Why is childbirth painful evolution

It seems that with time comes more opportunity to process the birth and with that more distress at the way a negative experience played out. Serious complications such as very preterm labour increase the risk for a negative recollection of birth over time.

There is no opportunity for a halo effect when a newborn in distress is rushed to the intensive care unit. A slightly depressing finding for those who plan to be on first name terms with their anaesthetist during the birth is that even when pain relief is used, it may not lessen the memory of pain overall.

However a child is brought into the world, there are many health professionals who can talk to women about their fears and anxieties about pain or the experience as a whole. Being psychologically prepared may assist some women, particularly those having their first child or those who have had a negative experience in the past.

There are lots of options for pain control in childbirth and like everything with parenting, you need to know yourself and your threshold for pain and work out a plan with your care-provider that feels right for you. Portsmouth Climate Festival — Portsmouth, Portsmouth. A recent paper by Holly Dunsworth of the University of Rhode Island and colleagues reexamines the predictions and evidence supporting the obstetrical hypothesis and suggests an alternative explanation.

For instance, human gestation is often said to be short relative to that of other primates, based on how much more growth is needed in neonates to achieve adult brain size. The shorter duration of gestation on first glance supports a prediction of the obstetrical hypothesis—that birth has evolved to occur earlier in hominids so that the baby is born before its head is too large to pass through the birth canal.

Actually, the duration of human pregnancy 38—40 weeks is absolutely longer than that of chimps, gorillas, and orangutans 32 weeks for chimps and 37—38 weeks for the latter two. When Dunsworth and her colleagues took maternal body size into account, which in primates is positively correlated with gestation length, they showed that human pregnancy is also relatively longer compared to that in great apes.

No wonder that the third trimester seems so long to many pregnant women. Another oft-cited fact supporting the obstetrical hypothesis is that, of all the primates, human newborns have the least-developed brains. This difference in newborn brain size seems to suggest that human babies are born at an earlier developmental stage than other primates.

Compared with the heads of other primates, the head of a human newborn is a very tight fit through the birth canal. For the sake of comparison, the drawings are scaled so that the transverse diameters of the birth canals are the same.

Image adapted by Tom Dunne from K. Rosenberg and W. The catch is that adult brain size in humans is much larger than in other primates for reasons having nothing to do with birth. This means that using adult brain size as a basis for comparing relative gestation length or newborn brain size among primates will underestimate human development. It is an issue of supply and demand.

Both facts suggest that pregnancy may push human mothers to their metabolic limits. The obstetrical hypothesis, in contrast, suggests that locomotion rather than metabolism is the limiting factor in birth size.

The underlying concept here is that wider-hipped women—capable of giving birth to larger offspring—should suffer a disadvantage in locomotion. Men and women are extremely similar in the cost and efficiency of locomotion, regardless of hip width. Enlarging the birth canal to pass a baby with a brain 40 percent of adult size, as is typical of newborn chimps, would require an increase in diameter of only three centimeters—just over an inch—in the smallest dimension of the birth canal.

The conflict between big-brained babies and upright walking may be more conceptual than real. Although the findings showing that human babies are not earlier than other primates are interesting, they still fail to identify what limits baby brain size. Dunsworth and her coauthors propose that the metabolic constraints faced by a mother limit the length of pregnancy and fetal growth.

They have dubbed their hypothesis the energetics-of-gestation-and-growth hypothesis. Holly Dunsworth and colleagues contend that because adult brain size in humans is much larger than in other primates for reasons having nothing to do with birth, using adult brain size as a basis for comparing primate gestation length or newborn brain size will underestimate that of humans.

Graphs adapted by Barbara Aulicino from H. Dunsworth, et al. As the baby grows in both brain and body in the womb, its demand for energy accelerates exponentially. Even following birth, the big-brained, big-bodied newborn needs a loving mother who will continue to feed and care for it while its brain continues to grow at a fetal rate.

In the womb, the fetus is basically part of the mother. Once born, the baby is effectively at a higher trophic level than its mother, like a parasite feeding on her, which increases the metabolic demands on her. During birth, a modern human baby must turn in the womb several times as it is pushed through the birth canal by the pelvic muscles. In sharp contrast, chimpanzees give birth in short order and appear to experience very little pain.

In this new effort, the researchers wondered about the birth experience for one of our ancestors, Australopithecus sediba —a hominin that lived approximately 1. To find out, they created a 3-D representation of an A. While they were at it, they also created 3-D representations of Australopithecus afarensis and Homo erectus. And for additional comparison, they also created 3-D images of a modern human and a chimpanzee pelvis.

To study the degree of difficulty of giving birth, the researchers also added baby human skull-sized objects to the 3-D images as they would normally sit in the birth canal. The researchers report that the size of the A. They suggest this indicates that compared to modern women, A. The researchers also note that contrary to popular belief, the evolution of the birth canal was not a clearly defined path from big to small—prior research has shown that an earlier ancestor, Lucy, Australopithecus afarensis likely had a difficult childbirth.

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