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Chances are you don't give your tongue the credit it deserves.
你很有可能没有给自己的舌头应有的荣誉。
That fleshy muscle in your mouth is so much more than a food-tasting organ.
你口中的肌肉不仅仅是一个味觉器官。
Without tongues, we might still be swimming around
没有了舌头，我们可能还游荡在水中
and staring longingly at the dry land we and all other backboned animals never managed to conquer.
并渴望地凝视着这片我们和其他所有的脊椎动物都没能征服的地面。
So today, let's take a trip through evolutionary history to see how the humble tongue was key to world domination.
所以今天，让我们回顾一下进化史，看看谦虚的舌头对征服世界是多么的重要。
The earliest vertebrates were fish, and fish don't have tongues.
最早的脊椎动物是鱼类，鱼是没有舌头的。
I know, you swear you've seen a fish with a tongue. But I promise, you haven't.
我知道，你发誓你见过有舌头的鱼。但我保证，你没有。
Many fish have a structure called a basihyal: a raised lump of bone or cartilage sits at the bottom of the mouth.
很多鱼都有一个叫做基舌骨的结构：一块位于口腔底部的隆起的骨头或软骨。
It can look sort of like a tongue. But it doesn't really move, and it has no taste buds.
它看上去有点像舌头。但它不能动，也没有味蕾。
So it's not a true tongue, it's just a tough shield to protect sensitive nerves and blood vessels.
所以它不是真正的舌头，它只是一个保护敏感神经和血管的坚固屏障。
And this all makes sense when you realize that most animals with tongues use them for catching and swallowing food,
当你意识到大多数有舌头的动物都用舌头来捕捉和吞咽食物，而且鱼不需要口肢就能做到这些时，
and fish don't need a mouth appendage for that. Most have a neat trick called suction feeding.
这一切都说得通了。大多数鱼都有一个叫做吸吮进食的小技巧。
When a fish spots a tasty morsel, it swims up to it and explosively expands its mouth.
当一条鱼发现美味的食物时，它会游到它身边，突然张开嘴。
The top of the skull moves upward, the lower jaw swings open,
头骨顶部向上移动，下颌张开，
and a bony throat structure called the hyoid moves down into the throat.
一种叫做舌骨的骨喉结构向下进入喉咙。
All this causes a quick drop in water pressure inside the fish's mouth,
所有这些都会导致鱼嘴里的水压迅速下降，
and water rushes in, dragging the tasty morsel into the mouth.
水冲进来，将美味的食物拖进嘴里。
Even fish that take bites of their prey often employ a bit of suction to move things toward the throat.
即使是咬猎物时，也会用一点吸力把东西吸向喉咙。
And those that don't employ suction can just open their mouths and swim to let water push things backwards.
那些不使用吸力的鱼会张开它们的嘴巴游泳，借助水把东西往后推。
But, while all of this works great in water, air is much less dense,
但是，虽然所有这些在水中都很有效，但空气的密度要小得多，
so it doesn't provide the force needed to drag or shove prey down the throat.
所以它不能提供足够的力量把猎物拖到喉咙里。
So fish were faced a problem as they expanded their horizons.
所以当它们扩张视野时，就面临着一个问题。
We know from the fossil record that one group of bony fishes – the sarcopterygians –
化石记录告诉我们，有一群硬骨鱼类—肉鳍鱼类—
made the move to land between 400 and 350 million years ago, during the devonian period.
在4亿到3.5亿年前，也就是泥盆纪时期，它们迁徙到了陆地上。
Tetrapods—the legged animals that they became, including all amphibians, reptiles, birds, and mammals—
四足动物—它们变成了有腿的动物，包括所有两栖动物、爬行动物、鸟类和哺乳动物—
would go on to conquer the land, the sky, and arguably, with us included, space.
将继而征服陆地、天空以及太空。
But first, they had to get out of the water.
但首先，它们不得不离开水。
Fossils of early tetrapods like the famous 'fishapod' Tiktaalik
早期四足动物的化石，如著名的提塔利克鱼
reveal just how much needed to be tinkered with to make this transition,
揭示了要完成这一转变需要做多少调整，
including changing up their limbs, backbones, skulls, eyes, lungs and more.
包括改变四肢、脊骨、头骨、眼睛和肺等等。
But they also had to change how they ate.
但它们还需要改变饮食方式。
Unfortunately, not a lot of fossil evidence has been found for the early evolution of tongues,
不幸的是，关于早期舌头进化并没有发现大量化石证据，
but by comparing fish to land-lubbers, we can see where the change happened.
但通过比较鱼类和陆生动物，我们可以看到变化发生在哪些方面。
It all has to do with that throat structure I mentioned earlier: the hyoid.
这都和我之前提到的喉道结构—舌骨有关。
In fish, hyoid bones largely support muscles of the gills. But tetrapods lack gills for the most part.
在鱼类中，舌骨主要支撑鳃的肌肉。但四足动物大多没有鳃。
So, the hyoid supports the muscles of the tongue instead.
所以舌骨转而支撑舌部肌肉。
We can even see this transition in action in modern-day amphibians!
我们甚至可以在现代两栖动物身上看到这种转变！
Larval salamanders live in the water, and their hyoid bones are part of their gill structure.
幼虫阶段的蝾螈生活在水中，它们的舌骨是鳃结构的一部分。
When they metamorphose into adults, these bones switch to supporting the tongue!
当它们成年后，这些骨头就会转而支撑舌头！
As for how this shift from gill to tongue happened… well, there are two main ideas.
至于这种从鳃到舌头的转变是如何发生的，主要有两个观点。
One hypothesis is that tongues first evolved to help food move from the mouth into the throat.
一种假设是舌头首先进化以帮助食物从嘴巴进入喉咙。
Picture an early tetrapod crawling along a Devonian shoreline like a weird slimy crocodile.
想象一下，一只早期的四足动物像一条奇怪的黏糊糊的鳄鱼一样沿着泥盆纪的海岸线爬行。
It snaps its jaws onto a small critter and tilts its head back to drop the food into its mouth.
它用嘴咬住一只小动物，然后仰起头把食物放进嘴里。
A simple tongue would have been very helpful just to move food to the right place.
简单的舌头就能把食物移动到正确的地方。
In salamanders that feed this way nowadays, the hyoid drops down into the throat to move the tongue.
那些如今以这种方式进食的蝾螈，它们的舌骨向下进入喉咙以移动舌头。
Since this is the same motion the hyoid makes during suction feeding in fish,
由于这和舌骨在鱼吸吮进食过程中所做的运动是相同的，
this seems like a pretty straightforward evolutionary step.
这似乎是一个相当直接的进化步骤。
But there's another hypothesis that suggests tongues first evolved to capture food instead.
但另一种假设是舌头先进化是为了捕获食物。
Lots of animals, such as salamanders and lizards, poke out their sticky tongues to snatch up their food.
很多动物，如蝾螈和蜥蜴，伸出它们黏糊糊的舌头来抓取食物。
A 2015 study found a similar strategy in an unusual fish that uses a hydrodynamic tongue.
2015年的一项研究发现了一种使用相似策略的不同鱼类，它们使用的是流体动力舌头。
That is, a tongue made of water!
就是说这是一条水做的舌头！
This study found that mudskippers carry along a mouthful of water on their trips onto land.
这项研究发现弹涂鱼在上岸时会携带着满嘴的水。
When they find food on the ground, they spit the water all over it, then suck it all back up.
当它们在地面上发现食物时，它们会水吐得到处都是，然后又把水吸回来。
It's sort of a loophole that lets them suction-feed on land. Kind of.
这是一种漏洞，让它们可以在陆地吸食。
And slow-motion X-ray video of the process revealed that when the mudskippers spit the water out,
慢动作x射线视频显示，当弹涂鱼吐出水时，
their hyoid bone moved upward toward the mouth.
它们的舌骨朝着嘴巴向上移动。
That's similar to the movement the hyoid makes in salamanders that catch food by sticking out their tongues.
这与蝾螈舌骨的运动相似，蝾螈通过伸出舌头来捕捉食物。
So, perhaps early tetrapods developed a forward-moving hyoid for water tongues, mudskipper style!
所以，也许早期的四足动物发展出了一种向前移动的舌状舌骨，就像弹涂鱼一样！
Then, a soft, fleshy tongue eventually replaced the fluid.
然后，一个柔软多肉的舌头最终取代了液体。
As of now, we can't say for sure if either hypothesis is totally correct.
到目前为止，我们还不能确定这两种假设是否完全正确。
It could even be that tongues as we know them evolved multiple times!
甚至它们的舌头可能经过了多次进化！
But we do know once our tetrapod ancestors were armed with proper tongues,
但我们知道，一旦我们的四足动物祖先拥有了合适的舌头
they were ready to feast all along ancient shorelines. That still left whole continents to conquer!
它们就准备沿着古老海岸线饱餐一顿。还有整个大陆要去征服！
Like modern-day amphibians, early tetrapods would have been restricted to environments with plenty of water available,
和现代两栖动物一样，早期的四足动物也只能生活在有充足水源的环境中，
partially because their eggs need to be laid in water.
特别是因为它们需要把卵产在水中。
But around 300 million years ago, one group of tetrapods developed eggs with sturdy shells that could be laid in drier places.
但在约3亿年前，一群四足动物的卵长出了坚硬的外壳，可以在干燥的地方产卵。
This group is known as the amniotes, and ultimately gave rise to all reptiles and mammals.
这群动物被称为羊膜动物，并最终延伸至了所有爬行动物和哺乳动物。
And as early amniotes moved into new environments, they needed new tongues!
随着早期羊膜动物进入新的环境，它们需要新的舌头！
Most amphibians have wet, squishy tongues. If they dry out, they can't eat properly.
大多数两栖动物的舌头又湿又软。如果舌头干巴巴，它们就不能吃东西了。
Reptiles and mammals, on the other hand, tend to have rough or scaly tongues covered in keratin,
另一方面，爬行动物和哺乳动物往往有着覆盖着角蛋白的粗糙或有鳞的舌头，
the same material that makes up your hair and fingernails.
这和构成你头发和脚指甲的物质是一样的。
This protects the tongue from losing moisture, so these animals can feed in less humid places.
它可以防止舌头失去水分，所以这些动物可以在不太潮湿的地方进食。
So tongues allowed vertebrates to move onto wet land, then wholly onto dry land, and thereby conquer every environment on Earth.
因此，舌头可以让脊椎动物移动到湿地上，然后完全进入陆地，从而征服地球上的每一个环境。
So, be kind to your tongue. You owe it quite a bit. Thanks for watching this episode of SciShow!
所以，善待你的舌头。你欠了它很多。感谢收看本期《科学秀》！
If you liked learning about tongues and how weirdly important they are,
如果你喜欢了解舌头以及它们有多么重要，
you might like our episode looking at 7 of the weirdest ones around today. And as always, don't forget to subscribe!
你或许会喜欢我们的节目—最怪异的7种舌头。和往常一样，不要忘记订阅！
