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In the deserts of the American Southwest, spadefoot toad tadpoles hatch in tiny oases.
在美国西南部的沙漠，锄足蟾的蝌蚪在小绿洲孵化而出。
Until they develop into toadlets, they can't survive outside of water,
在长成小青蛙前，它们不能在脱水的环境中生存，
but these ponds are transient and quickly evaporate.
但是它们生活的池塘转瞬即逝，水分很快就蒸发了。
The tadpoles are in a race against the clock to grow up before their nurseries disappear.
所以这些小蝌蚪需要和时间赛跑，要赶在池塘中的水分蒸发前长大。
So nearly overnight, some of the brood explode in size.
几乎在一夜之间，一部分蝌蚪迅速变大。
They use their jack-o-lantern teeth and huge jaw muscles to devour their smaller pond mates.
它们用了自己锋利的牙齿和巨大的鄂部肌肉来吞食身边更小的蝌蚪。
Nourished by this extra fuel, they develop quicker, leaving the pond before it can dry out.
通过这额外的食物，它们成长得更迅速，继而可以在池塘蒸发前离开。
The spadefoot toad is far from the only animal to eat members of its own species as a normal part of its life cycle.
锄足蟾远不是动物里唯一把吞食自己同类以生存作为正常生命周期的一部分。
All of these animals do. If that surprises you, you're in good company.
所有这些动物都是。如果你感到很惊讶，你不是一个人。
Until recently, scientists thought cannibalism was a rare response to starvation or other extreme stress.
直到最近以前，科学家以为同类相食是一个很稀有的、面对饥饿或其它极端压力才产生的反应。
Well-known cannibals, like the praying mantis and black widow spider, were considered bizarre exceptions.
已知的同类相食者，如螳螂、黑寡妇蜘蛛，曾被视为是奇怪的特例。
But now, we know they more or less represent the rule.
但现今，我们知道它们或多或少代表了普遍现象。
While it may seem counterproductive for members of the same species to eat each other,
同一物种互相捕食看起来可能对物种不利，
cannibalism can promote the survival of the species as a whole
但同类相食也可以帮助整个物种的存活，
by reducing competition, culling the weak, and bolstering the strong.
通过减少竞争，消灭弱者，让强者更强大。
Some species, like the spadefoot toad, cannibalize in response to environmental pressures.
有些动物，比如锄足蟾，是因为环境压力而吞食自己的同类。
Their situation is precarious, but cannibalism for them isn't a last-ditch attempt to avoid starvation.
它们的情况很危急，但对于它们来说，同类相食并不是为了避免饥荒的孤注一掷。
Rather, it's a way to more quickly outgrow a stage
相反，它是一种更快跳出某个阶段的方法，
where they're especially vulnerable to predation or dangerous environmental conditions.
在这个阶段中，它们很容易被捕食，或被危险的环境条件影响。
Other species, including many fish, indiscriminately cannibalize each other during foraging behavior.
其它种群，包括很多鱼类，觅食中会无差别的捕食同类。
Fish produce large numbers of tiny young,
鱼类生产大量的、个体小的幼体，
and adults exhibit about as much individual recognition of their offspring as humans do for a handful of raisins.
且成年的鱼识别它们自己的后代就和我们识别一把葡萄干一样差劲。
Fish eggs, larvae, and juveniles are easily available, nutrient-rich meals,
鱼卵和幼鱼是容易获得、营养丰富的一餐，
and with thousands of eggs in a clutch, plenty are still available to hatch after the adults have snacked.
并且鱼有着上千个鱼卵，成年的鱼就算吃一部分也还剩很多可以孵化。
Baby fish aren't just at risk of being cannibalized by adults -- siblings eat each other too.
幼鱼不只会被同类里成年的鱼吃掉，兄弟姐妹也会互相捕食。
Sand tiger shark eggs develop and hatch inside their mother's oviducts at different times.
沙虎鲨的卵会在不同时间段在母亲的输卵管里发育和孵化。
When the hatchlings run out of yolk from their own eggs,
当幼体用光了自己卵中的卵黄，
they eat the other eggs and hatchlings until one baby shark from each oviduct remains.
它们就会吃掉其它卵和幼体，直到每个输卵管里只剩下一只小鲨鱼。
When they emerge, the young sharks are well-nourished, experienced predators who stand a better chance of surviving.
出生时，剩下的小鲨鱼就有了充足的营养和丰富的捕食经验，这样就更容易存活下来。
Even when they aren't consumed for nutrition, young animals are especially vulnerable to cannibalism.
即便有时不是为了营养，幼年的动物也很容易被同类相食。
Hamsters, rats, and other rodent mothers will eat some of their young
仓鼠，老鼠和其它啮齿动物的母亲，会吃掉一部分自己的幼鼠，
if they're sick, dead, or simply too numerous to feed.
如果它们生了病，死掉了或者只是数量太多无法喂养。
In other mammals, including bears and lions, males will kill offspring sired by another.
其它动物中，包括熊和狮子，雄性会杀死其它雄性的后代。
That's because childless females become receptive to mating more quickly than if they were caring for a cub.
这是因为没有幼崽的雌性比她们在抚养幼崽的时候更容易继续交配。
Rather than waste nutritious meat, the males then eat the dead cubs.
为了不浪费营养丰富的肉，雄性会吃掉死去的幼崽。
Meanwhile, cannibalism is less common in birds than in other groups,
同类相食在鸟类中更少见一些，
but certain species will eat diseased or dead hatchlings as a way of disposing of the bodies before they can attract maggots.
不过某些鸟类也会吃生病或死掉的幼雏，以此作为在吸引蛆虫之前处理尸体的方法。
When adults eat each other, males are cannibalized more often than females,
对于成虫间的互相捕食，雄性比雌性更容易被吃掉，
usually during mating and generally because they're smaller.
一般在配偶期，原因通常是雄性体型更小。
Male Australian redback spiders mate with much larger females.
比如，雄性澳洲红背蜘蛛会和体型大很多的雌性交配。
Rather than scrambling away after mating, the tiny male does a somersault,
交配后，小小的雄性不会马上离开，而是翻个跟头，
bringing his abdomen into contact with his mate's mouthparts.
把自己的腹部移到配偶的口器旁边。
The female showers him with enzyme-rich gut juice and consumes his abdomen.
接下来，雌性用含有酶的消化液吃掉雄性的腹部。
Males not killed in the initial mating crawl back into the fray,
没有在初次交配中直接被杀死的雄性会回来，
often half-eaten, to mate again, after which they're dispatched to the spider pantry.
在一半已被吃掉的情况下，继续交配，然后成为雌性蜘蛛的食物。
So not only does the male provide the female with his sperm,
这样，雄性不只给雌性提供了精子，
but he also provides her with a nutritious meal to better ensure that she'll survive to pass on his genes.
他还提供了一顿营养丰富的晚餐来确保雌性可以生存，把自己的基因传下去。
All in all, it's clear that cannibalism is as much a part of life in the animal kingdom as other, better-recognized behaviors.
总的来说，同类相食无疑是动物王国生命中的一部分，和其它我们更了解的行为一样重要。
As we sink our teeth into the evidence of cannibalism in nature,
当我们继续深入探索自然界中同类相食的证据，
we might ask ourselves, what else have we missed by applying human standards to the natural world?
我们也应该问问自己，还有什么东西是因为我们把人类的标准用于自然界而被我们漏掉的？
