A Theory of Childbirth’s Evolution May Not Be What You’re Expecting
?1.嬰兒為何如此無助？引出舊理論

It’s a question on every new parent’s exhausted mind: Why are babies born so helpless? In 1960, an American anthropologist laid out an influential explanation rooted in human evolution.

lay out?提出
2.舊理論認為古人類演化出適合行走的小盆骨和更大的腦子，導致“分娩困境”

As our early ancestors began walking upright, Sherwood Washburn?argued?in 1960, they evolved a narrower pelvis to make walking long distances more efficient. At the same time, those hominins were evolving larger brains.?

And babies with big heads could get stuck in a tight birth canal during delivery, threatening the lives of mothers and babies alike.

According to Dr. Washburn, evolution dealt with this “obstetrical dilemma,” as he called it, by shortening pregnancies, so that women delivered babies before the infant brain was done growing.

walk upright直立行走

hominin?（hominini）人族，屬于人亞科（homininae），可分為人亞族（hominina）與黑猩猩亞族（Panina）。這里簡單翻譯為古人類。

obstetrical dilemma hypothesis?“分娩困境假設”，由Washburn于1960年提出，大概指女性分娩導致女性人類進化要平衡盆骨及產道大小與嬰兒大腦發(fā)育之間的矛盾。

?3.舊理論的影響很大，暢銷書《人類簡史》將該假設當作事實來陳述

Dr. Washburn’s theory was hugely influential and became a common lesson in biology classes. “Sapiens: A Brief History of Humankind,” a 2011?best-selling book, presented the obstetrical dilemma as fact. Many researchers still embrace it.?

?4.Anna Warrener指出該理論的證據(jù)不足，且固化了“女性有身體缺陷”這一敘事

But a detailed review of the evidence, slated to be published soon in the journal Evolutionary Anthropology, threw cold water on the idea.?

In the review, Anna Warrener, a biological anthropologist at the University of Colorado Denver, argued that the evidence to date did not offer strong support for the obstetrical dilemma, and that scientists had not paid enough attention to possible alternatives.

What’s more, the scientist said, the idea sends a pernicious message to women that pregnancy is inherently dangerous.

“It perpetuates a narrative of bodily incompetence,” Dr. Warrener said.

slate（=schedule）計劃，安排

throw cold water on（=disagree or discourage）潑冷水

the evidence to date?迄今為止的證據(jù)

pernicious?有害的

perpetuate?固化?

5.Warrener在研究生階段檢驗過Washburn的核心觀點之一

In graduate school, Dr. Warrener did not see any reason to doubt the obstetrical dilemma. For her dissertation, she investigated one of Dr. Washburn’s key assumptions — that women walk less efficiently than men do because their pelvis is wider for childbirth.?

But in 2015, after studying volunteers walking on treadmills, Dr. Warrener?found?that having a wider pelvis did not create a bigger demand for oxygen.

“The data came in, and I was like, Wait a minute — I may have gotten some of the story wrong,” she recalled.

graduate school研究生院

dissertation學位論文

6.Holly Dunsworth也對該理論祛魅

Holly Dunsworth, a biological anthropologist now at the University of Rhode Island, also became disenchanted with the obstetrical dilemma when she took a close look at the evidence. “I was scandalized,” she said.

scandalize?使……震驚，使……憤慨?

7. Holly Dunsworth研究發(fā)現(xiàn)體型越大的靈長類動物妊娠期越長，而人類的妊娠期不符合這一規(guī)律

In 2012, she and her colleagues published a?study?on the length of pregnancies in humans and other primates. They found that, in general, bigger primates tended to have longer pregnancies than smaller ones.

For their size, humans don’t have shortened pregnancies. If anything, human pregnancies are longer than one would predict for a primate of their size.

?8.Dunsworth認為分娩時機取決于嬰兒的體型而非頭骨大小，當母體無法提供足夠的能量時，分娩就開始了。

Since then, Dr. Dunsworth has become a strong critic of the obstetrical dilemma, arguing that the timing of childbirth is determined by the size of babies’ bodies, not their heads.

The birthing process begins when a fetus demands more energy than a mother’s body can provide, she proposes. “We’re giving birth to massive babies,” she said.

?9.支持舊理論的研究者認為男性與女性盆骨最大的差別在產道周圍

Other scientists, however, have come to the theory’s defense, while admitting that its original conception was overly simplistic.

In a study published?last month, a team of researchers argued that the difference between the male and female pelvis shows signs of natural selection acting in different directions.?

While human males are bigger and taller on average than human females, certain parts of their pelvises are relatively smaller. The biggest differences are in the bones that surround the birth canals in human females.

Despite these differences, the female pelvis still creates a tight fit between a baby’s head and the birth canal, sometimes putting both the baby and mother in peril.

simplistic?過分簡單的

a tight fit?意思是緊密貼合，沒有多余空間?

10.支持舊理論的研究者之一Nicole Grunstra認為女性盆骨緊密貼合嬰兒頭骨是為解決“分娩困境”

“So why did natural selection not manage to kind of resolve this situation and make birth a little less risky?” asked Nicole Grunstra, an evolutionary anthropologist at the University of Vienna and one of the study’s authors.?

“It has evolved to be an evolutionary compromise between competing demands,” she said — in other words, to solve an obstetrical dilemma.

?

11.支持舊理論的研究者之一Nicole Grunstra承認舊理論存在缺陷，是站立而非行走限制了骨盆的大小。

But Dr. Grunstra acknowledged flaws in Dr. Washburn’s original version of the theory. She suspected that walking may not have been the most important factor in the evolution of the pelvis.?

Merely standing upright, she said, might have put pressure on the pelvic floor, preventing the evolution of a more spacious birth canal.

?12.反對者并沒有被說服，Warrener認為新手母親更容易死于失血過感染，是經(jīng)驗而非盆骨大小決定了生育的危險程度。

The skeptics aren’t convinced by these arguments. In her new review, Dr. Warrener questioned whether babies getting stuck in birth canals have posed a major threat to women’s lives. It is far more common, she noted, for new mothers to die from blood loss or infections.

?

13.她批評了舊理論支持者的基礎假設，即所有人體解剖結構都經(jīng)過了自然選擇的完美優(yōu)化

She also criticized the way in which Dr. Grunstra and other defenders of the obstetrical dilemma make the case for their hypothesis. In her view, they assume that every piece of human anatomy has been fine-tuned by natural selection for a specific job.

make the case for?解釋?

14.演化常常是巧合，因為控制盆骨大小的基因也對其他骨頭的表達起作用，盆骨大小的演變僅僅是副產品，而不是為了適應行走或生育。

Sometimes, Dr. Warrener said, adaptations are flukes. For example, some of the genes that build the pelvis are also active in the development of other parts of the skeleton.?

If another bone in our body were to evolve into a new shape, the pelvis might change simply as a byproduct — not because it was evolving for walking or childbirth.

fluke?僥幸，巧合?

15.盆骨的性別差異好比一條紅鯡魚

“I think sex differences in the pelvis have been somewhat of a red herring,” Dr. Dunsworth said. Like other bones, the pelvis does not have a fixed shape encoded in a genetic blueprint.?

Its development is influenced by the tissues around it, including the uterus, the ovaries and other organs. The proportions of the female pelvis may result in part from all the organs that grow inside it.

red herring?紅鯡魚，表示“用無關緊要的信息轉移焦點”

uterus?子宮

ovaries?卵巢

in part?部分地?

16.“分娩困境假設”導致“女性有身體缺陷”的錯誤觀點廣泛傳播，影響了近幾十年的生育醫(yī)療手段。

Both Dr. Dunsworth and Dr. Warrener worry that the obstetrical dilemma leads to a widespread notion of the female body as inescapably defective.

“That just makes us feel like problems that need to be solved by medicine,” Dr. Dunsworth said. That narrative may play a part in the medicalization of childbirth in recent decades, she added.

17.世界衛(wèi)生組織警告醫(yī)生不要對孕婦及產婦過度醫(yī)療，而忽略其他更危險的現(xiàn)代病。

The World Health Organization has?warned?that doctors are increasingly performing unnecessary medical intervention on mothers, while chronic disorders that can threaten maternal health — such as high blood pressure, obesity and diabetes — get little attention.

“The way we live now probably doesn’t lead us to meet the challenge of childbirth as well as our?bodies did when they developed differently in the past,” Dr. Dunsworth said.

?18.但舊理論的支持者認為反對過度醫(yī)療不意味著進化論解釋錯誤

But recognizing the over-medicalization of modern pregnancy doesn’t end the debate about its origins, Dr. Grunstra said. “That does not in itself mean that evolutionary explanations are wrong,” she said.

歡迎指正，感謝閱讀。