pelvis of our ancestors. However, the available pelvic bones found can be used to create a reconstruction. While the exact shape of the birth canal of earlier Neanderthals is debated because of variations in constructions, it is generally agreed that the birth canal of Neanderthals was oval. This suggests that non-human primates did not rotate during birth until later in our evolution, when the birth canals became more circular.
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)

8. 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
Fetal rotation, in simplier terms is the ”twist” that occurs when an infant passes through the birth canal.
This is a baboon on the left and a human on the right.

9. The far left would be the great ape family, middle is “Lucy”
So, as Trevathan proposed, non-human primates do not have rotational birth and human primates do.

10. EMERGING FROM THE BIRTH CANAL
Non-Human Primates
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.
The secondary distinguishing feature according to Trevathan is how the infant emerges from the birth canal. Obviously, the rotation of human primates during birth changes how the infant usually emerges. Of course, there are always exceptions to the rule and human primates can give birth occiput posterior but can be problematic.

11. 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%
Also note that non-human primates often have more wiggle room, too.
Often within minutes of birth, non-human primates are already clinging to their mother or have climbed up to her nipples to eat
No known case of human infant assisting in birth.

12. 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
Largest width of shoulders is perpendicular to the width of the head. The head is designed for the passage through the birth canal, cranial bones can shift and are not as rigid as shoulders. The breadth of the monkey’s shoulders is not any wider than the head which also contributes to easier passage through the birth canal without rotation
During the rotation through the birth canal, the umbilical cord can get wrapped around the infants neck
We know that babies are gross when they emerge from the birth canal – they are covered in fluids which often block their airways. I am going to address this in a minute.

13. 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
Extends beyond the birthing process
Example: zuo yuezi (Raven et al., 2007)
Assisted birth in non-human primates does occur:
Pair bonds in New World monkeys
Orangutans
Protecting mother from infanticide
Very few cultures encourage unattended birth. Even while it is customary in a small number of cultures, attended birth in cases of complications do occur.
During evolution, the threat of losing mom or human infant’s life became more important than other potential threats, like potentially competing females.
Males in pair bonds take direct interest in birth
Essentially, sometimes males or other females will be the “bouncer” during birth
The challenges and complications of human birth, brought about largely by the skeletal changes and increase in brain size, created a need for reliance on another’s help during birth in order to survive. However, infants also need continued support to increase the chances of survival through infancy. So social support extends beyond the birthing process and often, at least in traditional societies, continues for the newborn and the mother. An example of this is the Chinese traditional practice of zuo yuezi. It was commonly practiced to help mother regain strength and protect future health. Including things like: eating protein rich foods, dietary restrictions, limitations on chores.
Major difference in assisted birth in human primates versus non-human primates:
Human primates more directly involved in assistance.

14. 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)
Evolutionary selection for bipedalism