(单词翻译:单击)
Thanks to Brilliant for supporting this episode of SciShow.
感谢Brilliant对本期《科学秀》的支持。
Go to Brilliant.org/SciShow to learn more.
前往Brilliant.org/SciShow了解更多。
Sea snakes are the most common group of marine reptiles in the entire ocean, with almost seventy individual species.
海蛇是整个海洋海栖爬行类群体中最常见的种类，有将近70多种。
But despite their impressive diversity, none of them live in the Atlantic Ocean.
但虽然它们种类繁多，却没有一种是生活在大西洋里的。
Which is weird, and also nice! There's a whole ocean with no snakes in it!
这很奇怪，也很好呀！这一整片海洋都没有蛇！
But also there's an entire ocean of snake food and living space out there, so what's going on?
但这片海洋中有供海蛇食用的食物和生存空间，这是怎么回事？
The answer lies in their evolution, their biology, and a weirdly "dry" part of the ocean.
答案在于它们的进化、生物性以及海洋奇怪的“干燥”部分。
The first reason is deceptively simple: modern sea snakes didn't evolve in the Atlantic.
第一个原因看似简单：现代海蛇并不是在大西洋进化而来的。
All sea snakes alive today evolved in a part of the Pacific known as the Coral Triangle and nearby regions,
如今所有现存海蛇都是在太平洋珊瑚礁三角区以及附近区域进化而来，
with most species evolving in the last two and a half million years.
大部分种类都是在过去250万年里进化的。
So they might not have started in the Atlantic,
所以它们可能不是起源于大西洋，
but they've had millions of years to theoretically move there and establish new populations.
但从理论上讲它们有百万年时间迁徙到那里并建立新种群。
But they haven't, in part because it's a pretty big ocean for such little reptiles.
但它们没有，部分原因是因为，对于这种小爬行动物来说，这是一个相当大的海洋。
Only one species of sea snake, the yellow-bellied sea snake, lives in the open ocean.
只有一种海蛇—长吻海蛇—居住在公海里。
Most of the others only live in near-shore shallows.
但部分其他种类只生活在近岸浅滩处。
The yellow-belly is the only species that would have much chance of making it to the Atlantic.
长吻海蛇是唯一一种有机会去往大西洋的种类。
But each of the different ways it could even hypothetically reach the Atlantic has its problems.
但每一种可能到达大西洋的方式都有其问题。
Like, going around the tip of South America or Africa might be too cold.
比如，去南美洲或非洲的端点可能太冷了。
Yellow-bellied sea snakes need temperatures above 20 degrees Celsius in order to be toasty enough to breed.
长吻海蛇需要20摄氏度以上的温度才能繁殖。
And too far below 18 and they'll flat out die.
远低于18摄氏度，它们会死得很惨。
Given an annual mean ocean temperature of less than 17 degrees off the coast of South Africa, that's a no-go.
鉴于南非海岸的年平均海洋温度低于17度，那里是不能去的。
Yellow-bellied sea snakes actually can live directly south of Africa,
长吻海蛇实际上可以直接生活在非洲南部，
but it might be that the ocean is too cold just west of there, so they still couldn't make the whole trip.
但也有可能是西边的海洋太冷了，所以它们仍然无法完成整个旅程。
Oddly enough, going around Africa might also be too dry. Sea snakes can't drink salt water.
奇怪的是，环游非洲可能也太干燥了。海蛇不能饮用盐水。
Instead, they drink a thin layer of rainwater that floats on the surface of the ocean after storms.
它们喝的是暴雨后漂浮在海洋表面的一层薄薄的雨水。
Yes, this is a thing. That's wild.
没错， 是这样，这很野蛮。
But the southwest coast of Africa includes the Namib Desert with its infamous Skeleton Coast.
但非洲西南部海岸包括纳米布沙漠和骷髅海岸
This region may go years without rain, even out at sea. Sea snakes going this way could become dehydrated and die.
这片区域多年不下雨，即便海上也一样。走这条路的海蛇会脱水死亡。
And they might not have any more luck trying to go the other way, where North and South America are the obstacle.
它们可能已经来不及尝试另一条路了，因为北美和南美是障碍所在。
Millions of years ago, there was an open corridor between the Pacific and the Atlantic in what is now Panama—
百万年前，太平洋和大西洋之间，也就是现在的巴拿马，有一条开放的走廊
a much warmer route than rounding the southern tips of Africa or South America.
这条路线比非洲或南美洲南端路线要更温暖。
Trouble is, the isthmus of Panama formed long before sea snakes evolved,
问题是巴拿马地峡早在海蛇进化之前就形成了，
blocking them from simply swimming from one ocean to the other.
这让它们无法从一个海洋游到另一片海洋中。
We humans have opened that passage back up in the form of the Panama canal.
我们人类以巴拿马运河的形式打开了这条通道。
And there have been reports of individual sea snakes on the Caribbean coast of Colombia, which presumably made the trip through the canal.
有报道称，哥伦比亚加勒比海岸中有一种海蛇，猜测可能是通过运河游过来的。
Even so, scientists think it's unlikely they'll establish an actual breeding population via this route.
即便如此，科学家认为通过这条路线，它们不可能繁育物种。
So in the end, even though it might seem like the Atlantic could be a nice home for the sea snakes with warm water and tasty prey,
所以最终，即便大西洋可能是海蛇的美好家园，这里有温暖的水和美味的食物，
their biology and evolutionary history put that possibility pretty much out of reach.
但它们的生物性和进化历史让这种可能性遥不可及。
If you're the kind of person who wonders why certain reptiles never moved to certain parts of the ocean,
如果你想知道为什么某些爬行动物从不迁移到海洋的某些地方，
well, you are as curious as we are.
那么你应该和我们一样有好奇心。
If you want to keep up your streak of learning new things, you might enjoy the daily challenges over on Brilliant.org.
如果你想继续学习新知识，你或许会喜欢Brilliant.org的每日挑战。
From stats to electricity to computer science, there are fresh new challenges every day.
从统计学到电力再到电脑科学，每天都有新挑战。
And whether you're commuting or just relaxing at home, they give you a fun, bite-sized way to learn, apply, and master new concepts.
不论是上下班还是在家休息，都可以用一种有趣的方式学习、应用和掌握新概念。
And if you like what you learned from a given challenge, there's a more in-depth course connected to each one.
如果喜欢每日挑战中的知识，可以去看看与之相关的深度课程。
And they're even free but Brilliant's premium members get access to the entire archive of challenges if you want to catch up.
课程是免费的，但Brilliant的会员可以观看所有往期内容。
The first 200 people to sign up at Brilliant.org/SciShow will get 20% off an annual premium subscription.
前两百名注册Brilliant.org/SciShow的观众将获得年度会员八折优惠。
So if that sounds up your alley, click on the link in the description, and thanks for supporting us.
如果喜欢，请点击下方链接，感谢支持。
