為什么生孩子很痛苦?
Y: Don, you sure are lucky don’t have to give birth. I’m glad we’re an intelligent species, but boy, that infant head feels mighty large going through that narrow birth canal. And then, after all that, the baby comes out facing down and backwards, which means you’re helpless to assist it, or even to untangle it from the umbilical cord.
D: Well, Yeal. According to evolutionary anthropologists, babies of the earliest humans had a fifty-fifty chance of coming out facing backwards. This was a result of humans learning to walk on two feet. As the pelvis became optimized for walking, the birth canal developed twists and turns that meant the baby had to rotate in order to keep its head and shoulders aligned with the widest part at all times.
Y: And then our brains also got bigger.
D: Which meant more twists and turns.
Y: And backwards-facing babies, stupid,huh?
D: Well,you know,Yeal.Some of the earliest humans learned to compensate for the difficulty of giving birth by receiving assistance during childbirth, which made a huge difference in terms of survival.
Y: So there might be an evolutionary advantage to having someone help you give birth.
D: Some anthropologists certainly think so and conjecture that human females who gave birth to backwards-facing babies, and females who had assistance because they felt particularly anxious about the birth, ended up doing better than females who didn’t. After all, if problems arise during labor, having another person around can make the difference between life and death.
Y: 唐,你很幸運不用生孩子。我很高興人類有著聰明才智,但是天啊,嬰兒的腦袋要從狹窄的產(chǎn)道出來,那是很痛苦的。而且,經(jīng)歷過這一切后,寶寶出來是面向下和倒過來的,你根本沒辦法協(xié)助它,或者甚至不能幫忙解開臍帶。
D: 根據(jù)人類進化學家,人類早期時候的嬰兒生出來是有二分之一的可能性是面向后面的。這是人類學習用兩只腳走路的結(jié)果。隨著盆骨越來越適應(yīng)走路,產(chǎn)道就變得迂回曲折,嬰兒就得旋轉(zhuǎn)過來保持它的頭和肩膀總是與最寬的部分在同一平面上。
Y: 然后頭也會變得更大。
D: 也意味著更多的扭轉(zhuǎn)。
Y: 倒著出生的嬰兒,很可笑吧。
D: 你知道嗎?最早時期的人類學會彌補分娩的困難,他們通過在分娩是接受援助,這在生存方面起了非常重要的作用。
Y: 因此,也許有一種進化優(yōu)勢能請人幫助你生育。
D: 一些人類學家當然也這么想過,并且他們推測那些女性生下面向后面的嬰兒,和在生育時得到幫助的女性比沒有援助的生育女性生產(chǎn)更順利。畢竟,在分娩時有問題出現(xiàn),有人在身邊是能夠于生死之間起到很大作用。