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This episode of SciShow is supported by Brilliant. To learn more about their Mathmatics Fundamentals course, you can go to Brilliant.org/SciShow.
本期节目由Brilliant赞助播出。登录Brilliant.org/SciShow，了解更多《Mathmatics Fundamentals》课程。
Human pregnancy typically lasts nine months. From when a sperm fertilizes an egg, to when a baby is born is roughly 38 weeks later.
通常人类孕期会持续九个月，从精子卵子受精到孩子出生，通常需要38周。
But some mammals do things differently: They can pause their pregnancies to put an embryo's development on hold.
但一些哺乳动物却不一样：它们可以暂停妊娠，以暂停胚胎的发育。
It's called embryonic diapause. And if you're wondering how that works so were scientists until recently.
这被称为胚胎滞育。如果你想知道这是怎么回事，科学家们也是最近才弄清楚。
Pausing pregnancy after conception might seem weird, but it happens in more than 130 mammal species, from mice to seals.
在怀孕之后暂停妊娠看似怪异，但超过130种哺乳类物种，如老鼠和海豹都有这种技能。
It occurs early, during the blastocyst stage, when the embryo is a quickly-dividing ball of cells.
这种情况发生在早期胚泡时期，此时胚胎是一个快速分裂的细胞球。
Normally during this stage, the embryo embeds into the uterine wall, where it keeps growing and becomes a fetus.
通常在这个阶段，胚胎嵌入子宫壁，并在这里继续生长并成为胎儿。
But in diapause, this gets delayed. The embryo just hangs out in the uterus, developing slowly or not at all.
但在滞育期，这一步被延迟了。胚胎仅在子宫内徘徊，缓慢发育或完全不发育。
And it can stay that way for months, or even a year. Eventually, though, the egg does implant, at no harm to the pregnancy.
这种情况可以持续好几个月，甚至一年。虽然最终，卵子会在不伤害妊娠的情况下嵌入。
This is a really useful trick, and it happens for one of two reasons: either to help an animal produce the most offspring,
这真的是一个非常有用的技能，触发该技能有两个原因：要么是帮助动物繁殖最多的后代，
or to delay birth until conditions are right for the newborn to thrive.
要么是延迟出生，直到环境适合新生儿的生长。
That first mechanism is pretty simple: When an animal is nursing, they experience a rise in hormones that prevents embryos from implanting.
第一个机制相当简单：当动物哺乳时，它们体内的激素会增加，从而阻止胚胎的植入。
This is common in mice and some marsupials, and it gives older siblings time to wean off their mother.
这在老鼠和一些有袋目的哺乳动物身上很常见，并且这给了哥哥姐姐们断奶的时间。
That second mechanism, though—that one confused us for a while. We knew it was common.
但第二个机制——曾一度让我们感到困惑。我们知道这很常见。
It happens all the time—mostly in carnivores, since they tend to endure harsh climates and food shortages times that are not great to have a baby.
这种情况一直都在发生——主要发生在食肉动物身上，因为它们往往要忍受恶劣的气候和食物短缺时期，而这些对生育来说不是什么好事。
In some cases, it even happens with every gestation. We also knew it isn't a conscious decision.
在一些情况下，甚至每一次妊娠都会发生这种情况。我们也知道这不是一个自觉的决定。
Instead, it's controlled by environmental cues, like hunger or temperature. But only recently did we begin to learn how it really works.
相反，这是由环境因素所控制的，如饥饿或温度。但直到最近我们才开始了解这到底是怎么回事。
We've started to understand that this kind of diapause happens because those cues affect the amount of mTOR.
我们开始理解这种滞育的发生是因为这些因素影响了mTOR的数量。
mTOR is an enzyme that's sensitive to a variety of molecules, like oxygen, glucose, and amino acids—things needed for cell growth and multiplication.
mTOR是一种酶，对各种分子都很敏感，如氧、葡萄糖和氨基酸——细胞生长和繁殖所需的一切。
It helps organisms regulate their growth based on how many nutrients are available.
它帮助生物体根据可用营养素含量控制生长。
And since it's sensitive to so many molecules, it can detect when a cell's nutrient levels are low.
由于它对众多分子都很敏感，它可以检测到何时细胞营养水平低。
Normally, this is important for growth in general. But around 2016, we began to find that this enzyme also plays a big role in diapause.
通常情况下，这对整体生长发育很重要。但在2016年，我们开始发现这种酶在滞育中也起到了重要作用。
Like, in a newer experiment published in 2020, researchers found that starving mouse embryo cells led to changes in the cells that suppressed mTOR.
比如在2020年发表的一项更新的实验中，研究人员发现饥饿的小鼠胚胎细胞会导致抑制mTOR的细胞发生变化。
And when that happened, the embryos went into a state that looked a lot like diapause. So most likely, this enzyme is also affecting this process in nature.
当发生这种情况时，胚胎会进入一种和滞育很相似的状态中。所以很可能，这个酶也影响了这个过程。
When something like a food shortage hits, the lack of nutrients might cause a drop in mTOR, and boom—you got a paused pregnancy.
当发生食物短缺等情况时，营养缺乏可能导致mTOR含量下降，突然，你的孕期就被暂停了。
Now, we still have a lot to learn about exactly how this works—because humans also have mTOR, and we cannot pause our pregnancies like this.
现在关于其中原理我们还有很多需要了解的——因为人类也有mTOR，并且人类不能像这样停止妊娠。
So there has to be something else going on. But this trick is helpful and convenient for the animals that can do it.
所以肯定还有别的原因。但是这个技巧对那些能做到的动物来说既有用又很方便。
And maybe someday, we'll find out if this biology can also help us.
也许未来，我们会发现这种生物学是否也能帮助我们。
If you want to keep learning this summer, you might enjoy one of Brilliant's courses—like their newly-designed Mathematical Fundamentals course.
这个夏天如果你想继续学习，你或许会喜欢Brilliant的课程——比如他们最新设计的《Mathematical Fundamentals》课程。
It will not teach you how to do embryonic diapause, but it does have new illustrations, interactive features, and challenges.
它不会教你如何进行胚胎滞育，但它有新插图、互动和挑战。
And like all of Brilliant's courses, it's available offline with their iOS and Android apps.
和所有Brilliant的课程一样，可以通过他们的 iOS和安卓应用进行离线学习。
So even if you have a rough internet connection, you can still check it out.
所以即便没有互联网也能观看。
To learn more about the course, you can go Brilliant.org/SciShow.
了解更多课程知识，登录Brilliant.org/SciShow。
And the first 200 people to sign up using that link will get 20% off an annual Premium subscription.
前200名使用链接注册的用户将获得年度会员八折优惠。
