外刊 | A Theory of Childbirth’s Evolution May Not Be What You’re E

A Theory of Childbirth’s Evolution May Not Be What You’re Expecting
 1.婴儿为何如此无助？引出旧理论

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.旧理论认为古人类演化出适合行走的小盆骨和更大的脑子，导致“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，属于人亚科（homininae），可分为人亚族（hominina）与黑猩猩亚族（Panina）。这里简单翻译为古人类。

obstetrical dilemma hypothesis “分娩困境假设”，由Washburn于1960年提出，大概指女性分娩导致女性人类进化要平衡盆骨及产道大小与婴儿大脑发育之间的矛盾。

 3.旧理论的影响很大，畅销书《人类简史》将该假设当作事实来陈述

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指出该理论的证据不足，且固化了“女性有身体缺陷”这一叙事

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）计划，安排

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

the evidence to date 迄今为止的证据

pernicious 有害的

perpetuate 固化 

5.Warrener在研究生阶段检验过Washburn的核心观点之一

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学位论文

6.Holly Dunsworth也对该理论祛魅

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……震惊，使……愤慨 

7. Holly Dunsworth研究发现体型越大的灵长类动物妊娠期越长，而人类的妊娠期不符合这一规律

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认为分娩时机取决于婴儿的体型而非头骨大小，当母体无法提供足够的能量时，分娩就开始了。

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.支持旧理论的研究者认为男性与女性盆骨最大的差别在产道周围

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 过分简单的

a tight fit 意思是紧密贴合，没有多余空间 

10.支持旧理论的研究者之一Nicole Grunstra认为女性盆骨紧密贴合婴儿头骨是为解决“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.支持旧理论的研究者之一Nicole Grunstra承认旧理论存在缺陷，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.反对者并没有被说服，Warrener认为新手母亲更容易死于失血过感染，是经验而非盆骨大小决定了生育的危险程度。

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.她批评了旧理论支持者的基础假设，即所有人体解剖结构都经过了自然选择的完美优化

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 解释 

14.演化常常是巧合，因为控制盆骨大小的基因也对其他骨头的表达起作用，盆骨大小的演变仅仅是副产品，而不是为了适应行走或生育。

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 侥幸，巧合 

15.盆骨的性别差异好比一条红鲱鱼

“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 红鲱鱼，表示“用无关紧要的信息转移焦点”

uterus 子宫

ovaries 卵巢

in part 部分地 

16.“分娩困境假设”导致“女性有身体缺陷”的错误观点广泛传播，影响了近几十年的生育医疗手段。

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.世界卫生组织警告医生不要对孕妇及产妇过度医疗，而忽略其他更危险的现代病。

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.但旧理论的支持者认为反对过度医疗不意味着进化论解释错误

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.

欢迎指正，感谢阅读。