In March of 2000, Sofia Pedro’s village in Mozambique was ravaged by floods. People were forced to higher grounds to avoid the floodwaters, and many people, including the heavily-pregnant Sofia Pedro, were climbed to shelter in the treetops. She was trapped in the tree for four days. On the third day, she gave birth to her daughter, Rositha.
Giving birth in the treetops is unusual for humans, but not for many primate species.
Stories like Sofia’s are particularly interesting because they pose the question: are humans unique in that they alone experience difficulties during birth? Do both human and nonhuman primates therefore adopt methods and strategies to minimize the risk and maximize survival of themselves and their offspring?
In other words, is there a gap in human and nonhuman primate parturition behavior?
To investigate the similarities and differences between human and nonhuman primate parturition strategies, one must examine 1.) the Anatomical characteristics to examine the physical difficulties humans and primates face when giving birth and 2.) Parturition strategies, in other words, how human and nonhuman primates manage birth and improve probability of survival of both the mother and infant.
The human and nonhuman birth canal divided into three transverse planes: the inlet, midplane, and outlet (fig. 1). Each plane is described as being either longest at either the anterior-posterior diameter or widest at the transverse diameter. Each plane may be aligned, meaning all three planes parallel to one another, or misaligned, the planes are perpendicular to one another, with the greatest diameter varying among the three planes
Figure 1. Pelvic inlet, midplane, and outlet
In the genus Pan birth canal, for example, the anterior-posterior diameter exceeds the transverse diameter. In Australopithecine (specifically A. aferensis) the pelvis inlet transverse diameter exceeds the anterior-posterior diameter, resulting in a platypelloid shape (i.e. a flat, oval shape). Among humans the three transverse are all misaligned; the inlet is widest transversely, and the outlet widest anterior-posteriorly; thus creating two perpendicular planes.
Figure 2. Comparison for the mechanism of birth in Pan, A.L. 288-1 (Australopithecus aferensis) and Homo (Tague and Lovejoy, 1986: 247)
The Australopithecine birth canal is an example of how useful it is to reconstruct and understand changes in birth and parturition among human and nonhuman primate ancestors.
Australopithecus serve as one of the earliest sources of fossil material for examining early human bipedalism, and for the purpose of this post, mechanisms of birth. The cranial capacity of Australopithecus similar to that of modern chimpanzees. Pelvic and limb morphology indicate Australopithecines was bipedal, not but obligatory like our hominid ancestors. Australopithecines also had an increase in shoulder breadth co-occurs with bipedalism, helping with balance.
Australopithecine birth canal would have restricted fetal head rotations at all levels within the canal. Yet, the birth canal was adequate to allow passage of a neonate’s cranium only if the infant’s head entered with its occipital bone oriented transversely with ansynclitism, meaning the neonatal head tilted towards its left or right shoulder, and exited without rotating. The shoulders which followed probably would not have been able to pass through without changing orientation.
It is more difficult, if not impossible, to determine whether or not Australopithecines gave birth in solitude, among conspecifics, or sought attendants to assist with birth. Trevathan (1987) suggests that the presence of attendants at childbirth has been part of the genus heritage for at least one million to two million years, originating with encephalization in our linage. Hominid ancestors would have been able to give birth without assistance, but having that assistance and support would have made the difference between life and death for mothers and their infants. A slight reduction in mortality would lead to selection for the behavioral characteristic of seeking companionship during parturition, resulting in its widely universal distribution in the modern human species.
Anatomical Features of Human and Nonhuman Primate Birth
Sherwood Washburn referred to the human birth as the “obstetric dilemma,” resulting from the shrunken dimensions of the human birth canal mandated by the mechanical requirements of upright bipedal locomotion and the evolution of progressively larger human brains (Washburn, 1960). Among humans, the fetal head must be flexed as it passes underneath the subpubic arch/pubic symphysis, with the occiput against the pubic bones, the frontal bone passing along the concave anterior surface of the sacrum. The infant’s head then emerges from the canal occiput anterior: meaning that the infant generally emerges from the birth canal facing the opposite direction from the mother.
Primate mechanism of parturition is slightly more difficult to investigate because observations and accounts of primate births in the wild are scarce. Primatologists who have observed primate births note the difficulties in differentiation between pregnant and non-pregnant females until the pregnant female is actually in labor. Also, some primates give birth nocturnally, thus lower the changes that they will be observed, and some even seclude themselves in the foliage of trees during parturition. Among greater apes, the spacious birth canal and large body size allow for the neonate to easily navigate the birth canal. Small-bodies primates and lesser apes (Ateles), proboscis monkeys (Nasalis), macaques (Macaca), and lesser apes or gibbions (Hylobates), have a smaller head-to-body proportions, thus potentially complicated the birthing process. In her PhD dissertation, Stoller (1995) examined radiographs of laboratory animals during parturition showed that squirrel monkey and baboon neonates entered the birth canal in various positions, but then rotate to exit face first, facing the maternal pubic bones with their heads in an extended position.
Human Primate Birthing Strategies
Humans have adopted many strategies to combat the risks and difficulties in childbirth, one of which is seeking assistance from medical professionals or family members during the birth. Humans do have the ability to give birth without assistance, yet today many women giving birth prefer not to do it alone. Before the advent of modern obstetric care, pregnancy and childbirth were risky and dangerous, and the complex anatomical features involved in parturition predisposed humans to certain conditions, such as obstructed labor, which could result in a myriad of injuries to both the mother and infant (Roberts and Mancester, 2007; Arrowsmith et. al., 1996; Wall et. al., 2005). Thus, many women in developed societies view childbirth as an event to be managed with the presences of a trained professional using technological intervention (Liamputtong. 2007) to ensure that their pregnant bodies and fetuses are completely controlled, and therefore, safe (Liamputtong, 2007). To be sure there are benefits in having a trained medical professional present at the birth.
Obstructed births are a common complication humans face, one type in particular is shoulder dystocia, which occurs when the shoulders are unable to pass through the pelvis after delivery of the head when the neonate is too large and the pelvis too small. The typical medical intervention is a surgical incision to remove obstruction, which may be dangerous as it sometimes results in tearing or hemorrhaging, either of which might cause permanent damage or be fatal to the mother, infant, or both. Midwifes, on the other hand, adopt different strategies to combat shoulder dystocia: typically the maneuvers the parturent mother into different positions to widen the birth canal.
Birth positions in particular vary cross-culturally. Even though the semi-upright positions of kneeling and sitting are the best positions for parturition, the supine position is the most common in developed countries where birth typically occurs in a hospital. It is possible that many women do not have the stamina to remain in kneeling or sitting position for the length of time usually required to deliver a child. The supine position allows the medical professional to have optimal access to the birth canal as well. Interestingly, Friedman (1978) found that in general, the upright position is optimal for increasing intra-abdominal pressure and the diameter of the pelvis. Women who were upright in a seated or semi-reclined position during labor had a shorter labor length compared to women in a supine position (Friedman 1978).
Many women assign certain meanings to the birthing process; they feel a sense of achievement and pride in their ability to cope with intense pain. Mayan women living in Guatemala stated that they accept pain as an obligation of a woman’s life, and consider it a point of pride to confront the birth with stoic dignity and courage. In fact, the indigenous word for birth (patan) literally translates into “burden.”
Expressing and vocalizing any pain was, to some women, considered shameful because they believe such actions like screaming diverted energy needed to give birth. This is particularly true for Chinese women, who are also expected to use soft voices and demonstrate quiet demeanor during parturition.
Parturition Behaviors Among Nonhuman Primates
Anatomically, it appears that the mechanism of parturition varies between primate species, specifically between large bodied and small-bodied apes. When scholars opine that primates have little to no problems during parturition, they do not consider the extrinsic challenges primates encounter when giving birth in their natural habitat. Observations of baboons reveals that females give birth among conspecific group members. Squirrel monkeys give birth within their group as well as a form of cooperation against predators, anti-predator vigilance, and defense of neonates. Among Chimpanzees, Goodall (1971) noted that pregnant females become more solitary as parturition approaches. Among some primates, females seek seclusion and take advantage of the tree foliage that provides a natural protection from terrestrial predators (Rosenberg and Trevathan 2002). In a study published in Primates in July 2014, primatologists observed a bonobo birth for the first time, and found that the parturent female was accompanied by two other females who, according the researchers, were “offering companionship and support.” After the birth, the mother as well as the so-called birth attendants all consumed the placenta.
Primate births may be diurnal verses nocturnal; in fact, primates give birth at times of day that offer the lowest predation risk. Among squirrel monkeys labor may being at dawn, and if the infant has not been birthed by daytime, labor will spontaneously stop and start again during the appropriate time, most likely during dusk.
Primates also maneuver into positions to widen pelvis, particularly among smaller-bodied primates with a very close caphalopelvic fit (e.g. macaca mullata). Primates also express pain when giving birth. Patas, Rhesus macaques, and bonobos have been observed having pained looks on faces and express said pain with vocalizations. Breeched births might occur among primates with a close cephalopelvic dimension, such as macaca mullata, rhesus macaques, spider monkeys.
So How Wide is the Parturition Gap?
The mechanism of birth appears to be more complex for humans, small-bodied primates, and lesser apes than compared to larger-bodied, greater apes. Humans opt to seek assistance during birth and while primates sometimes opt to give birth among group members, it is unclear whether or not primates actively seek birth attendants. Primates maneuver in positions optimal for birth while humans in medicalized cultures give birth in a less optimal, supine position; maybe humans should consider a primate model for birthing positions! Both human and nonhuman primates experience pain when giving birth, yet humans are unique in that they assign cultural meaning to their pain.
In sum, both face similar challenges when giving birth, yet the adaptive methods to overcome those challenges varies between species worldwide. It seems to be that the parturition gap between human and nonhuman primates is not a wide gap after all.
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