婴儿夜间啼哭，第一时间想到的是婴儿饿了，要吃奶了。最近，哈佛大学David Haig提出了新令人惊讶的观点，即婴儿夜间啼哭并非都是要求吃奶，而其真正的目的是为让母亲更加劳累、不排卵、从而降低再生孩子的几率，让自己独霸父母，这样自己的生存几率就会增高。

Somewhere between bliss and exhaustion.That's how the first few months of parenting often feel, as sleepless nightsblur into semicomatose days. Most of us chalk up a baby's nighttime crying toone simple fact: He's hungry. But could that chubby bundle of joy have adevious plan?

Harvard University's David Haig thinks so. Lastmonth the evolutionary biologist offered up a surprising hypothesis to helpexplain those 2 a.m. feedings and crying jags: The baby is delaying theconception of a sibling by keeping Mom exhausted and not ovulating, Haig writes in the currentissue of the journal Evolution,Medicine and Public Health.

Now, the baby isn't consciously trying tohalt Mom's fertility, Haig explains. But if that happens, it ups the likelihoodthat the baby's genes will be passed along to the next generation. In otherwords, the drive to wake Mom (or Dad) up is an evolutionary one: Babies thatscream and suckle in the wee hours are more likely to survive and have childrenthemselves.

"It's clear that babies can get enoughmilk even if they sleep through the night," Haig tells Shots. "Thewaking becomes a different issue. ... I'm just suggesting that offspring haveevolved to use waking up mothers and suckling more intensely to delay the birthof another sibling."

Sounds a bit crazy, right? But there'slogic to the idea.

When times are tough — say during foodshortages or when infectious diseases are common — babies and toddlers have abetter chance of surviving when their parents wait a while before havinganother child（资料来自网络：http://www.npr.org/sections/health-shots/2014/04/14/302912419/why-babies-cry-at-night）.