This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
2002 First Paper
The Socialization of Human Birth as Protection for Bipedalism
The topic of human birth is quite an interesting one. For example, why do we give birth the way we do? Why is labor so incapacitating to human females, and how has natural selection been a factor? I have investigated the way in which the process of human pregnancy has evolved over time, and found a strong link between the biological and the sociological. As humans evolved from quadrupeds to bipeds, the birthing process evolved from a private process to a social process. The socialization of human birth allowed bipedalism to flourish. If birth had remained private, the disadvantages to bipedalism in regards to the continuation of the species would have eventually necessitated a revision of the trait.
Comparing our birth process with that of our primate relatives gives a very logical argument to why human birth became a social process. "The baby monkey emerges facing toward the front of the mother's body so she can reach down with her hands and guide it from the birth canal...the human infant must undergo a series of rotations to pass through the birth canal without hindrance" (1). The sheer complexities of human birth naturally dispose it toward being a social act. Because of the necessities of bipedalism, the pelvis of a human female is much narrower than that of other primates, meaning that numerous physical complications arise, and birth is physically more painful.
Growth of brain and cranial size among hominids also added to the difficulty of labor and delivery. The human brain triples between birth and adulthood, whereas the brain of other primates only doubles. "What humans seem to have accomplished is the trick of keeping the brain growing at the embryonic rate for one year after birth. Effectively, if humans are a fundamentally precocial species, our gestation is (or should be) 21 months. However, no mother could possibly pass a year old baby's head through the birth canal. Thus, human babies are born 'early' to avoid the death of the mother." (2). Humans have maintained a gestation length comparable to that of chimpanzees (the gestation for chimpanzees is approximately 230 to 240 days), despite the fact that the young are born in such different stages of development relative to their adult selves.
Another very practical argument for necessity of socialization to bipedal survival is the fact that a human female is physically unable to assist herself or the baby during birth if something goes wrong. "I suggest that early hominid females who sought assistance or companionship at the time of delivery had more surviving and healthier offspring than those who continued the ancient mammalian pattern of delivering alone. Thus, the evolutionary process itself first transformed birth from an individual to a social enterprise..." (1). In cases when the baby is breeched, or with other complications arising when the baby is in the birth canal, assistance from another can be the difference between life and death.
Another danger in birthing alone, most women feel the need to push during contractions before their cervix is properly dilated (10cm), especially in the case of a longer labor or a breech, this results in the baby's head becoming trapped in the birth canal, then necessitating a rapid delivery to keep the child from attempting to breathe (as it will once its body is exposed to cooler temperatures), but increasing the risk of internal ripping of the mother's cervix and/or uterus with heavy bleeding, damage to other organs and death (3). Experience must have quickly taught early hominids that assisted birth was best.
Though the term "midwife" was not coined during the medieval ages, the role it describes is almost as old as bipedalism. Another part of the argument for this are references made to women in this capacity from Greek and Roman times, in medical documents, Egyptian papyri, the Bible, and Hindu scrolls. The documents indicate these women as having an invaluable, but more importantly established part of human society, already subject to its own set of rules (4).
Beyond midwifery, there are many factors that have been working to change the process of human birth. One factor is the development of more effective medicines for pain, tools such as forceps to use during delivery, and the advent of written record so that future generations could expound more easily upon the work of others (which is how the practice of caesarian section became such a viable option), even across certain geographical boundaries. Another was the changing diet and it's effect on the human body. I would argue that as these new factors came into play, natural selection began gradually to be overshadowed.
As man was able to control food sources (and consequently became less mobile) more effectively through farming, new foods became staples in the human diet. "Increased consumption of carbohydrate-rich foods, decreased mobility, and nursing at infrequent intervals all interact to make this possible, enabling women to conceive within 10-15 months of the last birth. Weaning earlier is made possible by the availability of appropriate infant foods in the form of cereal grains and, in some places, milk from domesticated animals. Ultimately the birth interval is reduced to approximately 2 years resulting in population increase." (2).
As the success of human birth and the ability to conceive more frequently in a lifetime became greater, the obstacles bipedalism presented were surmounted. Increased birth rates meant increased variation, providing a larger pool of genetic traits to be selected for or against. Early hominids used their intelligence to compensate for deficiencies in speed and agility. Birth evolved from a private to a social process in order to increase the rates of survival for both mother and child. With time, this socialization led to the development of various techniques and technologies capable of compensating for the physical limitations on birth in bipeds.
1) Bernard Bel, a quote from "Evolutionary Obstetrics" (In W. R. Trevathan, E.O. Smith & J.J. McKenna, eds., Evolutionary Medicine. New York: Oxford University Press, 1999, pg. 183-207), from Bernard Bel's "New Directions". An interesting site with intelligent arguments concerning all aspects of health, including the "medicalization" of human birth.
2) Glenn Morton's Creation/Evolution Page, Morton, G.R. "The Curse of a Big Head." Arguments as to the correlation between increased brain size and human sweat glands, pains during childbirth, and need for clothing. Inspired by Genesis 3:16-21, when God punishes Adam and Eve for eating from the tree of knowledge. The argument is supported by fossil record and other biological/anthropological evidence, and is, on the whole, not bad.
3) Glenn Morton's Creation/Evolution Page, a quote from Wenda R. Trevathan's Human Birth, (New York: Aldine de Gruyter, 1987), p. 92 from G.R. Morton's "The Evolution of Human Birth", an article providing information in support of the theory that human birth has not evolved significantly since Homo Rudolphensis.
3) Parkland School of Nurse Midwifery, a concise and informative page on the history of midwifery.
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