Upright posture made assisted childbirth desirable for humans

February 18th, 2009 - 12:19 pm ICT by IANS  

Washington, Feb 18 (IANS) While giving birth, women are usually surrounded by doctors, nurses and husbands in delivery rooms and sometimes even other relatives and friends. Assisted birth has likely been around for millennia.
It possibly dated as far back as five million years ago when our ancestors first began walking upright, according to University of Delaware (UD) paleoanthropologist Karen Rosenberg.

When our ancestors evolved to begin walking on two legs, Rosenberg says, this upright posture created a wide but short opening in the pelvis in which the baby must travel, requiring a new form of birth so that the baby could find its way through a now tight birth canal.

The average pelvic opening in women today is 13 centimetres wide at its largest and 10 centimetres at its smallest. The average infant head is 10 centimetres from front to back, and the shoulders are 12 centimetres across. And today the birth canal is a twisty tunnel subjecting the infant to a series of complex twists and turns on its way out.

“Humans need helpers in childbirth because it is difficult and potentially dangerous,” Rosenberg said. “While it’s not so risky today - maternal mortality is low - as recently as two generations ago, it was not uncommon to hear of women dying in childbirth.”

Through fossil records and comparisons of humans with other primates, Rosenberg said that anthropologists can now show how the uniquely human traits of walking on two feet, large brains, infant helplessness and social assistance all came together, resulting in the challenging and somewhat dangerous manner in which humans give birth.

“With childbirth, as well as many of the other things that happen to women - pregnancy, nursing, menopause - it’s really easy to see how natural selection works,” Rosenberg noted.

How will women and childbirth continue to evolve? Will the birth canal grow narrower, or wider? Will childbirth become more painful, or easier? Will more helpers be needed in future births? It’s really anybody’s guess.

“Evolution doesn’t have a direction,” Rosenberg says. “Knowing where we’ve been doesn’t give us any help in where we’re going. But it does help us understand what makes us human, as well as how we’re connected to the natural world.”

Rosenberg, professor and chairperson of anthropology at the U-D, made a presentation on natural selection and childbirth at the annual meeting of the American Association for the Advancement of Science (AAAS) in Chicago.

It was part of the symposium “The Invisible Woman in Evolution: Natural Cycle and Life-Cycle Events”, which Rosenberg co-organised, said an AAAS release written by Tracey Bryant.

The theme “Our Planet and Its Life: Origins and Futures” commemorated the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of the publication of his book “On the Origin of Species by Means of Natural Selection”.

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